solar battery charger for your cordless power tools by diy hacks and how tos

7/23/2019 Solar Battery Charger for Your Cordless Power Tools by DIY Hacks and How Tos

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Solar power is a great way to get electricity out to a remote project site. One

simple way to do this is to use a solar panel to charge the batteries of your

cordless power tools. In this project, I am going to show you several ways that

you can do that.

Safety Note: Any time that you use a DIY battery charger instead of a

commercial charger, you are accepting a certain amount of risk. So always use

caution. Don't over charge the battery and don't try to charge it faster than the

manufacturer recommends. There are many different kinds of batteries and they

all need to be treated differently. These instructions are designed for batteries

that are made of Nickle-Cadmium cells. I make no guarantee that theseinstructions will be appropriate for other battery types such as NiMH or lithium

batteries.

Recommendations

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ar Battery Charger For Your Cordless Power Tools http://www.instructables.com/id/Solar-Battery-Charger-For-Your-Cord...

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Step 1: Watch the Video

Here is video walk through of the project.

Step 2: Background: Cordless Power Tool Batteries and HowThey are Charged

There are many different styles of cordless power tool batteries and many

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different styles of chargers.

Most cordless tool battery packs are made up of several smaller batteries that

are all wired together in series. In the most basic models, the charger will

connect directly to the end terminals of the battery pack at two exposed pins.

The charger then applies a small direct current and slowly charges the battery

pack over several hours.

In more advanced models, the battery pack may have a number of internal

sensors. For example a Craftsman 19.2V battery has a thermal fuse and an

internal temperature sensor. To accommodate these sensors, the battery has

two additional terminals (a total of four). The charger connects to the battery

through the thermal fuse. If the temperature of the batteries ever goes above the

maximum safety threshold, the thermal fuse will disconnect the battery from the

charger. The temperature sensor allows the charger to actively monitor the

temperature of the batteries while they are charging. This lets the charger

automatically adjust the current to maximize the charge rate without overheating

the batteries.

If you want to use a DIY charger to charge the battery, your primary concern

should be safety. The safest way to charge a battery is to do it slowly. This will

sacrifice some efficiency but it will guarantee that you will not destroy the battery.

Step 3: Materials

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Materials:

Cordless Power Tools and Batteries

Solar Panel

Wires/Connector Cables (rated high enough for the maximum output of the solar

panel)

Charge Controller

Multimeter

Wire Cutters

Wire Strippers

Soldering Iron

DIY Charge Controllers Materials:

555 Timer IC

7805 5V Voltage Regulator

5V Relay (with a coil that is rated for less than 100mA)

2 x 0.1 Microfarad Capacitor

0.47 Microfarad Capacitor

2 x 10 kohm Resistors

68 kohm Resistor

33 kohm Resistor

2 x Diodes (rated for at least 1 amp)

Step 4: Identify the Terminals of the Battery

(http://cdn.instructables.com/F9U/T8J9/HXG6OQI6/F9UT8J9HXG6OQI6.LARGE.jpg)

(http://cdn.instructables.com/FE0/3YP0/HXG6O4DT/FE03YP0HXG6O4DT.LARGE.jpg)



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The first thing that you need to do is identify and label each of the terminals on

the battery. If your battery has two terminals then you can easily use a

multimeter to identify which one is positive and which one is negative.

If the battery has more than two terminals, then there are several things that you

need to check. Start by noting the position of the terminals on the power tool. A

power tool will usually connect directly to the positive and negative terminals of

the battery. You can then use a multimeter to measure the voltage of the

corresponding terminals on the battery to determine which one is positive and

which one is negative. Any additional terminals will probably be a thermal fuse

or a temperature sensor.

A thermal fuse is usually connected to the positive terminal of the battery. So if

you measure its voltage with a multimeter it will have the same voltage as the

positive terminal of the battery (or slightly less). The thermal fuse also connects

to the positive output of the charger. Once you have identified the thermal fuse,

any remaining pin will be the temperature sensor.

If you want to double check yourself to make sure that you have correctly

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Step 6: Charge Controllers

It is possible to charge the battery by connecting the output of the solar panel

directly to the terminals of the battery. However, if you are not carefully

monitoring the voltage of the battery, then you run the risk of over charging it.

This is why you usually want to use a charge controller.

A charge controller (http://en.wikipedia.org/wiki/Charge_controller) is any circuit

that limits the current that is sent to the battery in order to prevent over charging.

You can purchase a commercial charge controller (http://www.harborfreight.com

/7-amp-solar-charge-regulator-96728.html) at most stores that sell solar

equipment or you can build your own.

In a previous project, I showed how you can use an Arduino as a charge

controller. Because the Arduino has multiple inputs, you can use it to monitorand control the charging of multiple batteries. Check out the link to see how I did

it. http://www.instructables.com/id/Arduino-Controlled-Solar-Fountain/

(http://www.instructables.com/id/Arduino-Controlled-Solar-Fountain/)

You can also make a charge controller with a simple 555 timer IC. These chips

have an internal comparator that toggles the output on and off depend on the

(http://cdn.instructables.com/FD8/QYIK/HXG6PAF6/FD8QYIKHXG6PAF6.LARGE.jpg)

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input voltages. This can be used to connect and disconnect the battery with a

low power relay. This control circuit is discussed in more detail in the next step.

If you plan on leaving the battery connected to the solar panel overnight, then

you want to make sure that either the panel or the charge controller has a

blocking diode. This is a diode that is placed between the panel and the battery

to prevent the battery from discharging through the panel when it is dark. A

schottky diode gives the best performance for this.

Step 7: 555 Control Circuit Design

Here is one simple example of how to make a DIY charge controller.

This charge controller is built around a 555 timer IC. This chip has two inputs(pins 2 and 6). It compares these input voltages to a set of reference voltages

that are based on the supply voltage. If the voltage at pin 2 drops below the 1/3

of the supply voltage, then the output at pin 3 goes HIGH. If the voltage at pin 6

goes above 2/3 of the supply voltage, then the output at pin 3 goes LOW.

By using the 7805 voltage regulator, we can fix the supply voltage to 5 volts. So

1/3 of the supply voltage will always be 1.66V and 2/3 of the supply voltage will

always be 3.33V.

The input voltages at pin 2 and 6 are dependent on the voltage of the battery.

Each input has a voltage divider (http://en.wikipedia.org/wiki/Voltage_divider)

that is made of two resistors. The ratio of the two resistors determines what

percentage of the battery voltage is sent to the input pins. In this example the

pin 2 voltage divider uses a 68 kohm resistor and a 10 kohm resistor. This

means that the voltage at pin 2 will always be 12.8% of the battery's voltage.

Similarly, the voltage divider at pin 6 uses a 33 kohm resistor and a 10 kohm

resistor. This means that the voltage at pin 6 will always be 23.2% of the

battery's voltage. This is only approximate because all resistors will vary a little

from the indicated value.

When the battery's voltage goes above 14.4 volts, the output of the 555 goes

LOW and activates the relay. This disconnects the battery from the solar panel.

When the battery's voltage drops below 13 volts, the output of the 555 will go

HIGH and deactivate the relay. This resets the system for another charging

cycle. In the case of cordless power tool batteries, this will happen when you

disconnect the battery. But in a typical solar system, the battery stays connectedand the voltage will drop as the power is used.

If your battery has a different operating voltage, you can change the voltage

setting of the charge controller by using different values for the resistors. The 33

kohm resistor can be replaced using the formula R = (3 x Vcutoff) - 10 (in

kohm's). The 68 kohm resistor can be replaced using the formula R = (6 x

Vreset) - 10 (in kohms).

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Step 8: Assemble the Circuit

First prototype the circuit on a breadboard and make adjustments as needed.

Then once it is working, solder the components onto a breadboard.

In this case, I needed to make some modifications to the board. The pins on the

relay where positioned in such a way that there was no place that I could mount

it on the board where the pins could be isolated from each other. So I mounted it

in the middle of a set of columns. Then I used a knife to cut the conductors in

the middle. This separated the two halves and let me access the pins

independently.

I also used a Dremel to trim the edges of the circuit board. This let me easily fit

the board in a small plastic project enclosure.

Step 9: Cut Slots in the Project Enclosure

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The circuit board has four wires that connect to it. So we need to cut four slots in

the side of the project enclosure to accommodate these wires. I just used a knife

to cut two lines in the side of the housing. Then I used a pair of needle nose

pliers to break off the tab of plastic. Do this for all four locations on the top and

bottom of the housing.

Step 10: Test the System

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Now you need to test the system to make sure that everything is working

properly. The easiest way to test this system is to switch the battery and the

solar panel. The battery is connected to the input of the charger where the solar

panel would normally be connected. Then the solar panel is connected to the

output of the charger where the battery would normally be. Keep the polarities of

the positive and negative wires the same.

The battery supplies a stable power source for the charge controller circuit and

the solar panel acts as a variable voltage source. Start by covering up the solar

panel. You can either put something over it or turn it face down. Then slowlyuncover the panel. As more light hits the panel, its output voltage will go up.

When the voltage reaches 14.4V, you should hear a click from the relay

activating. Then slowly cover the panel. When the voltage drops to 13V, you

should hear another click from the relay turning off. If everything is working

properly, then you are done.

Step 11: Hook Up Your Finished Solar Charger

(http://cdn.instructables.com/F19/2JF5/HXG6PFJD/F192JF5HXG6PFJD.LARGE.jpg)

(http://cdn.instructables.com/F1N/QEKZ/HXG6PGEW/F1NQEKZHXG6PGEW.LARGE.jpg)

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Make Comment

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2 days ago Reply (CIGA8VGHY5NOYPS)

Now you are ready to connect all the components together. First connect the

output of the charge controller to the battery. Then connect the solar panel to the

input of the charge controller. The relay may turn on and off a few times while

the circuit is powering up.

Now you have your own solar charger. This will let you charge your batteries

anywhere that has sunlight. This can be really useful for working with power

tools at remote project sites.

warpspeed (/member/warpspeed/)

Wrong video was displayed, the video being shown is for a water to wine trick.

Please fix.

DIY Hacks and How Tos (/member/DIY+Hacks+and+How+Tos/)(author)

warpspeed

Sorry. It should be fix. Thanks for letting me know.

repworth (/member/repworth/) warpspeed

Its a miracle though!

parth_bhat (/member/parth_bhat/)

hi,

can you please please help me to f ind out my resistors value?

i have a black and decker cordless drill machine whose battery voltage is 14.4v

and when fully charged 15.5v and its adapter's voltage is 17v @ 200mA

i am going to use this project for automatic charging. instead of solar pannel ill be

using the original dc charger.

(http://cdn.instructables.com/F6M/PV8F/HXG6PO9I/F6MPV8FHXG6PO9I.LARGE.jpg)



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(/member/artchie/)

20 hours ago Reply (C9NIXHXHY7SZJWD)

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/dfietkau/)

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(/member

/deba168/)

3 days ago Reply (CBKOMAOHY3Z84GN)

Please can you help me to find the voltage divider's resistor's value?

Regards

parth temkar

artchie (/member/artchie/) parth_bhat

use 1k ohm's


parth_bhat

If yo are using the original charger, you shouldn't need a charge

controller. But if you want one just use the formulas at the bottom of

step 7.

"The 33 kohm resistor can be replaced using the formula R = (3 x

Vcutoff) - 10 (in kohm's). The 68 kohm resistor can be replaced using

the formula R = (6 x Vreset) - 10 (in kohms)"

dfietkau (/member/dfietkau/) parth_bhat

Doesn't Ohm's law for direct current fit here ?

i.e.:

U = R * I; R = U / I; R = 17V / 0.2 A = 85 .

Otherwise you might have to manually measure it step by step.

carlos66ba (/member/carlos66ba/)

Clever non orthodox use for the 555 circuit. Clever.

tutdude98 (/member/tutdude98/)

Ive put led instead of relay and i set to reset at 10v and cutoff at 12.6v but it

reset at 9.3v and it doesnt cutoff

anybody know why?

(http://cdn.instructables.com/FHS/SLBH/HY3Z9HSV/FHSSLBHHY3Z9HSV.LARGE.jpg)


tutdude98

Sorry, I can't really see any of the parts from that picture

deba168 (/member/deba168/)

Can I use a MOSFET instead of relay??


deba168

As long as it is rated for a high enough current it should be fine. I just used



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2 days ago Reply (CN18X0XHY3ZAA3A)


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3 days ago Reply (CT4DUNTHY21X5FE)

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5 days ago Reply (CZB0TY4HY12D4V1)

a relay because it

will work for almost

any application.

brmarcum (/member/brmarcum/)

I was just looking for a solar charger solution. This is perfect, thank you.

Danger is my middle name (/member/Danger+is+my+middle+name/)

This is awesome, I just got a cordless

drill, I'll have to try this!

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