Wednesday, August 1, 2007

Hacking the Regen System and Fixing Acceleration

Well, today was a good day. I got word back from Azure Dynamics after they analyzed my acceleration logs and they pointed me to the EE2NoAccelBat variable. Mine was set to 136 volts. It turns out that if the voltage coming from my batteries fell into the 136 to 149 volt range (EE2NoAccelBat + EE2AccelRamp = 149), then the controller would linearly limit the power going into the motor down to zero when the voltage reached 136.

With a 144V nominal pack, at moderate current draws, I was getting major power loss. Azure recommended setting EE2NoAccelBat to 127, so that this "scale-back" range was a more reasonable 127-140V. This made a HUGE difference in acceleration performance as my battery voltage rarely drops below about 138, even drawing 120 amps.

In other words: READ THE FRIGGIN MANUAL (RTFM) and understand all the graphs

The car was still rather difficult to drive with the regenerative braking happening when I released the accelerator. In a comment to a prior blog entry, Paul J suggested that I try using the brake light signal from the brake pedal to activate the regenerative system. With my driving frustration, this seemed like a good idea.

This change actually reverses the function of the regen relay. In the original kit instructions, the regen relay turns on the brake lights when the AC controller is in regen mode. With the PaulJ brake mod (I might just call it that...), I remove the regen relay and use a similar (normally closed) relay to activate the regen function when the brake lights come on.

Again, this involves purchasing a normally closed relay so that when the brake lights come on, it opens up and lets the regen circuit activate on the AC controller.

This worked like a charm! The car is soooo much easier to drive because it behaves much more like a gas powered vehicle. That is, you push the acclerator to go and press the brake to stop. The relatively weak brakes are augmented strongly by the regen function of the AC controller, so the brakes are actually much more responsive, despite the heavier car. I recommend this alteration to anyone using this kit!

A final task was to mount the ammeter that I had been using for experimental purposes. Until I get the cool looking dials from ElectroAuto, I just shoved the ammeter in the place where the engine temperature gauge was. I had to break off two of the long mounting pins so it would fit in the hole, but this will work until I get something better.

On another really bright note, I contacted the facilities manager at HP about having a plug-in at work for charging my vehicle. I had contacted him last October and he said he would get around to it. Much to my delight, the work actually happened without him telling me and there's a plug-in (with an Electric Vehicles Only sign!!!!) just outside my building!!! Yay!!! I'm sure this is all part of HP's plan to look more "green," but I'm still ecstatic that I don't have to walk halfway around the site just to plug in my vehicle. Here's a picture:

I've pushed really hard these past few days to get the car going. The Oregon Electric Vehicle meeting is tomorrow and EV awareness day is August 11th. Also, the NEDRA races are on August 17-18, so if I'm really lucky, I'll try to get the car to these events. The test drive with the improved acceleration and "PaulJ Brake Mod" makes the car feel much more road worthy.

Off for a quick test drive and then to collapse. Cheers!


Ross Cunniff said...

Very, very cool and encouraging. Regarding the "regen braking" - I'm very surprised that this was not the original design - in fact, when I browed the instructions, I assumed this was where they were going. Which relay did you purchase? Just some random "normally closed" 12V relay from an electronics store?

TimK said...

I purchased an 12V automotive relay from Napa auto parts. It's the same as the secondary charger interlock relay in the engine compartment, so you could take that in and get a second one. The automotive relays often have a flyback diode across the relay coil to prevent inductive overshoot when the relay opens.
Cheers, Tim

pjorg said...


Great to hear that the car seems to be running correctly now. Glad to hear the Regen circuit works. Is the regen function just an on/off function or can it be set up with an analog input?

I think we are all looking forward to hear what it is like driving to work. How fast will it go, etc. You may still have some more tweaking with the controller to do. I think we would appreciate a list of the parameters you used so we all don't have to go through the same frustrations. Good luck with your next drive.


TimK said...

Hi Paul, I'm going to try driving to work next week after going to the OEVA meeting tonight (short drive) and getting some more driving experience in over the weekend. The regen circuit is just an on/off switch, not analog. I believe you can control regen torque ramps in the controller, so it doesn't jerk you around. Cheers, Tim