Lifepo4 cells catch fire!

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Beemer
Posts: 294
Joined: Sat Jun 04, 2011 12:10 pm

Re: Lifepo4 cells catch fire!

Postby Beemer » Mon Jun 25, 2012 10:14 am

I've seen Damiens video's. His cells have been tested strictly within the same voltage and temperature ranges of any LiFePo4. He follows the Jack Rickard School of battery testing and balancing.

It's said a CALB has been taken to 20C. I've seen a damage free 8C.
30C offers nobody any advantage unless they are at Santa Pod. Such rates are simply crazy!

Few speak of the Voltage at C which A123's excel at. Ideally, for safety a cell would deliver to a point then plummet. This is achieved with the cells Tesla uses. They have a PTC resistor mounted inside the end of each cell. They are set to resist at 1C (forgot the temp, I think 40~50 centigrade). Anything that makes them warm makes the cell series resistive. A zener/SCR with each cell could save them from over (dis)charging too but its all about the money work and volume.

However, large cells under load are easier to measure. Longer to heat up. Easier to balance. Disasters happen more slowly so can be caught. Fewer cells to maintain checks with and are proven to be far more consistent.

But like I said before. We have both made a similar decision. I've bought A123's that have quickly lost their lead over Sinopoly/CALB for energy density and all have a power density that I cannot really use.

wattsin
Posts: 3
Joined: Fri May 18, 2012 12:29 am

Re: Lifepo4 cells catch fire!

Postby wattsin » Thu Sep 13, 2012 12:57 pm

Hi All,

After using a small pack of 8 headway cells for general use on a road trip I have gained some insight to their issues. By gain I mean I lost 2 cells in this period!! So when I asked back on the 19th May about any fires from cells not being charged or used the answer was "no known fires". Good. Having just returned & checked this forum, the report from Grumpy-b is interesting & indicates something I encountered. I managed to flatten out all the cells due to a poor connection external to the pack. As soon as this was found I started to charge the pack & it looked like everything was OK. The charge source was then continued within the car via a 10amp fused lead. The paralleling was by a solid single copper wire on each pair of cells with the idea it would provide some balancing & equated to an approx 50a fuse. It started Ok but some short time latter there was a smell & the copper wire had vaporized indicating the problem was at the battery & not the supply from the car. Had this been a more solid link I think the result may have more like what Grumpy-b reported!!. Looking at the picture provided the control board looks like it is not effected & the use of smaller capacity cells may be better than larger cells for safety. The use of a light gauge wire as a fuse to parallel (for balancing) in 12v applications instead of large strapping bars seems to have merit. There was no temperature rise in the failed cells. All over very quickly!!

Regards Bill

Beemer
Posts: 294
Joined: Sat Jun 04, 2011 12:10 pm

Re: Lifepo4 cells catch fire!

Postby Beemer » Thu Sep 13, 2012 3:51 pm

wattsin wrote:Hi All,

After using a small pack of 8 headway cells for general use on a road trip I have gained some insight to their issues. By gain I mean I lost 2 cells in this period!! So when I asked back on the 19th May about any fires from cells not being charged or used the answer was "no known fires". Good. Having just returned & checked this forum, the report from Grumpy-b is interesting & indicates something I encountered. I managed to flatten out all the cells due to a poor connection external to the pack. As soon as this was found I started to charge the pack & it looked like everything was OK. The charge source was then continued within the car via a 10amp fused lead. The paralleling was by a solid single copper wire on each pair of cells with the idea it would provide some balancing & equated to an approx 50a fuse. It started Ok but some short time latter there was a smell & the copper wire had vaporized indicating the problem was at the battery & not the supply from the car. Had this been a more solid link I think the result may have more like what Grumpy-b reported!!. Looking at the picture provided the control board looks like it is not effected & the use of smaller capacity cells may be better than larger cells for safety. The use of a light gauge wire as a fuse to parallel (for balancing) in 12v applications instead of large strapping bars seems to have merit. There was no temperature rise in the failed cells. All over very quickly!!

Regards Bill

Hi Bill. Yup, if you flatten your cells; game over.
If you have a top balancer so you cannot be bottom balanced then there is a good chance the lowest (least capacity) cells will be dead because they were forced into a reverse voltage. They would of become mad hot and will do the same when attempting to recharge them. Not healthy!
It's always a good thing to watch your Voltage under load and AH from charged so you never go there. Not knowing what you are running, don't you have anything like a Cycle analyst connected up?

A good resource for for people who understand Headways are http://www.evbmw.com and http://tovey-books.co.uk/

All the best, hope you sort it.
Andrew


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