[wherethefmi]

I can get my hands on free Lion, rechargeable AA I think they are 700mAh not sure, how many of these would I need to create a battery that would support a motorcycle with say 50miles of range. Forgive my ignorance if this is a dumb question.

[MrCrabs]

Ok so lets say you want 72 volts.
72 / 1.2 (AA voltage) = 60 cells in series to get 72 volts.
Lets say your bike uses 200 Wh/mile.
50 miles * 200 Wh/mile = 10,000 Wh.
10,000 Wh / 72 Volts = 139 Ah needed.
139 Ah / .7 Ah = 200 cells in parallel to get 139 Ah.
200 strings of 60 cells or 12000 AA cells.

This a very rough estimate, not sure how efficient a bike is, I know they aren't very aerodynamic, but they are lighter. And the conversion from Wh to Ah is also just an estimate. As you discharge the batteries the voltage drops, so you need more current to get the same Wh out.
So make it 220 strings in parallel to account for that, so that would mean 13200 cells.

[wherethefmi]

and that would probably be a PITA to package in a bike, though they are still free, does this sound way too complicated for a beginner to accomplish with minimal help.

[MrCrabs]

I think it would be to big of a PITA to attempt to use them.
How to mount that many cells?, how to keep them from overheating?, how to charge them?, how to keep that many cells balanced?
Whats the internal resistance of the battery? What would the resistance be in each connection to each battery? There would be a lot of connections, and it would add up.

[joseph3354]

there are quite a few motorcycle conversions claiming 100wh/mi or less out there now.if the claims are true you would need only half that 139ah.but again a major PITA putting together a 6000 plus cell pack(ala tesla roadster).if the cells were larger capacity it might not be too bad an idea.with that many cells just think how many different connections could go bad,then try finding the bad connections!

[3dplane]

Hey guys!
One little thing that might change those numbers: I'm willing to bet that the AA size lithiums are 3.6 volt instead of 1.2(ni-cd,ni-mh)I've got some.And 700mah sounds about right. Mine are 600mah. Barna

[frodus]

wouldn't Li-ion require balancing? and a special charger too?

I agree, it'd be a PITA and expensive after you DID get the pack together.

[joseph3354]

ok,if they are 3.6v you would ONLY need 3000 cells.
and some serious battery management.

[3dplane]

Yeah quite time consuming to assemble a pack like that even if you used some pre-made battery holders like at radio shack.Lots of soldering but the free price might make it worth a try. Barna

[mattW]

I have worked out I should be able to get a 50 mile range on 60Ah of lithium @ 72V, 200Wh per mile is enough for 2-3 bikes. emoto gets 75... 72V is 24 cells and you would need 85 in series for 60ah.. thats 2040 cells... It would take a lot of soldering etc but it would also take a lot of working to earn the money to buy a normal pack so you'd have to just weigh it up...