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Re: (ET) Ground fault from hell
That's the beauty of tracking these down. <VBG> You have to find the
fault on BOTH sides, positive and negative.
This seems to be a single fault; if it was a double there would be a lot
of sparks. That said, I am tracing it by bonding positive to the frame
and going in from the negative side.
1.) Armature contactors.{Includes armature resistor bypass
contactors.} Especially the melted plastic bushings on the high current
connections.
Possible, however the fuse FU3 is out, so the contactors should be
isolated.
2.) Armature terminals / brush rigging in the traction motor.
Probably not. According to the wiring diagram, in order for - to get to
the motor with no voltage drop 1A-3A would have to be in. Or are the
resistors low enough to miss.... Hm.
I should probably disconnect the shunt plate and see if it's still
there. Then disconnect each of the bottom wires till the relay falls out
(the FW relay being on is my canary).
3.) Lift motor and associated wiring.
No, lift motor is out.
4.) Lighting wiring compromised by armature resistors.
Possible, however why would that affect the FW relay?
5.) Harness damaged by traction motor belts and / or pulley.
*nod* Very possible. Maybe what's going on is the field wires were
damaged, and the FW relay is clicking on because a path is going back
via the field.
Other possibilities might be:
1) Wire 16. This comes off the top of the card 4, then goes to the CC
and SW1,2,3 at the throttle box. If that wire went to frame, then there
would be + on it and that goes right to the FW relay. This connection
goes thru P2; disconnecting that might tell me something.
2) Wire 40 or 45. They're attached to the FW relay.
3) Traction motor field. Another possible connection. This one goes thru
plug P3.
The field has the added benefit of the fact that if it collapses you
have a *massive* voltage spike. It might be going frame-field-FW
relay-shunt-negative. I might try isolating a relay, connecting it to 36
volts, and seeing if there is a big voltage spike when I disconnect it.
Now that I think about it, a little analog ammeter was reading 3-4 amps
across that line. I thought it was meter error; bit large for a relay,
but not for the relay plus the main field in series...
Hm..........
Chris
Chris
What fun.
Chris
----- Original Message ----- From: "Christopher Zach" <czach computer org>
To: "Elec-trak list" <elec-trak cosmos phy tufts edu>
Sent: Sunday, July 17, 2005 9:03 PM
Subject: (ET) Ground fault from hell