Re: (ET) Motor puzzler and Alltrax

["Konstanty, Walter (GE Energy Services)" <Walter Konstanty ge com>]

Steve,
   A Monday morning brain teaser....
- DC motors develop torque by having field current (flux) and armature 
amps.
   The field has the leverage.
- Loss of field causes over speeding.... less/no flux to limit armature 
rpm.

  Field resistance is approximately 17 ohms.

  Your symptoms indicate a field issue - high amp draw, chugging and then 
overspeed....
Suggestions:
- measure resistance between shunt field and armature
    (it should be high - megohms with good insulation)
- measure resistance between either shunt field wire and ground 
    (it should also be high and not grounded)  You could have a ground in 
the field.
- measure voltage across the motor when you energize it - 12, 24, 36 volts 
during stepping.
- also measure field current (if you have a clamp on meter) to see if it 
is changing.

  If all of these checks are good, you might want to take the motor apart 
(or take it to a small service shop) to look at the brushes and commutator 
and inspect the windings.  The brushes may be worn out and making poor 
contact.  Clean slots, sandpaper commutator, and blow out thoroughly and 
check insulation again.  An armature "intermittent" short is never for 
long - it will blow a hole somewhere.

  It's probably not a good idea to connect up the Alltrax unit until you 
make sure the motor is good.  That won't fix this problem.

...Walt

-----Original Message-----
From: Steve Gaarder [mailto:gaarder ecovillage ithaca ny us] 
Sent: Saturday, November 05, 2011 3:09 PM
To: elec-trak cosmos
Subject: (ET) Motor puzzler and Alltrax

The best answer I got on this problem was that it could be a shorted 
armature.  However, the problem has gone away, so maybe we have an 
intermittently shorted armature :-(.

Just to complicate things, we recently purchased an Alltrax for this 
machine (an E15).  So my question is: is it safe to go ahead and install 
it under the circumstances?  What will an Alltrax do if the armature is 
partially or fully shorted?  Any other thoughts?

thanks,

Steve Gaarder

Steve Gaarder wrote:
>       I'm having trouble with an E-15.  It looks like a missing field;
>       it "chugs" at high current draw on the slowest speed, then
>       overspeeds when you bring it up to full.  However, it still does
>       that when I connect the field directly to the battery, and I
>       measure the field resistance at 17 ohms, which is what I believe
>       it should be.  So I don't have an open field, and the field
>       circuitry is not the problem.  Any ideas?
>
>       thanks,
>
>       Steve Gaarder
>