Capacitor Query

[Mustbemad]

Hello all, I have a theory question for you.

240V gate motor - forward/reverse operation.
300W, 1.3A
Wire 1- COM
2 - Phase 1
3- Phase 2
4 - Earth.
These would be connected to a control board.

A 8uF non polarised capacitor is connected between the two phase wires. Plastic body, only connects at those two points.

Q; Is this a start/run device? How is this working?

Thank you for your educational help.

 

[ricicle]

Is it theory or not

Can you provide a photo or drawing ?

 

[flameport]

The capacitor is used to shift the phase of the other winding, so there are 2 different magnetic fields which turn the motor.

Without it, you only have 1 magnetic field, which can't be used to rotate anything - the motor will just buzz, not move and eventually overheat.

It's not the most efficient design, but it is cheap and reliable.

The motor can be run in either direction simply by applying power to either Com & P1 or Com & P2, as you are transposing the positions of the two magnetic fields.

 

[Mustbemad]

Hi ricicle, this is definitely theory, although it exists in increasingly common real applications.

Hi flameport, thank you for your reply. That makes sense now. I think that what was confusing me is that I was expecting a capacitor on each phase & not a shared capacitor. The joys of modern progress.

 

[ban-all-sheds]

It's a single phase motor, you do not have 2 phases available to connect to it.


Are you just studying this on a self-taught, out-of-interest basis, or are you taking a course?

If the latter, then you really really should tell your lecturer that you haven't understood what you've been taught that was supposed to enable you to answer that question.

If you really don't understand the books, notes, or what your lecturer is saying then something is going wrong. If you can only find out by coming here, then your lecturer is going to have a false impression about how well you're doing, and will also get a false impression about how well he himself is doing in imparting knowledge, and neither of those situations do anybody any favours.

If you don't understand a question, ask your lecturer, or he will think that you are perfectly OK with what he is teaching you. Believe it or not, lecturers do actually want their students to learn, not to be confused.

You get asked to go away and answer questions like that because your lecturer(s) need to know how you are progressing. If you get other people to answer questions because you can't then you are misrepresenting your progress to your lecturer(s) and are leading them to believe that their teaching is adequate when maybe it is not. Do it in an exam and it's called "cheating".

If you are supposed to be able to answer that question then your lecturer needs to know that you aren't.

 

[Space cat]

I was expecting a capacitor on each phase & not a shared capacitor.

It would be more accurate to say "each winding" rather than "each phase". Like BAS says, you're running this motor from a single phase supply. The capacitor isn't shared. One winding gets a direct supply while the other is fed through the capacitor, the effect of which is to make that winding 'see' a second phase. Flameport said it already:

The capacitor is used to shift the phase of the other winding

PS: Just for you BAS, no smileys.