An adventure with John
John is my neighbor. I call him the rocket scientist. He worked in Canada’s rocketry program. Back in the day.
Recently I had a nice adventure with John. We tried charging the “bad battery.”
My Chevy Volt pack came with one battery with a bad cell. Or I thought it was one bad cell. Once I got my cell log I found out that the bad battery had 3 cells that are low. Hmmm. Each exactly .2v lower than all 69 of the other cells. Makes me wonder if there was something wrong with the BMS. That would be odd. But so is the idea that 3 cells went exactly .2 volts “bad” at the same time and then remained at that state of charge. A bad pouch (each cell being made of 3 pouches) should drag the whole cell down. No? And not affect its neighbors. And drop to 0. So there you go.
Small battery meets low amp charger
Anyway. I take the battery over to John’s and he hooks into two of the bad cells and sets them to charge. Low amperage charger. Two and half hours later they are only half charged.
After a trip home to do some lawn mowing, I get back to his place. He greets me with uncharacteristic enthusiasm. I’m like. What’s up? Oh, he says, I have an idea.
Uh oh, I think.
He’s dragged out this huge old unregulated power supply. Well, dragged out is the wrong word. Dusted off. It weighs over 100 lbs. So he was dragging it nowhere.
The “beastie” can do 20 amps. He enthuses. Think your battery can take it? Now of course it can. It could take 135 amps. Sure, I say.
Out comes a huge plastic bar wrapped with coils of ni-chro wire. Same stuff they use in toasters, he says. We’ll put a resistor in line, he says. I nod my head and hope I look like I know what he’s talking about. It’s a half ohm he says.
All set up he gets down on the floor. Starts fiddling with knobs. Uh oh. Somethings not working. I (correctly) diagnose that the knob has screws and maybe the set screw is loose. Eventually that proves to be the case. We get the screws (knob is held on by a tension screw and then a set screw keeps it in place) tight.
A smell of burning wood
John knocks on an orange bulb cap. This is the warning light. If this goes off we’re in trouble. He cackles. The cap promptly falls to the floor.
I haven’t used this thing for awhile, he says. As he tries to get the orange cap to stay on the machine. Finally achieving a state of semi, but precarious, attachment we’re set.
I attach my cell log. He attaches his made in China multimeter.
Did I mention this is an unregulated power supply? It has some regulation. His hand turning the dial. On goes the switch. The light on the half ohm resistor lights up. The light on the orange warning light lights up. Hmmm. So far so good.
I check the cell log. John checks the multimeter. By both accounts the voltage in the battery is rising.
The battery is slowly charging. No drama.
A time for going back in time
We talk. We tell stories. He brings out the neatest pictures of Canada’s rocketry program from back in the day. He was a tech up in Churchill. He has a really cool picture of him calibrating and assembling some fancy battery.
Oh. John’s multimeter has a temperature gauge on it. John gets out the thermocouple for it. Plugs it in. This is neat, he says. And he touches it to the aforementioned resistor wires. 60, 110, 160, 200, 230 Celcius and climbing. He takes the thermocouple off. That’s getting hot he says. He goes and gets some asbestos plates to put underneath. Yup. We’re doing things old school. Certainly explains the burning wood smell.
Finally. 3.83. Much faster than the other charger. Huzzah.
He turns off the regulator. The battery voltage starts to drop. I’m looking at the cell log thinking. Gee, I haven’t seen this kind of fall back on the lithium before. I wonder why? Then a light goes on. I unhook the negative lead from the battery. The voltage drop stops.
We puzzle at what might have started draining the battery.