should cross over to the darkside?

[mechanix]

I'm in the process of planning a downhill/pit-bike hybrid build and have been trying to figure out what batteries to use. I was initially pretty excited about cellman's batteries, but the future availability of those cells looks kind of bleak. Looking around, it seems as though my only option for the performance/weight i need out of my batteries is to go lipo. I've dealt with lipo before with rc cars, but to be honest, 4kwh of lipo downright scares me! I've been looking at hobbycity and the zippy 6s 5000mah packs look pretty good. I can make a 24s8p pack for about $1500. Any suggestions? Pros and cons are all welcome.

Once I get started I'll be sure to post a build thread.

Joel

 

[mechanix]

I guess I have three main questions:

What are the statistics of catastrophic failure for this type of chemistry? I'm aware of the "golden rules" and that if you take care of your batteries they should be trouble free, but what are the chances that I follow all of these rules and one little thing goes wrong causing thermal runaway? 32 of these cells could cause a lot of damage!

Are there any Lifepo4 battery options that even come close to the same energy/weight or power/weight ratio (with the price in the same order of magnitude)?

How is the cycle life and calendar life of this chemistry? I saw on hobbycity that the new turnigy cells have some sort of "nano carbon additives" that give better cycle life.

Joel

 

[dnmun]

if you are concerned about all the cells cooking off, them assemble the pack so you can pull it apart if you do overcharge it and it catches on fire.

 

[cell_man]

I've been trying to find Chinese manufacturers of high C rate LiFePO4 pouch cells. They don't quite have the energy density of the A123 but they are still pretty good. The discharge on paper also looks pretty good, but their prices are high. Like higher than I paid for the cells I've been selling. Hopefully I can find something that has a good performance to cost compromise. I believe that a LiFePO4 pouch cell which can maintain approximately 3.0V for most of it's discharge at 5C without excessive heat is more than good enough for the vast majority of users.