Tuesday, September 9, 2008

Lead Acid or LiFePO4 (lithium Iron Phosphate) batteries?



In a previous post I indicated that I would most likely purchase the the Trojan T-145 Deep Cycle lead acid battery http://www.trojanbattery.com/Products/T-1456V.aspx. They are supposed to be one of the best deep cycle sealed lead batteries. They are relatively cheap (approx. $3000 total for 24 batteries). Unfortunately, they are also EXTREMELY heavy weighing in around 1700 pounds. Added weight will decrease range and performance. Based on my calculations and verified by several EV'ers that I have contacted I may only see a range of 40 miles using lead acid batteries.  While this may be enough to support much of our daily driving it just doesn't feel like enough for me. Especially when you combine the fact that these lead batteries require regular maintenance (watering) and will degrade over time when not fully charged.  


There may be an alternative... Lithium Iron Phosphate batteries. This battery technology suffers from none of the pitfalls that I mentioned for lead acid batteries and contains many times the amp hour capacity. Plus lithium phosphate cells are 20% of the weight of lead acid batteries which will increase performance. 


I have been researching Lithium batteries for a couple of years and many of you may remember that Jared and I built custom A123 Lithium Nano-phosphate battery packs for our electric bicycles a couple of years ago. The batteries were extremely successful but a lot work, soldiering, etc... In addition, the A123 cells are very expensive. To achieve a range of 75 miles in my S10 EV I would need well over $20,000 worth of A123 cells that must be surface welded "soldiered" into custom packs.


Recently, however, I have rediscovered a potential alternative. Thunder Sky (http://www.thunder-sky.com/products_en.asp?fid=66&fid2=70) LFP cells. I did a little research on these cells a few years ago but found several people who were having problems with some cell batches. However, apparently, newer versions of these cells are popping up in a few Electric Vehicles around the globe and appear to be performing quite well. 
The cells are manufactured in China. I have contacted their primary distributer and it seems that I could get my hands on these 160 amp hour LiFePO4 cells for about $9,000+ shipped to nearest SEA port. I estimate about 75 to 100+ miles range for this amount. Plus no soldiering hundreds of little cells as the Thunder Sky cells are manufactured in large form factor. Just 45 cells will be tied together with bolts and electrical cable. I'm considering purchasing even higher amperage 300 amp hour cells which would cost more but could increase my range to possibly 200+ miles. Yes, I'm drooling...


Anyway, I have been reworking my battery rack design to accommodate either battery technology in case I actually get my hands on some of these cells. :)







4 comments:

Anonymous said...

You should look at this site where these batteries are being used.
http://www.buildcoolstuff.com/wordpress-car/2008/08/
He is building a cool BMS also.

Kurt Clayson said...

Thanks. I have seen his site...in fact I sent him an email with a few questions a while back but have so far received no reply.

Huang Lissa said...

Oh I know what you're thinking -- it's those incredibly thermodynamically unstable lithium ion batteries up to their old tricks again. Wrong!! This culprint in this case was a lead acid battery for a lift truck.

Anonymous said...

did you ever think about alternators. i have a proposal, and it might be worth a ton of money, im giving it out for better economy. if you hook up alternators to a pulley belt system, they will charge the battery's from the motor being turned. if you have ever rotated a alternator pulley they easy to turn, hook a belt to that, send the electrical staight back to the battery's or even to the motor, and it can add a ton of AH!!! there is a man who created a motor that doesnt need 25 batteries, he doesnt need any. it runs off itself, look it up on youtube.