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Re: (ET) Triage - ideas from an unexpected result
Max,
Sorry about the clothes dryer
incident.
Couple of thoughts;
- DVM's don't measure resistance accurately below 40 ohms
or so.
- The field ohms is direct Ohm's Law...
- Armature resistance practically determines "inrush
current".... once it rotates, a DC armature generates a back EMF or internal
voltage and will keep drawing amps based on RPM per armature volts input until
the back EMF almost equals this applied volts. So, it really doesn't mean
too much as brush contact drop influences the resistance and a bunch of other
stuff.
Try it on the bench and see if it runs.
...Walt
You guys, I came upon a little mystery. At least, it's a mystery to
me!
I have an e-motor that I thought was just a run-of-the-mill shunt-wound
(run-of-the-mill except for being really large)... but when I measured the FIELD
windings' resistance, I got about .6 ohms, and when I measured the ARMATURE
resistance, I got about 30 ohms. Is it because my brothers put me in the clothes
dryer (and turned it on) when I was little, or is that just perfectly backwards?
(And yes, I'm sure the armature measurement is the armature... not just because
of the giant "A"s stamped into the metal, but also because you can see the
physical connection between the A terminals and the brushes.)
Thanks for any light you can shed, ETers. Maybe I'm gonna wind up doing
armature weakening to make this one go fast...
And since this is tangent to ElecTraks themselves, I guess I should suggest
responses off-line to my regular e-ddress, mhall maxmatic com... but I also
guess that, unless I'm just backward anyway, the story might be
interesting.
Best to everyone,