18650 banks in series/parallel

[Briansterling]

I came across this item on eBay yesterday while browsing the 18650 battery accessories.
http://pages.ebay.com/link/?nav=item.view&alt=web&id=311137679822

When I saw that it could be sent to 21 V it occurred to me that this may be a viable option to power my electric motorcycle. I had avoided these cells because they seemed like a lot of trouble when it comes to balancing them, charging them, and safety. This power bank has variable voltages, overheat protection, overvoltage protection, reverse voltage protection, dedicated chargers, and cell balancing features. For all intensive purposes it seems to be a BMS in a box.

I'm curious if anyone has thought about using these for their electric vehicle. On paper it seems to make sense to put three or four of these in series and then have another set or two in parallel to build up the AH. That's a lot of batteries but they are pretty cheap and this would have the benefit of easily switching out bad cells whenever you like for cheap. Lithium is of course lighter and more powerful than acid batteries so the bike should go further since it's lighter. Having these smaller battery sizes would also help in placing them on a motorcycle chassis which has limited space.

I'm sure there something I'm missing but I'm not sure what it is. Otherwise tons of people would be using these for this purpose.

Motor: Etek-RT 72v 360A (max)
Controller: Alltrax 7245 350A

 

[Ohbse]

You'll notice that the maximum output power is 75w. Your motorcycle will happily consume 15,000w based on the controller specs and likely more. That means you need 200+ of these at a minimum. In practice, this would be a nightmare and likely catch fire immediately. You would introduce literally thousands of cheap, underspecced components to what could be a very simplistic solution. Not to mention that you're going to spend $4000 with no cells.

I recently built a 72v nominal 25ah pack from high power 18650's complete with BMS. It weighs just under 10KG and will put out 15kw and cost ~$1200USD including building my own spot welder to assemble it. This would actually run your motorcycle, however still not to its full capability.

 

[dogman dan]

Oh my, these things again. Sure, it could be done, but there are much less costly sources for 18650 cells.

 

[Briansterling]

Excellent information. I felt there was something missing on these batteries. Think I'll stick to the tried-and-true method of some AGM batteries.

 

[Ohbse]

AGM?! There's no justification for running lead these days. There are cheaper, safer, lighter, more power dense and far more long lived lithium options. Look into purchasing used Nissan leaf cells. Come in convenient, large format cans with easy terminations and are vastly superior in every respect to lead. There's a wealth of information on these around this board and elsewhere on the internet and availability is getting better all the time.