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solar powered battery charger

donkey

Feb 26, 2011
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hey guys I got one of those battery chargers that charge from aaa all the way through to 9volt. the issue I have with rechargeable batteries is the money I spend on electricity is less than buying new batteries all the time, but its still money. (thank you carbon tax its getting a bit more expensive now)
the idea is to make a solar powered version. the ones I find are for AA batteries. I was hoping of finding something that can charge 4 1.5v batteries (ni-mh) and 9volt batteries.
my IDEAL is to find something to build at home.
 

Harald Kapp

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Do you want to retrogit the existing charger or build a new one from scratch?
You'll find lots of articles about the latter on Google (search: build solar powered battery charger). Mostly they seem to not to be very sophisticated, not using a charge controller at all.

Retrofiting your existing charger might be difficult as it is designed for mains supply, thus assuming a steady supply of primary power. How will the charger react if the primary power supply is variable - as a solar panel is?
It might be better to build one using a specialized ICsfor charging from solar (Google: solar charge controller ic).
 

(*steve*)

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The issue with solar chargers is that for most battery types you're likely to have in the form factors you mention, a charging regime is recommended that relies on power always being available. With solar, you simply can't rely on that.

The simple answer is to use solar to charge some other battery type (that is easier to charge) and to use the power from this battery to charge your other cells. This means you can use a standard charger (or standard charging circuitry) and have it "not have to worry" about a charge cycle being interrupted, or insufficient energy being available.

I would tend to suggest that you use LiPo cells to store your power form the solar panels, and then use these to power the charger.

LiPo are relatively easy to charge, and have a very simple detection of end of charge that is simply based on the cell voltage. If using a battery, it is best to ensure that you have some form of monitoring for each cell to ensure that the failure of one cell does not lead to overcharge and destruction (perhaps pyrotechnically) of other cells.

A safer battery type is lead acid. Provided these are kept reasonably charged, they are pretty simple. The change in voltage with temperature means that charging should be temperature corrected, but there are plenty of circuits to do this.
 

wingnut

Aug 9, 2012
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Inspired by this thread and a sunny day, I unearthed some old rechargeable NiMH AA batteries reading .85V each. Hooked these up in series with two 2.5V solar panels connected in series through a LED and a 20 ohm resistor for luck.

Left them in the sun for 2 hours (covering the batteries so they dont overheat). Each cell charged up nicely to 1.52V.

To try to improve the circuit, for the last hour I added a simple voltage regulator/limiter consisting of two white diodes and a 30 ohm resistor in parallel, so that if the voltage rose too high (4V), these would leak away the excess.

There are many different solar battery charges out there, but I don't know enough to recognise their merits. For me, for now, the prime merit is "do I have the component"?

Some use a LM338 current and voltage regulator, or a single transistor to prevent overcharging.
 

donkey

Feb 26, 2011
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guys consider me a monkey. You can tell me what to include in the circuit but I can't figure out how to hook it up, a diagram is nice.
I was thinking of grabbing a 12v 7ah sla deepcycle (they are cheap enough) and have a small solar panel and charge controller then using that to power the charger for the AAA-9v batteries.
having said all that I was looking at using a rotary switch and battery holders. so I could could charge 4 AAA or AA or C or D or 1 9volt (5 positions +1 for off) this way my darling children won't drain the sla too quickly. so in essence its 2 circuits, 1 to charge 4 1.5volt batteries and the other for a 9volt.
hope this helps, if not a really bad diagram can be supplied :D
 

(*steve*)

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OK, you need 2 things.

1) a battery charger designed to operate from 12V. You connect that up to a lead acid battery.

2) a solar charger to connect between your solar panel and your lead acid battery.
 

Harald Kapp

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It's not that simple.
For charging the 12V battery from the solar array I'd recommend an off-the-shelf solar charger. That shouldn't be difficult to buy.

As for charging the different cell types from the 12 V main storage battery: A simple rotary switch won't do. Apart from adjusting the charge voltage you need to adjust the charge current for the different cell types. I suggest you buy a universal battery charger with a 12 V Dc input (possibly sold with an adapter for a car's lighter).
 
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Harald Kapp

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Steve, you beat me by 9 minutes, but you git the sequence reversed :)
First charge the 12 V battery from the solar panel, then the children's toy batteries from the 12 V.
 

donkey

Feb 26, 2011
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ok this is alot easier than I thought, but its all premade stuff, I thought I could build one, but as we all know its usually cheaper to buy one already made.
also steve in my last post I already said charge controller for my solar, I just put it at the end not the middle like I should have. sorry bout that.
I still have alot of issues with this wattage rating and solar, it should be straight forward but I think I am overthinking it somehow, or underthinking it.... or not thinking at all...but thats for another thread and another time, time to sort out the solar recharger
 
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