Multicam Blower Motor will not operate

Woodshop MultiCam SIG
#1

The motor for the blower that provides vacuum holddown for the Multicam will not start. Problem is known. Cause is not. Troubleshooting will continue and status will be updated as soon as practical.

Motor safety disconnect has been opened. Please do not mess with it if you are not an expert in 3 phase motor operation. If you are, your help will be appreciated!

What’s known:
Phase to phase voltages are normal at all points through and including the outlet of the motor starter.
Ohm measurements on motor leads phase to phase = 0.3
Ohm from each phase to ground shows open circuit.

Motor get very hot, doesn’t rotate and starter switch opens after a few seconds.

#2

Sounds like the starter cap has gone bad.

#3

If can do so safely, apply power, then with a stick give the blower a spin in the correct direction.

If it starts, then cap is the problem.

If not, you need more expertise than I have. Will run the symptoms by an expert at work tomorrow if one hasn’t chimed in before then.

#4

A three phase motor should not have a starting capacitor. The capacitor in a single phase motor creates a second phase that ensures the motor starts rotating and in a known direction.

It’d be interesting to measure current in one of the phases, I think we have a clamp meter somewhere. Perhaps a winding was shorted by sawdust or something.

#5

I’m closer to knowing just enough to be dangerous than I am to being an expert, but wouldn’t a shorted winding have shown up on the measurement of ohms between a lead and ground?

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#6

I was thinking one winding could be shorted to another, effectively bypassing the winding. Maybe knowing individual phase currents could tell you if a winding failed open but I haven’t really seen this in practice.

I assume the motor isn’t locked up mechanically, it spins freely otherwise?

Other things to note, it’s really very difficult to get a good winding resistance reading with a handheld meter. In some motors the resistance is just so much lower than the meter can measure that the small change when a winding opens doesn’t register.

#7

Hard to check this without some dismantling. Will do though.

#8

Depending on how the wiring is set up it might be easier to check currents first then. We should have a clamp meter, which if you get access to each individual wire makes it easy.

My guess is if you see one phase with notably higher current than the other two then there’s a winding issue in the motor.

Other than a winding issue, mechanical stuff is all I can think of, sorry.

#9

There is only a very short window for measurement. The starter must has some kind of safety feature that trips after a few seconds. Probably due to this, the breaker never trips. Guess you could measure each phase on a different start attempt to get some idea. Motor will be really hot after three tries if done close together.

#10

Yeah, it’s probably some form of overload protection. As with most safety features, probably best to leave it in place. Hopefully someone else can chime in with some better answers.

#11

Well we will find out later today. Hopefully sooner than later.

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#12

Multicam is functional again. Appears blower overheated and seized. After a very long day overhauling same with many thanks to Chuck (@dallasmagna who tried to pretend this was some kind of motorsport) it is back in place and ready to work.

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#13

Pretty sure he is ready to use it as a supercharger

#14

I don’t think he wants to see it again … ever!

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