help confirm my diagnosis...dead static phase converter

[lavrider]

Hello all. First or second post here but I like the general feel of the Forum here (relaxed!) and look forward to learning and contributing.

I received my South Bend Fourteen (14x40) lathe about 4 years ago. It's the 1970's variable speed with variable pitch pulleys, not to be confused with the older 14 1/2" model. The lathe has a 3HP, 3-phase motor which runs (ran) off a Phase-A-Matic PAM-300HD static phase converter (SPC). The SPC is rated for 1-3HP and is the heavy duty model. The input to the SPC is 230V single phase off a 20A breaker. IS 230V weird? Each leg is 114-115V WRT ground at the outlet.

So the SPC worked ok for the first 4 years I owned it a presumably several years prior. The motor always buzzed for 5-10 seconds on start up. I figured that was the time needed for the motor to come up to speed and for the SPC to reliably generate the 3rd phase. Sometimes it buzzed longer than others.

Last weekend I was using the lathe and it was starting as normal, then on a start attempt, the motor buzzed but did not rotate. I found that if the lathe was in low gear, I could give the chuck a spin and the motor would slowly spin up to speed, then the buzzing would stop. This did not work in high gear.

I did a little voltage diagnostic last night. The way the lathe is wired now, L1 and L3 are the two 230V lines from the outlet and L2 is the 'generated' 3rd phase from the SPC. Before you wonder if the lathe is wired correctly or if the motor is mistakenly wired for 440V, the lathe has been working OK for the 4 years I've had it.

So, running (after I give the chuck a spin in low gear), the voltages at the lathe circuit panel are L1-L2 192V, L2 L3 226V, L1 L3 194V. Stopped the voltages are L1 L2 0V, L2 L3 227V and L1 L3 227V.

Further, when the lathe is trying to start with motor buzzing but not turning, voltages are L1 L2 108V, L1 L3 218V and L2 L3 110V.

The SPC has a light on the box that according to the instructions should go out when the motor is at operating speed. My light stays on all the time. Because its on the end of the lathe, I usually don't see it and can't say for sure about the light function in the past. The motor spins freely and does not seem to heat up more than I'd consider normal.

So I'm 70% sure the SPC is toast. Your thoughts? Although a VFD would be great, the variable speed function of the lathe works OK so its hard to justify the cost differential compared to a new SPC. Has anyone had experience with SPCs from ebay like this: http://tinyurl.com/9lp3c9q

Thanks for the help,
Paul

 

[Tony Wells]

I would strongly suspect the capacitors in the unit. If you can remove them, some appliance repair centers can test them for you. or if you have a capacitor tester type DMM, they can give some indication of their condition. If you have an analog meter, you can do some testing yourself and see if they are shorted, or open, and with a little guidance, sort of test their capacity.

 

[lavrider]

Tony, I never considered replacing the caps in the Phase-A-Matic. Might be a good idea.

Frank, Is the start relay you refer to inside the static phase converter? Also the 2 or 3 caps you refer to? I need to take the SPC apart and see what makes it tick.

I never considered other capacitors that might be in the machine. Do 3 phase motors have start and run capacitors that would have been necessary when the lathe was wired directly to 3 phase power? There does not appear to be a capacitor on the motor itself and nothing looking like a big capacitor inside the electrical panel.

 

[lavrider]

Frank,
The link in the original post is one I was thinking of buying.
The one I have now is:
http://www.phase-a-matic.com/StaticDescription.htm

I'll be out of town until middle of next week. My first priority will be opening the SPC I have and seeing if there's anything amiss in there. I'll also look over the rest of the lathe for start and run capacitors.

Thanks!

 

[Tony Wells]

Frank, that picture is of the lathe box, not the converter. The converter box will have the caps inside, and the lathe will not have any caps mounted on it other than on the motor, if there are any at all, which I doubt. I'd focus on the converter.

 

[lavrider]

Just an update on the static phase converter. Opener her up and capacitor oil all over inside. Only on cap in there plus a relay and another black box. Replaced the cap with same from McMaster Carr ($13) and away she went! I think she starts better now too. Best $13 I've spent in a while. Thanks for the ideas all.

BTW, no start or run capacitors on the motor or elsewhere on the lathe.

 

[Tony Wells]

I've never really been a fan of the Phase-A-Matic units, but they are inexpensive, and lots of people use them. Mostly until they can do better though. Glad yours was a simple fix.