Reversing an induction motor with no centrifugal switch

[Fazerruss]

Good evening all, I'm on with another project which requires the motor direction reversing. This is a cheap designed for the job motor without the start and run windings connections in the terminal box so I've stripped it down to get to the windings connections. Before I go any further is there an easy way to do this. I can't make out any differing wire size to indicate separate run and start windings and there is no centrifugal switch on either of the flanges. There is an externally mounted capacitor.
So what kind of motor is this and is there an easy way to reverse it? Would changing the capacitor polarity have an effect or kill it? I only need to permanently change direction so no need have it switchable.
It's off a Rexon bandsaw that I'm modifying so will be cheap Chinese.

Thanks

 

[mike 109444]

I have before now just took the two ends off, pull shaft out, flip and refit. No rewiring needed. Does depend if end plates allow for this.

 

[Fazerruss]

I have before now just took the two ends off, pull shaft out, flip and refit. No rewiring needed. Does depend if end plates allow for this.

I did think about doing that as the flanges can be swapped. Problem is though the windings aren't in the middle so the rotor won't be in the correct place. I guess it would probably work but be less efficient.

 

[mike 109444]

Bit like this

 

[Seadog]

If you remove the power connection that goes to the capacitor/winding and reconnect to the opposite side of it, then that should do the job.

 

[Fazerruss]

If you remove the power connection that goes to the capacitor/winding and reconnect to the opposite side of it, then that should do the job.

Can you clarify for me please? The mains in goes to 1 and 2. The cap goes to 2 and 3

 

[Seadog]

Remove the mains lead going to two and reconnect it to three. If you want a switched reverse you can achieve it like this.

 

[Fazerruss]

 

[Fazerruss]

Remove the mains lead going to two and reconnect it to three. If you want a switched reverse you can achieve it like this.

Thanks I'll give that a go. I didn't think it would be so simple.
When I fitted a single phase motor to my car lift the motor required the start windings to have their polarity switched to change direction but none of the wires were disconnected like in your diagram for this motor.
Is that diagram typical for these type of none universal type motors?

Do you have a link to the source of this diagram? I'd like to read up on the theory of this type of motor.

 

[Seadog]

It's the only configuration possible for an induction motor with a just a run capacitor. Since both windings are permanently in circuit they are electrically identical. The capacitor gives the second winding a 90° phase shift.
By swapping the mains lead in your motor, all you doing is swapping the 'main' winding for the 'run' winding. In the other type you mention the start winding is not rated for continuous running, hence the centrifugal switch (the click as the motor runs up to speed), which disconnects it as soon as the motor has started in the right direction. To reverse that style of motor, which I would say is probably the most commonly found, you do need to reverse one or other of the windings, but they must retain their function for the reason stated.

 

[Fazerruss]

I'll do the swap tomorrow night as I've had enough this evening.
Just noticed the mains coming in to number 2 has two windings connections plus the cap and number 3 which i will be swapping it to has only one winding connection plus the cap. Why is this?



Sorry for all the questions, I like to know how these work.

 

[Seadog]

Is there a rating plate on the motor? It sounds like it may be three phase, but it's missing a wire if that's the case.

 

[Fazerruss]

It's deffinatly single phase. I bought new from an eBay seller 10 years ago and it's worked fine.
All this is so I can fit an Kopp Allspeeds variator so I can slow the blade down for cutting metals rather than wood.

 

[Fazerruss]

 

[Seadog]

I give up
Is there the possibility of turning the motor 180° and swapping the fan to the other end?

 

[mike 109444]

Perhaps two is a "tapping" at the middle and Therefore just a loop out and back (like they use on mig power transformers).

 

[Seadog]

Mike, if that was the case, then the centre point should just have incoming mains and no capacitor connection. The capacitor should go between the other two leads and the remaining mains lead to one or other of them (as per my diagram).

 

[Fazerruss]

After sleeping on it I reckon the motor is star wired as below...



What do you think, is this a possibility?
If so, then could swapping the polarity of the coil top right change the direction?
I have a good book somewhere on induction motors explaining how to run a three phase motor off single phase by adding a start cap that is disconnected when up to speed. This motor has me confused with it being single phase yet there are six wires for the windings.

 

[Seadog]

If it was star-wired where's the connection with three wires? You have never mentioned 6 wires, just three ends, which is why it's all so confusing. It is possible to run a 3-phase motor using two windings and a capacitor. It has less torque and doesn't run very smoothly, but is quite often used for, say, suds pumps on 3-phase machines being run from a VFD.

 

[Seadog]

Neither of these configurations match with your description of how yours is wired.