Mark VII motor not starting

[Ash1562]

Hi guys

I've tried to search this forum for an answer but I'm still iffy so here goes: I'd been turning a bowl on the lathe and missed the "lubricate every 8-10 hours part". My major blunder. Upon trying to start her up, the breaker tripped. I unplugged, lubricated and turned by hand to get it mixed in. I tried to fire it up again and it jerked forward but tripped again. I put on my sanding disc and gave it a spinning start, powered on...it went for maybe 2 seconds and again tripped.

Now it wont even try to move...just trips the breaker.

I'm going to do a full breakdown...but before I do, any ideas on what's up? Did I fry the motor wiring?

[JPG]

Hi guys

I've tried to search this forum for an answer but I'm still iffy so here goes: I'd been turning a bowl on the lathe and missed the "lubricate every 8-10 hours part". My major blunder. Upon trying to start her up, the breaker tripped. I unplugged, lubricated and turned by hand to get it mixed in. I tried to fire it up again and it jerked forward but tripped again. I put on my sanding disc and gave it a spinning start, powered on...it went for maybe 2 seconds and again tripped.

Now it wont even try to move...just trips the breaker.

I'm going to do a full breakdown...but before I do, any ideas on what's up? Did I fry the motor wiring?

Maybe

A (hopefully) more likely culprit is the power switch.

Have you tried to start in reverse direction?

Your description of events lacks some detail(humming, timing ...).

It may require manually connecting wires that are attached to the power switch to track this down.

We will need to know which motor you have and if it has a start relay.

The fact that it was still running before gives us some hope. This may be a loose wire causing short(immediate trip).

If the power switch is faulty you may need to replace it with a toggle switch or two.

[Ash1562]

Thank you, as always, JPG.

The motor does not hum when powering and it still trips the breaker when I try to go in reverse. I had an issue a few months back where the motor was humming cuz the relay had come loose and was shorting out cuz it was contacting the headstock body. I fastened it down in during that breakdown, I noticed the relay is new (i.e. less worn and dirty than the rest of the parts) so it might not be the issue...unknown right now.

I'm not sure what you mean by timing, however.

I have seen a few youtube vids where guys test the motor leads using an ohmeter, so that's my next step. I'll provide updates and photos soon!

[JPG]

IMHO Testing motor run windings with an ohmmeter is more wishful thinking thana realistic possibility of gleaning anything useful.

The resistance is extrenely low and a shorted winding(the cause of winding failure/burning) will be impossible to detect.

By timing I was referring to time between energizing and breaker trip as well as time between attempts. It may be that all were of extremely short duration.

You got a GE motor or an A.O.Smith motor with relay?(the wire colors are different). Time I think to try motor/cap/relay /power cord only. If so need summary of wire colors exiting the motor to verify.

Checking the motor windings to frame resistance of the motor may reveal clues.

Do you recall which relay terminal was shorted to frame?

[Ash1562]

Ok - initial test: tested resistance of hot lead and ground on the SS plug:

- with the switch in off position --> open (i.e. infinite resistance)
- with the switch in ON (either fwd or rev position) --) 2.5 ohms

I think we have a short somewhere! Onward...

[Ash1562]

Regarding timing: it's basically instantaneous. As soon as I push the fwd button, it trips.

And no, I don't recall which lead on the relay was shorting to the headstock body. It had basically fallen off the mounting plate it's on and was dangling around, so it could have been any of them.

The other thing I _just now_ tested was that with the SS unplugged and power on, I see a short between the plug's hot end and the upper shaft. Not sure what that means but I don't think it's supposed to be like that...this is my first time attempting to electrically test stuff so I'm totally open to your suggested diagnostic steps.

[JPG]

Ok Good clue(and makes sense re instant trip).

Does the short disappear with the power(switch) on?

Which of the three plug terminals are you referring to as the "hot end".

Be prepared to 'drop' the motor pan and motor/power switch/relay.

[Ash1562]

Ok, so let's define the outlet wires

Green - ground
Black - cold
Tan - hot

With the switch on, I see 2.5ohms resistance between ground/cold and ground/hot AND cold/hot. With switch off, it's an open and no short

I switched my meter to DC volts, put switch to Fwd, put the probes on Hot/Ground and cracked the shaft by hand - and I see voltages spiking up and down. So I presume my motor wiring is ok?

Opening motor pan next. Be right back

[Ash1562]

Ok, the motor is GE, model 5KC37PG 479. The SOB relay plate has now come off. So that was probably the culprit. Going to test.

[jsburger]

Ok, so let's define the outlet wires

Green - ground
Black - cold
Tan - hot

With the switch on, I see 2.5ohms resistance between ground/cold and ground/hot AND cold/hot. With switch off, it's an open and no short

I switched my meter to DC volts, put switch to Fwd, put the probes on Hot/Ground and cracked the shaft by hand - and I see voltages spiking up and down. So I presume my motor wiring is ok?

Opening motor pan next. Be right back

What are you calling ground, the motor case? 2.5 ohms across the motor winding's (black and tan) might be right. However with the switch on either motor wire to ground should be open.

Your DC measurement means nothing. The motor does not generate any voltage when spun mechanically. It is a motor not a generator.

Depending what you are calling ground it sounds like your motor winding's are shorted to ground. That would cause the circuit breaker to pop immediately.