[Oeva-list] Ev Batteries

[Graunke, Gary]

Looking at the Sandia report, these batteries should be great in an EV. It doesn't answer the question of quality of manufacturing, but covers everything else.
Our experience with A123's LiFePO4 was that 1-2% have a higher self-discharge rate, but they are otherwise very consistent and meet and exceed specs in every way.
These also meet or exceed specs in every way, according to the authors.

To deal with these kind of variations, I would suggest the 12V 40AH to 80AH batteries (maybe even the 120AH if you have a pickup truck), so you have 4 to 12 cells in parallel.
The 26 to 34 lb batteries are easy to life by hand if you need to work on them. The AH depends on your desired range and/or $ you have to invest.

The low temperature performance is better than lead-acid as well, losing only 25% at freezing (about our low in Portland) or 34% if you live in Bend. The high power of the cells helps the low temperature performance, however, compared to lead, and you still can put in battery heaters or an insulated battery box if this is a concern. An insulated battery box would also help if you have a catastrophic cell failure with 160C temperatures. (Always vent the box to the outside (not cabin) for this reason, though it is not critical).
There is no high temperature concern (life with most other batteries!).

Buying the batteries in this package makes it difficult (if not impractical) to do individual cell group management, but it sure is convenient!  However, it may well be that monitoring the battery voltage at 12V will be good enough (that is what we are forced to do with lead acid batteries in any case). (The issue is that one should slow down/shut off the charger when a cell reaches maximum voltage to avoid overcharging it). The self-discharge rates on a cell mean that you may want to charge individual cells (or cell groups if they are in parallel) to keep them in balance. I do this manually right now every 10 months or so with A123 cells, but will eventually put in equalizers to do this continuously.

Bottom line-I would have used batteries like this in my Insight had they been available 3 years ago. Let us know how much they want for them.

Other sources are thunder sky (though they have not met specs in their early offerings), peak battery (K2). I am running K2 batteries in my plug-in Prius from EEtrex-they have less (but still adequate) power than A123's, but 30% more energy per same size and weight cell.

It is important to assess the quality of the batteries. It helps to know someone who has been using them, but this is difficult with new batteries. The Sandia report is very helpful in this regard, but there is always a concern that they "cherry-picked" the cells that they sent for testing (rather than a random sample from their production).

Keep us informed with your progress!

Gary

________________________________
From: oeva-list-bounces at oeva.org [mailto:oeva-list-bounces at oeva.org] On Behalf Of Rob Russo
Sent: Friday, October 09, 2009 6:45 PM
To: oeva-list at oeva.org
Subject: [Oeva-list] Ev Batteries

Thanks to all who responded.
I guess my main concern and probably the first decision I have to make is the type and voltage of the battery pack. I want to avoid lead acid batteries because it seems counterintuitive to add all that weight to such a light vehicle.
Is this battery pack practical for my application?: http://www.lifebatt.com/HPSpacks.asp . Are there any alternative sources for this type of battery?

Thanks,
-Rob



-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/attachments/20091010/790890ea/attachment.html