Inside the MaxFire

Understanding the MaxFire Room Heater 2009

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Notice: This is an unfinished manual. I am still working on the troubleshooting section which when completed will be added to this document. I felt it would be best served in its raw state now as the heating season begins. Comments at this point are welcomed. For errors or suggestions, please “PM” Quark on the iburncorn.com Bixby Forum. Thank you for your patience. Quark 11.03.2009

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Forward: This document is written for all levels of experience and knowledge of the MaxFire stove; how it works and how to troubleshoot it. For the beginner, there may be information that may be far too technical. For the average user it is meant to enhance the experience of using the MaxFire. For the advanced user and repair person, it is meant to give insight to the sequence of the operation of the MaxFire and to make troubleshooting and repair easier and quicker. When the MaxFire is running well, there is no need to know much more then filling it with fuel, empting the ash drawer and some adjustments of the trim pot knobs. If the MaxFire is not running well or not at all, it helps to know what each part does and the sequence of the operation of the stove to make an informed assessment of the problem and where or what to look at. Although one may gain a lot of knowledge from any manual, hands on experience is still the best teacher. It is also helpful if one “toys or plays” with the trim pot knobs to see what happens to the flame and the operation of the stove at different settings of the trim pot knobs. How the flames looks and what it is doing is the key to keeping the stove running at its’ optimum performance.

When we look at the MaxFire (and UBB) from the outside, we see clean lines and something that fits into the décor of a room. On the Control Panel is a Touch Pad with four buttons and eight LED’s. We also see the hopper, firebox and ash bin drawer. It seems simple enough. Now let’s look inside of the stove. By removing the right and left side panels we now see one or two printed circuit boards, two motors, two fan/motors, three switches, three sensors and a wire called a thermocouple. Now it’s beginning to look a little more complicated; but if we were to take out every part and lay them out on the floor, each part would not look as complicated. Just knowing this makes the stove a little less scary and easier to understand. But it still doesn’t tell us a whole lot about the how the stove works. To understand how the stove works, it helps to know what the function of each part is. So let’s look at the parts one at a time to get an idea of what each is and what its function is. Although I have tried to be as accurate as possible, the information contained within has been accumulated through my experience working with the MaxFire stove and working as a Tech Support Rep. for Bixby energy Systems. This manual will cover on the software released by Bixby Energy and not the beta versions. You will find more information on the 2.71 version of BixCheck on the “iburncorn” web site. When you reach the section about troubleshooting the stove, remember that there is more than one way to track down a problem. My belief is to go for the simplest approach first. Also keep in mind that there are three separate entities we are dealing with; the stove, the fuel and the operator. I have learned that biofuels are not like natural gas, propane or fuel oil. The biofuels have a much more complicated aspect to them, namely where they were grown, moisture content and the way the growing season happened. To troubleshoot, we must first decide which is the problem, the stove, the fuel or operator error? Most of the troubleshooting section will be dealing with corn as a fuel. As there are so many variables, keep in mind this is just a general guide but it will apply mostly to all Biofuels. Never be afraid to ask a question because you think it is dumb or silly. The only dumb question is the one not asked. Sometimes it helps to talk to someone just to hear yourself asking the question. When working alone we can become stuck in one direction, so we must keep an open mind and be prepared to walk away. Sometimes just getting up and getting some fresh air and thinking of something else can give you a new direction to look in. The purpose of this manual is to give you as much information as possible. Read on and enjoy. Alan Malley Technical Support Representative Bixby Energy Systems

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Index

Chapter 1: The physical devices in the stove. Printed Circuit Board (PCB) The Main Control Board…..……………….……………………………………………………………… 1 Description of other parts on the PCB………………......................................................... 2 Main Control Board – Component placement…………….…………………………………... 3 The Igniter Board…………….………..…………………………………………………………………… 4 Motors

Exhaust fan……………………………….………………………………………………………………… 5 Convection fan…………………………….……………………………………………………………….. 6 Important Note – Voltmeter usage………………………….……………………………………………. 6 Motor thermoprotector…………………………………………........................................................... 7 Feed wheel motor…………………….………...…………………………………………….…………….. 7 Burn drive motor………………………………………………………………………………………….... 9

Operation of the brake……………...………………………………………………………….… 9 Burn drive motor – Rex Engineering…………….....…………………….……………10

Burn drive motor – SPG Co………....……………………………….…………………11 Air Pump……………………………………………………………………………………………………..

Switches………………………………………………………………………………………………………………12 Door switch………………….………………………………………………………………………………12

Ash drawer switch………………….………………………………………………………………………14 Burn drive motor switch……………………………………………………………………………………15 Touch Pad…………………………………………………………………………………………………..16 Hopper Snap Switch……………………………………………………………………………………….18 Current coil (sensor)……………………………………………………………………………………….19

Thermocouple………………………………………………………………………………………………20 Exhaust fan sensor………………………………………………………………………………………...21

Feed wheel sensor………………………………………………………………………………………… Wiring diagrams

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Notes

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Printed Circuit Board (PCB) The Main Control Board Let’s look at the heart and brain of the stove; the printed circuit board. The printed circuit board (PCB) has several functions. One function is to change and isolate the 120vac power coming in to a lower voltage of 5 to15 vdc which is used for the control of the higher 120vac. By using the lower voltage for the control of the stove, everything can be made smaller and safer. Also we are working with lower current flows. This doesn’t mean the risk associated with the 120vac is totally removed, but does limit the amount of exposure. Control is accomplished by using a low DC (DIRECT CURRENT) voltage on the PCB to control a switch. The switch used on the PCB is called a triac. A triac is a device which can turn on and off at very high speeds to control an AC (alternating current) device full on, full off or anything in between. It works somewhat like the dimmers we have in our homes that control lights and ceiling fans. The PCB has both inputs and outputs. Most inputs are low voltage (low current) DC while the outputs are usually high voltage (high current) AC. The inputs tell the software program on the PCB what is happening at any given moment. The outputs are then turned on or off according to the software program to activate a device or devices. The PCB cannot do anything without having a program installed on it to tell it what to do. This is done in two steps. The first step places the program onto a Central Processing Unit (CPU). The CPU is a microprocessor chip on the PCB. Software is a set of instructions that is called a program. The program instructions allow the PCB to receive feedback from external devices and to control external devices. The software is not changeable without re-writing the software which requires a special knowledge of computer languages and an understanding of how the device you are controlling works. Depending on what the inputs to the CPU are doing, the CPU can make a logical decision on what it needs to do. It then turns on or off one or more outputs according to its’ logical decision. The CPU contains a non-volatile memory; meaning that even if we were to remove power from the CPU, it would still retain the program in its’ memory. The second step of installing the software on the CPU is to add variables to the program. Within the program, there are places where changes can be made or altered. These are software changes and require an interface such as a computer. The changes are made by using a special program called “BixCheck”. Using BixCheck allows the user to make (allowed) changes and to see in real time some of the things that are happening with the stove. This type of circuitry is called “solid state”; meaning that there are no moving parts. With the advent of the solid state circuit, things were able to be made smaller and smaller and to consume less power. Some of the parts we use on the PCB are: transformers, capacitors, resistors, IC’s (integrated circuit), transistors, diodes, LED’s and triacs. The PCB may also have connectors, switches, heat sinks, current transformers and fuses. There usually is a power supply which converts the high voltage AC (alternating current) to low voltage DC (direct current). The power supply is made up of several components;

A transformer (T1, T2, etc) is used to isolate and increase or decrease the voltage. Rectifiers (D1, D2, D3, etc) convert the AC to DC by allowing current to flow in one direction only. The inductor (L1, L2, etc) opposes a change of current flow. The capacitor (C1, C2, C3, etc) opposes a change in voltage. There may also be an IC (U1 or VR1) used to regulate the DC output to a steady voltage.

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Following is a brief description of other parts on the Main Control Board (PCB). Capacitor: Used for filtering, isolating or timing of a circuit; opposes a change of voltage (C1, C2, etc). Resistor: Used to limit current flow and as a voltage reference. (R1, R2, etc). IC’s: There are many types of IC’s that do different jobs. (U1, U2, etc). Voltage regulation (VR or U) Voltage isolation Logic operations Sensors Power management Amplification Filtering Mixing There are many uses for the IC’s in both analog and digital circuits. Some IC’s are use as Microprocessors or Central Processing Units (CPU). Transistor: A device that controls a larger load with a small current in a DC circuit. (O1, O2, etc). Diode: A device that allows current to flow in one direction only. (D1, D2, D3, etc). Diac: A device that is non-conducting until a certain level of voltage is reached. The Diac is

used as a surge protector to help protect components on the PCB from spikes and surges

(TB1). LED: A solid state indicating device; Light Emitting Diode. (LED1, LED2, etc. or DS1, DS2, etc) Triac: A device that can control a larger load with a small amount of current in an AC circuit. Connector: Use to facilitate easy connection and removal of wires. (J1, J2, etc). Switch: Used to control current or used as an input to a circuit. (SW1, SW2, etc.) Heat Sink: A piece of metal used to dissipate the heat developed by a device.

Fuse: A safety device which opens to disconnect power from a circuit when a pre-determined amount of current is exceeded within a pre-determined amount of time. (F1, F2, F3).

Current Transformer: This is located on the igniter board on the model 110 and 115, and the main control board on the model 100 and the UBB’s. Its purpose is to isolate and measure 120 volt current flow and change it to a small usable current for use in the low voltage circuit. (T1, T2 etc). Do you really need to know what everything on the PCB is? Not really, but it does help when discussing a problem with someone or just trying to figure out why something works or does not work. Of course we will be replacing the whole PCB if it is bad rather than a part on it. If we call the parts by their correct or trade name, it will be a lot easier communicating with others and solving the problem in a timely manner. The physical parts are easy to see, but we do have one more item on the main control board that we cannot see. This is the software. Just as a part can keep a stove from running, so can the software. We need to understand the software enough so we can make an educated guess as to if it is the software causing the problem or a defect in a part or even the fuel. We will discuss the software and fuel later after we have finished with the mechanical parts on the stove. In the following illustration some of the components are pointed out. Keep in mind that the entire board is replaced rather than individual parts. Of course if this is too much information, you may skip over this next page and just think of it as “all those little parts”.

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Fuse_F3

Diac_TB1

Transformer_T1

Isolating IC_U14

Capacitor_C11, C14

Inductor_L1

Diode_D7,D8,D9,D11

LED_DS1

CPU IC_U3

IC_U4, U7

Resistor_R23

Resistor_R95

Capacitor_C23

Connector_J15

Triac_Q8,Q9,Q10

Capacitor_C10, C12

Resistor_R40

Connector_J18

Clock Timing Crystal_X1

Power Supply

Isolating IC_U15, U16

Heat Sink

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The Motherboard uses 8 sensors to control the various stove functions:

1) Feeder Wheel Sensor 2) Exhaust Fan Tachometer 3) Ash Drawer Switch 4) Door Switch 5) Exhaust Thermocouple 6) Burn Drive Motor Limit Switch 7) Hopper Snap Disc 8) Igniter Current Sensing Coil

1. A Magnetic Sensor below Feeder Wheel senses 4 magnets that are pressed into the Feeder Wheel as

the Feeder Wheel rotates. The stove will reposition the Feeder Wheel so each hole will align in the correct position at the proper time.

2. The Exhaust Fan Tachometer gives the stove’s computer feedback as to the actual speed of the fan.

This also is used to determine if the Exhaust Fan is working correctly. The Exhaust Fan uses this input to run an exact speed.

3. The Ash Drawer Switch lets the stove know if the Ash Drawer is in the closed position or not. If the

Ash Drawer is not in the closed position, it will cause an error (#5 light blinking) and the stove will not do an ash dump. Eventually fuel will build up in the Burn Pot if the Ash Drawer is not replaced or closed properly. After 20 minutes the stove will shut down to prevent a build up of unburnt fuel.

4. The Door Switch tells the stove if the door is closed or open. If the door is open, it will cause an error

(#4 light blinking) and will shutdown in one minute.

5. The Exhaust Thermocouple is used to measure the temperature of the exhaust. The Thermocouple is also used to adjust the Convection Fan speed. If the temperature of the exhaust is getting too hot (losing efficiency), the Convection Fan will speed up to put more heat into the room. The increase in the Convection Fan speed will aid in lowering the exhaust temperature. If the exhaust temperature continues to rise to a critical temperature, then the stove will move itself to a lower heat level setting until the exhaust temperature has lowered. If the temperature still does not come down, then the stove will shut down with a #3 light blinking.

6. The Burn Drive Limit Switch gives indication to the stoves computer that the paddles are in the run

position and the ash dump worked correctly. The switch is activated by a cam that is on the burn drive motor.

7. The Hopper Snap Disc is another safety device that senses the temperature of the bottom side of the

Hopper. The #3 light will begin blinking if the Snap Disc has been activated and the stove will shutdown. The Snap Disc will automatically reset as the stove cools.

8. The Igniter Current Sensing Coil checks both igniters for current draw before the stove starts up. If either of the igniters is bad, the stove will show an error code. The Left Igniter, as you look at the stove, will have the #7 & #1 lights blinking simultaneously, the Right Igniter will have #7 & #2 blinking simultaneously. If both Igniters are bad, lights #7 & #1-2 will blink. Unplug each Igniter and check with an ohmmeter to verify that the Igniter is bad. The resistance of a good Igniter will be 22 to 28 ohms.

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The Igniter Board On the MaxFire there is a smaller PCB called the igniter board. The function of the igniter board is to control the two igniters in the burn pot. The main control board controls the igniter board. You will notice that the board uses many of the same components that the main control board uses. It also has one component that the main control board does not have; a current transformer. The current transformer is shaped like a donut with an opening in the center. The wire that passes through the current transformer, called a jumper wire, is common to both igniters. The total sum of the current that flows through each igniters flows through this wire. As current passes through the jumper wire, a magnetic field develops around the wire. The magnetic field induces a voltage in the current transformer proportional to the amount of current flowing through the jumper wire. On the MaxFire 120’s and the UBB’s, the current transformer is of another style. This type has a wound primary and a wound secondary wound on an iron core which uses the core for magnetic flux path. The intensity of the current flow in the current transformer circuit is analyzed by the software which determines if both igniters are operating when called to operate. If either the right or left igniter does not operate, an error code is indicated by the LED’s on the control panel. If the igniters operate at anytime they are not supposed to, the software program will run the air pump to avoid damaging the igniters. The 120vac power into the stove goes from the power cord to the igniter board and from the igniter board to the main control board. It does not matter where the 120vac plugs into; either J6 or J4. When the stove is built, the power into the board goes to J6 while the power out of the board goes to J4. If a fuse blows, ALWAYS replace them with a 5 or 6 amp 125 volt fast blow fuse. Replacement of a fuse with a higher rating or a slow blow could cause damage to components on the PCB. Note: It makes no difference of the direction that the jumper wire runs through the current transformer.

Note: On the MaxFire 120 and the UBB’s the “igniter board is incorporated onto the main control board eliminating the separate igniter board.

Control Cable_J3

Current Transformer_T1

Power Out_J4

Power In_J6 Right Igniter Connector_J7

Left Igniter Connector_J5

Right Igniter Fuse_F2

Left Igniter Fuse_F1

Heat Sinks

Triac_Q2 & Q3

Unused Connectors

Common Igniter Wire

Thermo sensor

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Exhaust fan The exhaust fan consists of five parts: the motor, motor cooling fan, exhaust fan speed (tachometer) sensor, fan housing and the impeller. The motor is: 1/20 HP (horsepower), shaded pole, 120 volt AC, 1.35 amps, 3000 RPM, with Class B insulation and thermoprotection. Class B insulation is rated at 130ºC (266ºF). The motor is designed to work well in the ambient temperature that it is exposed to. The motor is a shaded pole motor with sealed ball bearings and has an internal thermo protector (TP). If the motor gets too hot, the thermo protector will open and stop the motor. After the motor cools, it will restart. It is normal for shaded poles motors to run hot due to internal core losses in the metal caused by circulating currents call eddy currents. The motor will in no case run any faster than the rated RPM. Second is a small cooling fan blade for the motor. This serves two purposes, cooling the motor and a reference point for the speed sensor. There are 10 blades on this fan. The cooling fan on the motor shaft is positioned to allow the tachometer sensor to be centered on the blades and in close proximity to the blades of the fan. Third, a sensor positioned over the fan blades send a pulse to the CPU each time a blade of the fan passes under the sensor. The sensor has a built in magnet. When a ferrous metal object deflects the magnet field of the sensor, the sensor sends a pulse to the CPU. The CPU counts the number of pulses it receives in a given period of time. This count is converted to a number which multiplied by 24 is the RPM of the exhaust fan. This circuit is a feedback circuit that the CPU uses to confirm the exhaust fan is running and at what speed. If the CPU sees the actual RPM is different than the exhaust fan target RPM, the CPU will try to correct the speed of the motor to comply with the exhaust fan target RPM. The RPM, as seen in the telemetry of the BixCheck software monitoring program, is displayed as both a number between 0 & 255 and the RPM. The temperature of the exhaust also has some effect on the speed of the exhaust fan. This is a simplified cause and effect of what takes place and how it affects the speed of the exhaust fan. The fourth and fifth items are the fan housing and the fan. The fan housing contains the impeller (fan blade) that moves the air while the fan housing directs the air to the venting system. The exhaust fan is located on the exhaust side of the burn chamber. When it is running the fan creates a negative pressure inside the burn chamber. The outside air pressure is higher than the burn chamber and tries to equalize the pressure inside the burn chamber. Fresh combustion air is thus drawn into the burn chamber. The exhaust venting is under a positive pressure while the outside pipe for the combustion air is under a negative pressure. Any venting installed on the stove will have an effect on the amount of air the fan can move. When the fan is running and pushing air though the venting, a static pressure (resistance to the movement of air) is created in the venting. The venting and any elbows (45º or 90º) that are connected to the system will have an effect on the amount of air the fan can move at a given RPM. In short, the shorter the venting, the easier it is for the fan to move the air through the venting.

Cooling fan blade

Exhaust fan housing

Exhaust fan sensor

Exhaust Fan Motor

Fan propeller (blade)

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1) Exhaust Fan Cooling Propeller 2) There are 10 blades on the propeller. 3) The Exhaust Fan Sensor sends a pulse to the Main Control each time a blade passes under the Sensor. 4) For one complete revolution of the Exhaust Fan, 10 pulses are sent to the Control board.

1) The exhaust fan sensor is a non-contact ferrous metal (having the presence of iron) detecting device 2) The sensor is a HALL EFFECT transducer, (changes one form of energy into another form of energy), which varies its output voltage in response to a hanging magnetic field. 3) The Sensor has an imbedded magnet. 4) The blades of the propeller distort the magnetic field of the Sensor.

Direction of rotation. The Air / Exhaust pathway

up to this point is at a Negative Pressure

The Air / Exhaust pathway starting at this

point is at a Positive Pressure

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Convection Fan The convection fan is a backward curved 530 CFM (Cubic Feet per Minute) capacitor start, capacitor run centrifugal fan. The fan has ball bearings and an internal thermal protector. The motor consumes a maximum of 100 watts at 120 volts AC and runs at a maximum RPM of 2550. The fan is a single speed fan controlled electronically as a variable speed fan. The fan is controlled somewhat like a ceiling fan controlled by a variable speed wall switch. The speed of the fan is dependent upon the settings in the program and the temperature of the exhaust. The minimum speed of the fan is set at 25% of maximum or approximately 637 RPM. The convection fan will begin to run above the 25% value at 50º C (122ºF). The fan is preset to run at 100%, (2550 RPM), when the exhaust temperature reaches 170º C (338º F). These values can be changed by using the BixCheck software in the Monitor window. More on this later. An internal thermo protector (TP) embedded between the windings of the motor (set to open at 104º F) is automatic resetting. The convection fan needs a capacitor to start and run. There are two windings in the motor, one is called the starting winding and the other is called the running winding. Some motors use a capacitor just for starting the motor and then removes it from the motor circuit using a centrifugal switch. The switch is built into the motor and opens the starting circuit once the motor reaches 75% of its’ rated speed. The capacitor with this motor is used to start and run the fan by creating an electrically magnetic phase shift between the running winding and the starting winding. The capacitor allows the motor to have higher starting and running torque. If the capacitor were to be removed or to fail while the motor were running, the motor would stop. The capacitor is sized by the manufacture to match the starting and running characteristics of the motor. If needed, the capacitor must be replaced with a capacitor that has the same ratings in voltage and capacitance. Important Note: When using a volt meter or ammeter on either the exhaust fan or the convection fan, a special meter must be used for an accurate reading. Most digital meters and analog meters read what is termed as the “average voltage or current” of the circuit, then the reading is displayed as “RMS” (Root Mean Square) of the circuit. These meters are calibrated and are meant to be used on a pure sine wave alternating current (AC) circuit. In the United States we have 60 Hz (cycle) AC. One cycle (Hertz) consists of a positive rise in voltage / current from a zero value to a maximum value and down to a zero value. At this point the voltage / current reverse direction and rise to a maximum negative value and then back to a zero value. In each cycle there are two zero values and two maximum values. So within one cycle, the voltage (current) is being turned on and off two times in each cycle. This happens 60 times each second. The control of the exhaust fan and the convection fan is done by using all or only a portion of each sine wave. The motors are being turned on and off 120 times second. The RMS value of an AC voltage (current) produces the same amount of work as an equivalent direct current (DC) circuit of the same voltage would. You need a meter that is a “True RMS” reading meter. A “True RMS” meter is designed to read correctly on a sinusoidal or a non-sinusoidal waveform weather it’s a modified, chopped sine wave or square wave and usually can be used on a wide frequency range. When using an average reading meter on anything other than sine wave, the readings could be from 10% high to 40% low. If you are just looking to see if you just have a voltage present and don’t care about an accurate reading, any meter will do.

Motor

Backward Curved Impeller

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Thermo protector: All the Bixby motors have thermal protection, so what is thermo protection? It has many names; Klixon (trade name), snap disc, thermal overload, thermal cut–out, etc. A thermo protector is a bi-metallic disc or strip, or simply a simple and accurate thermostat used to convert a temperature change into mechanical movement. They consist of two types of different metals which expand at different rates as they are heated, usually steel and copper. Electrically they can be either normally open or normally closed. Operation of the thermo protector: The operating principle of the thermo protector is both simple and effective. At the heart of the protector is a bimetal snap–action disc. When the temperature of this disc reaches its pre-calibrated temperature it snaps open, resulting in an open circuit. This temperature is reached during a fault condition, caused by either an increase in ambient temperature, an increase in current flowing through the discs, or a combination of both. After the thermo protector breaks (opens) the circuit, the system cools and the thermo protector automatically resets, allowing power to be restored to the circuit. The thermo protector can be either automatic resetting (the type Bixby uses) or manual resetting requiring action by someone after the thermo protector cools enough to allow resetting. Feed Wheel Motor: The feed wheel motor is classified as a gearmotor. The purpose of a gearmotor is to increase or decrease the speed of the output shaft or reverse the direction of the motor. Torque of the motor is inversely proportional to the speed increase or decrease. Thus, if we change the gear ratio to increase the output speed, the torque is reduced. Another way of stating this is; speed increase, torque decrease or speed decrease, torque increase. The gearmotors that we use have a shaded-pole motor attached to a gear box. A shaded-pole motor has low torque and only one winding (other motors have two windings; a start and a run winding). If you look closely at the motor you will see two fairly large copper wires that wrap around the motor laminations (core) in two places which are exactly 180º magnetically and physically from each other. Without these wires the motor would not run. These wires are the shaded-pole of the motor. When current flows in the windings of the motor they create magnetic poles; one north and one south magnet pole. The magnetic field created by the main winding induces a voltage in the large copper wires. As the current in the shaded-poles fluctuate up and down, they create magnetic poles that lag behind the main magnetic poles. This creates a rotating magnetic field which the armature of the motor follows. Because of this shaded-pole, a shaded-pole motor will run hotter than a split phase motor due to the higher core losses of the motor. The motor and the gear box are a single unit. If one or the other goes bad, the whole unit is replaced.

Types and placement of some thermocouples

Contacts open on temperature rise

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Since the shaded pole motor has low torque, by adding a gear box to the motor, we decrease the output speed and at the same time increase the output torque. The gear ratio is approximately 1827:1. This means that when the motor is running at 3288.6 RPM, the output shaft is turning at 1.8 RPM. There is either an internal self-resetting thermoprotector built into the motor or the motor is impedance protected. A motor that is impedance protected means that even if the motor were to stall (locked rotor), the current rise of the motor would not be enough to damage the motor or the circuit that it is connected to. When the motor is running it draws 0.19 amps. Note: Both the feed wheel motor and the burn drive motor are two pole motors. The theoretical speed of a two pole motor is 3600 RPM. Only special AC motors called synchronous motors are capable of running at 3600 RPM. Due to slippage, windage and bearing resistance, all AC motors will run at something less than 3600 RPM such as 3450 RPM. The load on the motor will also have some effect on the motor speed. As example, the feed wheel motor by itself will run approximately 3300 RPM with no load applied to it.

Note: Threaded Shaft

MaxFire 110 Feed Wheel Motor

MaxFire 115 & UBB Feed Wheel Motor

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Burn Drive Motor: The burn drive motor drives the upper and lower paddles of the burn pot. The movement of the paddles is how the stove does an ash dump. The burn drive motor is also classified as a gearmotor. The operation is the same as the feed wheel motor (see feed wheel motor). The gear ratio of the burn drive motor is 532:1. When the motor is turning at 3458 RPM, the output shaft is turning at 6.5 RPM. One difference between the feed wheel motor and the burn drive motor is that the burn drive motor has a mechanical brake on it. This brake is located at the bottom of the burn drive motor. Operation of the brake: The brake consists of three parts. The first part is a two slot gear attached to the motor shaft. This gear is not solidly connected to the motor shaft but is held on by a spring mechanism that acts somewhat like a clutch. So as the motor is running and the brake sets, there is some slippage between the gear and the motor shaft. This slippage prevents any damage due to a sudden shock to any of the individual parts of the system. The second part is a short arm that pivots so it is inserted into the slots on the gear attached to the motor shaft. This short arm is held with a spring forcing it into the gear slot. So when the motor is de-energized, the brake is set. It acts as a parking brake to position the arm attached on the top of the motor (that is attached to the burn pot paddles) to position the paddles in the burn position. The third part is the armature. Part of the armature is made of metal. When the motor is energized (power applied) the area at the shaded pole becomes an electromagnet. The magnetism of the shaded pole pulls the armature towards the motor. An arm on the armature engages the short arm pushing it away from the gear thus disengaging the brake and allowing the motor to turn. When power is removed from the motor the shaded pole is no longer a magnet. The spring attached to the short arm pulls the arm into the gear and stops the motor. One reason for the motor not stopping in the correct position is that the brake does not completely set completely, Meaning the latch on the short arm does not quit engage the slotted gear. The purpose of the burn drive motor is three fold:

1) To clear the burn pot before the start of the stove and to clear the burn pot at shut down. 2) To empty ash from the burn pot during the burn cycle. 3) To close off the burn pot should a blocked flue condition exist. This is done to snuff the flame as

quickly as possible Burn drive motors from two different manufactures are used; Rex Engineering and SPG Co. Ltd. Both perform the same function and carry the same specifications. The difference is in the design of the brake and gearbox. The next two pages will show the difference. Keep in mind that both manufactures motors are interchangeable with each other. .

The brake stops the motor when the arm hits the switch – This is the burn mode

Burn drive motor brake armature

Brake armature pivot point

The arm is shown in the

ash dump position

Shaded pole of the motor (1 of 2)

Burn drive motor brake armature

Brake armature pivot point

The motor is shown positioned in the ash dump

mode

Shaded pole of the motor (1 of 2)

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Rex Engineering: Although you will never have a need to disassemble the brake mechanism, it is easier to see how it works if we break it down into the individual components.

Notice that although the output shafts on both motors turn in the same direction, the motors turn in opposite directions

This is all (4) of the brake components removed from the gearmotor

This is the two slot gear mounted to the motor armature. It is attached by an

assembly that allows it to act as a clutch. It will allow the gear to slip to relive any stress

that would be cause by a sudden stop

With the brake components removed, we can see the lower

ball bearing and the two shaded poles

Ball Bearing

Shaded poles

The motor armature with the two slot gear has been added

The short locking arm and spring has been installed. Notice

that the spring pulls the arm towards the center and into a slot

Gear box

The brake armature has been added. Observe the

armature resting against the locking arm and the gap of the armature to the motor frame when the motor is

de-energized

The brake armature has been added. Observe the armature

resting against the motor frame and the lack of a gap of the armature to the motor frame

when the motor is energized

The upper bearing assembly is now installed and the brake is completely assembled on the

motor. The gearmotor is ready to

install in the stove

Gap

Gap

Ball Bearing

Shaded poles

Gear box

No Gap

Gap

13

SPG Co. Ltd.: Although you will never have a need to disassemble the brake mechanism, it is easier to see how it works if we break it down into the individual components.

This is all (3) of the brake components removed from the gearmotor

This is the two slot gear mounted to the motor armature. It is attached by an

assembly that allows it to act as a clutch. It will allow the gear to slip to relive any stress

that would be cause by a sudden stop

With the brake components removed, we can see the lower

ball bearing and the two shaded poles

Ball Bearing

Shaded poles

The motor armature with the two slot gear has been added

The short locking arm and spring has been installed. Notice

that the spring forces the arm towards the center and into a slot

Gear box

The brake armature has been added. Observe the

armature resting against the two slot gear and the gap

of the armature to the motor frame when the motor is

de-energized

The brake armature has been added. Observe the armature

resting against the motor frame and the lack of a gap of the armature to the motor frame

when the motor is energized

The upper bearing assembly is now installed and the brake is completely assembled on the

motor. The gearmotor is ready to

install in the stove

Gap

No Gap

Gap

Ball Bearing

Shaded poles

Gear box

14

Air Pump: The Air Pump is a dual diaphragm Oilless Linear Pump that feeds an equal amount of air to each Igniter. The air pump runs any time the igniters are energized but usually only during the startup period. Approximately 15 seconds after the air pump starts the igniters are energized and will continue to run for approximately 30 seconds after the igniters are de-energized allowing the igniters to cool. This extended time on also provides injected air into the burn pot to help the burn establish itself. The filter may be cleaned as necessary.

Hiblow USA

When the alternating current is applied to the electromagnet as in the figure above the actuating rod moves first in the direction of the arrow as shown in Fig. A and then in the direction of the arrow as shown in Fig. B, by the magnetic attraction and repellent forces exerted between the electromagnet and the permanent magnets attached to the rod. The rod vibrates at the same frequency as that of the power supply and changes the volume of the space enclosed between the casing and the diaphragm. Thus, the air intake, compression and exhaust can be performed through the valves.

Filter Material on bottom of the air pump

15

Switches: A switch can control a device (output) or be used to provide a signal (input) to a controller. They come in all types, sizes and some have an actuator mounted integral to the switch. Some switches can be adapted to many different styles of actuators such as push buttons, key switches, spring actuators and actuators that perform several different actions within the same actuator. Fortunately, the Bixby stoves use the simplest of switches which perform only on/off operations.

Besides differences in type or size, the switch also has ratings that need be matched to the application of the switch. These ratings are; voltage, amperage and AC or DC rated. The ratings cannot be exceeded or damage could come to the switch. A single switch can contain more that a single set of contacts. The contacts can be made of silver, copper or coated with gold. The way the stationary and moveable contacts interact can be a simple butting of the contacts, wiping (self cleaning), roller or knife/blade combination. Other differences can include a simple make/break, make before break or break before make contact arrangement. Again, the Bixby stoves use only very simple switches. When looking at a wiring diagram of any circuit, the circuit is always shown with all switches and devices in the non-power on mode, i.e., off and ready to run. In all circuits it is important to know this. With this knowledge, one should be able to look at the circuit to determine what needs to happen in order to make the stove run. A well designed circuit will always use switches in a “fail safe” manner. This means that the switch can be monitored while it is in use and if it were removed or failed, the circuit would shut down. As an example, the door switch is in the closed position while the door is closed. There will be a completed circuit through the switch, which tells the controller that it is in the circuit and all is O.K. If the switch opens, it is an indication that the door has opened (or the switch has failed) and the controller will start a sequence to shut the stove down if the door is not closed in a predetermined (1 minute) amount of time. If the switch was used as a normally open (with the door closed), the switch could be bad or even removed from the circuit and the controller would not know the difference. The door could be opened and remain open without the stove ever shutting down. A switch can be designed normally open (N.O.) or a normally closed (N.C.). When holding a switch in your hand, as an example, it may be a normally open switch. But, we need to know that the switch is used as a normally closed switch; i.e., the door switch. The door is closed when the stove is running so we must look at the switch as it is being used in its’ normal position of operation when the stove is running. Door switch: The door switch is used as an input to the controller and in this case located in the low voltage circuit. With the door closed the switch contacts are closed and remain closed under normal operating conditions. The switch is actuated indirectly by a rod that is pushed in towards the back of the stove and onto the switch actuator as the door is closed. As the door opens, a spring on the rod pulls the rod towards the front of the stove and off of the actuator of the switch thus opening the switch contacts. The switch should be adjusted to “click” as the door handle is about half way down (about a 45º angle). The adjustment should be made by loosening the two screws holding the switch to the switch bracket. The bracket is slotted to allow movement of the switch front to back. It is not recommended adjusting the switch by bending the actuator on the switch. Care must be taken to not over tighten the two screws as this could damage the switch. Keep in mind that the door switch is a SAFETY switch. Its’ purpose is to shut the stove down if the door were to be left open longer than one (1) minute. If the door switch were to become defective needing replacement, the stove should not be used until the switch is replaced. An easy and simple test of the switch is to open and close the door noting a flashing #4 error code light when the door handle is moved more than 45º towards open. If the light does not come on, the switch may have failed in the closed position. If performing a test using either an ohmmeter or a continuity tester, there should be no continuity with the switch actuator NOT pushed. With the actuator pushed you get a continuity indication or a reading of zero ohms. You will always hear a click when it is actuated. Do not use sound alone as a test to determine if the switch is good.

16

The following is a picture of a door switch used on the MaxFire (115) and the UBB. The model 110 used a slightly different looking switch and a little different mounting means but the principal is very similar to that of the one pictured. The moving part that applies the operating force to the contacts is called the actuator, and may be a toggle or dolly, a rocker, a push-button or any type of mechanical linkage.

Door Push Rod

Door Switch Assembly

Push Rod Spring

Door Switch Location

Stove is shown without front wrap for clarity.

Com NO 1 3

Door Switch Assembly

Door switch mounting bracket

Switch actuator

Mounting and adjusting screws

Wire connections to switch

Switch plunger Door Push Rod

17

Ash drawer switch: The ash drawer switch, like the door switch, is also a SAFETY switch and is on the low voltage side of the control board. The switch is a plunger style switch and is actuated directly by the ash drawer. Two styles of switches are used for the ash drawer switch and both are directly interchangeable with each other. Style “A” has the plunger actuator built into the switch. Style “B” is actually a two piece assembly. The manufacture can assembly the plunger actuator with several different types of switches dependent upon what the customer needs. The contact designation is usually marked on the switch; i.e., common (com), normally open (N.O. or no) and normally closed (N.C. or nc). At times there may only be numbers near the terminals. If this is the case there are either markings on the box or an instruction sheet showing how the contacts are situated. `

Normally Closed Normally Open

Common

Style B Assembly

Style B Switch

Style A Switch

Com

mon

Nor

mal

ly

Ope

n

nc

1

2

4

Com NC

NO

1 2

4

Normally Closed Normally Open

Common

Style B Assembly

Style B Switch

Style A Switch

Com

mon

Nor

mal

ly

Ope

n

nc

1

2

4

Com NC

NO

1 2

4

Location of ash draw switch

Normally Closed Normally Open

Common

Style B Assembly

Style B Switch

Style A Switch

Com

mon

Nor

mal

ly

Ope

n

nc

1

2

4

Com NC

NO

1 2

4

Location of ash draw switch

Normally Closed Normally Open

Common

Style B Assembly

Style B Switch

Style A Switch

Com

mon

Nor

mal

ly

Ope

n

nc

1

2

4

Com NC

NO

1 2

4

Location of ash draw switch

18

Burn drive motor switch: The burn drive motor switch’s primary job is to position (limit) the cam on the output shaft to set the upper and the lower paddles in the burn mode position. The switch is a normally closed switch, but in its normal use (when the burn drive motor is in the burn position), it has its contact in the open position. When the burn drive motor is running, the contact on the switch closes. This closure of the contact tells the computer that the upper and lower paddles are not in the burn position. The computer cannot tell exactly where the arm on the burn drive motor is except when it is parked in the burn position. The second job of the burn drive motor switch is that of a SAFETY device. When the stove is running normally, this switch will be normally open telling the computer that all is well. But should the arm on the motor stop anywhere but on the switch for a pre-determined amount of time, the software will start a process to shut the stove down and to show an error code with the #7 light flashing. There are two issues that could cause the motor not to stop in the burn position. First and most likely would be a hard clinker that would get jammed in the burn pot. A jammed clinker would not allow the motor to turn past the jam and not allow the motor to rotate to the parked position and actuate the switch. One rotation of the burn drive motor takes about nine seconds. There is an allotted amount of time for the burn drive motor to turn a complete 360º of rotation. If the timing sequence were twelve seconds, then the switch needs to be sensed and remain open in less than twelve seconds and remain open. The contact being open on the switch indicates that the ash dump sequence has operated as it should. Normally, the switch is actuated before the timing sequence times out. Should the motor become jammed or not stop on the switch for any reason, power will be removed from the motor at the end of the timing sequence and the #7 error indication will appear on the touch pad. The second issue that could cause the motor not to stop on the burn drive motor switch is the brake on the burn drive motor. We looked at the two styles of brakes that are used on the burn drive motors and have seen that they are very similar to each other. Both styles of brakes are actuated in the same way. When the motor is de-energized (off), the brake is set, holding the armature of the burn drive motor stationary (a parking brake). When the motor is energized a magnetic pole is formed at the shaded poles of the motor. This basically it is an electromagnet. The magnetic force pulls the armature of the brake in towards the motor frame which allows the motor armature to turn. When power is removed from the motor, the magnetic force disappears and the brake should set and stop the armature. When this doesn’t happen, the motor can coast past the switch. As it passes the switch, it will activate the switch momentarily. Since the computer is looking for the switch to remain open, it generates an error code, #7 flashing light, and will go into the shut down mode. The burn drive motor switch is very similar to the door switch. Like the door switch, it only has two terminals so there is no confusion about where the wires go on the switch. It does not matter which wire goes to which terminal as they will work either way. You can see the plunger on the switch. The switch itself, like the door switch, is not operated directly by the arm on the burn drive motor. The arm on the burn drive motor pushes the actuating arm into the switch which depresses the plunger which actuates the switch. If the switch needs to be adjusted, loosen both mounting screws. With the switch sitting on the cam, move it in until the switch clicks and then just a little more. Gently tighten the mounting screws.

Com

1

NO

3

Stationary mounting screw – (pivot point)

Plunger

Moveable mounting and adjustment screw

Actuator

Switch terminals

Burn drive motor limit switch

19

Touch pad: The touch pad is a membrane or bubble switch. The American Society for Testing and Materials (ASTM) defines a membrane switch as “a momentary switch device in which at least one contact is on, or made of, a flexible substrate.” Membrane switches usually consist of 2 - 4 layers of PET:

1. The first layer PET (Polyethylene terephthalate) with circuit printed. 2. Second layer acting as a spacer can be another PET film. 3. The third layer as a circuit closer. 4. The front panel, a PVC or Polycarbonate layer with button pattern and picture printed.

This view is from the left side of the stove. Notice that the cam is sitting in the ash dump position (180º out from the switch).

Location of the burn drive motor switch

Air pump

Burn drive motor

Burn drive motor switch

Cam

20

The touch pad the Bixby uses is a seven (7) layer membrane switch. One layer is imprinted with the printed circuit, switch contacts and LED’s. The printed circuit used can be copper, silver or graphite. Metal snap domes are installed in a layer over the ON/OFF and UP/DOWN switches to give a feedback feeling to the switch. The following illustrations give examples of how a membrane switch is constructed.

or features must be met in order to be classified as a membrane switch:

Wiring diagram of the model 115 touch pad

1

LED

Switch configurations

(side view)

21

Sensors A sensor measures a physical quantity and converts it into a signal which can be read by an observer or an instrument. There are several types of sensors:

1. Thermal 5. Optical 2. Electromagnetic 6. Mechanical 3. Chemical 7. Ionizing 4. Acoustic 8. Others

Of all the types of sensors, the Bixby stoves use types 1, 2 and 3. The thermal sensors that are used would be the hopper snap disc and the thermocouple. A brief description of each follows. Hopper snap disc: The hopper snap disc is attached to the left side of the hopper wall. This snap disc simply senses the temperature of the hopper wall but is also influenced by the air temperature surrounding it. The snap disc is a simple switch that has two positions; open or closed and can be either manual or automatic reset. Snap discs come either normally open or normally closed. They come in a variety of temperature ratings. There are two temperatures attached to the snap disc; a temperature at which the snap disc operates and a lower/higher temperature that it will reset itself if it is an automatic reset. In other words the snap disc can be either a high or a low cutout. The snap disc used on the MaxFire and UBB is a normally closed switch that resets automatically. It is rated to open at 105ºC (221ºF) and to reclose (reset) when the temperature drops down to 66.22ºC (144ºF). The snap disc is a SAFETY device and wired in series with the feed wheel motor. When the snap disc opens (high temperature), it keeps the feed wheel motor from running and adding fuel to the burn chamber. When the snap disc cools enough, the feed wheel motor will begin to operate again. The snap disc is either good or bad and there are no adjustments to be made to it.

Door switch

Snap disc

Upper right hand corner on left side of stove

Shown actual size

Contacts open on temperature rise

22

Current Coil The CT (current coil) (MaxFire models 110 & 115) is labeled “T1”, located on the igniter board and looks somewhat like a black donut (Figure A). The CT senses the amount of current flowing through a wire that passes through the opening in the current coil. On the 110 & 115, the CT senses only the amount of current flowing through the igniters. A jumper wire connected to terminals ST15 and ST16 runs through the center of the current coil. This wire is common to both igniters, meaning that all of the current running through each igniter runs through the jumper wire. It does not matter which direction the jumper wire runs through the current coil. On the UBB control board, the current coil label “T2”, is located near the bottom of the control board and looks more like a small transformer (Figure B). The UBB is similar in the way it works. All of the current flowing on the control board runs through the current coil. This means the stove can read the current going to every motor and fans. Through the software, we can see the current usage on all the motors and fans. This configuration makes the software more versatile and allows one to see the health of the stove better. There are two types of current transformers that are used in the Bixby stoves as mentioned. MaxFire models 110 and 115 use a “torroidal current transformer” where as the UBB uses a “wound primary current transformer. They both perform the same functions; they measure current and the isolate the circuit being monitored from the circuit doing the monitoring. There is a difference in how they do their job. The torroidal CT monitors a primary wire or wires that pass through the hole in the CT and has no electrical connection to the circuit being monitored. The wound primary CT has the primary wire build into the CT. This CT is inserted in series with the circuit being monitored. The wound primary CT in its design has a higher accuracy then the torroidal CT. How does the current coil work? First, the current coil is used only on an AC circuit. The principle of operation of the current coil is, a voltage is “induced” into any wire that runs parallel to a wire carrying an AC current. OK, so what does that mean? When an AC current flows through a wire, a magnetic field is developed around the wire as it is changing amplitude and direction. It is the movement of the lines of force that induce a voltage in a conductor This “field of force” (magnetic field) is not present when a DC current flows through the wire because once the DC current reaches its’ maximum intensity, the magnetic field becomes static. Without movement of either the field of force or the conductor, there will be no induction. To measure current in a DC circuit, a “shunt” is used and the volt drop across the shunt is measured and an amperage value is calculated.

Model 110 & 115 Wound primary

Current Transformer

Secondary winding Primary winding Primary winding

UBB

The voltage induced into the secondary of a transformer is proportional to the turn’s ratio of the primary to the secondary. Current is inversely proportional to the turn’s ratio. Output

equals the input of a transformer (VAOutput = VAInput).

Current flow Conductor

Electromagnetic lines of force

Conductor Current flow

Electromagnetic lines of force

Conductor

Torroidal Current Transformer

B A

Secondary winding Primary winding Primary winding

A B

Secondary winding Primary winding Primary winding

A

23

When two wires of dissimilar metals are joined at both ends and one of the ends is heated, there will be a continuous current which flows in the thermoelectric circuit. This effect was discovered in 1821 by Thomas Seebeck for whom the effect is named.

This is an example of the Seebeck voltage. This voltage cannot be measured directly as a new junction is created when a voltmeter is connected to the thermocouple. A voltage can be measured but it will be inaccurate.

Thermocouple: The thermocouple converts heat (thermo-energy) into an electrical energy. The relationship between the temperature difference between the (hot junction) and reference (cold junction) and the output voltage of a thermo-couple is nonlinear so it must be used with a digital circuit designed to give the desired results. The thermo-couple is made from two dissimilar metals that are welded together at one end forming a junction. There are more than10 types of thermocouples; i.e. K, V, T, J, E, N, R, S; all which have their own temperature and voltage characteristics’. The colors of the outer wrap and of the wires tell what type of thermocouple cable it is. Type “K” is used in the Bixby stoves. The K type has an outer wrap of BROWN with a YELLOW trace, a RED wire (CHROMEL (NI-CR) - MAGNETIC) which develops a negative voltage while the YELLOW wire (ALUMEL (Ni-Al) – NON-MAGNETIC) develops a positive voltage. Standard ANSI color-coding is use for each thermocouple type. The temperature range of the K type thermocouple is 0 Cº to 1250º C (32ºF to 2282º) and has an accuracy of 0.75% ºC. When heated, each conductor develops a voltage potential which is different from each other. The output voltage developed by both of the wires is the combination of the two individual voltages which is approximately 41 µV/°C for the K type thermocouple. The voltage range of the thermocouple is typically within -6 mv (milli-volt) to 70mv DC (0.001 of a volt) dependent on the temperature of the junction. The final number that the computer comes up with is a calculated number derived from the difference between the “hot junction” and a “cold junction.” The hot junction (thermocouple) is inserted into the exhaust manifold and the cold junction is built into the control board. Thermocouples are generally good or bad but occasionally a thermocouple can get out of calibration but this is not the usual case. When checking the thermocouple for continuity or resistance, you should be finding a reading very near zero ohms. To check the thermocouple in the stove (without a computer connected to the stove), pull the thermocouple out of the exhaust manifold and using a match or lighter, heat the junction (end) of the thermocouple. The convection fan should start to run if it is good. Using a computer and BixCheck, go to Monitor and watch the thermocouple number in the telemetry window as the stove is running or by heating the junction of the thermocouple. The number should change as the thermocouple is heating and cooling.

Connector to main control board

Hot Junction

24

Magnet in the sensor

Exhaust fan assembly showing sensor position on

the fan assembly

Motor cooling fins

Exhaust fan sensor: The exhaust fan sensor is a non-contact ferrous metal (having the presence of iron) detecting device. The sensor is a HALL EFFECT transducer, (changes one form of energy into another form of energy), which varies its output voltage in response to a changing magnetic field. There are two types of Hall Effect transducers; one detects a magnetic field and one which has a magnet built into the sensor and detects a ferrous metal. The exhaust fan sensor used on the Bixby stoves has a magnet built into it which when a ferrous metal comes close to it, the magnetic field is distorted and the sensor produces an electrical analog wave. This is seen outputted as a pulse each time one of the cooling blade fins pass the sensor. The cooling fan blade has ten fins so for every revolution of the motor the software is seeing ten pulses. As an example, if the exhaust fan were running at 1,500 RPM (revolutions per minute), the number of pulses the control circuit would be seeing would be 15,000 PPM (pulses per minute). So for every ten “ticks” the software sees 1 RPM. The exhaust fan sensor is used as a tachometer which enables the software to know the speed of the exhaust fan which is then compared to an expected value. If the actual pulse count is not the same as the expected value, the software will increase or decrease the speed of the exhaust fan. Take note that the measurement of the motor RPM’s is divided by 24 (by the software) which brings up a number between 0 and 150; i.e. if the RPM of the motor is 1800, then divided by 24, the software will see the number 75. This is the number (0-150) that is used for the control of the fan. A number between 0-150 is used because of several limitations of the CPU and the phase control circuit. Because of this, the motor can vary by 24 RPM before a correction is made. This means that the motor could go -24 RPM to a +24 RPM before a correction is made by the software. It seems some stoves are more prone to this “hunting” or “wandering” then others. This may be why some owners notice the sound of the exhaust fan more than others. It does not indicate that there is anything wrong with the stove, but it can be a normal annoyance. The sensor must be in close approximation to the cooling fan blade fins to sense properly and is either good or bad. A couple of items that can cause problems with the sensing circuit are; the distance to the fins may be too far away, a loose cooling fan blade (rotating slower the motor shaft), one or more fins being bent out of alignment or the cooling fan blade being misaligned on the motor shaft in relation to the sensor. If a fin is bent out of place, the sensor would miss count the pulses; i.e. if the sensor counts only nine of the ten fins every revolution, the software will determine that the exhaust fan is running too slow and increase the speed of the fan. This would show up as a lean burn with the trim pot knobs needing to be set richer than normal. If the sensor were to go bad, an error code of a flashing number six (6) LED would appear on the touchpad. If you were to connect a milli-volt meter to the leads of the sensor (polarity for this test makes no difference), and then pass I small piece of metal across the sensor, you would see a small voltage being produced as the metal is moving passed. The sensor would be bad if no voltage were produced.

25

Notice the Sensor bracket is held on with 2 nuts. These can be removed so the Sensor can be replaced outside the stove.

Notice the Sensor is close to centered on the blade of the propeller. This needs to be within 1/16” to 1/8” of the blade. Turn Sensor in until it touches a blade, back off 1 to 1½ turns. Rotate blade checking that no blade comes in contact with the Sensor.

26

Feed wheel sensor: The feed wheel sensor is similar to the exhaust fan sensor in that it is also a Hall Effect sensor. Where the exhaust fan sensor has a built in magnet, the feed wheel sensor detects an external magnetic flux (field). The feed wheel sensor is polarity sensitive in that only a South Pole of a magnetic flux will trigger the sensor. The magnetic field that is sensed is that of the four imbedded magnets in the feeder wheel. The proximity or closeness of the sensor is not as critical as that of the exhaust fan sensor. The output of the sensor is a digital signal. With this sensor we are using is as a positioning device. When one of the magnets imbedded in the feed wheel passes over the sensor a signal is outputted turning the feed wheel motor off. The positioning of the wheel is such that a solid portion of the wheel covers the feed tube in its’ resting mode. This helps contain any transfer of air between the burn chamber and the fuel hopper.

Sensor is adjusted flush and then back off 1 to 1½ turns

The Hall effect describes what happens to current flowing through a conducting material - a metal, a semiconductor - if it is

exposed to a magnetic field B

Top of Wheel

Bottom of Wheel Feed Tube

Bottom of Feeder Wheel White Dot (South Pole)

Showing

27

You should now have a fair understanding of what the parts look like, what they do and how they work. There are times when you need to work on an appliance of any type but have no idea of how it works. A lot of the items we work on are fairly straight forward and have no software. If I were to make a guess at the percentage of trouble the software presents, it would be less than 5%. There are events that can alter or completely destroy the software, but these are more rare than common. Software problems happen mostly because of user input. So the first thing I look at is the hardware. When you look into an appliance you see a lot of wires and things. So how can we somewhat tell how the appliance might work? Most appliances will have a wiring diagram somewhere, whether it is in the owners' manual or attached to the appliance somewhere. There are several ways to present a wiring diagram. There can be a simple diagram showing the parts as a drawing depicting what they look like and the wires and where they go. The wiring diagram used in the UBB owners’ manual is called a line diagram. In the wiring diagram of the UBB, we see the individual parts and where the wires go on the control board. With this type of diagram we can only tell where the wires from each device plugs into the control board, but there is nothing to indicate the voltage of any single device. We could make the assumption that all of the motors are 120 volts, but there is not a real good way to tell short of reading the name plate on the motors. For safety, if an assumption is made, assume the higher voltage rather than the lower voltage. As for the switches, they could either be high or low voltage. Some diagrams will show the location relationship of the parts to each other but the UBB does not. It does show the shape of each device so when looking at a certain device you will have some idea of what the part is. One item that is missing is the rating of the fuses. A fuse will have three characteristics; amperage, voltage and type. The type may be a slow blow, fast blow or high energy. When replacing a fuse, always replace with the fuse with a fuse of the same type, voltage and amperage. If you can’t find the same amperage, choose smaller rather than larger. Fuses are sized by the manufacture to protect their product. Using a larger amperage fuse or a different type could cause costly damage to the product and possibly void any warranty that may be in effect. There is no diagram of the circuitry of the PCB because there are no user parts to repair.

HOPPER SNAP DISC

HOPPER SNAP DISC

UBB Control Board Wiring Diagram

28

This is the UBB PCB. Notice all of the parts and connectors are marked as to what they are. If you ever replace a UBB PCB or just need to disconnect wires or a wire, you will always know what goes where.

Convection Fan

Fuel Type

Future

Exhaust Fan

Feed Rate

Ash Content

Computer Connection

Touchpad

Thermocouple 1-4

Feed Wheel Motor

Spare - Future

Burn Drive Motor

Air Compressor

Exhaust Fan

Door Switch Ash Drawer Switch Hopper Door Switch Burn Drive Motor Switch

UBB Control Board

Convection Fan

Convection Fan Capacitor

Power In

Left Igniter

Right Igniter

Thermostat

PICkit Terminal

Feed Wheel Sensor

Exhaust Sensor

29

Another wiring diagram style is used on the MaxFire 115. The biggest difference is the PCB is shown as a box with connectors on it and the individual wires going to the devices. There is a little more information shown; i.e. the wiring of the touchpad, wire colors of all the devices, fuse sizes and the wiring of the trimpot knobs. Notice that there are two PCB’s. The larger of the two is the main control board and the smaller is the igniter board. The two boards were combined into one on the UBB. I do need to point out a small problem with this wiring diagram. Wiring diagrams are drawn with the appliance in the shut down mode and ready to start. This means that any and all safety devices will be shown in their normal operating positions. The switch that starts the appliance will be a normally open switch. In this diagram, all of the safety switches are shown in the open position which would not allow the stove to start. I do not know why it was drawn like this, but I do know that it is not the industries standard way of showing a safety switch. From this wiring diagram we get a little more information than what we have on the UBB wiring diagram. For a picture of the main control board, see page 8 and for a picture of the igniter board, see page 10. A wiring diagram is basically a picture that represents the circuit. There are several different types of wiring diagrams and standards.

NOTE Safety switches – The switches should be shown as closed (red

dotted line)

This is the symbol for the ground connection

Motor capacitor

Feed thru power on the igniter board

Fuel select switch:

Note switch position

LED’s

Fuse Size Fuse Size

Fuse Size

Should be “NC”

30

Example – Ladder Diagram

T1 Control Relay

Power Relay

Indicator Light Normally Closed Contact

Controller

Normally Closed Switch

Normally Open Switch Normally Open Contact

CR1

H1

R

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The Ladder Diagram. This diagram simply shows how switches, contacts, relays and indicators relate to each other electrically. It does not represent the physical relationship of the parts to each other. When looking at a ladder diagram, all of the contacts and switches are shown in an off power mode, as if it were being operated for the first time. There are a couple of things you need to know when looking at the ladder diagram:

1) Power is disconnected to the machine or appliance. 2) All switches are shown in their native position. 3) Some switches or devices may have to change position to operate the appliance. 4) Some diagrams will use the line numbers for reference. 5) The numbers in the Red Squares are the number assigned to an individual wire or conductor. 6) Switches can have operators (the part of the switch that moves the contacts) as follows:

a. Maintained – Once moved to a position, the operator must be moved again to change the state of the contacts associated with the operator.

b. A maintained operator can be either turn or push/pull c. Momentary – The contact will change state as long as the operator is held in a position. d. Delayed – After the operator has been moved, the contacts will change states after a timed

period. 7) All safety devices, switches or contacts will be in the closed position. 8) The X,s and the O’s tell us when the contacts change state; X=change state; O=no change

Why am I going through all of this when the diagrams the Bixby stoves are of another type? The Ladder Diagram is the easiest to learn how to read an electrical diagram. If we can get to know how to read this type of diagram, the other will follow much easier. Understanding the 8 steps above will allow you to “reason” how an appliance works. A long time ago, I was asked to design a plating process for printer circuits. This particular diagram is relatively simple to follow and analyze. Although it has nothing to do with the Bixby stoves, it will help you to read and understand most any electrical diagram. Let’s go through the Ladder Diagram and see if we can decipher how the appliance or machine works. This project involved a tank for the plating process of printed circuit boards. The process in a way is very simple. Circulate a fluid in a tank, warm the fluid to a set temperature and then through a rectification process, plate a printed circuit board with copper for the conductors. This diagram of the Copper Tank is showing only the low voltage control circuit. How do we know this? Look under “L1” in the upper left hand corner of the diagram. It states “From Control Transformer”; which usually is a lower voltage than the motors it is controlling. What will it take to turn this appliance on? What needs to happen to make the “Copper Tank” run can be summed up in the following steps? We will take one item at a time because to get to “x” going from “a”, we must follow the steps that lead to the next step. Although things may look to happen all at one time, everything happens step by step. Note: a) We will be talking about current flowing from “L1” to “Neutral” or Left to Right. b) N.O. = (Normally Open) c) N.C. = (Normally Closed)

1) Power is stopped at both the Control Power Switch and the CR1b contacts (lines 10 & 107) because of the open circuits (contacts).

2) Closing the Control Power Switch (line 104), CR1 becomes energized. We know this by looking at the contact position notation by the switch:

a. In the OFF (O) position no current can flow. b. In the ON (X) position current is allowed to flow to CR1

3) All CR1 contacts change state – going from either N.O. to N.C. or N.C. to N.O. 4) CR1a (line 104) closes allowing the Control Power Indicator to illuminate. 5) CR1b (line 107) closes allowing current to flow past the contacts. 6) Power to Level Control - LC (line 117). 7) Power to Temperature Control - T1 (line 122).

At this point nothing else happens other than having power to the Level Control (LC) and the Temp Control (T1). Now we are ready to start the appliance. The Filter Pump Switch is maintain – maintain – hold. The three switch positions are marked; OFF (maintain), RUN (maintain) and HOLD START (hold).

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If the switch is put in the RUN position, the only contact to change states (X) is the bottom contact. Following the flow of current through the switch on wire no. 0106, the flow has two ways to go. 1) From the switch to the Filter Pump Pressure Switch (PS) BUT the switch is open so that is as far as it goes. 2) From the switch to the CR2 contacts where current will flow through the top closed contact (wire 108,

line 113) which goes to the Low Pressure Indicator which lights up telling us we low pressure in the system.

We are now ready to start the Filter Pump. Putting the switch in the Hold Start position we need to hold it in that position. Two things happen here. Both the top and bottom contacts close.

1) From the top switch contact (wire 105, line 108) power goes to Relay M1 energizing the relay and closing contact M1 (line 115).

2) As the pump starts to run, pressure starts to increase in the system and finally the Filter Pump Pressure Switch closes.

3) With the Pressure Switch closed, power follows (wire 107, line 110) energizing the Holding Relay CR2.

4) All CR2 contacts change state. 5) Contact CR2 (9-6) close allowing power to (wire 105, line 110) which brings power to coil M1 setting

up a holding circuit. 6) Contact CR2 (8-2) opens dropping power on (wire 108) turning the Low Pressure Indicator off. 7) Contact CR2 (8-5) closes energizing (wire 109). 8) With contact M1 closed, power on (wire 110, line 115) turning the Filter Pump Run Indicator on. 9) With the Filter Pump Run Indicator on, we can let go of the Filter Pump Switch which returns to the

RUN position. The system has been started and is circulating the fluids in the tank. We now have to heat the fluid and turn the Rectifier on to begin the plating process. We will start with the heating of the fluid.

1) Turning the Temp Control Switch to the ON position energizes (wire 118, line124). 2) Looking at the contacts of Level Control - LC (line 124) we need to know that in the out of the box

state, the contacts are opposite of how they are shown. The purpose of this set of contacts is to shut the heaters off of the fluid level gets too low – protection for the heaters.

3) The LC contact (line 124) energizes one side of the contacts; Heater High Temp, H1, T1. 4) Contact Heater High Temp (a high temp safety contact) is closed and energizes (wire 114, line 124)

bringing power to contact T1 (5-6).

a. Contact T1 (5-6) will cycle open and closed as the temperature of the fluid changes. When T1 (5-6) is closed it energizes (wire 115, line 124) which turns on Relay H1 which controls the in tank heating elements and closes contact H1 (line 125).

b. Contact T1 (8-9) will cycle close and open as the temperature of the fluid changes. When T1 (8-9) closes it energizes (wire 117, line 127) turning on or off the Cooling Valve and Cool light.

5) Contact H1 (line 125) powers (wire 116, line 125) which turns Heat Indicator on or off. 6) If the level of the tank becomes too low, the contacts of the Level Control will change states. The

closed contact LC (line 124) will open dropping power to Relay H1, Heat Indicator, Cool Indicator and the Cooling Valve shutting the process down. Contact LC (line 125) energizes (wire 119) turning the Low Level Indicator on.

7) To start the actual plating process the Rectifier Power needs to be turned on. 8) Turning the rectifier Power Switch to the ON position energies (wire 111, lines 119 & 120). 9) Relay R1 energizes turning the Rectifier on and closes contact R1 (line 120) which lights the Rectifier

Power On Indicator (line 120).

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What the heck are you talking about and what does this have to do with the Bixby? GOOD Question. The Copper Tank circuit has nothing to do with the Bixby. It does have a lot to do in showing the how and logic to go about troubleshooting. The circuit we just went through has everything needed to walk through the circuit to see how it works. This is also called Relay Logic. You don’t have any hidden items or secrets to hide. Without even knowing what this circuit is supposed to do. Before I go on, let’s just try this circuit again but less wordy.

1) Turn the Control Power Switch to ON energizing CR1. a. CR1a (6-9) closes lighting the Control Power Indicator. b. CR1b (5-8) closes energizing Level Control LC and Temp Control T1.

2) Turn Filter Pump Switch to HOLD START energizes Filter Pump Relay M1 closing contact M1. a. The Low Pressure Indicator lights. b. On raising pressure, the Filter Pump Pressure Switch closes energizing Holding Relay

CR2. c. CR2 (6-9) closes holding Relay M1 on. d. CR2 (2-8) opens turning off Low Pressure Indicator. e. CR2 (5-8) closes lighting the Filter Pump Run Indicator.

3) Turn Temp Control Switch to ON energizes Relay H1 closing contact H1. a. Closed contact H1 lights Heat Indicator. b. If tank temperature is high, contact T1 (5-6) will open de-energizing Relay H1 opening contact

H1. i. Contact T1 (8-9) will close energizing Cooling Valve CV and lighting the Cool

Indicator. c. If tank temperature is too hot, the Heater High Temp contact will open turning Relay H1 off. d. If tank level is too low, contact LC (N.C) will open shutting down the heating and cooling

circuits. i. Contact LC (N.O.) will close lighting the Low Level Indicator.

4) Turn Rectifier Power Switch ON energizes Rectifier Power Relay R1 closing contact R1. a. Contact R1 turns the Rectifier Power On Indicator on.

Example – Ladder Diagram

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We have walked through a circuit that we really didn’t know anything about other than it is titled “Copper Tank No. 6 Control Panel – 120v.” Let’s see if we learned something by using the Copper Tank Control Panel circuit. Some things I did not cover or mention because you have to do a little thinking on your own. Question 1: What is the voltage used in this circuit? Question 2: If the fuse blew, what size fuse would you put in? Question 3: There are Red rectangles with numbers in them. What do they represent? Question 4: What state is the circuit in as drawn? Question 5: Next to each switch contact is x’s and o’s. What do these stand for? Question 6: What is “R1”? Question 7: If the ”Filter Pump Pressure Switch” never closed, how would that effect the circuit? Question 8: What is the purpose of contact CR2 (6-9)? Question 9: If this circuit were running and the Control Power Switch was turned to off, how would this effect the circuit? Question 10: What does “CV” stand for? Advanced Questions for those familiar with using a multimeter (combination voltmeter, ohmmeter and ammeter). Question 11: I want to test for voltage. Which scale do I use? DCA, VAC, VDC, Ω, R10 or dB? Question 12: If your meter had the following ACV settings; 0-4, 0-40, 0-400; which setting would you use on this circuit? Question 13: With the Temp Control circuit energized and running, what voltage reading would I expect to have across the “Heater High Temp” contact (wire 113 to wire 114)? Question 14: “Control Power Switch” is on, “Filter Pump Switch” is in the run position and all other switches are off. What voltage reading would I expect to have if I measure across the “Rectifier Power Switch” (wire 104 to wire 111)? Question 15: The circuit is as stated in Question 14. I am looking for continuity across the ”Heater High Temp” contact. Which scale would I set my meter to? DCA, VAC, VDC, Ω, R10 or dB? Question 16: Power is disconnected to the circuit. I want to test for continuity of contact T1 (5-6). What are the two (2) first things I do with my meter? Question 17: Power is connected to the circuit. I want to check to see if there is voltage to the circuit before I work on it. What are the two (2) first things I do with my meter? For answers to questions 1 thru 17, please send a stamped self addressed envelope with two Wheaties box tops to……….Ok, see below. Q1: 120volt. Q2: ¾ amp. Q3: Wire numbers. Q4: Unpowered, ready to run. Q5: X=closed contact O=open contact. Q6: Rectifier Power Relay. Q7: Filter pump would run only in the HOLD START position (Filter Pump Switch). Q8: Holding circuit for Filter Pump Relay M1. Q9: The circuit would shut down. Q10: Cooling Valve. Advanced Q11: VAC (Voltage AC). Q12: 0-400. Q13: Zero. Q14: 120volt. Q15: VAC – Never use Ω or R1 or any ohm scale on a live circuit. Q16: Set the meter to an ohm setting, short the leads together to make sure the meter is working. Q17: Set the meter to the appropriate ACV voltage scale, test the meter on a known source to make sure the meter is working properly.

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Since this is not an all inclusive manual on electricity and trouble shooting, I suggest to those that would like to know more about how electricity works, start with a basic course in Direct Current (DC) and then a course in basic Alternating Current (AC). There are many fascinating things about electricity and the knowledge of the basics will be a big help in trouble shooting any electrical problem. We have looked at a complete basic circuit that shows us all of the parts required to make the circuit work. If this circuit were laid out and drawn like the one used for the Bixby stoves, it may look something like this. Looking at this diagram complicates things a little. The first thing you notice is the lack of knowing what is controlling what. Without knowing more about how the appliance is supposed to work, it makes things a lot more complicated. We could do a lot of guessing what happens first, next and last. There are some clues for the more experienced repair person, but more than likely there will be a lot of guessing on their part. So what do we do when there is so much missing information? You call Bixby Tech Support right? What? It’s 10pm and your stove just shut down. At a moment like this an old saying comes to mind -

“When in trouble, when in doubt, run in circles, scream and shout.”

Now this never helped me, but I always felt a little better and really silly for doing that. I really have no idea what that means! Well, we need to start somewhere so let’s start at the beginning. Let’s look at how the stove starts and how it runs on a step by step examination of the operating system (software). Since I have never had the privy of seeing the software, I will walk us through this the best I can with and without mistakes.

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Firebox: The area where fuel is burned. Flash point: A scientific attribute, the temperature at which a liquid or solid can ignite. Gear-motor: A self contained motor connected to a series of gears designed to increase torque at

the output shaft. Hall Effect: The Hall Effect is the production of a voltage difference across an electrical

conductor. Heat Exchanger: A device built for efficient heat transfer from the exhaust gas to the convection air, and

is separated by a solid wall so that they never mix. Hopper: A holding bin for the fuel. Igniter: An electronic device used to heat the air to 1400* during ignition. Joule: Measure of electrical energy, also refers to a surge suppressor’s ability to absorb

energy. Mother board: The main circuit board that controls most of the stove’s functions. Oscillating: A flame that periodically reverses direction. Program: A set of written instructions imbedded within the stoves’ computer chip telling the

stove how to react to various inputs. Snap Disc: A thermally actuated switch which changes state at preset temperatures with a set

temperature differential between the high temperature and the low temperature. Surge Protector: An electrical device designed to protect electrical devices from power surges and

voltage spikes. Tachometer: A device that indicates the speed of the exhaust fan, converted to RPM. Thermocouple: A thermocouple is a sensor that is used to measure (sense) temperature. Touch Pad: Bixby operator control panel. Trim Pot: Usage of the term potentiometer (or 'pot' for short) describes an electronic

component which has a user-adjustable resistance. Vortex: A vortex is a spinning, often turbulent,flow. Any circular or rotary flow that possesses

circulation.

Glossary of Terms (cont)