Thursday, August 23, 2007


Despite the issues with the car, I've decided to start commuting 15 miles each way to work to see how the car does. By not revving the motor above 5000RPM, I can minimize the vibration problem.

The batteries are starting to break in. I'm getting slightly more power on the freeway now and starting from a dead stop is acceptable. I've taken the 914 up to 70mph. It doesn't have the pep that the original 2.0 liter engine had, but I still haven't really cranked up the AC controller and done a parameter analysis.

The car wobbles at 60mph with a low-frequency side-to-side shaking, so I took it into Les Schwab this morning and they found one of the back tires to be significantly out of balance. I'll take it back up to 60mph on the trip home.

In general, I'm pleased with the freeway performance. Although, if I put the car under heavy acceleration for a long period of time, the batteries "brown-out" down to 128V or so and the controller cuts back the power significantly as the voltage drops. Letting up on the accelerator allows the battery voltage to come back up and power comes back. I could adjust the parameter in the AC controller to set the voltage cutoff lower, but I fear damaging the batteries.

I looked at installing the PakTrakr battery monitoring system last weekend; however, the wiring distance between the front and back of the car is longer than the provided cables. Ken Hall (makes PakTrakr) said that I could extend the cables as far as necessary, so I grabbed some 4-wire cable and will be extending things soon.

I've given several people at work rides to show them the technology and everyone has been very supportive.

Next up: More commuting and checking out PakTrakr


Joe said...

Have you ruled out the transmission as being the source of the vibrations? After assembly, you could put it in neutral and rev the motor to 5K (after adjusting the torque and max RPM on the controller). The motor seemed to be OK prior to installation.

TimK said...

Hi Joe, that's exactly what I did. I put the tranny in neutral, pushed in the clutch and revved it to 5K and got the vibrations. The only time I didn't get the vibration was spinning it up to 5K with just the flywheel. I should have added the clutch pressure plate to see if that caused any issues before putting the whole thing in the car. I'm going to keep the RPMs low and try again in a few weeks after I get my motivation back. Thanks for the suggestion.

onei57 said...

I don't think this rules out the transmission. The tranmission is not moving @ motor speed when the clutch is disingaged. I think the halfshafts need to be disconnected and ran up to 5k for this to be eleminated. The cracked bearing you had in the transmission has me wonder if a shaft is bent or something of that nature that may be causing the vibration.
Cool to here you are driving it and the speed is getting better. If they say the the pack is empty at 80% (115 volts), why is the low in the controller 128 volts (88%)?

TimK said...

Good Point about testing the transmission half-shafts given that the bearings were shattered.

The low voltage of 126V represents the 20% point of discharge. I suppose I could push it down a bit more, but I do want the batteries to last awhile. It's doing fine for now, so I'll see how it goes.