What sort of motor have I got?

[Richard]

Hello,

I have a motor that I have recovered from an old table saw. The blade on the saw had develpoed a fault whereby it would only spin depending on which way you span the blade (safe eh!!). Anyway the motor has now been removed from the saw and as a project I want to try and repair it (and hopefully learn more about motors).

What I'm after is firstly to identify my motor.

It has one capacitor
Single Phase
there are 4 cores that dissappear into the motor

Would I be correct in thinking its a capacitor run motor?
and would I be right in thinking that the possible cause of it's spinning problem is a faulty cap?
and how would I prove this? (obviously apart from replacing)

Thanks in advance

 

[telectrix]

could be the start winding is down. on the 4 terminals, you should read continuity on 2 pairs.

 

[Richard]

Hi telectrix,

I'v drawn a diagram of how the terminal box looks. Hopefully it makes sense! I'll check continuity in a bit.

Thanks

 

[Richard]

Sorry thats really small! I'll try and enlarge.

 

[Flyingsparks]

If the windings are both OK it is usually the cap that has gone when it does this.

Best thing to do is change the cap , you can get one from RS for a reasonable price.

 

[Knobhead]

You’re all ignoring the fact a capacitor start motor will have a centrifugal switch. Being a mechanical device, prone to failure. First place I’d look especially as it’s been used on a saw bench.

 

[Richard]

Hi again, and thanks for all the input. I tested resistance accross the windings, and got the following:

U winding = 5.26 ohm
Z winding = 1.19 ohm

 

[telectrix]

tony will correct me if i'm wrong here, but that suggests to me that the windings and the centrifugal switch are OK. the higher reading of the 2 is the start winding inc. the switch.

 

[Knobhead]

The windings seem OK, time to look at the switch and capacitor.

Sorry I’m using the old terminology in my Brook pocket book.

View attachment 11094

As Tel says the higher resistance will be the start winding, Z1 & Z2

First test is the switch made when at stand still?

Second test is is the capacitor OK, you will need a 250V Megger to do this. If you don't know how to do this, get back to us. Then more explaining will follow.

 

[Knobhead]

One killer for capacitor start motors is the centrifugal switch not opening at run speed and so toasting the capacitor. It’s only short term rated.

As I said the switch would be my first suspect if any dust has entered the motor. Clean it with compressed air, don’t use any lubricant on it. Oil is a dirt magnet!

 

[Knobhead]

For interest, this is a capacitor start, capacitor run motor.
View attachment 11095
Think it’s time I did a single phase motors post in the “Motors” sticky section. There’s more to it than meets the eye when you take physical phase shifts in to account.

 

[Richard]

Thank you kindly for all your input!!

I am off to work now, but will read over all this properly tonight.

Thanks again