Re: weird DC motor

OK guys!

Photos are at http://home.mmcable.com/mediasmith/

Look for DCmotor.jpg for the motor photos buried with a bunch of gold mine equipment I'm trying to get rid of for a lady.

Specific comments are below. Look for +++


Date: Thu, 08 Nov 2001 16:55:20 -0000
From: stevesng@...
Subject: Re: weird DC motor

Dale,

A motor with two sets of high current (16 gage wire) brushes
running on two separate commutators is new to me. Multiple
sets of brushes running on one commutator is common for
high quality servo motors designed for low torque ripple.
Many servo setups have a motor and tach on a common shaft
with two separate sets of everything including brushes, but
the tach brushes and wiring are typically much smaller.

+++Everything appears to be equal and the exit points of the wires indicate the brushes may be 45 or 90 degrees offset from each other.


The nameplate data seems out of porportion with the rest
of the description. The current seems low for the size
of the motor and the size of the wires.

Oh, I did just remember one type of setup with a set of
dual commutators.... a co-wound DC motor-generator like
the type once used to generate the high voltage for tube
type radios in mobile equipment. Not likely related to your
stuff because they were still different size brushes on
the two ends and because your motors seem to have tachs
or encoders on them.

+++That would be a dynamotor.... My dream back in the '50s

Feel free to e-mail or post additional info, I love a
mystery!

Regards,
Steve Stallings

++++Consider it did!
From: Jon Elson <elson@...>

I'd measure the resistance across each set of brushes. If they are
the same (roughly) then I'd probably connect them in parallel. If the
resistance of one set is higher, that is a tachometer output, not a
motor input.


+++ Grab a tight hold! The resistance is about the same. One set of brushes reads from 0.4 to 0.7 ohms. the other set reads from 0.6 to 1.0 ohms on both of my incredible Radio Shack DMMs. Something must be wrong with Ohm's law. I keep winding up with somewhere between 220 and 440 amps at that voltage/resistance; 100 amps if wired in series.

Before I can tell you how to use it, you need to tell me what you want
to do. CNC retrofit a manual mill, maybe? T

+++The original idea was variable drive for my lathe, mill and drill press but any girl in town will tell you that I'm easy.
I am not opposed to whatever I can use them for. After all, I have $75 tied up here. CNC Rototiller? Anyone for converting my big war surplus Horiz mill to CNC?



The 220 V .4A rating is only 88 W, which is rediculous for a 15 Lb (estimated) motor.

+++About half right. My scales show 32 pounds each.


I wonder if the data plate is wrong, and these are 4 A motors. That
is more reasonable for the size. let me know the resistance and I
can try to figure that out. When measuring motor resistance, you
have to move the shaft in small increments and take the lowest
steady reading. (Brush contact is real bad when the motor is not
turning.)

+++I noticed that. I also noticed that I could not find a pair of wires I thought was a tach output on one of the motors. I may have either been drinking at the time or, more likely, wishing I was. (Buying motors like this wil drive you in that direction.)

Jon

Thanks to all!

wdsmith
(I love a mystery too but I like the ones with a possible solution much better)




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