Sunday, November 21, 2010

Back on the road

It's been awhile but I have been working on the car as often as possible and I'm finally back on the road.

The original BMS didn't have any wire protection, if for some reason a wire got shorted out and burned up, you'd have to rerun that wire. I added small inline fuses to each cell at the battery. It's a little more cost and time, but something that's worth it in my opinion.

Here is a picture of the completed front end. Six batteries were removed from the original design to all for the AC compressor and pulley assembly. The good news is I finally have AC, but the news is it's winter time and I have to wait awhile to use it. However, part of this was to add the heater and on the cold mornings it really heats up the small cab space of this car quickly.

The motor controller was modified in multiple ways. First the Curtis "whine" was removed and the car is now completely silent, as an electric car should be. The maximum voltage was increased to allow for my fully charged voltage on 54 cells (I charge up to about 184v). Finally the amps was increased from 500 to 750. This made a huge difference in acceleration and overall power. My 0-30 went from (I think it was 7 seconds) down to less than 4 seconds. Overall the total power of the controller went from 72kW to just over 130kW.

I removed that large, and unreliable BMS screen from the dash and replaced it with the E-xpert Pro. This has turned out to be a great little display. On top of showing pack voltage, amps, Ah, and remaining runtime, it has some other extras and is highly configurable. You can customize this meter to your battery, driving needs and how hard you want to push your battery by setting what is considered full, empty, when to raise alarms, etc. So for example I setup mine to alert me when the pack is 30% SOC and to consider 20% SOC empty. This affects how the "fuel" gauge displays its bars. I also turned on a feature that will automatically add the back light as long as >1 amp is going through the shunt. As I drive the back light is on, and 10 seconds or so after stopping it turns off. I also configured the meter to consider the battery full when 184v is reached and the charger is at about 2 amps for at least 1 minute. This then resets the Ah counters and gauge and avoids any calibration errors that might allow the meter to slowly drift over time.

Here is the trunk now. I wouldn't call it finished because things are still a little messy and I'd like to get carpet back in there. Trunk space is still reduce, but I can at least fit something in there now if needed. The little black things on top of the charger are the new Cell Log 8 modules that I'm using to monitor high and low voltage conditions. These are about $13 a piece and will monitor 8 cells each. I build a little circuit board for each to simplify the wiring. They have an internal relay that allows you to provide signalling to the charger, a buzzer, light, etc. They are not isolated, however, so expect to use an additional relay on each module to isolate it. These modules will turn on when the charger is connected to AC power or the key is on.

Another thing I modified this round was the suspension. I added another 9 cells (over 100 lbs) and with so much additional weight in the rear I knew I couldn't avoid it this time. Online I found the spring rates saw that the rear springs were much stiffer than the front. The front springs were 245 lbs/in while the rear springs were 311 lbs/in. I moved the rear springs to the front of the car and replaced the rear with 10" (original springs are 11" unbound) 400 lbs/in springs. The put the rear exactly back to stock ride height and my front is still 1/4" lower but I think within range for alignment. I still need to take the car back down for an alignment to see if this will do.

It's great finally being back on the road. The gas to drive my truck 70 miles to work each day was really adding up. That and I just missed my car, too much fun to drive. I'll keep you posted on miles. I think around 16-17k miles total at this point.