Thursday, September 29, 2011
Electric Truck: Working out all the bugs
Costco batteries have a 75 amp rating of 115 minutes. When I am cruising on the highway at 50mph, my sustained current draw is about 120 amps. If I were to conservatively assume that my batteries will only last 60 minutes while pulling 120 amps, I should still be able to go 50 miles before they are discharged. For some reason, I am killing them early. Perhaps it's the periods when I am pulling more amps (like going up a hill or accelerating to freeway speed). But then there are also times when I am coasting down a hill or using the breaks where I am consuming no power. Hmmm.
I found one of my batteries had a lot lower voltage than the others. Even after equalizing all of them, when the truck was discharged to 30%, this one battery still showed very low voltage.
I also found several batteries had loose connections. While tightening them up, one of the posts ripped out of one of the batteries. I returned both batteries to Costco and got replacement ones. I also bought a battery load tester at Harbor Freight so I could determine if any more batteries were dead.
I replaced my clutch plate, disk and thrust bearing. Now I have a working clutch. It is possible to shift without a clutch but with an electric motor, you have to be patient while the it spins down to a low enough RPM for the shifter to fall into the next higher gear. Now with a working clutch, I can shift nearly as fast as in a normal gas car.
I built a better motor mount after my first one broke at the welds. This 2nd mount uses a wide piece of flat steel to carry the weight of the motor and a Tee shaped piece of steel fastened to the firewall to keep the motor from twisting under high torque. This tee mount held the motor great but caused lots of transmission noise to resonate into the cab of the truck. I removed the tee and replaced it with a light weight, 1” wide metal strap screwed into the truck frame. No more resonance but now the strap is causing an annoying squeaking sound every time the motor tries to twist under torque, I learned that the twisting force on the motor is quite high and after 50 miles, it snapped a spot weld off of the strap.
Onto plan “D”. I welded 2 pieces of flat metal from the flat metal motor strap to the motor itself. Bingo! No more squeak and no more resonance. So far so good.
More recently, my flywheel has started making a lot of vibration at higher rpm's. It's kind of annoying and detracts from the quiet ride of the electric truck. I am waiting for the weekend to pull the engine back apart to have a look inside. That's the good thing about EVs. They are super easy to work on. One hour of work and the whole motor is out. 90 minutes later and everything is back together again. No oily grease, no seals to worry about, no fluids to drain, no filters, no fuss.
I replaced the 6 pack of large 50uF capacitors (that looked like a 6-pack of soda) with 4 smaller footprint 200uF capacitors.
This allowed me to have a lightweight on-board battery charger with higher charge current (7-19 Amps depending on the batteries state of charge) and smaller footprint size. They get kind of hot when the batteries are charging at the fastest 19Amp rate. I may have to install a small fan on them so they don't dry out.
I built a nice battery box to cover up all the batteries in the truck bed. It looks very unassuming until you peek inside.