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Looking at a control box for a marine Air Conditioner and it has a HUGE capacitor in it. The schematics label it a "Motor Run Capacitor", but I always thought it was just used to start the motor.

What function does a huge cap like this have in running the motor?

The Air Conditioner is being run off AC power from a generator, no DC involved.

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2 Answers 2

up vote 11 down vote accepted

It's more than likely a single phase induction motor.

Unlike a 3 phase motor that can automatically generate a rotating magnetic field, a single phase induction motor has to manufacture one by using 4 stator poles. Two of them are fed with the regular AC voltage and the other two are fed AC via a capacitor. If the value of the capacitor and winding inductance is chosen to electrically be a low Q resonant circuit at the AC frequency supplied, the voltage phase difference between the two sets of stator coils will be approximately 90 degrees and this will set the motor spinning. Here is a decent link and below is a snapshot: -

enter image description here

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I don't want to speak more about it because by a bit googling you can find some good answer for your question! for example good look these both link:

Motor capacitor

Motor starting capacitor

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Starting capacitor is a different beast altogether and will probably explode if you use it as a run capacitor. (Higher value, generally not continuous rated, disconnected from motor when it's running, often by a centrifugal switch) –  Brian Drummond Mar 1 at 17:09
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Answers which are strictly "GTFY" (Google that for you) are discouraged. Please add some content or at least paraphrase what you're linking to (in case the target links change). –  Adam Lawrence Mar 1 at 18:12

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