Last week, I had made a date with my friend Tom G (who you might remember from the AC Dodge Neon project) to come out to my house and show me how to use a variable frequency drive. Tom has lots of experience working with AC motors and owns a few salvaged drives.
I had already started work disassembling the Mitsubishi i-MIEV’s motor controller. Getting the top cover off, it really didn’t look bad at all inside. Next, I started removing the electric connections and cooling lines to pull the entire controller out. That’s about when Tom showed up. He worked on getting the corroded battery cables out of the controller while I went under the car to remove the cooling lines. Electric car coolant IS delicious, as it sprays all over the bottom of the car, but at least I did manage to get more of it in the bucket than in my mouth…. Ick. Still better than when I drained the gas tank on the Geo Metro.
Once everything was disconnected from the controller, we pulled the entire box out and set it to the side. We now had a good view of the motor and differential and access to the three motor cables. Tom set up the VFD and we plugged it into my 240VAC electric outlet that I had installed for my welder. On the other end of the VFD we connected the output wires to the cables going to the motor. I already jacked the car into the air and then lowered it onto jackstands. The iMIEV is rear-engine/real-wheel drive. With the wheels up in the air, and the temporary motor controller hooked up, in theory, we should be able to make the wheels spin.The gear selector cable had already been removed from the transmission, so I could just reach down there and manually put the car into park, reverse, neutral, or drive. I popped the car into gear, and we were ready to give it a shot.
Tom turned on the controller and activated the run mode. Odd musical notes started playing from the car’s motor. I know that this has to do with electronic switching happened at a frequency within the range of human hearing, but it’s still weird to HEAR a motor playing techno-bagpipe music. A moment later, the right rear wheel started to slowly spin.
We played with the VFD for a little bit. The left wheel was dragging a bit. I think there is some rust on the brake or bearing, it didn’t seem to spin as freely as the right wheel. Turning it by hand would briefly make both tires rotate. Tom said that the motor was drawing more current than he expected and that we should have been able spin the motor faster than that as well.
His brief diagnosis? The motor worked, but was NOT in healthy tip-top shape.
So what’s the next step? Perhaps removing the motor and transmission. Both parts are pretty easy to get to under the car. The transmission would pop right out if I could figure out how to remove the drive-shafts. I haven’t worked on a car before that has the style of suspension that the iMIEV has in back. I’m not quite sure How I would remove the wheel assemblies to make room to pull the drive axles so I could drop the transmission. Oh well, that’s for another day anyways.
Returning my attention to the car’s original motor controller, I flipped it over to access the bottom cover. The controller is a big aluminum box with liquid cooling and holes for the battery and motor cables. It’s also multi-dimentional – two layers of electronics in one box. I pulled the dozen or so 8mm hex bolts from the bottom cover and then pried it off. *Sigh* I saw about what I expected too. Sea water had gotten inside and then sunk to the lowest point completely corroding and destroying all the electronics inside. I poured out what looked like sand. I guess it sort of was. Combine oxygen in saltwater with aluminum and some electronics and you get aluminum oxide and silica.
So, the controller is toast, but on the upside, the IGBT modules on TOP of the unit look just fine. Perhaps they could be pulled and used as part of a DIY Open Source AC controller?
Again, this project has been an interesting combination of disappointment at the damage and fun of taking it apart. It’s not every day that I get to take apart an otherwise brand-new electric car!
Til next time, stay charged up!