What's the best battery type for charging from solar?

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Shawn1990
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What's the best battery type for charging from solar?

Postby Shawn1990 » Sun Oct 05, 2008 3:25 pm

Hi there

I am in the process of constructing a lightweight solar-assisted recumbent trike. The aim of the project is to develop a prototype vehicle which will allow for 100% carbon emission free travelling.
Once complete, I aim to put the vehicle through its paces in a sponsored tour of Europe, to raise money for charity.

At the moment however, I am currently trying to sort out batteries. My vehicle is based on a tadpole design (two front wheels for steering, one rear for driving) and uses a rear 250w hub motor (the legal maximum for a power-assist trike) and requires a 36v supply. The project is highly sponsored and I am lucky to have a company that produce the latest in lightweight, flexible solar modules, as one of these sponsors. My battery supply needs to be as light as possible and able to withstand the varying supply that a solar source throws at it. Does anyone have any ideas?

Shawn

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retepsnikrep
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Postby retepsnikrep » Sun Oct 05, 2008 4:04 pm

Lithum-Polymer pouched cells would get my vote for simpe, lightness and energy density.

By the way who is your solar sponsor and what lightweight solar cells are you using I might be interested in some.

Good luck Peter
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

Shawn1990
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My Lightweight Solar Panels

Postby Shawn1990 » Sun Oct 05, 2008 4:42 pm

Hi Peter

Thanks for your prompt reply. I have been looking into Li-Po but have heard various conflicting views when it comes to charging them from solar. Quite a few people I have talked to have had cell-balancing issues.

The panels I am using are from a company called DBK Technitherm, who produce their own panels from scratch in a small factory in Pontyclun, South Wales. Their main application is as a source of power for the next generation of solar road-side signs. Their website is [http://www.uk-solarpanels.co.uk/]. The panels they have provided me with are their '70w Flexi' type.

Cheers, Shawn

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retepsnikrep
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Re: My Lightweight Solar Panels

Postby retepsnikrep » Sun Oct 05, 2008 4:49 pm

Shawn1990 wrote:Quite a few people I have talked to have had cell-balancing issues.


Shawn you need a BMS of course. Cell balancing in the RC world where these cells are very popular is usually done by the charger I understand.
You need an independant system IMO monitoring the cells and doing the balancing. How many cells are you envisaging?
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

Shawn1990
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Postby Shawn1990 » Sun Oct 05, 2008 5:12 pm

I am of course aware of BMS, and would be using one. One of my contacts however is a guy who converts mobility scooters to solar, and uses a BMS with Lithium Polymer packs. He was using a supply he constructed from surplus Li-po cells and had issues with odd cells randomly failing.

I'm not quite sure how many cells I would be using, as I am still in sponsorship discussion with a battery supplier. But they have a wide range of different rated packs, and it would be a case of choosing those that best fit into the space available.

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Jeremy
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Postby Jeremy » Sun Oct 05, 2008 5:12 pm

Cell balancing for a low capacity pack on an ebike is pretty easy. Li Ping in China sells a very good BMS that will balance 12 LiFePO4 cells very easily and provide a good LVC to protect the cells from over-discharge.

Last time I checked the BMS was around $47 plus avbout $15 for shipping.

You could do worse than buy a complete battery pack with BMS from him. I have a 36V 10Ah pack from Li Ping that is proving to be excellent on my recumbent bike. It could very easily be charged from a small solar array, as there is no real intelligence built in to the mains charger.

Jeremy

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retepsnikrep
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Postby retepsnikrep » Sun Oct 05, 2008 5:17 pm

I agree with Jeremy, Ping does have a good reputation. Not sure about his BMS though, but I may be biased :wink:

But for this application it does make sense, so keep it simple and buy the whole kit from him IMHO.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

Shawn1990
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Postby Shawn1990 » Sun Oct 05, 2008 5:58 pm

Thanks chaps. This is all very useful advice. I was told that the BVS was a good thing to join, and that is definately proving the case!

Would that be a Scrapheap Challenge uniform I see, Jeremy?

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Jeremy
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Postby Jeremy » Sun Oct 05, 2008 6:50 pm

It is indeed, there are at least two of us Scrapheap bods on here. Quite what this means I'm not sure, but it's fair to say that quite a few Scrapheap experts already knew each other before the series came about.

If you are interested in a pack from Li Ping your best bet is to email him directly, rather than wait for the right pack to pop up on eBay. His email address is pingping227@hotmail.com. He will build a custom pack for you at a fair price, with a good warranty.

Jeremy

NickJ
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Postby NickJ » Mon Oct 06, 2008 9:16 pm

Hi

The main problem with PV as a charge source for batteries of any kind is that although the output voltage (open circuit) remains fairly constant above a certain light level it is temperature dependant (higher module temp lower voltage) and the current varies all over the shop in proportion (ish) to light level. With most PV systems being static lead acid is preferred as it is quite "tolerent" of varying charge at constant voltage, especially flooded cells, but these are pretty useless for your project. A decent BMS is obvious but as it will be very hard to get constant current at any point and at times the charge may fall to near zero it is a very different kettle of fish to a "normal" charge. Im not a BMS expert but one though is that if the PV was connected to a lead acid battery of appropriate size and voltage in a static charging point at home then it could provide a constant current/voltage charge to balance the pack and recover on the solar.

Just a thought, may not be practical.


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