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12v solar battery charger

Hedley-Lamarr

Oct 18, 2022
2
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Oct 18, 2022
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Hi everyone, newbie on this site with a question - I'd like to use these instructions to build a solar 12v battery charger. I have a small solar panel (about 8" x 3") which I found in a shed clearance years ago, which looks like it might do the job, and outputs a healthy 23.5V on my multimeter in full sunlight.
The instructions state this... "Yes, you can charge a 12V battery with a 5W solar panel. You just need to make sure it’s a 12V solar panel. Anything less, such as a 6V or 9V solar panel, won’t work."
How do I know what voltage rating my little panel is? There's nothing written on it, no branding or anything.
Many thanks in advance :)
 

Bluejets

Oct 5, 2014
5,989
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Oct 5, 2014
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5,989
@23.5v open circuit, should be ok.
Consider the solar panel as a bucket of water and your battery as an empty receptacle, difference in level (voltage) will allow current to run.
Have you done a short circuit current test??
I can imagine it won't be much.

You will need some type of blocking diode minimum which will drop your voltage a small amount.
Should not need a regulator unless planning to leave connected indefinetely.

As they say, suck it and see.
Your quoted output I imagine was in full sunlight so don't expect to see that all day, every day.
 

Hedley-Lamarr

Oct 18, 2022
2
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Oct 18, 2022
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Cool, thanks for the reassuring (and prompt) response. I'll go ahead and give it a try.
 

Mouthpear

Jul 20, 2020
24
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Jul 20, 2020
Messages
24
Hi everyone, newbie on this site with a question - I'd like to use these instructions to build a solar 12v battery charger. I have a small solar panel (about 8" x 3") which I found in a shed clearance years ago, which looks like it might do the job, and outputs a healthy 23.5V on my multimeter in full sunlight.
The instructions state this... "Yes, you can charge a 12V battery with a 5W solar panel. You just need to make sure it’s a 12V solar panel. Anything less, such as a 6V or 9V solar panel, won’t work."
How do I know what voltage rating my little panel is? There's nothing written on it, no branding or anything.
Many thanks in advance :)
First, I'm not saying this to be mean, I would not trust information from a site that says "make a battery charger" when the charger (solar charge controller) is already made. All they are doing is wiring it up.

As to what the rating of the solar panel is you may never know. Without the paperwork or an actual make and model these are very generic. That being said you basically already know 90% of what you need to know. The voltage at peak sunlight. This will tell you what size controller to buy. The solar controller is what regulates the voltage to the battery. Look for one that can handle that peak power.

One thing to consider is wether to get a PWM controller or a MPPT controller.

PWM controllers are cheaper and can handle charging a battery. But will not convert that extra voltage to charging amps. You lose/not take advantage of the extra voltage.

MPPT controllers are a little more expensive but they convert that extra voltage to charging amps/current. Way more efficient.

So if you have a small lawnmower battery that you just need topped off when not in use a PWM controller may do you just fine.

If you are charging batteries that used more often or longer periods of time, like a home battery bank or some type of feild equipment (like those roadside radar detectors that flash your speed at you), a MPPT controller may be what you need.

But an 8" x 3" I'm gonna say a PWM will do you.

Last thing. A blocking diode was mentioned. While it's good to add one at the panel it mostly isn't necessary with a tiny panel. Most of the solar change controllers have build in anti drain circuitry. Read the manual for any controllers you are considering.
 
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