Use Solar Panel with battery charger?

System · September 2006

Greetings,

I'd like to get a small multi-purpose solar panel, but one which I can specifically use either 1) with a standard two prong USA current ni-mh AA/AAA battery charger; and/or 2) with some other kind of AA/AAA ni-mh batter charger (recommendations needed for this, I have no idea)

Is this even possible? For all the variety of adapters I've seen that solar panels come with, I've yet to see one with which you could use a regular two prong plug. Does such a thing exist?

Alternatively, does a ni-mh AA/AAA battery charger exist that will accept one of the single round adapter plugs that typically come with a solar panel?

If yes, I could also use a recommendation for a small good quality solar panel that won't break the bank.

Many thanks in advance.

regards,

stevenjs
______________________________
"I am but an egg."
--Stranger in a Strange Land

niel · September 2006

Re: Use Solar Panel with battery charger?

if you are limiting yourself based on a connector you will never achieve your goal as connectors can be changed. there are chargers that do operate on an inputted dc voltage like that of a car, but that is more of a regulated voltage than that coming from a pv as pvs exceed 20v open circuit in full sunlight. the pv could have a regulator with the simpler controllers available like the sunsavers from morningstar. depending on the number of batteries you intend on charging will determine the capacity from the pv that'll be needed plus some leadway to allow for clouds or partial shading and/or not optimally aimed if it's to be used portably. most chargers i've seen do not exceed 8 batteries with 4 batteries being typical of what's out there. now going with the latest battery capacities you shouldn't need more than about 3amps right now (fastcharge) for a 12v pv as the battery capacities are closing in on 3amps. typical long chargetime chargers will need 1/10th of the battery current rating minimumly. with only 4 batteries being charged it may be possible to lower the current requirement of the pv somewhat. if you wish, you could oversize the pv in anticipation of future higher capacities and be done with it. fast chargers do use much higher current rates too so it's all up to you in your choices. it'll go pv to controller to your new connectors spliced into place to go to the charger and don't forget to put in fuses and an on/off switch to the charger. some of these chargers, i should add, start the charging process over again when the charge cycle is interupted as solar would do due to timers in some of them so the choice of the charger is critical in that it will not overcharge a battery that has part of the charge already in it. my charger can charge 8 at a time, but it's input voltage is about 20vdc to do that on mine and it uses and is done on a 110vac walwart and not a 12v source. for me to use it in solar i would either raise the input voltage by going with a pv that is higher on it's voltage rating with a special regulator or only charge up to 6 batteries using a standard 12v pv.
note here that the nimhs are usually in series on chargers so the current needed stays the same while the charger voltage requirement goes up. i hope all of this makes sense to you and i hope i didn't leave anything out as i've been up all night and i'm very tired.

Patman3 · September 2006

Re: Use Solar Panel with battery charger?

Lowe's and Home Depot sell these little outdoor light sets that include a small solar panel that holds 3 NiMh AA batteries. http://www.lowes.com/lowes/lkn?action=productDetail&productId=9091-251-LZ635RPL4&lpage=none

It would charge your small batteries during the day and you could take them out for use and charge another set the next day and just don't use the lights.

Roderick · September 2006

Re: Use Solar Panel with battery charger?

Most garden lights, I've found, use NiCd batteries. This is no oversight. NiCd batteries can be charged with very low current, with essentailly no penalty in capacity. Also, you'll probably find that the batteries in a garden set are rated for higher temperature, because the manufacturer expects the assembly to be in the sun.

NiMH batteries require pulse charging at a significant fraction of their capacity, C. For example, if the battery's rating is 2000 mAH, to charge at 1/4 C, you would need to have an average current of 500 mA. But to get a good charge, this might be a 5A pulse with a 10% duty cycle. There are also overheating and overcharging concerns. The upshot of all this boring talk is, short of designing your own charger, if you want to charge NiMH, you really need a charger that's designed for that.

A charger that's made to plug into a cigarette lighter outlet of a car would probably work with a 12V panel. A car's voltage isn't terribly well regulated, anyway, and a solar panel is not going to present anything near its open circuit voltage under load. Because of the pulse charging characteristic mentioned earlier, you may need to add a large capacitor across the power terminals. A car outlet has no problem delivering a 5 amp spike on demand, but a solar panel sized appropriately for a battery charger won't be able to do so.

I would be skeptical of a device sold as a ready-made, solar powered NiMH charger. There are probably such gimmicks out there, but if they worked well, I would think they would be in more common use. To put together something that charges batteries as well as your wall charger would take about $100, I would think, $80 for the solar panel, alone. To get the price down to what a lot of people might buy, a product designer might put a very small panel on the charger, and just hope the consumer accepts that it might take days to charge their batteries. But I would love to be proven wrong.

niel · September 2006

Re: Use Solar Panel with battery charger?

my solar lights are using a 700ma nimh battery. most likely very old batteries that a company bought up to use in the capacity of the solar garden lights. it does work and will charge, but just not as efficiently as it idealy should and will no doubt degrade the battery life. i'm not too sure as to what circuitry is used inside mine as it does shut off the led during the daytime and i'd guess it to have a blocking diode to prevent battery discharge into the cells, but i'm not sure. it uses 4 solar cells so that is a fit to the battery charging, but white leds tend to need higher voltages to operate properly so these may not be as bright as they can be with only 1 battery per garden light. has anybody torn these apart as i'm not ready to do so with mine for they are still working good for me just yet? they are entering their second year of continuous operation. i've seen them die out in the winter before dawn so the batteries won't be good for too long, i'd suspect, as they've been drained beyond 1v per battery.

System2 · September 2006

Re: Use Solar Panel with battery charger?

Roderick wrote:

NiMH batteries require pulse charging at a significant fraction of their capacity, C. For example, if the battery's rating is 2000 mAH, to charge at 1/4 C, you would need to have an average current of 500 mA. But to get a good charge, this might be a 5A pulse with a 10% duty cycle.

That explains the slight buzz from the charger that came with my Fuji camera. It will accept 12 volts DC and that's how I use it. Also came with an AC adapter, which I no longer use.
By the way, I was looking at Kodak NiMH, 2500 ma AA's the other day and their package stated something like this: "Standard charge: 230ma, for 18 hours." Interesting. That = 4.2 ah.
Wayne

Brock · September 2006

Re: Use Solar Panel with battery charger?

I would think the cheapest way to do this would be to get a small battery pack, like one of those jump start battery packs (or if you don’t care about looks a cheap UPS battery) and change that via a smaller solar panel, then connect a 12v charger to that. I would think that is the best way to do it. The problem with a 12v charger connected directly to a solar panel would be the voltage fluctuations as clouds might pass over thus restarting the charger and in full sun I would bet most chargers would shut off thinking it was in an over voltage situation.

This would also allow you to charge the main battery all day and you could charge the NiMH cells anytime.

Use Solar Panel with battery charger?

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