Can Someone Explain the Shunt to me?

Can Someone Explain the Shunt to me?

Postby jtcweb » Sat Jun 28, 2014 5:53 pm

It just looks like a piece of metal, what does it do? On the top of it I got some meltey wires and I'm trying to figure out why.

FYI - I have an E20
Last edited by jtcweb on Sat Jun 28, 2014 6:10 pm, edited 1 time in total.
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Re: Can Someone Explain the Shunt to me?

Postby jtcweb » Sat Jun 28, 2014 6:09 pm

Also if someone could include a photo of how it is supposed to be that would be great. I suspect someone has done a "repair" to it in the past and I'm not sure it is was put back the way it is supposed to be. For example the bottom stud looks like it is way too close the the steering wheel shaft, and then I noticed the stud is not threaded into the back-plane like everything else. Also the threaded rod that makes up the stud is bent.
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Re: Can Someone Explain the Shunt to me?

Postby FarmallMan » Sun Jun 29, 2014 4:33 am

The current from the drive motor flows through the shunt, inducing a voltage. The control card, Card 4 with the plastic connector on it, "reads" this voltage. If it is above a given level (too much current) the card will remove power from the FW relay coil, thus disabling field weakening. The bottom line is that it is a protective element. However, the current for the drive motor needs to go through it for the motor to function, so if it's in bad shape, the motor will have issues.

There was a service bulletin issued by GE fairly early on with instructions on fixing the wire connections to the shunt. They citied that it could cause the FW relay to chatter. What seems to happen more often, however, is that loose connections increase resistance. With increase resistance comes more voltage drop, and therefore power dissipation. A loose connection coupled with a drive motor with a heavy pull can easily overheat the wires. It's very common, by the way for this to also warp and discolor the shunt.

I will try to get a picture soon, but don't know when I'll have the chance. The two posts are insulators. I can't recall for sure if the bolts go all the way through, or if one side is a bolt and the other is a stud. In any event, I'm pretty sure that Jim C (www.electrictractorstore.com) has the replacement parts.

Nick :cool:
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