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Old 04-25-2015, 07:33 PM   #1
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Solar and lithium batteries

I've got some spare solar panels and I'm wondering about charging lithium batteries. For the most part, these batteries came with boxes and cig lighter plugs to charge from the 12v system. Of course that gets up around 13.8v or so during travel, so I assume they can handle that. There doesn't seem to be a way to figure what the top end is though, but I assume they have circuitry to prevent say the use of 14+v. But not sure.

So...how to charge these with a panel? I've got one that does 18v, for instance, and another at 22v, measured in full sun with no load. I first thought of attaching a step down I had that can take up to 30v and output 3, 5, 12, etc. But can I assume that the battery charger for the lithiums I'd connect would be one way, in essence? Or should I use a spare Sunguard 4.5 amp controller and then the 12v charger for the lithium battery?

I realize there are special controllers for these batteries, but are they for bare battery packs? I would think so, since all the batteries I have are meant to be charged with wall warts, USB or car DC power.

But before I blow myself up thought I'd get it sorted....

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Old 04-26-2015, 09:28 AM   #2
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Re: Solar and lithium batteries

Rob,

I think most packaged lithium batteries do come with a control circuit that limits overcharging and over discharge but is not a complete substitute for a proper lithium charger. Lithium batteries are very sensitive, especially to over discharge. A lot of the lithium or multi-chemistry chargers are driven by 12 volts though and are getting quite inexpensive. You could just run the panels through the charger to your battery packs.

I no longer charge my RC and bicycle batteries inside after a nasty and messy fire. They were in a fireproof charging bag on a concrete floor in my study but still made a scary mess when they went up. Having proprietary chargers and control software seems to help the safety issue but obviously even Boeing didn't get it right first time around...
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Old 04-26-2015, 10:48 AM   #3
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Re: Solar and lithium batteries

I was looking into using the solar with the XP-10 Micro Start jumper battery as an example; I emailed them but haven't heard back. I'm not sure how smart their charging circuitry is; I know some guys who use RCs have chargers that can also regulate the storage voltage (which is less IIRC) and optimize charging. Not sure these are that sophisticated, but I also read that they could just plug into solar...but it wasn't clear if they assumed a controller or not. They have circuitry these days to prevent the vehicle power from flowing back into the unit via the jumper cables, but I would imagine that's not the same circuit as the DC charging circuit.

Several of the other lithiums are USB charged.

I am leaning toward using the buck converter I have. I would think that just getting 12v out until it drops too low to produce that would work fine; the charging circuits in the jump starter, camera battery chargers, laptop batteries, etc would handle it just like when you leave them plugged into your cig lighter and you run your starter battery down....
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