Introduction: Solar Ni-cad or Ni-mh Battery Charger.

Picture of 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

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

i used my scanner to get this pic.

Step 1: Materials:

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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!

Picture of 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


spikeychops (author)2009-09-27

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

itsthatsguy (author)spikeychops2009-09-27

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 (author)itsthatsguy2013-05-31

You get a better reading if you let the batt sit for a hour or more so the ions can realign.

spikeychops (author)itsthatsguy2009-09-30

Ah right, thanks for that.

doo da do (author)2013-05-22

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

hsdoofc (author)2010-08-15

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

dlowther (author)hsdoofc2011-10-05

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

golddigger1559 (author)2010-07-23

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???

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 =(

jasongroupindustries (author)2010-05-20

Hi, nice job.
I would like to know what is the current rating of the calculator solar panel.

Hmmmm, i never did an actual test, but i can estimate about 83 maH

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.

max1zzz (author)2010-04-05

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

hansonsux (author)2010-03-29

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)

newberrys (author)2009-05-20

Will it damage a NiMH battery if you continue to supply power to it after its charged?

itsthatsguy (author)newberrys2009-05-20

yes, but not to the point of battery leakage.

newberrys (author)itsthatsguy2009-05-20

can it still be used or will it function noticabley less if i use it and recharge it repeatedly?

itsthatsguy (author)itsthatsguy2009-05-20

I recommend checking on the batteries from, time to time.

wcdeich4 (author)2009-05-06

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 ... ?

hobbles (author)wcdeich42009-05-19

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

itsthatsguy (author)wcdeich42009-05-06

all solar cells are rated in voltas, if a power going into the charger from the batteries is more than the voltage of the cells it can case the batteries to short heat up expand and possibly explode. This will also damage the cell.

fang113 (author)2009-05-05

what calculator did you buy?

itsthatsguy (author)fang1132009-05-06

it was an old broken solar TI calculator.

Phil B (author)2009-02-20

I do agree a more complete drawing of the circuit would be helpful. For a simple way to do it, see my Instrucable on using MS Paint for such things.

itsthatsguy (author)Phil B2009-02-20


PKM (author)2009-02-20

Any chance of some photos of your charger? These images have a slight Googley tang to them, unless you built a beautiful softbox to take photos of your wire in and borrowed your multimeter from Physics 3-202 :P You also didn't mention which way around the diode goes- presumably it's to stop current flowing from the battery through the solar cell. Drawing a circuit diagram (even in MS Paint, as long as you save it as a PNG or GIF not a JPEG) and uploading as an image is much better than drawing an ASCII diagram.

itsthatsguy (author)PKM2009-02-20

like i said in the intro, my camera broke

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