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Hairyloon

Electric motor starter capacitors...

I've acquired a non-working air compressor, if you put power to it, then it sits there humming and starts smoking after a short while.
It looks like it is not all there: there are a pair of wires feeding the motor and another pair coming off it ending in loose spade terminals. With the power on, they have about 150V across them.
I'm guessing that it should have a big capacitor across them, but anyone any clue how to decide how big?
Or any other guesses?
12Bore

Manufacturer's spec sheet?
Hairyloon

Manufacturer's spec sheet?

Looks to be a bit of an obscure brand... Or maybe a common brand rebadged.
Looks pretty old, so I'm not very hopeful of manufacturer's support.
Will have another look for clues later...
RichardW

Before you spend any money try this.

Apply the power & quickly try to spin the motor in the correct direction. If it runs (turn it off before it burns out if it does not run) then I (not suggesting that you do this) would test the spare leads for voltage. If there is no voltage then you need a start cap. If there is voltage you need a start & run cap. Some are dual purpose.


Re the value, as I have a box of various sizes I would try them starting at about 7uf & stop at about 40uf. I would expect the best results around 20-30uf.
Hairyloon

Before you spend any money try this.

As if. Wink

Quote:
Apply the power & quickly try to spin the motor in the correct direction. If it runs...

It doesn't.

Quote:
Re the value, as I have a box of various sizes I would try them starting at about 7uf & stop at about 40uf. I would expect the best results around 20-30uf.

Ah, if only I'd gathered my various sizes into a box...
Hairyloon

Ah, if only I'd gathered my various sizes into a box...

I am now in the right building at least... now, which are the promising boxes...
RichardW



Quote:
Apply the power & quickly try to spin the motor in the correct direction. If it runs...


It doesn't.



I think its stuffed.

When you power it up is there any current flow?
Hairyloon



Quote:
Apply the power & quickly try to spin the motor in the correct direction. If it runs...


It doesn't.



I think its stuffed.
Quite likely, but for the sake of rummaging the random box, I might as well throw a capacitor across it...
Coming soon to a forum near you: a question about motor rewinds. Wink
Quote:
When you power it up is there any current flow?

I haven't put a meter to measure, but it hums, so I think that's a yes.
RichardW


I haven't put a meter to measure, but it hums, so I think that's a yes.

That sounds odd. Normally if the motor is ok & you put power across & hand spin it then it will run.
Hairyloon

Maybe the brushes are toast.
Perhaps I should've kept on with the strip down and not got distracted by the lack of capacitors. I'll carry on when I get back... though I was going to do that anyway since I plan to go back with some capacitors...

Ah well...
Hairyloon


I haven't put a meter to measure, but it hums, so I think that's a yes.

That sounds odd. Normally if the motor is ok & you put power across & hand spin it then it will run.
That convinced me that it wasn't (just) the capacitors and knocked it well down the list of things to do.
It just found itself at the top again and I've pulled it apart to find that it definitely isn't the brushes: it's another induction motor.
Part of one of the coils looks decidedly scorched.

I am not doing well with induction motors: that is three that I've got that aren't working, 2 cooked and one just a puzzle.
I've not yet tried putting 240V across that last one, not having worked out which wire is which... maybe I should just take a guess?
Falstaff

I hate induction motors - the minute you overload 'em they just drop out and sit there burning varnish ! It's as though they go into a sulk and commit suicide !

Once motors start smelling and smoking, it's usually too late to do anything about it I'm afraid Sad

No way you can cut the motor off and replace it with a nice grunty brush motor off an old washing machine I suppose ?
Hairyloon

No way you can cut the motor off and replace it with a nice grunty brush motor off an old washing machine I suppose ?
I've got plenty of enamelled wire: for a moment I was trying to persuade myself that I could pull it apart and rewind it... I was not convinced.

The original plan was to put an engine on it... Not sure yet how practical that idea is.
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