Is my motor especially weak , or is it something else?

[bulgie]

Fascinating answer RJSakowski but there's no way I'm going to do that, too complicated for me, math and everything... I don't even know what a resistor is or where to buy one really, let alone a "high value" one!

I hope it's not too frustrating to you, to answer a question so thoroughly only to have the guy with the question say "duhh... what?"
I appreciate the effort anyway.

More my speed:

1. Use it as-is for now since it works OK. I seldom need much torque at high spindle speed.
2. Replace the motor with a 3-phase + VFD as soon as I can, like next paycheck.
3. Give this motor away for free with the explanation that the Run cap might need to be replaced.

 

[markba633csi]

FYI: The run cap is usually a small value like 20 to 50 microfarad (mfd or uF)
The start one is usually several hundred microfarad and a bit larger in size
-Mark

 

[bulgie]

OK I took the covers off and I can see the Run cap is 35 µF, but it says it's 450 VAC. From my reading, it looks like you can use one with a higher voltage rating but not lower. Grainger (the 1st and only place I looked) has no 450 V caps, their next size up is 480, and they're oval not round, won't fit my motor.

Would you guys use a 440 V cap to replace one that says 450 V on it? The 440 V cap they sell is Dayton brand, made in China (man I hate buying anything made in China...) Maybe a brand name is more trustworthy than the generic that's in there now. Or even if it's crap, at least it's new...

How about this one, Titan HD brand, made in USA (yay) but it's rated as 440/370 V, what's up with the two voltages? Could that be a replacement for my 450 V cap? It's only $5 more than the China-made one.

I bought what looks like a decent capacitance meter used on ebay, not here yet, but hopefully soon I will know if the one in the motor is within spec.

As far as the spindle bearings being a possible cause of the low torque at high rpm, I ran it at ~2500rpm for about 10 minutes (no load), then checked for bearings warming up. Hard to get near the inner bearing, but the ones I can get my fingers near, seems only sorta barely noticeable temperature increase. I hope that's a good enough test — comments? On my lathe, they want to see some temperature rise in the head bearings or else the preload is too low.

Thanks for reading.

 

[pontiac428]

The 440v cap will be fine. I also agree with your quick n dirty bearing preload test as a sanity check.

Does your motor get warm? If the motor is relying on the start cap to maintain RPM, it will get warmer than it should under normal use and the RPMs will climb when load is removed (a normal load, not an overload).

 

[bulgie]

The 440v cap will be fine. I also agree with your quick n dirty bearing preload test as a sanity check.

Does your motor get warm? If the motor is relying on the start cap to maintain RPM, it will get warmer than it should under normal use and the RPMs will climb when load is removed (a normal load, not an overload).

Dang, I didn't lay a hand on the motor after the 10 minute test, guess I will have to re-run the test, oh no!

My motor does slow down under load and speed up when the load is removed, but some of that is normal, unavoidable. I don't know if we've established yet, whether my amount of slowdown is just normal slip. But it seems excessive to me, a non-expert.

Thanks, I'll get back to you on the motor warming question.

 

[pontiac428]

If the motor races back to rated RPM and bogs too easily as load is applied, then test carefully so you don't burn yourself.