http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Home   Sign Up!   Browse   Community   Submit

   All     Art     Craft     Food     Games     Green     Home     Kids     Life     Music     Offbeat     Outdoors     Pets     Photo     Ride     Science     Tech

EVERYONE Needs a Multi-Meterby Phil B on May 14, 2011

Table of Contents

EVERYONE Needs a Multi-Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Intro:   EVERYONE Needs a Multi-Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 1:   Will I electrocute myself? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 2:   So, what can a multi-meter do? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 3:   Your car battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 4:   Corrosion? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 5:   Light bulbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Step 6:   Fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Step 7:   Your air conditioner unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Step 8:   The electric clothes dryer does not dry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Step 9:   Electrical outlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Step 10:   Cords and other things . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Step 11:   Lightning and your telephone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Step 12:   Reading amps. (current draw) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Step 13:   Shocking, simply shocking! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Step 14:   Another use from the past . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Step 15:   Auto ranging meters and reading the meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Step 16:   Accessories and features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Step 17:   User serviceable things . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Step 18:   Additional resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Author:Phil BI miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying postingthings I have learned and done since I got my first tools.

I enjoy studying the Bible and I am also a Lutheran pastor. I like to dabble with some electronics projects. I have a lathe, a radial arm saw, a router, and a fluxcore wire feed welder.

I appreciate Instructables from others that are practical and address real problems with useful solutions. These are the type of Instructables I try to write andpublish.

Intro:  EVERYONE Needs a Multi-MeterA multi-meter can save the average person a lot of money over a few years, even though ladies who choose to buy one may not carry it in their purse when going out forthe evening. You will often be able to solve many problems yourself in less time than it would take to get a technician to come to your home. This Instructable will showhow to do that simply and easily.

I often meet handy people, both men and women, who do not go near to anything electrical because they are frightened of electricity. It is good to have a strong respectfor electricity. It is also good to know how to make basic electrical measurements around the home. A multi-meter is the tool every home ought have. They eliminate theguess work from so many things and can save a lot of money. 

A suitable multi-meter for occasional use around the home and automobile can be had for less than $ 5. This link is to a very inexpensive meter that includes somefunctions found only on meters costing twenty times more just a few years ago. More expensive meters do not necessarily have more features. They give greateraccuracy for professional work, and they are more rugged in their construction and durability.

Step 1: Will I electrocute myself?No, that will not happen if you follow a few simple precautions. Most home uses of a multi-meter will be done with the power disconnected, or with very harmless lowvoltages. Regardless, you will always handle the probes by their well-insulated, completely safe plastic "handles." Usually, you will hold one in each hand.  

The black probe is normally associated with the ground or negative terminal. The red probe is normally associated with the "hot" or positive terminal. For household usesillustrated in this Instructable you can ignore all of that and use either probe on any terminal. 

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Step 2: So, what can a multi-meter do?See the first photo. You can test common batteries, but that is only the beginning of what you can do with a multi-meter. Set the selector to DC volts. Notice the symbolsfor AC (alternating current) voltage and for DC (direct current voltage) as highlighted by the yellow text boxes. Batteries use only DC voltage.  Set the selector to theproper range on the DC scale. Household batteries like AA and AAA are rated at 1.5 volts. On this meter, select the 4 volt range on the DC scale for common batteries. IfI were testing a 9 volt battery with this meter, I would need to move the selector to the 40 volt range.  

(This meter has an ON/OFF slider switch. Many meters turn on when the round selector switch is moved to any setting range. OFF is at the top of the selector dial onthose units. Meters have internal batteries. Turn the meter OFF when finished to save the batteries. Many meters switch themselves off automtically after a few minutes.)

See the second photo. Touch each end of the battery with a probe.  Ideally, the red probe touches the "+" end of the battery and the black probe touches the "-" end ofthe battery, but in practice it does not matter for this purpose. A minus (-) sign will appear in front of the numbers if the red and black wires are reversed when testing thebattery. You are interested in only the numbers. A 1.5 volt battery is "dead" when it registers 1 volt or less. If a device does not work, but the 1.5 volt battery registers (forexample) 1.38 volts, a new battery will not make it work. There is another problem to be solved. A 9 volt battery is "dead" when it falls to read about 7.5 to 8 volts. But,when a battery is "dead" also depends on the application. I use a 9 volt alkaline battery in a wireless microphone. I have learned by experience that a battery with avoltage below 8.5 volts will not last through a one hour church service.

Shown in the photo are several types of common batteries: a 3 volt camera battery, a 9 volt "radio" battery used in smoke detectors and other things, a button batteryused in watches and other instruments, and a common AA battery. In this test the AA battery registers 1.59 volts, which is new in condition.

There are dedicated battery testers you can buy, but a multi-meter costs about the same and does so much more.

Image Notes1. This is the symbol for alternating current (AC) voltage. After failing to distinguishcorrectly between these settings because I did not look closely enough in poorlight, I engraved "AC" and "DC" on the meter surface and filled the markings withwhite paint.2. This is the symbol for direct current (DC) voltage. It is used for testing batteries.The meter is set to read up to four volts. The 400m setting is for millivolts.

Step 3: Your car batteryOne morning you turn the key in your car, but the motor turns over too slowly to start. You suspect the battery may be dead. Set the meter selector to 15 volts DC ormore. Touch the meter probes to the terminal posts on your car battery. The meter will read 12 to 13 volts, but you want to know what the voltage reading is when thebattery is under a load. Have someone turn the key while you watch the meter. If the meter reading drops to around 9 volts or less, you need to charge the battery andsee if that solves the problem. If you still get a reading of about 9 volts under load after a sufficient period for charging, you probably need a new battery for your car. 

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Image Notes1. No reading shows because the meter is actually "off." This battery actually reads 12.54 volts when the meter is "on."2. Black (negative) side post battery terminal.3. Red (positive) side post battery terminal.4. Top of the car's battery5. Air intake duct--You may want to remove this for better access to the battery terminals, especially if it becomes necessary to remove one or both cables from thebattery.

Step 4: Corrosion?See the first photo. Your car battery may be in good condition, but the starter still barely cranks the engine. The problem could be corrosion at one or both of the batteryterminals. Sometimes you will see white or blue powder around the terminals, but often the corrosion is not visible. The photo shows an old-style battery terminal.  If yourcar (or motorcycle or riding lawnmower) has this type of terminal, see the text boxes for where to place the voltmeter probes. Set the voltmeter to a DC setting slightly inexcess of 12 volts. Have a helper turn the key to crank the engine.  If the battery connections are good, the voltmeter reading should remain at zero (0).  If the batteryconnections are corroded, they will provide a high resistance, perhaps even an open circuit, and current will try to go through the voltmeter as an alternate route. Thevoltmeter reads the difference in voltage between one probe and the other. That means the voltmeter will show a reading equal to the voltage of the battery.  Clean orreplace the battery terminal by taking it apart, dissolving the corrosion with baking soda in water, and scraping the parts of the connection. If you use your multi-meter justonce for this, you will have saved enough money to pay for it.

See the text boxes in the second photo. The newer side post battery terminals are now more common than the old-style shown in the first photo. Much of the terminalis covered with insulation. One meter probe touches the terminal's bare metal bolt. The other probe can touch a straight pin pushed through the cable's insulation. 

(The first photo is from Bing Images.)

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Image Notes1. Scrape away the gray lead oxide and touch one probe here.2. Touch one probe to the copper wire here on this connector. Scrape thecopper wire to make it bright.3. If the connector on the end of the battery cable is not the removable typeshown in this photo, but the wire is molded into a lead end, scrape away thelead oxide and touch the test probe here.

Image Notes1. Push a straight pin from a sewing kit into the cable insulation until it makesgood contact with the stranded copper cable inside. Use a pair of pliers to keepthe pin from bending back on you while pushing it into the cable.2. Battery side post3. Connector for an engine sensor. This could be disconnected for testing to givemore access. Be sure to put it back when fininshed.4. Cable armor--slide this back to expose the red battery cable.5. Side of the car's battery

Step 5: Light bulbsIs your light bulb burned out, or is there a problem with your lamp? The first test is to check for a circuit through the light bulb. Use a low resistance or a CONT setting.This test will not work with the compact fluorescent bulbs, nor with fluorescent tubes. Those do not have a continuous conductor running through them, like anincandescent light bulb.  Rather, they are filled with a gas that becomes a conductor when exposed to a high voltage electrical charge. 

If the bulb tests good, some further checks on the lamp socket are necessary. See the second photo. Set the meter to the 400 volt AC selection. Touch one probe to theside of the bulb socket.  Touch the other to the tip at the bottom of the socket. The meter should read about 120 volts. (Note: I live in the USA where most electricaloutlets operate on 120 volts. Heavy duty appliance circuits (electric stoves, clothes dryers) use 230 volts. In many other parts of the world the standard voltage inhousehold electrical systems is 230 to 240 volts. Adjust the readings you expect according to the normal voltage provided in your locale.)

You may find the expected voltage in the bulb socket and the bulb is good, but the lamp still does not light. If the socket is older, the contact tip at the bottom of the socketmay have lost its springiness and it may not make dependable contact with the center tip of the bulb. Use a popsicle stick to lift the tip. If you can be sure there is noelectrical power to the socket, you may use a screwdriver. Then screw the bulb into the lamp socket and it should work. In time you may want to have the lamp socketreplaced, but it can work this way for a long, long time.

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Image Notes1. Center tab--Raise this a little, if necessary. Be certain the power is "off," or use awooden popsicle stick.

Step 6: FusesMany devices use fuses, from your automobile to your household air conditioning system. A fuse is an electrical conductor designed to fail when a pre-determinedthreshold of current is present in the circuit. Their purpose is protect the rest of the circuit from a current load that would destroy it. 

Sometimes fuses are out in the open where they are visible. Sometimes they are under a cover marked "Fuses." Sometimes they are inside an appliance with no noticeof their presence. This is true of some microwave ovens and some television sets. Open the case and look for a small cartridge fuse like the one shown in the photo. Thefuse will usually be near where the electrical cord comes into the appliance. You may have thought you need a new microwave, but the real problem may be only a smallfuse costing less than a dollar. Sometimes there is a more serious problem that will cause a new fuse to "blow," too. But, more often, the old fuse simply became weak or"blew" because of a momentary electrical surge. If your multi-meter saves you from replacing an appliance that failed due to a blown fuse, your meter will have paid foritself many times over. 

It is always good if you can have extra fuses available for whenever one needs replacement. When you need to buy a fuse, take the old fuse with you to the store so itcan be matched. Fuses come in a variety of physical sizes and types. It is important to replace a fuse with one exactly like it. Some fuses are available at your localhardware or building supply store.  Some, like small cartridge fuses similar to the one shown in the photo, are available only where electronics parts are sold, or on-line.Identifying numbers are imprinted on the shiny metal end caps.

The fine wire in cartridge fuses is often so fine that it is difficult to see with the unaided eye. Some fuses have a solid body that blocks vision. When testing fuses set themulti-meter to CONT. for continuity. Touch the probes together when on this setting and you will hear a shrill tone indicating there is a continuous circuit through the fuse.The words "continuity" and "continuous" are purposely related.

WARNING: If you open the case on a television or a microwave, be careful not to touch components other than the fuseholder. There are parts that retain a high voltageelectrical charge. It is not likely you would touch these, anyway; but, if you did, they can kill.

 

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Step 7: Your air conditioner unitAir conditioning systems always seem to fail during the hottest, most miserable weather. No one wants to spend a muggy night trying to sleep with no air conditioning. Ifthe problem is only a fuse, your meter can save you the cost of a service call by a technician, and you can have your system up and running again before the house haseven warmed up inside.

Your air conditioning system may have more than one set of fuses protecting it. There may be a set of circuit breakers in your main electrical panel. Check to see that thecircuit breaker toggles have not moved to the "off" position due to a sudden overload. Go to the air conditioner unit outside your house. Look for any cable conduits (metalpipes, some flexible). Follow them with your eye and look for any metal boxes that might contain fuses. The fuses will likely be mounted in a fuse block that can be pulledfrom the box. Use the continuity setting to check the fuses. The first photo shows a control box near our heat pump/air conditioner. It looks like it might contain fuses, butit contains only a disconnect switch.  

See the second photo. It shows the inside of the fuse box that controls our air conditioner. The yellow text box contains information on the ON/OFF switch. I overlaid thephoto with capital letters as markers. Those in red make a "hot" circuit even when the switch is "off." Keep your hands safely away from these terminals.

Set the meter to the 400 volt AC setting. If you place one probe on A and the other on B, the meter should read about 230 volts. That is true whether the switch in the boxis "on" or "off." Place one probe on A and the other on C. The meter should read about 115 volts. Place one probe on B and the other on C. The meter should again readabout 115 volts. Readings between F and C or G and C should also each give a reading of about 115 volts when the switch is "on." These readings indicate the fuses aregood. With the switch in the "off" position, readings between F and C or G and C should be zero volts.

If you wish to check the fuses without them being electrically charged, move the switch lever to the "off" position. Set the meter to CONT. Touch one probe to D and theother to F. You should hear the meter's shrill chime tone. Now place one probe on E and the other on G. You should hear the tone again. This also indicates the fusesare good. If one of the fuses does not test good, be certain the switch is in the "off" position. With your fingers or a pair of pliers or a wooden stick to pry, remove the badfuse. Take it with you to a hardware or building supply store and get a replacement. Use a fuse. Do not use a piece of metal, a piece of copper tubing, or a wirewith alligator clips to bridge the space for the fuse. In the days when most homes had screw-in plug fuses some people sometimes put a copper penny behind a blownfuse when they did not have a new fuse. Then they often forgot about the penny. Pennies do not burn away like a fuse does when there is an overload. Pennies used thisway often caused house fires. There was a frequent saying that, "The words 'In God We Trust' were placed on pennies for the benefit of those who use them as fuses."

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Image Notes1. ON/OFF switch in the OFF position. It must be in the OFF position to open thebox lid, although it is possible to switch it to ON after the box has been opened.

Step 8: The electric clothes dryer does not dry.The wet clothes in your dryer are still wet after running for the full cycle. The drum turned. The dryer went full cycle. What could be wrong? First check for a clogged filteror vent pipe. If those things are good, the problem may be electrical, and a multi-meter can help you find and fix it.

Dryers operate on two different circuits at two different voltages. The motor that turns the drum works on 115 volts. The heating element works on 230 volts. The electricaloutlet behind your dryer that powers the dryer looks like this. 

Set your meter selector to 400 volts AC. Put one probe into the "A" slot. Do not touch the other probe, but insert it into the "B" slot. The fit may not be tight. You may needto wiggle the probes to touch the metal inside and get a reading on the meter. The meter should show 230 volts. "C" is the neutral wire. "D" is the ground wire. Place aprobe into "A" and the other probe into "C" or "D" and the reading on the meter should be 115 volts. The same should be true of a reading between "B" and "C" or "D." Ifyou do not get these readings, check to be sure one circuit breaker or one fuse is not blown. There is the possibility that the dryer's heating element could be burned out,but that is not as likely. You can access it from the back of the dryer. Remove a cover over its terminals. Be sure the power to the dryer is disconnected. Use an Ohmssetting on your meter and check for an open circuit. Testing an oven element in your stove is very similar. Remove the screws that hold the element in place and pull itfrom the oven. Do a resistance check on the two terminals.

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Step 9: Electrical outletsSometimes you need to check an electrical outlet, or replace it. See the text boxes in the photo. Set the meter to 400 volts AC. Place a probe in the "hot" slot and anotherin the neutral slot.  The meter should read about 120 volts. Place a probe in the "hot" slot and in the ground slot. The meter should read 120 volts. Place a probe in theneutral slot and in the ground slot. The meter should read zero volts. Check outlets with your voltmeter before removing the cover and beginning to work on them. Youwant to be certain the power is "off."

Image Notes1. "Hot" side (black wire inside the wall)2. Neutral (white wire inside the wall)3. Ground (bare or green wire inside the wall)

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Step 10: Cords and other thingsI have added alligator clip attachments to the probe ends on my meter. They are a very handy accessory I got at Radio Shack. They are like an extra hand. 

This toaster works well, and the meter shows a resistance reading due to the heating element inside the toaster. This is normal and good. This test could indicate there isa break in the circuit within the toaster. Further testing would be necessary to determine which part of the circuit is defective. Then a decision would need to be made asto whether the appliance can be repaired and whether it is worth the effort.

Whether it is a toaster, or a phone charger, or a power cord for a computer; cords often fray internally within an inch or two of the plug. This is very understandable. Thatis the area of the cord that is frequently flexed back and forth. If something, like a phone charger, works some of the time, but not at other times; attach the meter with aresistance scale setting. Gently flex the cord back and forth near the plug end. Make fairly sharp bends. Watch the meter reading to see if it fluctuates between a normalreading and no connection. If it does, ask someone with a soldering iron to cut the cord back and reattach the plug end for you. 

Image Notes1. Alligator clips--These are an accessory sold by Radio Shack at the time I bought my meter. They are like an extra hand. Just stick the probes into the narrow endsof the alligator clip attachments.. They are insulated over the alligator clip, too.2. This toaster does not stay "on" unless the power is connected, which it is not for a test like this, so I am holding the actuator lever down with my hand.3. Bend the cord back and forth in this area and see if the meter reading fluctuates between a resistance reading and no reading that would indicate an open circuit.

Step 11: Lightning and your telephoneThis is an illustration of what is possible with a meter.  It is not intended that most users would ever do this. Yet, many on Instructables experiment with LEDs (lightemitting diodes), and it would pertain to that.

During the 1980s I was the pastor of a church in a rural setting. Lightning sometimes struck the utility company's power distribution lines and jumped to telephone linesrunning into our building. Once our telephone would not work. Twice the phone answering machine would not work. I was able to use my meter to rescue the telephone. Iwas also able to rescue the answering machine once, but not the second time. After the second strike we added a surge protector and had no problems after that.

See the first photo. The selector is set to the diode checker. Diodes are one way electrical valves and are very sensitive to surges of electrical current, especially withthings like lightning. The arrow with a line across the arrow point is the standard symbol for a diode. Not every meter has a diode checker setting. Because diodes arevery sensitive to current overloads, the diode checker limits the current in amperes that flow through a diode while testing it.

The second photo shows the circuit board from a telephone. The yellow text box identifies a bank of four diodes. Although diodes can come in many sizes and shapes,those commonly used on circuit boards like this one are small black cylinders about 5/16 inch long and about 5/32 inch in diameter. At one end is a gray band. A wireruns out of each end of the diode.

You may notice the probes do not look anything like the probes you have seen before.  This is another accessory I got at Radio Shack. It is a set of clip on probesdesigned to grasp the small wires of electronic parts to make getting an accurate reading easier.

When testing a diode, you are looking for a relatively high current reading when the red and black leads are attached one way, but a relatively lower reading when theconnections are reversed. Note that the red probe is above the black probe in this photo and the reading is 1.585.  See the third photo. The black probe is now abovethe red probe and the reading is one-third the previous reading, which is considerably lower. These readings are the sign of a good diode.  

Often a diode can be checked without removing it from the circuit. Sometimes the readings are confusing. Chances are current is feeding through some other electroniccomponent to cause an undependable reading. Then it becomes necessary to desolder one of the diode leads to isolate it from the circuit for accurate readings. 

In the lightning incident I mentioned, there were only a couple of diodes. One of them failed its test. For less than a dollar I was able to replace the defective diode and thephone was good ever after. At the time a new phone was about $20.

See the fourth photo. It is a Maglite flashlight that now has one of their LED bulbs. It quit working and I needed to know if the LED was still good or not. I did a diodecheck with my meter and discovered the switch was the problem.

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Image Notes1. Bank of four diodes

Step 12: Reading amps. (current draw)Although often used interchangeably in this Instructable, and wrongly so, "current" and "voltage" are actually different from one another. Voltage concerns the pressure atwhich electrons flow, like water pressure in a pipe.  Current (amps. or amperes) deals with the volume of electrons flowing at the operating voltage. A device may appearto work, but makes an unusual noise or quickly overheats. A check of the amps. drawn by the circuit can tell you if there is a problem, even though it will not identify theexact problem.  

First, check the device specifications.  Look for a plate or label on the back or bottom of the device. It may tell you the device is designed to draw (for example) 2.3 amps.at 120 volts. Or, it may tell you the device uses 276 Watts at 120 volts. (Watts equals volts multiplied by amps., so divide Watts by volts to determine the proper amps.) Ifthis device were found to draw (for example) 4.5 amps., you would know immediately something is wrong.

Reading amps. is different from reading voltages. Voltage readings are the drop in electrical "pressure" across two points in a circuit, or a whole circuit. The meter is notpart of the circuit, but reads what happens across or between two points in the circuit.  When reading amps, the meter must become a link in the circuit, just like a link in achain. See the graphic showing how you can make a sandwich with two conductors and a piece of plastic between them. This sandwich can be placed between twobatteries in your device to see what the current draw is. The alternative is to break the circuit by cutting a conductor and connecting the meter to the ends of the cutconductor. You would need to reconnect the cut connector when you are finished. Set the selector for DC amps in the desired range.

You may need to change the holes into which the probes connect on the meter. See the second photo.

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Image Notes1. Black probe2. These holes are for measuring amperes. Choose the appropriate hole for thered probe according to the range to be measurerd.3. The normal hole for the red probe for most readings, including current below 4milli-amperes.

Step 13: Shocking, simply shocking!My father had a small electrical business when I was in high school.  I was often his helper. Many of his customers lived on farms. A frequent complaint was a tingle (mildelectrical shock) when taking a shower bath. Invariably, there had been a lightning strike nearby recently, and the lightning surge had shorted an electric water heaterelement to ground through the water inside the water heater tank. Turn off the power to the water heater at the circuit breaker. Remove the cover plates over the heaterelements and pull the fiberglass insulation back. Disconnect the wire from one of the terminal screws on the heater element to isolate it from any possible feedbackthrough another part of the circuit. This is to avoid false readings. Set the Ohms scale to a high range. Look for this symbol: ? to identify the Ohms or resistance scale.Touch one probe to one of the heater element terminal screws. Touch the other probe to bare metal on the side of the water heater tank. If the element is not shorted tothe water inside the tank, the meter reading should be zero.    

A few years ago we had a neighbor who avoided having grandchildren visit because anyone who touched the built-in kitchen stove received a mild electrical shock. I setmy meter to an AC voltage setting in the 150 volt range and placed one probe on the chrome oven handle and one probe on a sink faucet. My meter told me the electricalcurrent registered about 40 volts AC. It took me some time, guess work, and checking; but I found someone had disconnected the thin green wire that connects the metalframe of the stove to that home's grounding circuit. When I reconnected the wire, the stray voltage disappeared. The green ground wire was located on the back of theoven.

Image Notes1. Water heater element--Set the meter for 400 volts AC. Touch the probes to thetwo screws to be certain the power is "off." Remove one wire from one of thescrews. Set the meter to a high Ohm resistance reading. Place one probe on oneof the screws. Place the other probe on the steel water tank. The meter should

Image Notes1. The symbol for Ohms or resistance. K means 1000. M means 1,000,000.

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

show no current flow if the element is not shorted to ground. (The photo is fromGoogle Images.)2. Thermostat

Step 14: Another use from the pastThe person to whom this Instructable is geared will not likely do this, but it is an example of yet another helpful use for a multi-meter. We parked our car in a store parkinglot. When we left the store, it would not start. The battery had failed because the battery post had become disconnected from the internal circuitry of the battery. When Iinstalled a new battery there were immediate signals that all was not well with the car's charging system. I did some reading in my auto manuals. I learned a poor batteryconnection can cause the rotating field of the alternator to burn out. The resistance of the field coil (rotor coil here) should be 1.5 Ohms. That is tiny. I set my meter for avery low Ohms reading, touched the probes to the slip rings, and found there was far less than 1.5 Ohms of resistance. The wires in the rotor coil had burned theirinsulation and shorted. This did not save any money, but it saved time for me. Suddenly I knew what the problem was and knew what to do to fix it. I also needed a newalternator. Without a good multi-meter, I would have only continued to guess about the problem.

(The photo is from Bing Images.)

Step 15: Auto ranging meters and reading the meterIt is easy to forget to set the meter to the right range for the type of reading you will be making. With an analog (needle indicator) meter, that could be fatal to the meter.Some digital meters are "auto-ranging." That means the meter automatically makes the right setting. My meter has circuit protections built into the meter. Part of this istwo fuses designed to "blow" before the circuitry can be harmed. I try to keep extra of these fuses on hand, just in case. See step 16 for a photo with the location of thefuses.

On my meter the digit "3" indicates an open circuit (= no path for electrical current). If I am using the Ohms (resistance) scale, the digit "3" appears until I attach theprobes to the device I am testing. Sometimes the digit "3" remains when attached to a device known to be good. There should be an actual reading, but the reason thereis not is that I have the meter set to an incorrect range. The device I am checking may have (for example) a resistance value of 12,500 ohms. If the meter is set to arange too low, perhaps to the 4K range, the digit "3" will appear on the display. If I move the selector to the 40K range the meter will suddenly give the reading I amseeking. I try to remember to begin at a very high range that may not give me as many numbers in the reading as I hope to see. Then I move the selector to lower rangesettings until I see the number of digits in the reading for the accuracy I need. 

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Step 16: Accessories and featuresI have already mentioned two accessories available for my meter: insulated alligator clips and spring clips for grasping electronics component wires. The photo shows atelephone pigtail that makes connecting to the telephone lines for a voltage check easy. I used my alligator clips to connect to the red and green wires on the pigtail. If allis well, the voltmeter should read about 50 volts DC. See my earlier Instructable. This can be a big help when you are reporting a service outage. The pigtail has twoother conductors. I taped them so they would not touch anything and create a short. Note: 50 volts DC is low enough that you can touch the bare wires without a shock.Still, do not stand in water when doing this. Water multiplies the danger.

Sometimes you need an extra hand. Multi-meters come with a fold out stand on the back of the meter. These usually can also be flipped up to function as a hanger forthe meter. This frees both hands for manipulating the probes, especially if the voltages could harm someone. See the text box in the photo for details on the Hold button.  Sometimes you may be able to reach terminals with the probes, but may not be able to read the meter. If youcan manage to press the Hold button and release it, the meter will freeze the reading so you can move and see what the meter recorded.

Image Notes1. Hold button

Step 17: User serviceable thingsVery little on a multi-meter requires attention. There is a door or plate on the back that opens by removing a few small screws or with a snap that can be opened with afingernail. Inside are the batteries that power the circuits in the meter. There may also be some fuses. Very cheap meters may not have fuse protection.

When the batteries grow weak there may be a weak battery indicator on the display screen. You will notice the display numbers grow more weak and difficult to seeunless viewed at just the right angle. If the meter will not be used for very long periods of time, it is a good idea to remove the batteries so they do not begin to leak andruin the metal tabs in the battery compartment. This meter uses three AA batteries. Many meters use one 9 volt battery. Notice that this meter has two fuses. One is afast blow fuse designed to protect the meter from the wrong setting on the meter's selector switch. I have a few extra fuses in a small plastic bag. The bag fits into thebattery compartment. Notice that the fuse specifications are also molded into the plastic case.

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Step 18: Additional resourcesIf you want even more ideas for how to use a multi-meter to solve problems at home, get a copy of this book. A similar book appeared after this one. I bought this about20 years ago and it is very helpful, although it tends to go into a next level beyond this Instructable with more applications and more detailed tests. 

Do not be cavalier when working with electricity. Take many precautions. Check and double check to be certain a circuit is not live. Many important measurements thattell you about the health of a device can be made without power to the circuit, other  than the small batteries inside your meter. Using a multi-meter can help you fixproblems safely without an expensive service call by a technician. 

http://www.instructables.com/id/EVERYONE-Needs-a-Multi-Meter/

Related Instructables

Real-time WebBasedHouseholdPower UsageMonitor byjasonT

Build a simpleAmperometer*(Ampmeter) byagis68

Parasitic WindTurbine by ToolUsing Animal

Solar PoweredTrike bydpearce1

Increasingcurrent on 78xxseriesregulators byTalkingElectronics

Arudino- NoBlinky bymsuzuki777