3 Phase motor problem

[spongerich]

I've got a line on a Hardinge DV59 that won't run. Owner says that when he puts an ammeter on it, one phase shows 3 amps draw (which I believe is the stated rating) and the other draws 5 amps. Without seeing it, does that sound like something that might be repaired, or should I plan to just find another motor? Anything special about those Hardinge motors (I believe it's from the late '50's) or will any decent motor work?

Unfortunately, I don't have 3 Phase in my shop, so I'm limited in my ability to really test it other than static tests with a multimeter.
I'm going to look into renting or perhaps buying an inexpensive 3 phase converter. (Naturally, I sold the one I had since I didn't think I'd ever need one)

He's only asking a couple hundred bucks for her, so it seems like a low-risk proposition even if I have to replace the motor.

[macona]

If one phase is drawing less than the others you probably have a bad contactor or switch.

Get a cheap megger off ebay, they can check the insulation in the motor and often have a low ohms scale to check resistance on the windings. Generic DMMs dont read so accurate at low ranges.

[superUnknown]

Plan for another motor.
You could ask for a couple simple checks with a cheapo meter:
Resistance from motor windings to ground, should show infinite and be equal on all phases.
Resistance from phase to phase, should show equal on all phases.
Otherwise, motor is shot.

[J Tiers]

A 3 phase motor doesn't have one showing 3A and *the other* showing 5A...... you left one phase out..... Maybe the owner did too.....

1) do resistance checks. Unequal resistance to ground/case isn't a guarantee of a "shot" motor.... it may just reflect how it is wound, which winding is a hair damper than the others, etc.

Resistance should be up around a half megohm at least. After running, if it does run, and getting warm, then being allowed to cool, it should be higher, since probably any dampness has been driven off.

Anything under 100k should be very suspicious, and the motor should not be run.... put it in a warm dry area for a while, or run low current through the windings to drive out water, then check again. Another failure is grounds for not using it (assuming it is a normal low HP unit)

2) double check the way it is wired... paying attention to any voltage setting connections, they are often screwed up, and will cause bad current readings if so.

3) To check running w/o 3 phase, you can rope start it, getting it spinning with a rope (no belts or loads), and run on single phase.... try all 3 combinations of wires.

Pull rope, switch on. It will either run at a reasonable current (about 40% or so of full load) or it will do something else. Any of the "else" are probably bad. Might pull more current in some windings, might not run at all, etc.

[lane]

Those are not just any old 3 phase motor. They are special 2 speed motors. I would have a motor shop check it out , if it were me.

[wmgeorge]

It would have been nice to have all three phase amp readings. Sometimes a bad contractor or starter as worn out contacts can cause low amps on one phase or no amps depending on how bad. Bad fuse or connection someplace in the 3 phase circuit or just a bad motor, one winding open.
Since your buying it cheap and have no use for the three phase motor, it would still be nice to know in case you want to use a VFD or RPC.