Solar Ni-cad or Ni-mh Battery Charger.




hey guys i broke my wrist this instructable took awhile lol. anyway this is a way to charge 2 batteries of your choice using the sun!

every material used as recycled

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i used my scanner to get this pic.

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Step 1: Materials:

-an old broken solar calculator to take apart for the solar cell.

-a side style 2 cell AA battery holder buy one or get one from an old kit or electronic device that is broken.

-a diode - just an ordinary diode NO LEDS THEY WASTE POWER


-a volt meter or multimeter

Step 2: Disection

take out the screws from your solar calculator.
cut the 2 wires leading from the circuit board to the solar cells, give your self room to work with.

Step 3: Voltage Check

check the solar cells voltage using your meter, make sure the cell is in direct sunlight when your measuring it.

if its 3 volts use a 2 cell AA holder
if its 1.5 volts use a 1 cell AA holder

Step 4: Wiring and Soldering

uhhh this is easy
the red wire on the cell goes to the diode and then the red wire on the holder
the black wire goes to the other black wire

solder all this together

Step 5: Glue the Solar Cell

glue the solar cell so that it holds onto the battery holder in a way where it will face the sun while staying still.

Step 6: Done!

this takes a while to charge 1-3 days for a full charge depending on the Mah

3 days for 2500 Mah batteries
1 day for 1000 Mah batterries

Have fun.

every material used as recycled

if you like this instructable please vote for it in the epilog '09 contest

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    27 Discussions


    10 years ago on Step 6

    OK, this takes a while to charge them, but how to you prevent overcharging and killing the batts?

    3 replies

    Reply 10 years ago on Step 6

    You'd have to create a charger circuit, i just monitored my batteries every 2 hours with a charge meter (Measures charge) i was trying to make it as small as possible so i didn;'t add one.

    doo da do

    6 years ago on Step 6

    I think you would get best reading after letting the batteries set for at least an hour. The ions would have time to realign.


    9 years ago on Introduction

    Thank you for making this so simple! I do have a question though, does a diodes forward voltage drop mean that the amount is lost? and why is this, is it higher drop if the diode can take more voltage or what? the only diodes I could find in my house have a peak inverse voltage of 50v and a forward voltage drop of 1.6v at a forward current of 1amp. thank you

    1 reply

    Reply 8 years ago on Introduction

    You do lose that Voltage. Most will recommend a schotkey diode because forward voltage loss is only .15 to .45 volts. They can be had for pennies on ebay

    would this circuit have any problem fitting inside a lightbulb with a photo cell and led? and would it have any problem powering the led???

    1 reply

    The circuit is very small, it will fit in most things, such as a light bulb, even smaller, it should be able to power several led's but i can't be sure without building one myself, but i lost my device =(

    Ok, as i test mine and obtain around 20ma with a light source an A/C bulb.
    Thanks for the information.
    I know now that in sunlight i can have more.


    9 years ago on Step 6

     you could use 2 or 3 cells to make charge time 1 day!


    9 years ago on Introduction

    Thing is - a calculator's solar panel produces a miniscule amount of power.  I think it would take months to get one full charge. (self discharge aside)


    10 years ago on Introduction

    Hi. Does the diode protect the solar cell from being damaged as the voltage of battery rises? I'm working on something similar & noticed that it's hard to find diodes w/ forward voltage drops of less than 0.2V, which can be significant. I'm wondering what would happen if we just hooked the solar cell directly to the battery ... ?

    1 reply

    Reply 10 years ago on Introduction

    The diode keeps the batteries from discharging into the solar cell when the lights go out.