Re: (ET) E12 lost power

[Chris Zach <czach computer org>]

Question: Could one check for an armature short by simply applying 12 
volts to the field (or 36, knock yourself out) then turn the armature 
and see if there is any "balkiness". A good armature will not feel 
especially different with field on or off. A bad one though will feel odd.

I have noticed on the mower motors that one can feel a short by spinning 
the shaft with nothing connected. Instead of being smooth, it goes "chug 
chug". This is because a shorted armature winding acts as an electronic 
"brake" whenever it passes thru the field. Open windings do not do this.

Is it safe to power the field without the armature?

Chris


Jim Coate wrote:

> In general the drive motor is the last thing I'd suspect (anyone ever 
> blown one?), so I'd agree with the plan to check the field circuits very 
> carefully. If the motor did burn out, I'd expect it to smell terrible so 
> it would be obvious.
>
> But as long as you have the motor off, could test it as a confidence 
> booster. Hook the field to 12 volts, then hook the armature to 12 volts 
> and watch it go.
>
>
> Richard Zachary wrote:
>
> > Put in new solenoid coil at 1F just 3 weeks ago and everything seemed 
> > fine.  Mowed weekend before last and everything was like new.     Went 
> > to mow today and seemed fine for two seconds, it went about a foot and 
> > half, and then POW! everything stopped.  99.9% of power lost (very 
> > slight amount of movement possible both forward and back, but the 
> > power usage gauge was pinned to the highest point).  Noticed an 
> > electric smell, and found a lot of heat up front.  Three coils in 
> > front of the charger where RED and giving off loads of heat.  One of 
> > the large wires coming off coil 2F was also hot.
> > I tried the PTO switch and the mower deck by itself ran just fine, 
> > leading me to believe that the batteries are OK.
> > Pulled the motor off and tested the resistance across the two main 
> > connection posts.  The meter went to the top indicating a short across 
> > these posts.
> > Had the motor redone with new bearings, brushes, rotor cut in April.
> > Question is, could it be something other than the motor?
> > Thanks in advance for any advise,
> > Richard "Zack" Zachary
> >
> >
> >
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