i-MIEV: Charging Lithium

Since I got the rest of the lithium cells out of the Mitsubishi battery pack, it gives me a chance to start charging and testing them.

Of course, I have to pound some juice in there first!

The main problem I’m running into so far is that the cells are at ZERO volts! They are so discharged that the fancy battery charger I’m using simply will NOT charge them. So, I need to get some sort of bulk charge into the cells before I can do anything at all.

I’ve gotten plenty of advice from folks, use a cell phone charger, hook them up to a bench power supply, etc, etc. NONE of which actually works! The guys who work with remote-control model airplanes have lots of advice as well, but they use tiny lithium cells compared to these 50AH cells in the car.

And that’s when I turn to jumper cables. ( Kids, don’t try this at home! Seriously though, I had safety glasses, temperature monitoring etc.)

The one thing that I have figured that DOES work is “War-Charging”, an uncontrolled charge by charging batteries directly with other batteries. The idea is pretty much the same as when you jump-start a car – just hook both batteries up to each other in parallel.

My Electrak electric riding lawn mower has six batteries in it. I hooked up the jumper cables to two of them (for 24 volts) and the other end to an 8-block of lithium cells. Right away, the resistance of the lithium cells cause it to start drawing about 20 amps, tapering down to 10 amps or so by 15 minutes later. In theory, the lithium can never go above 24v, as there’s never more than that available from the two batteries that’s powering it.

However, the solid flow of current DOES bring up the state of charge of the lithium.

Once I had some juice in the cells, I could then connect one up to the Cell-Pro-6 charger, and do a proper charge/discharge/fully-charge cycle on it. The downside is that it takes about two and a half hours, and I can only do one cell at a time. The upside is that I have a laptop connected to the charger to log data, and save it for future reference. It even tells me the capacity of the cell after testing. (Thanks to my buddy, Tim, for loaning that to me!)

What I’m seeing so far is that the first and last cells in a group of four tend to be pretty GOOD, and the middle two tend to be pretty BAD. It may have to do with the battery management board that’s on the cells, how it’s connected, and how it’s corroded from the salt-water.

I am now cycling the cells that were at 2 volts or higher after war charging. The two that I’ve done so far came in at 38AH capacity and, is this right? Maybe I’m not reading the machine correctly – 47AH! Hmmm 47AH capacity on a cell with a faceplate rating of 50, but it’s been soaking in Atlantic Ocean for a few months? I guess we’ll see how good that one actually turns out or not!

After charging these, it made me wonder about self-discharge. So, I went back to the first (and up until now ONLY) cell that I was able to charge, and checked its voltage. I’m happy to report that it has no significant voltage drop since charging, which was what, a month ago, two months?

As some people have already noted, individually testing, charging, and cycling lithium cells one at a time is going to take a while. Tim, thanks for loaning me your charger, but you aren’t getting it back any time soon!

Since we were fortunate enough to have some nice weather, while one of the cells was cycling, I worked on the headlight. It took a little figuring to decide I needed to remove the bumper to get at the headlamp and then remove several bolts to get the assembly out. I popped out the bulbs and rinsed the inside of the headlight with the garden hose. The flood silt is really stuck in there. I used a long bottle-brush, and got a fair amount of the dirt out, but certainly not all. Looks like I’ll need some sort of special tool to really get the insides of the headlights clean.

Hopefully, next time I chime in on this project, it will be with continuing good news on the batteries.

‘Til then,

-Ben