Question about solar chargers

LEDrock

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I'm planning to get a solar charger with the main purpose of charging AA and AAA batteries. I have about 50 different flashlights and other battery powered lights and they all use AA or AAA batteries.

One thing people have advised me about is that solar charging isn't as reliable, and that solar chargers will often lose power when a cloud passes over the sun, and then doesn't recover afterward, requiring unplugging the charger and then plugging it back in to to a faster charge. Otherwise, it continues charging very slowly even after full sunlight returns.

When I see this mentioned, it's always in the context of charging a smart phone. What I'd like to know is whether or not this problem also happens if a solar charger is used with a battery charger. My guess is that it doesn't because the recommendation is to use the solar charger to charge a battery bank, and then use that to charge the phone. If the drop in charge rate from passing clouds affected a battery charger, then it would affect the battery bank being charged. But then again, that's a lithium power bank rather than a charger for AA Ni-MHs. Does that make a difference?
 
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Nocturrne

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If you try to power the chargers directly from a solar panel, it will be very unstable. The best solution is to get a cheap MPPT charge controller ($20) and a small 12V lead acid or lithium iron phospate battery. The MPPT will regulate the current and maintain the battery charge, even while you are using the battery to power your battery chargers.
 

3_gun

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Solar chargers are as unreliable as the weather fore casts. Best to use solar to charge a battery bank and then charge batteries from it. I have a smaller "smart phone" sized 4 panel, 25000mah bank that is USB output only. With strong sunlight it takes about 4x the time to recharge the bank as to run it dry. Still that size full charged is enough to give me about a week of hotspot/phone/tablet/flashlight use W/O any solar recharging. Of course you can plug it in to any outlet to rapid charge the bank. Larger banks have 12v outputs which would allow using a standard charger for bulk recharging. Of course you'd need much larger panels for this kinda set up to work


corrected, nice catch LEDrock
 
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KITROBASKIN

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Some battery chargers can handle intermittent sunlight. Perhaps you might consider going big with a solar system that can do more than just some batteries?
 

Dave_H

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When I see this mentioned, it's always in the context of charging a smart phone. What I'd like to know is whether or not this problem also happens if a solar charger is used with a battery charger. My guess is that it doesn't because the recommendation is to use the solar charger to charge a battery bank, and then use that to charge the phone. If the drop in charge rate from passing clouds affected a battery charger, then it would affect the battery bank being charged. But then again, that's a lithium power bank rather than a charger for AA Ni-MHs. Does that make a difference?

That's the way I do it. If something goes wrong with the solar charger (like it shorts and allows 12v or more through) it will only take out an inexpensive battery pack, not the phone. This is less efficient, but safer, and you can use the pack to charge or power something else.

Dave
 

LEDrock

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Solar chargers are as unreliable as the weather fore casts. Best to use solar to charge a battery bank and then charge batteries from it. I have a smaller "smart phone" sized 6 panel, 25000mah bank that is USB output only. With strong sunlight it takes about 4x the time to recharge the bank as to run it dry. Still that size full charged is enough to give me about a week of hotspot/phone/tablet/flashlight use W/O any solar recharging. Of course you can plug it in to any outlet to rapid charge the bank. Larger banks have 12v outputs which would allow using a standard charger for bulk recharging. Of course you'd need much larger panels for this kinda set up to work
I've never seen one of those that had 6 panels before. Only up to 4.
The one I had in mind is the Nektech 21 watt( which has been highly rated in reviews), and the charger I'd be getting is the Tenergy TN474U. I've tried posting links to the Amazon listings, but they never show up when I post for some reason.

EDIT: I noticed your edit about how many panels you have. Yeah, I've noticed many of them with 4. The Nektech 21 watt I wanted to get has 3, but they are much bigger. From what I've read, bigger panels with more panels make them more consistent in their output.

I guess the reason I wanted to just get a solar charger without a battery bank was because I'd be charging batteries anyway, except they'd be AA instead of a lithium power bank. Seems a little redundant to charge up a lithium power bank, and then use that to charge 4 AA nickel metal hydrides. But I could see a case for it if a lithium power bank is somehow more able to withstand variations in solar power better than the 4AA charger.
Also, charging a phone would be secondary. I mainly want to charge up AA batteries. I know there are charger specifically made for doing that with solar, but they all seem cheap and have bad reviews. Plus, they're all-in-one units which would allow the batteries inside to get very hot, which isn't good for them. That's one other reason I don't like the idea of the smartphone-sized solar battery banks. It puts the battery in the sun with the panels which makes the battery very hot.
 
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LEDrock

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That's the way I do it. If something goes wrong with the solar charger (like it shorts and allows 12v or more through) it will only take out an inexpensive battery pack, not the phone. This is less efficient, but safer, and you can use the pack to charge or power something else.

Dave
Wouldn't the phone or battery charger regulate how much power goes into it from the panel? I've heard that devices like those take care of what goes into them from an outside source.
 

LEDrock

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That's the way I do it. If something goes wrong with the solar charger (like it shorts and allows 12v or more through) it will only take out an inexpensive battery pack, not the phone. This is less efficient, but safer, and you can use the pack to charge or power something else.

Dave
But if the main thing I want to use the solar charger for is to charge AA batteries, would it be safe for doing that? The solar charger I have in mind is the Nektech 21 watt, and the battery charger I'd connect it to is the Tenergy TN474U.
 

LEDrock

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Take a look at the output of the panel you are looking at, and the power required by the battery charger.
The solar panel is 21 watts, and it's USB ports put out 5 volts and 2amps maximum each.
The charger specifies that its DC input is 5volts and 1 amp, and output is 450ma per battery (up to 4).

Seems like a good match to me. Are there any other specifications to consider?
 

snakebite

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what charger?
some do fine with solar and others are useless.
some reviewed chargers are tested for solar performance.
and making up a "dumb" solar charger for ni batteries works too.
i have several small panels that will just put a full charge in a specific size in 1 day of good sun.
ex 6v 250ma panel does 4 aa nimh in a day.
 

LEDrock

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what charger?
some do fine with solar and others are useless.
some reviewed chargers are tested for solar performance.
and making up a "dumb" solar charger for ni batteries works too.
i have several small panels that will just put a full charge in a specific size in 1 day of good sun.
ex 6v 250ma panel does 4 aa nimh in a day.
The charger I was going to get is the Tenergy TN474U. I tried posting a link to it and the solar panel before but they don't show up for some reason.
 

KITROBASKIN

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OK. Seems like you could get by with a more compact panel if you wanted. The charger is using 5 watts nominal. All four slots filled with depleted batteries might only be getting 250mA each. Someone correct me if this is in error.
 

lumen aeternum

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I have seen solar panels with a couple of Li Ions batteries built-in, but only with a fixed voltage output. Are there any with a variable voltage output? Or can I buy something that will accept the fixed input voltage (I guess they only come in 12v or 5v ?) and allow me to select the output voltage? I want to be able to connect various things with one solar panel - D battery operated radios, etc.

"MPPT charge controller" - ??? MPPT ???
 

LEDrock

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OK. Seems like you could get by with a more compact panel if you wanted. The charger is using 5 watts nominal. All four slots filled with depleted batteries might only be getting 250mA each. Someone correct me if this is in error.
Actually, the ad says that each battery gets up to 450MA, although I wouldn't mind seeing that slowed down since I'm not really a fan of fast charging. I am going to assume that if I wanted to reduce the charge rate, I could reduce the amount of sunlight hitting the panels. There are 3 panels, and I could close one of them. In fact, one of the things I look forward to trying out after getting it (I placed the order today!) is trying it out on a cloudy day to see what it can do. I've heard solar technology today is such that charging can be done even under clouds. Maybe not fast, but I'll bet it would charge 1AA battery in a day if that's all I put in the charger. It will be a fun little experiment.
 

Dave_H

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The 21W panel is very likely peak watts which is under ideal conditions and the average will be below (maybe well below) this. So powering a 5W input charger is not so much overkill as it seems. You might get away with something around 10W.

If the charger is charging at constant current (it should be), trying to lower this by "current-starving" it at the input is not likely to work well. 450mA to me doesn't seem that high. However, look for a possibly older charger with lower fixed rate (usually doesn't go much lower). In many cases the cell rate is lower for 4 cells than for 2.

Dave
 

LEDrock

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The 21W panel is very likely peak watts which is under ideal conditions and the average will be below (maybe well below) this. So powering a 5W input charger is not so much overkill as it seems. You might get away with something around 10W.

If the charger is charging at constant current (it should be), trying to lower this by "current-starving" it at the input is not likely to work well. 450mA to me doesn't seem that high. However, look for a possibly older charger with lower fixed rate (usually doesn't go much lower). In many cases the cell rate is lower for 4 cells than for 2.

Dave
I've already placed the order.
I already have another charger, but it is AC only, and it specifies that it's output is 360 mah for 4AA. This made me think 450 mah for each battery was kind of high.
 

Dave_H

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Second-hand stores often end up with slower chargers which are perfectly good but ditched as they are too slow for some users; but perfectly good for small solar charging setup. They are usually only a few dollars each. I keep an eye out for those which charge cells individually versus in pairs; separate charge indicators are nice but not essential. Also, ones with dc input jack, usually 12v (careful, some may be 5v).

Most of these seem to recover gracefully from power interruption at the input, but check that cells are not drained by leakage back into the charger with no sustained input i.e. at night.

Dave
 

LEDrock

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Second-hand stores often end up with slower chargers which are perfectly good but ditched as they are too slow for some users; but perfectly good for small solar charging setup. They are usually only a few dollars each. I keep an eye out for those which charge cells individually versus in pairs; separate charge indicators are nice but not essential. Also, ones with dc input jack, usually 12v (careful, some may be 5v).

Most of these seem to recover gracefully from power interruption at the input, but check that cells are not drained by leakage back into the charger with no sustained input i.e. at night.

Dave
Well, I got my order today from Amazon. I tried everything out with interesting results.
First, under cloud cover, I plugged in my phone which was at 56%. After 25 minutes, it was up to 60%. Pretty good for being under the clouds! The battery charger I got with it is another story. When I plug the solar charger into it, the display on the battery charger is erratic, even under sun light. It's fine if I plug it into my laptop though. Not sure what the deal is.
 
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