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Re: (ET) Motor puzzler and Alltrax
On Mon, 7 Nov 2011, Konstanty, Walter (GE Energy Services) wrote:
A Monday morning brain teaser....
- DC motors develop torque by having field current (flux) and armature
The field has the leverage.
- Loss of field causes over speeding.... less/no flux to limit armature
Field resistance is approximately 17 ohms.
Yes, that is what I have measured.
- 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
I had not thought of that - thanks. I will make those measurements.
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.
I'm not sure I trust myself to take it apart (actually, get it back
together again) and, sadly, our local motor shop is no more. I do have a
spare motor which seems to work, so I could swap it out.
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.
I'm sure it won't fix it. But if I can't reproduce the problem, I'm up
for going ahead with the Alltrax if a recurrence (which, as you say, will
happen sooner or later) won't blow the unit up.
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?
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?