Capaciter Start Motor converted to flick-of-the-finger-start query

Marti · May 5, 2018

Hi Guys,
Looking at a motor problem today. Nothing big, just interesting.
An SP 400 watt motor with, it appears capacitor start phase shift. Press the start and the motor hums and gets warm but doesn't spin. Having tested all the lives with a MM I removed the capacitor. If I flick the cooling fan the motor runs. Suspecting a dead start cap' I discharged it and tested with an ohm meter - an open circuit either way round. Suggests the Cap' was OK so what have I missed?

[ElectriciansForums.net] Capaciter Start Motor converted to flick-of-the-finger-start query

Marti · May 5, 2018

Excuse the spelling error in the title; can't seem to edit title - only the body text.

Pete999 · May 5, 2018

Marti said:
Hi Guys,
Looking at a motor problem today. Nothing big, just interesting.
An SP 400 watt motor with, it appears capacitor start phase shift. Press the start and the motor hums and gets warm but doesn't spin. Having tested all the lives with a MM I removed the capacitor. If I flick the cooling fan the motor runs. Suspecting a dead start cap' I discharged it and tested with an ohm meter - an open circuit either way round. Suggests the Cap' was OK so what have I missed?
View attachment 42086 View attachment 42087 View attachment 42088

Could be a fault with the centrifugal switch on the motor shaft which switches the start capacitor out of circuit, at about 75% full speed.

westward10 · May 5, 2018

May not have a centrifugal switch if it is permenant split. Can you show the rating plate.

Pete999 · May 5, 2018

westward10 said:
May not have a centrifugal switch if it is permenant split. Can you show the rating plate.

Was just posing a possible scenario that may be of help, that's all.

Marti · May 5, 2018

TBH it's not professional kit with a plate; just tile cutter I was investigating out of curiosity. Seeing the little dial on the back of the stop/start I wondered if the start cap' was on a timer?

Pete999 · May 5, 2018

Marti said:
TBH it's not professional kit with a plate; just tile cutter I was investigating out of curiosity. Seeing the little dial on the back of the stop/start I wondered if the start cap' was on a timer?

Most cases the start cap will be centrifugal switch controlled but without a picture it's nye on impossible to tell

Andy-1960 · May 5, 2018

Capacitors can also degrade over time, can you measure the capacitance to confirm its value?

Marvo · May 5, 2018

Marti said:
.........I discharged it and tested with an ohm meter - an open circuit either way round. Suggests the Cap' was OK so what have I missed?

Usually you'd get a brief reading on an ohmeter whilst the cap partially charged then when you reverse the probes you'll get a bigger 'kick' or reading whilst it discharges which will diminish as it recharges again.

As mentioned above use a capacitance tester to test it properly or just replace it anyway because they're cheap

HandySparks · May 6, 2018

Worth checking that the start winding has continuity. If not, it's probably not economically repairable. Otherwise likely to be a dead capacitor.

Capaciter Start Motor converted to flick-of-the-finger-start query

Marti

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Marti

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Pete999

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westward10

Pete999

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Marti

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Pete999

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Andy-1960

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Marvo

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HandySparks

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