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1981 SCT VW Rabbit Controller Problems

Posted: Tue Apr 15, 2008 10:23 am
by mcswensen
Hey all,
I was poking around the web looking for some info on this neat EV i'm now working on. it is a 1981 SCT VW Rabbit. this thing looks exactly like the one on sharkeys site, right down to the rims except mine has a brown interior not a blue one like sharkey's has. anyway i'm having some problems. the vehicle was running for sometime until recently on one day when i went to take the car out for a spin. the accelerator seems to have no effect on the rpm of the motor. I think (i'm no engineer) I have narrowed it down to the Field strength regulator. has anyone worked on these vehicles? i would love to compare notes. i have a ton of schematics and drawings for the vehicle that i would be willing to trade for advice/help on what to test or replcae to get this fun vehicle back up and running.

Any help would be greatly appreciated.

SCT controller problem

Posted: Mon Aug 04, 2008 1:12 pm
by steve
here's a couple of ideas fr trouble shooting the EHV 1 controller.

does the motor start and run at base speed? If yes, but it does not change speed when you depress the accelerator I'd start by looking at the transistor that chops the field. you can measure the votage on the field terminals of the motor. if it matches the pack voltage you probably have a transistor problem.

do you have a scope to look at waveforms?

i can probably help you more if i had controller schematics. it's been a while since i was inside the EHV-1.

do you know if PECO has any more rabbits kicking around? i'm teaching a technical course in a public school. i'd love to get an EV up and running

Posted: Mon Aug 04, 2008 6:18 pm
by Sharkey
Yes, the pass transistor for the field control is prone to shorting. The original is a GSDS50020, which is a military specification high voltage transistor in a TO3 package. Here is the PDF data sheeton it, they are no longer available as far as I know. I replaced that transistor with a 2N3055 because that's what I had in my junk box. It would burn those out if the battery pack was freshly charged. This is one of the reasons I got stranded in Mitchell, Oregon one summer.

I eventually changed the pass transistor to a high voltage, high current NTE Electronics replacement part, and have had no problems with it since.

The schematic for the field controller and armature contactors is located in this PDF.

There is also a small DIP relay in the controller PC board that has failed on me once. Its normally open contacts are in series with the PWM drive signal going to the field Darlington pair transistors. After replacing that, the field weakening was operational again. I believe that the relay is actuated by the main contactor coil signal, and is there to prevent weakening the field during motor starting, and thereby put undue strain on the process.

I have a series of photographs of the controller schematic, but have not had time to render the schematic into a file that can be easily read as a PDF file. It's an extensve project. So far, I have only drawn up the DC-DC converter part of the controller power supply. Maybe I'll take on that project next winter.

Posted: Fri Oct 24, 2008 11:42 pm
by anekut
did this problem ever get resolved? I had a similar problem caused by a fault in on of the interlock subsystems..have to search my records. I managed to drive around anyway by slipping the clutch.