Motor running the wrong way

[John Rumm]

A friend asked me to come and help him swap the motor on a small table saw today. Anway the new motor was already in when I arrived - much the same location as the previous one, with pullys and belt suitably set and adjusted. So I wired it up via a NVR switch with built in adjustable current trip, plugged it in, pushed the button, and it all sprang into life.

Then we noticed the saw blade was going round the wrong way!

The motor is about 1.5hp I would guess looking at the size of it. It was reclaimed from something else and hence the original plate lable is now mostly unreadable.

I am not sure what type of motor it is, but there is no external start capacitor visible. Also when it spins up I could not hear a click from a centrifugal switch (not that this is any guarentee that it does not have one).

So taking the cable entry plate off reveals six connection studs - one of which is earth. The others are arranged thus (the letters are those marked by each stud):

# Z # T

# S

# A # Az

The incoming mains is currently connected to A (Neutral) and Az (Phase)

In addition there are also wires that emerge from the motor body and connect to the terminals:

A Red and Black (+ mains in Neutral) Az Red and Red/Blue linear stripe (+ mains in phase) S 2 of Red/Green radial stripe Z Black and 2 of Red/Green radial stripe T Red/Green radial stripe and White

The red and black wires have a little slack in them and look as if they could be repositioned to alternative connection points.

Sugestions for an alternate wiring pattern to get it spinning in the other direction?

[Howard Neil]

Is there room for a longer belt and twist it through 180 degrees between the pulleys?

[John Rumm]

We did consider that, and I guess it will be the practical solution if I can't find an electrical one. It would mean rotating the motor a bit though to prevent the belt rubbing on itself though.

[Dave Baker]

Try asking in uk.rec.models.engineering. Lots of people in there who play with lathe motors and it must be a common enough problem.

-- Dave Baker

"Why," said Ford squatting down beside him and shivering, "are you lying face down in the dust?" "It's a very effective way of being wretched," said Marvin.

[Andy Wade]

Hmm, I've not seen one like that before. Sometimes there's a wiring diagram on the rating plate or inside the terminal box. Any manufacturer's name?

Failing that I'd be inclined to disconnect everything (having first carefully noted ...) and sit down with an ohmmeter and identify which pairs are the ends of individual coils. You seem to have 11 'ends' - so there must be at least one tapped winding or double lead-out (possibly before and after a thermal fuse or PTC device at the end of one winding, if it's modern enough to have such things).

Essentially/usually there will be two windings (possibly made up of multiple coils in series) across the mains - one permanently and one via the centrifugal switch and/or series capacitor. If you reverse either of the two it should run in the other direction. (HTH, IME, YMMV.)

[nightjar]

That is why I like three phase. Every motor is guaranteed to start up in the wrong direction, but you only have to swap any two wires to get it going the right way.

Colin Bignell

[neilr]

It may sound silly but, is it possible you have fitted the saw blade the wrong way around?

[Mark]

snip

when I had this problem and after spending hours with a dvm and hundreds of bits of paper diagrams, I gave up and took it to an electricmotor re-winders, 10sec later and two swapped wires job done.

[Broadback]

Though I cannot answer your question I have a garden shredder, a switch reverses the motor, so I guess it is a wiring error.

[Fred]

I assume this is a single phase motor with a capacitor housed in a power bulge. Can you confirm?

If so there'll be 2 windings, 1 powered directly with mains the other indirectly through a capacitor. If the 2 windings are identical then the capacitor may be swapped from one winding to the other. If they are not identical it can't be reversed without overheating and/or loss of performance.

[John Rumm]

Yes, single phase. In fact it has two "power bulges" on the top at 11 and 1 o'clock.

I presume reversing the supply to either one of the windings would also do it...

[Fred]

Ooops yes it would! Best way to do it.

[John Rumm]

My mate did as you suggested, and they swapped over the red wires on A and Az - sorted.

[The Natural Philosopher]

yes.