# how would this work out...



## wherethefmi (Apr 24, 2008)

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.


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## MrCrabs (Mar 7, 2008)

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.


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## wherethefmi (Apr 24, 2008)

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.


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## MrCrabs (Mar 7, 2008)

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.


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## joseph3354 (Apr 2, 2008)

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!


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## 3dplane (Feb 27, 2008)

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


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## frodus (Apr 12, 2008)

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.


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## joseph3354 (Apr 2, 2008)

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


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## 3dplane (Feb 27, 2008)

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


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## mattW (Sep 14, 2007)

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...


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## MrCrabs (Mar 7, 2008)

If you only needed 2040 cells it would be much more feasible.

What could be used for a BMS? With that many cells you would want to prevent cells from getting out of balance, or over-discharging and reversing.

The cells are free, but you would need to buy hardware to balance and monitor them, and spend plenty of time assembling them (plus wiring and hardware costs to assemble them)


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## JohninCR (May 6, 2008)

If they are new, free, and availably in the thousands, let's work out a deal that will net you enough to have someone build them into packs including a BMS (Battery Management System)?


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## wherethefmi (Apr 24, 2008)

they are new and free and getting the necessary numbers for this project is going to take some time, (I can't take thousands at a time) I could get away with like 40ish a month. I'd have to hoard them for a while, would keeping them new in the package be good for the amount of time I'd need to get them all, also what kind of motor would be ideal for say 45mph with a 20-40 mile range. What about Nimh, we have those at work too. How hard would it be to assemble these packs, would basic soldering skills be good enough?


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## frodus (Apr 12, 2008)

wherethefmi said:


> they are new and free and getting the necessary numbers for this project is going to take some time, (I can't take thousands at a time) I could get away with like 40ish a month. I'd have to hoard them for a while, would keeping them new in the package be good for the amount of time I'd need to get them all, also what kind of motor would be ideal for say 45mph with a 20-40 mile range. What about Nimh, we have those at work too. How hard would it be to assemble these packs, would basic soldering skills be good enough?


40 a month, might take a while....

for a smaller motorcycle, something like like the emoto on evalbum made from a Lifan motorcycle, you could use an Etek motor from electricmotorsport. Its 48V, and will scoot around pretty good, efficient, and from what I hear, pretty good on the RPMS. 40 mile may be pushing it with AA batteries, but 20 might be doable if you could put together a pack.

Its not hard to assemble, but soldering would be almost impossible for that many cells (you'd get tired of it quick). Solder doesn't stick really well to the ends (from my experience) You really want to weld tabs on the ends of the batteries... so take that into consideration.

It will most likely be alot of work, and not give you the performance you want, but its doable.


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## MrCrabs (Mar 7, 2008)

2000 cells / 40 cells/month = 50 months = 4 years to collect the batteries.


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## wherethefmi (Apr 24, 2008)

Yeah 4 years sounds a little too long to wait, I'm trying to get this done as cheap as possible but not that CHEAP lol.


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