Tearing out and Testing a Lithium Cell

by Ben N on February 22, 2013

Yesterday, I got one lithium module out of the car.

Here’s the video showing the removal.

The main battery pack is built from 22 units of 4 cells, built together with a BMS board. Each one then is basically a 12V battery.

I got the cell block out, washed it in the bathtub (second time I’ve done it. Wife hasn’t killed me yet, but this time I was smart enough to wash the tub REALLY good afterwards and then CHECK with her if it was good enough, preemptively saying how I would be HAPPY to wash it again if it wasn’t up to her standards!)

And then dismantled it into the single cells. None of them looked swollen or otherwise weird. The plastic overwrap is cracked on many of them. All the cells were pretty much at zero.

The first block that I pulled out (day before last) I decided to try to charge. The cells are listed as 4.2V max voltage, which means a regular 12V lead acid battery won’t overcharge 4 lithium cells. I put the cell block in the middle of my driveway and ran jumper cables to a large lead acid battery to “War-Charge”.

When connecting the cables, the lithium drew 15 amps. I left it connected for about an hour, occasionally checking voltage and temperature of the terminals.

The next day, I checked voltage of the cells again. Two of them were back down to just above zero, but the other two were still in the 3V range.

Last night, I visited my buddy Tim, and we hooked up a cell to a CellPro PowerLab6

A totally dead cell would NOT take a charge, because the charger was too smart for its own good, where it would think that there was no cell hooked up. We were able to get one of the “war-charged” cells to charge, as it had high enough voltage for the charger to recognize it.

We used the LiFePo cell preset to get a 10-amp charge going into the cell for a good hour or so. The cell didn’t get hot or do anything else freaky. We had a laptop hooked up to the charger for data-logging, and the graph looked like what a person would expect for charging a lithium cell.

I borrowed the charger and laptop and hope to go through testing the 8 cells that I have pulled from the car. As for the dead dead dead cells, I’ll need to get some voltage into them for the charger to recognize them at all. Somebody told me to try using a low-voltage wall-wort, like a cell phone charger to get some charge into those batteries. It would be a very low current and about the right voltage. It should be pretty darn hard to accidentally overcharge a 50ah cell with a charger designed for a tiny cell phone battery!


PS: Here’s some more info on what the batteries are.

A link with overview of specs
pdf with much more technical specs

{ 3 comments… read them below or add one }

1 Jarkko Santala February 22, 2013 at 11:35 am

According to Wikipedia the i-MiEV uses Toshiba’s SCiB battery. It also says it has a lower voltage than usual Lithium batteries. Just thought it would be something to take into consideration so as not to overcharge them. Don’t know what the actual voltage range really is.

2 Ben N February 22, 2013 at 11:43 am

That’s some of the first information that I saw as well. It’s also completely wrong. It may have been that that’s the battery pack that was used on an earlier or different version of the car, but it’s not what’s sitting in my garage.
If you take a look at these links, it’s pretty obvious which cells are in this car.

A link with overview of specs

pdf with much more technical specs

3 JoeS February 23, 2013 at 7:21 pm

Ben, thank you for all these great posts and videos! As the owner of an i-miev and unsuccessful bidder for this car, I wish you all the best, and look forward to you hopefully getting this car on the road with not too much more damage to your wallet.

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