Saturday, December 1, 2007

150 miles, and some tuning

I was out of town for 10 days since my last posting, but this past week I've been commuting exclusively with the Volt914. I hit the 150-mile mark today, and finally decided it was time to do a little tuning. The first thing to tune was the pedal - although I've adjusted the cable as much as I can, the max reading the controller sees is about 50%.

From the manual, here are the programmable parameters for the pedal:

The default settings were these:

This means that my pedal never hit the max acceleration. Additionally, that "0.5" reading was with the pedal completely floored - I had to screw the throttle stop almost all the way in to get that - and that was incredibly annoying (and somewhat dangerous - the pedal would sometimes stick all the way down). So, I decided to divide everything in half, so that a reading of 0.3 (30%) would hit max accel:

This made a huge difference - I backed the throttle stop back out to a reasonable level, and the car is definitely more responsive.

Next, I did some research on max amperage limits for my cables (2/0 welding cable) and came to the conclusion that I could raise the limit from 200 to 250 amps. These are the parameters I tweaked for that, from:


This also made a fair difference - but it also lead to occasional controller cut-outs - where the controller stops applying power. Browsing TimK's blog, I decided to tweak down the max torque to one that matches the AC24 motor specs:


This seems to eliminate the cut-outs. Finally, I enabled regen braking and played with it much of the day today. Unfortunately, there seems to be something weird going on. The regen cuts in, the car decelerates nicely, and then it cuts out and the car, of course, lurches. This happens at about a 1-2 second frequency. It is very annoying, and probably not good for the mechanical parts. I have a theory what's going on - see this diagram:

The main parameter is "EE2NoRegenBat", which is set to 150 volts. Above this point, the regen is not enabled. Below this point, the regen is limited until it gets below the area delimited by the "EE2RegenRamp." The theory is that the pack is below the threshold, and the regen kicks in, but that puts the net voltage abovethe threshold, and the regen cuts off. One way to test this would be to set "EE2NoRegenBat" high enough that it never cuts off, but to adjust the "EE2RegenRamp" such that not too much power is put into the battery when it is well charged.

I've posed this theory to the kind folks at Azure, and I'll wait to hear back from them before I attempt it. In the meantime, I've disabled the regen again (by setting EE2NoRegenBat way low - 100 volts - such that it never engages).

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