Re: (ET) Small E20 fire: What is it with MOVs?

["Christopher Zach" <cz alembic crystel com>]

E20 aa

The motor does leak to ground but nothing else does. Irrelevant because the mov is tied across the armature and not to ground
C

Sent from my Droid thing

----- Reply message -----
From: "RJ Kanary" <rjkanary consolidated net>
Date: Sun, Mar 13, 2011 5:58 pm
Subject: (ET) Small E20 fire: What is it with MOVs?
To: "Chris Zach" <cz alembic crystel com>, "elec-trak cosmos" <elec-trak cosmos phy tufts edu>

       I've never had that issue. BTW what flavor is your E-20 ? I've 
gots to know. <G>

A SWAG would be looking for something that gone to chassis. Or possibly 
TWO somethings that have gone to chassis. That would create 
unexplainable havoc.

RJ

Chris Zach wrote:
> So I was using the E20 pretty heavily today in the yard, mostly to tow 
> the trailer full of dirt. Once done I drove it up to the top of the 
> driveway to get the paper, then let it coast in L down to check the 
> brakes.
>
> Brakes stink like normal but can still stop the tractor (new brake kit 
> going on after spring work). Fired it up again, let it build up speed, 
> then engaged the motor to slow it down.
>
> *Foom* Big cloud of white smoke from under hood. That's always bad. 
> Motor still had power, but I stopped the tractor and hit the main 
> disconnect. Smoke continued to pour out for a moment, then it 
> lightened up.
>
> Hm. Opened the main panel, and looked at card 4. Everything was intact 
> (I have bigger diodes on that) however on the resistor card there was 
> a smoking disc where the MOV once was. Looks like it blew up.
>
> So what is it with E20's and MOVs? I know they're there to catch the 
> back emf from the motor or the spikes or whatever but they just seem 
> to explode every year. Can one get bigger/higher capacity MOVs? Can 
> one parallel them? Do something else?
>
> Chris
>
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