3 replies to this topic

[Ted Bier]

I have an MPC #613 Dyn-O-Can quick change armature.

 

I looks new to me  Can I take an ohmmeter across the armature where the brushes ride to see if its good?

How many ohns am I looking for? Anybody know?

 

 

 

[Mike Patterson]

I don't know what the readings should be, but they should be similar. Also, check to make sure the arm isn't shorted by putting a test lead on the shaft, and the other one on a comm segment.

 

Or you could just power it up and see if it runs.

[Bill Seitz]

Most multimeters used to measure resistance haven't much resolution below 1 ohm, at best maybe to 1/2 ohm, and some will read anything between 0 and .5 as 0 and some at whatever their min measuring capability is - mine is .4. My guess is this armature if good will be around 1 ohm or less. It looks pristine with no signs of being burned, so the most likely faults would be an open winding or shorted to the stack. As Mike mentions, a reading from the comm to any of the steel parts should show an open circuit / no continuity. A pole winding shorted within itself (turn to turn) will be almost impossible to detect with a typical multimeter because the resistance is just too small even with a good arm, but each pole should give about an equal measurement. I've measured known burned arms (shorted turns but not open) with my multimeter, and it can't tell the difference.

 

If you have a milliohm meter, then that should detect a winding fault. There are some available under $200 now, and I suppose one of these days I'll need to get one and see how well it works. They're advertised as .00001 resolution with a Kelvin (4-wire) measurement.

[zipper]

I put some voltage running thru and measured the amperage - Ok if the three poles were identical.