Battery help with solar
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Battery help with solar

by c131frdave on Thu Mar 14, 2013 2:14 pm

Hello again. I finished my project building a solar lighting system for my mother in law who lives in Tanzania (explained in another post). Briefly, she doesn't have access to grid electricity, so I made a system that used 5 watt high power LEDs to provide light. The system has 3 LEDs in series and uses about 1 amp with a 12V car battery.

Well, after doing the math, I found that I needed a 5 amp hour battery or more for her daily need. The solar panel was enough to keep the battery charged, so It seemed like I was done. The problem is that the battery I chose is a sealed lead acid battery (8 amp hour), which is fairly small, but the airline says no way, not on our airplane. I went down there and talked to the manager to see exactly what was possible to bring, and they said only lithium ion or similiar "dry" batteries could be put on the plane.

So I found this battery: http://www.amazon.com/Portable-Battery-7800mah-Lithium-Electronics/dp/B00AVLI58M/ref=sr_1_18?ie=UTF8&qid=1363283743&sr=8-18&keywords=lithium+ion+battery+12v

Now, what I am worried about is the fact that the battery has a "limited charge voltage" of 12.6V. Well, the solar panel unloaded measures 22 volts under direct sun, and varies between 15 and 19 under the clouds. So, can I use this to charge the LiIon battery?

Oh, one other thing, I am using a regulator to manage the system. It can be seen here: http://www.amazon.com/gp/product/B004XCZN5S/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1

Thanks for your help!
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Re: Battery help with solar

by Zener on Thu Mar 14, 2013 5:07 pm

The charge controller should limit the output voltage to the battery. However, there is no datasheet at Amazon so the exact specs are unknown.

The FAA battery rules are stranger than I thought. I found this chart on the web.
Batteries.jpg
Batteries.jpg (403.44 KiB) Viewed 452 times
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Re: Battery help with solar

by c131frdave on Thu Mar 14, 2013 6:43 pm

Thanks for the reply. Yes, the TSA battery rules are strange- and every person I've talked to at the TSA has different opinions about the rule. When I sought absolute guidence from the manager of our local airport's TSA manager, he said "it depends on who's working the security checkpoint". Gotta love government run enities...
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Re: Battery help with solar

by john444 on Thu Mar 14, 2013 9:33 pm

C131,

The sealed lead-acid battery and the charge controller was a good choice.
Lead-acid batteries are very tolerant of how they are charged.
Also, the MPP charge controller would get the most it can from the solar-panel.
Your alternatives are not nearly as good.
The next best would be something like a LiPo.
However, I am unaware of any 3-cell chargers that would like being powered from a solar-panel.
Next might be NiH or NiCd. They will need matching chargers.
It will take several 'banks' of parallel cells to get up to 5~6AHr @ 12-V but it can be done.

Sorry, none of the alternatives are as low cost and easy to implement as the lead-acid.
Are you convinced that you will not be able to just mail the lead-acid battery & charger to someplace in Tanzania where your wife could pick it up on her way to her mothers?
John
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Re: Battery help with solar

by tastewar on Thu Mar 14, 2013 10:26 pm

Sourcing the battery locally really would make more sense. Sorry that's not an option in your case.
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Re: Battery help with solar

by c131frdave on Sat Mar 16, 2013 9:01 am

It is an option, actually. Though they don't have electricity, they do have plenty of cars. I was just worried about having an old car battery (and probably one in terrible shape) inside her house. I know from living there for 9 months that the vast majority of car batteries are made in China and still have the little caps on the cells where you add acid. I remember reading somewher that the fumes from these batteries could be dangerous indoors.
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Re: Battery help with solar

by c131frdave on Sat Mar 16, 2013 9:04 am

john444 wrote:The next best would be something like a LiPo.
However, I am unaware of any 3-cell chargers that would like being powered from a solar-panel.


Thanks John. I do have a lipo charger for three cell that came with my radio controlled mustang (airplane). It accepts 9 to 24V DC and charges through the balance port. I'm not sure if it has a minimum supply wattage though. It automatically tries to charge at 1C, and there's no way I could get 5-8 amps (depending on the lipo) from the solar panel.
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Re: Battery help with solar

by Zener on Sat Mar 16, 2013 5:02 pm

Have you looked at International Priority mail? If it is less than 2" thick, and under 4#, then you can ship it for 24.00 and it will get there in 10 days. Just an idea.

Yeah, a car battery will off-gas so I would keep it outside.
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Re: Battery help with solar

by c131frdave on Sun Mar 17, 2013 7:31 pm

Okay, I went to a battery store and found two 6V 5 amp hour batteries that will fit inside the post office box international thingy. Thanks for all your input!
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