# Battery Pack Techniques: LiFePO4 Cells



## ClintK (Apr 27, 2008)

200AH LiFePO4 Battery Test Results

Suggestions for dealing with Prismatic LiFePO4 cells:
Original Discussion Thread

1. When you build up a pack of cells, say a 12.8volt nominal battery of 4ea cells. Be sure, and place restraining plates on the end faces, bind the whole assembly with strapping to keep the cells from ever having the chance to bulge. If they ever bulge, and I've had brand new unused cells do this on their own, the internal plates start to spread apart, dry spots will develop and your capacity will slowly dwindle, to the point the battery will fail. I know this from dissecting a failed battery. 

2. Interconnecting busbars, should be sized large enough that there is very, very little noticable change in the busbar's temperature after your typical EV drive. NTEAA members have progressed to using 1" wide x 1/2" thick aluminum bars, which accomplishes several things. The posts of the LiFePO4 cells are aluminum, therefore using aluminum threaded studs screwed into the cells, with aluminum busbars, held down with a double nut system, all lathered up with "No-Ox ID A" for electrical connections. There is very little heat generation at the busbar, and the batteries operate nice and cool. Keeping the cell studs and busbars aluminum also eliminates dissimiliar metal reaction or galvanic corrosion.

3. Charge regulators, are installed on each individual cell, which once a cell reaches 3.65vdc, that particular cell stops taking on energy, shunting the majority of it over the the remaining cells. The experience has been, once one regulator comes on, showing a cell is fully charged, the remaining regulators for the rest of the pack, usually engauge within just a few minutes. If you remain within the nominal discharge C rating of your LiFePO4 cells, and you truely balance them during every charge, they want to stay balanced during the discharge cycle. Use your controller's internal cutoff setting to keep from over discharging the pack, and stay within limits of your pack discharge C rating. For the most part drive sensibly.

4. Capacitor Bank, I've only just started testing with this, but so far the results look good. What I'm proposing, is build up a large capacitor bank for the pack voltage you are using, place it between the controller and traction pack. For the most part, paralleled onto your traction pack, as close to the controller as possible. What it does, is it smooths out the pulsing of the power extraction from the batteries, that occurs when the controller requests energy. The O'Scope shows the power extraction to be in pulses, similar to what is being sent to the motor, and the capacitor bank, helps smooth out these pulses so the traction pack doesn't receive such a constant electrical shock. It keeps the energy extraction at a more constant level, thus in theory, extending the life of the traction pack, controller, along with the traction pack running cooler under load, and extending the range just a smidgen....... Update, We're obtaining higher sustained MPH with less amperage with the current capacitor bank, and it feels like more power to the wheel according to the independent driver who did the with and without testing.

For photos of what I've along with others in our www.NTEAA.org club are doing with LiFePO4 batteries, charge regulators, restraining, pack build, monitoring, etc. look at:


http://www.flickr.com/photos/mbarkle...7609086829232/

http://www.flickr.com/photos/mbarkle...7604137306905/

I hope this helps you with your LiFePO4 pack, and would be grateful for any information that you've experienced as well.
-Thanks to TexomaEV for suggestions.


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## Jason Lattimer (Dec 27, 2008)

I like the idea, but it sounds like it would make an already expensive setup even more expensive. It would be great on lead acids that only have a limited output amperage for those quick takeoffs without burning up your battery pack.

Question: would that setup on leads increase your range by not allowing you to use your traction pack peak or just smooth it out.


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## Cebela (Jan 18, 2011)

Here you can order the "Bat-Guards" used in the E-Fiero Conversion Project:
http://www.anidatech.com/LLLabs.htm


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