Mill capacitor centrifugal switch issue?

[petertha]

My new mill is down. So while I'm waiting for Mr. Technician to arrive, I figured I'd post & solicit some advice. It was running fine & then it seemed to me the motor started making a noise that didn't sound right. Then it tripped the breaker. The motor noise didn't really sound 'mechanical' like grinding or friction, but I'm no expert & maybe this was wishful thinking. Anyway, no heavy load or anything like that. Maybe a couple hours of cumulative running time. A few repeat tries of this startup with & no progress. If I start it in neutral it ran a tad longer (but always rough sounding) then trips breaker. If I put it into gear it trips breaker almost immediately. The motor is a 240V single phase 3 hp.

Tech visit number #1. <insert self ass-kick here> The first thing he notices is my panel breaker is 15A & the motor is 20A. DOH! Nowhere in my purchasing discussions did the topic of available amp duty come up. Its not even specified in the brochure or Taiwan manual. Now I am smarter about such worldly matters & will never make this error again. I will ask for motor plate specs up front. Anyway, I'm told start-up current can be higher than running current, so this needed to be dealt with first.

So I just finished installation of new 40A breaker on my panel, ran a dedicated AC 8/3 ( 8 gauge 40A) armored cable direct line & 240V 40A outlet to my mill area & new range style plug on the mill. Now I can use this outlet or at least this upgraded line for a TIG welder one day. Measure 240V at the panel, 240V at the plug, so far so good. I plugged the mill in, flicked the switch on for 2 seconds, it started immediately. But to my ear the exact same kind of ratchety sound. I started again, ran it for about maybe 5 seconds and then BANG. Pretty sure the capacitor blew because I think that's what lives in the little cover pod on the motor side & where lots of magic smoke came from. Well, crap!

This got me Googling motor capacitors & related problems. I found this article & similar ones that suggest if the centrifugal switch is faulty, then it can overload the capacitors. https://cdn0.grizzly.com/manuals/g2529_m.pdf
Maybe the capacitor was bad or incorrect spec. We will never know because it surely must be shrapnel. Do you think its possible that the centrifugal switch migrated or slipped out of position & was the main culprit all along? Do you think my low 15A breaker configuration was tripping early & prolonging the inevitable when it finally had full 40A & went pop?

I cant see any detail in my 'abbreviated' user manual for the motor itself. Do you think my centrifugal switch / related hardware might be on top of the motor can where it could be readily examined & replaced without hauling that big muther motor off? Anything else you can think of that could explain this situation? Can windings & such be diagnosed on the machine?

 

[JimDawson]

Could it be that the motor is wired for 120V and you're feeding it 240?

Or maybe the wrong value capacitor was installed at the factory.

 

[petertha]

Nope. Well... unless they put the wrong spec plate on.

 

[JimDawson]

Well, I guess open the capacitor box up and see what's in there. Maybe you can still read the values. I think the voltage rating should be 370V for a 240V system

 

[mksj]

The Jin Shin motors are made in Taiwan and yours has a production date of 2018, so should be more reliable given it is essentially new. Unlikely to have the start switch fail at this point, but you can take the motor apart and inspect the points to see if they are burnt or sticking. If it is a newer machine it should be covered under warranty. Take off the motor cover and the capacitors should be labeled if still intact or refer to the manual which should give you the information.

Please note that one of the limitations of single phase motors is that the start capacitor will go quickly with frequent start stops, as the electrolytic capacitors will overheat quickly. It is unclear if the switch might have been damaged from a wrong size breaker if it did not trip immediately with start up. If the motor does not come up to full operating RPM quickly due to low voltage, the starter switch would not disengage and the start capacitor would fail. The capacitors must be AC rated and the same or higher voltage value with a uF rating of probably +/-20%. They should be available from the manufacturer, size is often an issue of finding replacements that will fit under the cover.

 

[petertha]

Sorry with the late pics boys, I was doing laundry. Had to get the brown stain out of my pants LOL. Here are the caps under the right hand cover.
I'm not electrically savvy but is W.V. 125 VAC on the left hand (blown = starter) capacitor incorrect voltage? The right hand one is 250 VAC.
I'm not even going to comment on the blue electrician tape.

 

[JimDawson]

The voltage seems a bit light, I would take a hard look at this one

https://www.mcmaster.com/7245k732

 

[BROCKWOOD]

Date codes all attest to this being a new motor - parts are only now a year old. I'd say it's time to contact the dealer, rep, company that sold this to you.

Just food for thought: Installing a bigger breaker where a suspected problem is only lets more smoke out & allows for more damage.....

 

[petertha]

Would you concur that the W.V. 125 VAC labelled on the blown = starter capacitor is incorrect / insufficient voltage? If its a 240V motor, I am just assuming both capacitors should be 240+V right?

Brockwood, I think the job of the panel breakers is to protect the wiring under a short circuit. A motor will draw what it will draw. A 15A motor in a 50A outlet will just draw 15A. But a 20A continuous motor that draws say 30A on startup inrush will pop a 15A breaker. There is another level of protection on the mill itself that has to get installed before its CSA certified.

 

[JimDawson]

Since the capacitor is in series with the winding, the theoretical voltage across it might be in the 120V range at Asian 220V power, but at the 240+ volts that we have here in North America it might be a bit light. So if that cap was marginal to start with, I could see it failing.