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Battery Recommendations — Parallax Forums

Battery Recommendations

ercoerco Posts: 20,256
edited 2008-08-20 01:38 in Robotics
Looking to move past lead-acid technology for my electric bike which·may be·similar to some of the big robots you guys are building. I've seen several posts at Electric Vehicle forums that Lithium-Ion batteries are now as cheap as Nickel Metal Hydride, but I haven't seen it yet. Ebay is my reference, and there are several·China-direct importers that have bidders lined up for lithium batteries: http://cgi.ebay.com/36V-20AH-LiFePO4-Electric-Scooter-E-Bike-Battery_W0QQitemZ200244551507QQcmdZViewItem?hash=item200244551507&_trkparms=39%3A1%7C66%3A2%7C65%3A13%7C240%3A1309&_trksid=p3286.c0.m14 That's $600 for a 36V 20 AH LiFePO4 battery, including a smart charger. They claim thousands of recharge cycles are possible.

But Ni-MH seems to be the best bang for the buck. 10 AH D-cells·(1.2V)·are selling for about $6 apiece: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=330248714629&ssPageName=STRK:MEWA:IT&ih=014
so that would be $180 for enough cells to assemble a 36V 10 AH battery pack, or $360 to make a 20 AH pack comparable to the lithium battery. Heavier, of course, and you gotta roll your own charger.

I welcome input and·recommendations from this group, which is considerably better technically informed than the EV groups I have discovered thus far.


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·"If you build it, they will come."

Comments

  • SRLMSRLM Posts: 5,045
    edited 2008-08-20 01:13
    I got my batteries at the local RC car store. They have a shelf where they toss all their discontinued products, and I found some nice NIMH batteries there. I got 6 at $12 a piece: 12V 2200 mAH. So thats $72 for 36v 4400mA. Not bad...
  • ercoerco Posts: 20,256
    edited 2008-08-20 01:38
    Interesting point. What's the best way to wire small cells in parallel to increase capacity? I have had a lot of individual NiMH cells go bad in Roomba battery packs. All it takes is one bad cell to kill a pack so it can't hold 14.4 volts, and it's useless.

    If you have a good string of series cells in parallel with a bad string of series cells, that's no good. Is it better to put two or more small cells in parallel, then put those parallel packs in series?

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    ·"If you build it, they will come."
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