Best portable solar charger to charge AA nimh?

[JollyRoger]

Can anyone give me advice on "the best value" portable solar charger? It needs to charge nimh AA's, any capacity. It should also have built in "smart charging," that won't overcharge the batteries if left in the sun all day for a couple of days....(i'm doubting you can charge 2 AA nimh fully with a "small" solar charger in one day).

If anyone can build one, too....i'd be interested.

 

[JollyRoger]

Here's another related question. If you're going camping for a week (and you're away from your car--no car charger to use, etc.), what do you bring with you? I would assume that one of your lights/power sources would be rechargeables and a solar charger? Bringing a bunch of alkalines is fine, but I'd rather use the nimh batteries I have....

 

[ikendu]

I had just such a need when my daughter went to the Phillipines for a month of field research on worms. She was going to be in the "outback" with very doubtful access to electricity or fresh batteries.

So...I sent her with an Infinity Task Light (yellow), a 4 AA lantern and a ICP Battery Saver AA solar charger.

Results:

The batteries (NiMH) for the lantern ran down in the first few days. The solar charger never did recharge fast enough to be really useable. They were on the move every day so how do you place the charger in a place to get a full day's worth of sunshine if there is no real base camp?

Bottom line...the lantern, 4 NiMH AAs and the solar charger were just so much excess baggage. The Infinity Task Light lasted the whole month on the one, originial battery! Later my wife took that same Infinity and same AA battery camping in South Dakota for another week! and...it is still going strong as we use it around the house sometimes at night rather than turn on the bright lights.

So...at least for lighting, leave the solar charger behind and take an Infinity with a spare AA. It will last for a REALLY long time.

Since then, I've been following the posts in the LED forum about the solar rechargeable LED "FreeLight". This thing is about the size of a small box of matches. A full day of sun will give about 2 hours of light. So...you just velcro the FreeLight to the top of your cap and it charges while you walk around.

I'm sure the ICP Solar charger is a fine unit (about the size of a paperback book) but recharges so slowly as to be almost unusable.

 

[JollyRoger]

Thanks, ikendu....I was thinking about buying that charger, but I guess I might just hold off now, since I'm getting a bunch of Free Lights!

 

[ikendu]

If you really wanted to solar charge AA batteries, I'm thinkin' that the hot set up would be the Maha 204s smart charger and find some kind of folding, portable solar panel that will put out juice at 12 volts DC.

Such as 12v Foldable solar panel

Or ...12 volt Solar Panel for 500 ma

That Maha charger will give you first class charging although, it does want about 500 ma.

 

[**DONOTDELETE**]

70 ma at 12 volts (the short circuit voltage is much higher, like 19 volts, so it really can charge a 12 volt battery)
140 ma at 6 volts, (switchable)
somewhat bulky..
..only $29..! http://thomas-distributing.com/icpg-04041_solar_battery_charger.htm

 

[ikendu]

This charger you show looks definitely better than the smaller one I have.

What I realized (really a little too late for my daughter's Phillipine trip) is that you need some decent surface area to really use the sun to recharge AA NiMH batteries that have large capacity (like 1700 mah).

The solar charger I have looks like it might be half the surface area of the one you show, but even with double the area I'm guessing that recharge rate will still be a little slow.

The reason that the Maha charger wants so much juice is that it can charge 4 AA NiMH high capacity batteries in about 3 hours. If you were hiking with a digital camera and taking lots of pictures, you'd need a good charger (like the Maha) and a solar panel with maybe 2 square feet of surface area (not something you'd likely want to lug around backpacking ...but if you returned to a "base camp" each day where you'd left your car with the solar charger, that might be workable).

I wish I could find a "Solar Forum" as active as this LED forum...but so far no luck. I'd really like to get connected with some folks that have some real experience in this area (I'm definitely just learning myself).

 

[JollyRoger]

OK, here is what I'm looking for in a solar charger:

1) Fairly small size. Ikendu, that BatteryPal seems like a nice size. I don't want anything too much bigger than that...

2) Charge nimh or nicad in a "smart" way...(don't overcharge them).

3) I don't mind if it takes 5 or 6 hours of sunlight to charge high capacity nimh AA's and AAA's.

Do you think this charger will do it? http://www.siliconsolar.com/solar_battery_chargers1.htm

I'm going to check out that thomas distributing link now...

 

[Michael]

I too have used the ICP Battery Saver AA solar charger and have been disappointed with its slow charge rate, especially for larger capacity NiMH (1600 mA-hr) AA cells. It takes days (3-4) sitting in a sunny window to decently charge the cells, but they never reach a full charge as when I use an AC charger. The surface area of the solar charger is probably the most important factor for determining the effective current and thus the charge rate. And I doubt that anything truely portable would charge those high capacity NiMH cells in 5-6 hours. And I wouldn't worry too much about overcharging the cells in a portable solar unit, unless in very bright, direct sun, since the current is really not much greater than the trickle charge mode of those "smart" AC chargers. In fact, I've now relegated my ICP solar charger to the role of charge maintainer and use an AC unit to get the cells fully charged. Hope this helps.

From another lurker.

 

[Brock]

ikendu, I regularly am also on the Windsun http://disc.server.com/Indices/58324.html board, but it isn't very active. If you find a good solar message board let us know.

I use the 204 charger and charge directly from my 12v battery bank which are charged by 4 Siemens SP 75w solar panels and a Solar boost charge controller. I really like the way the 204 charges the batteries. I would bet about a 30w panels would run the 204 charger, but you would need some small 12v battery to maintain the voltage otherwise if you had a shadow go over the panel the 204 might start the charge process over again.

 

[ikendu]

The Battery Pal charger mentioned above may indeed work fine. I've not used it or found any comments on the web from people that have.

There IS a big variation in solar cell efficiency and the Battery Pal people claim to be using the best.

JollyRoger...you haven't mentioned what you want to use the batteries for. If it is for a high drain application (like a digital camera), it seems unlikely that the Battery Pal or any small charger will be able to keep up with the usage.

If it is to run a radio or modest lighting needs, you might be able to keep up.

If you get a Battery Pal, I'd be very interested in your experience and comments!

 

[sflate]

I'm a big solar fan, but in this case I would go with the alternatives. Check out the Aladdin Handheld generator (or Stepcharger if you can find it) Aladdin Homepage Also, don't forget about the Glow-in-the-dark powder or sheets.

 

[ikendu]

Interestingly, the conversion of mechanical motion to electricity continues to be a viable method of energy independence, even with our high tech batteries, solar cells, fuel cells, etc. I see that there is now a more compact version of the FreePlay wind up, clockwork radio.

Compact FreePlay wind up radio

 

[**DONOTDELETE**]

also there's this one, semi-flexible mounted on plastic, light enough to consider packing on the back -- 4 watts, 9 volts; (but you'll have to get your own battery holder), http://www.ccrane.com/sangean_solar_panel.asp

 

[VidPro]

i would have an idea of how i would Attempt/test build one. as i altered one for Li-Ion charging in similarity.
use 3x.5v 3amp cells , assemble without diode, and manually remove when no sun. that would make a Brute force ~1.5V source. as the batteries charged up, the voltage differential drops and so does the speed of charging. make a 4xAA or 8XAA parellel holder.
then test adjust, test adjust. put fully charged batteries in, hit it with full sun, and determine that the RATE then had dropped to below 10% C or .1C or 1/10c when the batts are fully charged.
not enough power (via voltage), then add in one more .5V solar cell item (~2V) to increase the voltage Test again. Then use shotkey dioding (~1.7V), to decrease the voltage a touch, and finish up with reverse protection, which i dont think is totally nesssiary when the human can control it for a few days things. test again. get the voltage primed for the batteries you intend to use with it, a tiny bit of resistance or diode differance can also tweak things and add or subtract voltages a bit.

simple cheap, rude, manuel, minimal losses, and sort of "self regulating". when the batteries were really low , it would pound power into them, when they were mostly charged it would lighten up.
then make the solar cell group a Lean-To so it could shade the batteries, and also allow the solar to be turned into the sun. make sure that the Lean-to includes the batteries holding the thing down in the wind.

with glass 3"x6" cells which max out at 3amp a system could be designed that is about 7x10" or 7x13" and weighing about 6-8oz, and would charge 4-8 cells up mostly in a single day. just not Sold because it would be highly dependant on the user knowing what occurs, what is happening, how the battery they use reacts, and taking care of it and the cells proper. the solar cells would have to be encapsulated in epoxy or whatever.
there probably exists a led somewhere in this world that barely lights up with 1.5v, or some minor boost driver thing that could be a simple status to be tossed in somewhere, even if that meant wiring in some $14 single battery light head thing from china to get a quick manuel status via a switch that jumped from the solar to the battery to check what was going on.

something like that.