Lithium Swap 8 - Road Test

It was unavoidable, the time had come to try the car out on the road. I washed the windshield, put on some shoes I could hike in in the event I had to walk home, and drove down the driveway and across the bridge.

Out on the road, the car performed normally. It was actually kind of peppy. I decided to drive it east to the end of the pavement, where I turned around.

On the way back, I decided to check out the acceleration and draw some current so I could check for warm connections in the battery pack. Punched it hard in second gear at the first straight section, slammed it into third and nailed it again. By now, I was going 45 MPH, and there was a curve coming up. Got on the brakes pretty hard, downshifted back to second, and hit it hard coming out of the turn on the second straightaway.

About then, the smell of something hot/burning filled the car. I hit the brakes again and stopped, shutting off the motor. Opened the hood and hatch and frantically started looking for smoke, feeling all of the electrical connections for overheating. I couldn't find a source of the burning smell. All of the battery interconnection straps were flat-out cold. Took the cover off the controller under the hood and felt the main power input terminals. They weren't hot. The motor was warm to the touch, but I expected that, the cooling blower was fubar. The whole car just generally smelled of something electrical burning.

Decided to get back in and drive home slowly, since I couldn't find anything wrong. As I was shifting into second, I figured it out. This car hadn't been driven in eight years. I just ran it up to highway speed, then jammed on the brakes, not once, but twice. I was smelling the brakes heating up, not an electrical problem.

The last, steep part of my driveway is always a struggle for front-wheel drive vehicles to climb, the wheels spin in the gravel unless you get a run at it and have some speed up. I wasn't sure I should do that, and ended up clawing my way to the top, spraying rock the whole way. I'll need to figure out how to get this car up with less drama. All of the other trips up the hill had been with the pusher behind for additional traction.

Put the car in the carport and sniffed the wheel wells. Yep, sure enough that was the smell, the brakes were the source.

I had used 15 ampere hours out of the battery and gone 3.5 miles. Not good mileage, but I was jamming on the accelerator, and that included all the running and testing before I took it out of the carport. Add to that the dragging disc brake pads and rusty brake rotor friction, and I didn't think it was at all out of line.

These batteries don't sag as much under load. Add to that the car being 700 pounds lighter, and upping the system voltage to 125 from 108, and you get better performance, but likely also better range and mileage, as it takes fewer amps to make the same amount of power, and less of that is necessary due to the lighter weight. Should be a winner when I get it all broken in.

The Manzanita Micro battery charger is a different matter. I couldn't get it to turn down the charge current, the lowest it would go was 17 amperes, which my load center breaker would only tolerate for 15 - 20 minutes at a time before tripping on a thermal overload.

I dug out the old Lester charger that was installed in the car from the factory. I had sent a bunch of time ten years ago building and installing all new control circuitry in it, using modern phase-control integrated circuits. It worked perfectly, I turned it down to 5 amperes, which was a good match for the amount of power that my solar panels were making at the time. I'd need to modify this charger to interface with the BMS if I was going to use it now, but for this charge, I just stayed close and checked the system often, listening for the alarm buzzer on the BMS in case of trouble.

A few days later, I decided to take the car out for another test run, turning out the driveway towards town. I thought that I'd go a few more miles this time, and see how it felt.

I discovered three miles into my trip that both the front and rear calipers on the left side are dragging pretty badly. Could probably have lit a cigarette on the rotors, even the wheels were hot to the touch. Had to sit alongside the road for 15 minutes to let them cool off before proceeding to home at 25 mph. I'll have some brake work to do, hopefully, it's because the carriers were sticky, and not because the pistons are seized up in the bores.

The next morning, I disassembled the left rear disc brake assembly, adjusted the parking brake (entailing running the piston all the way to the bottom of the caliper bore), put a block of wood slightly thinner than the rotor and pads into the caliper and pumped the pedal until I got resistance. Ran the piston to the bottom again, reassembled it all and then it seemed to work OK. I did the right side as well, might as well get everything limbered up.

Took the car out about 6pm that evening. I wanted to pull about 20 ampere-hours out of the batteries and check the brakes for heat.

Went all the way to the last houses on Upper North Fork (about 4 miles), and turned around, parked and felt the rotors. Cool in front and barely warm in back. The car is much more responsive now, I rarely pulled more than 100 amps out of the batteries, even going up slight hills. Ran 35-40 MPH in second and third gear. Motor pulled about 70 amps at 40 MPH steady, about the same as with lead-acid.

When I got back to my driveway, I had only removed about 15 ampere-hours from the battery, so I drove past and went to the end of the pavement and turned around. After climbing the steep part of the driveway and putting the car back in the carport, I was at 11.4 miles and 18.5 ampere-hours of consumption.

This is half the consumption of the lead-acid days, and 2/3 the energy consumption overall (the energy figure isn't half because the battery voltage is higher. Higher voltage means lower ampere-hours (ignores higher voltage), but the energy consumption takes into account the higher voltage, so it's not as dramatic an improvement).

Still, overall, it's a significant improvement. If the batteries were able to supply their full capacity without damage, the car would have a range of 100 miles. Realistically, I should have no problem getting a comfortable 40-50 mile range, assuming that there aren't any dud cells in the pack that will croak suddenly at some partial capacity.

The car is pretty much ready for a trip into town and back (after charging up there, don't want to push things too fast). I have been keeping the batteries about 5-8 ampere-hours away from fully charged, because LiFePO4 doesn't like being fully charged, unlike lead, which requires it. I'll do a full charge and balance before I take off for town.