Reversible motor

[Munroast]

I have a single phase induction motor, that wont run in one direction, it blows the fuse everytime, it works fine in the other direction

would switching the wires to the capacitor over help, the switch is back to front (it runs backwards when in forward, then when in Reverse it tries to forwould but trips the fuse) , but it is still only the anticlockwise direction it will run.

I don't understand how it could burn out for one direction? surely its working exactly the same after the capacitor has chosen the direction ?

edited to try and make it sound sense

 

[flameport]

Capacitors for motors do not have polarity, swapping the connections will do nothing.

If it's designed to run in both directions and has a switch for that, then it's more likely the switch is wired incorrectly.

 

[Jackrae]

The capacitor doesn't "chose" the direction, and reversing it's connections will have no effect on direction. The capacitor provides the phase shift in the start winding and it is this phase shift that determines motor run direction. To reverse motor direction you need to swap the winding terminals on the starting winding

 

[Munroast]

so what has possibly went wrong to stop the motor spinning in one direction when it works well in the other direction ?

in the direction it fails, it will turn the motor correctly but tips the fuse before a whole turn

It is designed as a forward reverse motor with a switch to change direction

 

[flameport]

so what has possibly went wrong

Has this motor ever worked?
Or was it working and then failed?
Has it been moved, rewired or anything else changed?

If you have swapped two wires and it changes the behaviour of the switch, those wires were not connected to a capacitor.
Do you have further details about the motor, photo of the data plate, control gear, wiring, etc.?

 

[Jackrae]

Take a photograph of the motor terminals and detail how it was originally connected and how you connected it up when you tried to reverse its direction.

 

[Munroast]

Has this motor ever worked?
Or was it working and then failed?
Has it been moved, rewired or anything else changed?

If you have swapped two wires and it changes the behaviour of the switch, those wires were not connected to a capacitor.
Do you have further details about the motor, photo of the data plate, control gear, wiring, etc.?

Yes, it works perfectly well spinning anticlockwise (reverse direction) when the switch is on Forward. When the switch is on 'reverse' the motor turns a little clockwise (forward direction) then trips the fuse.

And No, I have never known it to work properly. It is a second hand machine.

so it makes no difference the polarity of the capacitor

What I am really wanting to know here is. Is it likely the motor needs replaced or is it more likely to be a switching/wiring problem. Don't want to get involved in expensive repairs if it is something simple.

 

[ericmark]

There are multi ways of reversing a motor, some will have two windings and swapping just one of the windings around will reverse the motor, but that is not the only method.

I remember working on a Flyght pump, and the two windings were nearly the same resistance, and ended up getting the two mixed up and burning out the motor. That one had a relay to start it as well as the capacitor.

And today often motors are three phase even if on a single phase supply, and powered with an inverter.

 

[SimonH2]

And No, I have never known it to work properly. It is a second hand machine.

I think it's a fairly safe bet that the thing is not correctly wired or the switch is faulty.
As already mentioned, one very common method for reversing a motor is to swap the connections round on the starting winding (or second winding if it's a permanent capacitor run motor).
I'm going to take a guess ... in the direction it doesn't run, does it just hum (and perhaps the shaft vibrate a bit but not really start turning) until the fuse blows ? If so, that's a fairly good indication that the start/second winding isn't connected - faulty switch or wiring.

BTW - what size is this motor.
Got any photos of the rating plate, terminals, perhaps a connection diagram on the inside of the terminal box cover, and the switch wiring ?

 

[Munroast]

Spent more time faffing with it today. Have come to the conclusion the switch is fine, it has just been wired back to front! May be in a bid by the previous owner to get it to work in the correct direction!

This is a 370w single phase induction motor off a small miiling machine. The motor is conected to a triple set of v-belt pulleys. When I remove the belts to allow the motor to run freely, it will work in both direction and sounds as sweet as a nut. Couple it back up to the pullies, it will run anticlokwise although starting does not sound good and takes a while to get up to speed. However in clockwise, it just trips the fuse.

I can't find any undue resistance in the pulley system, I can turn them in either direction reasonably easily with one finger. And the motor, when running and up to speed seems powerful. I was trying to slow the motor by pressing a 4x2 into the spinng pulley and wsn't slowing it that much.


Could it be a capacitor problem ? I was under the impression that these start capacitors ither worked properly or failed. Could it be only half working and not getting up to speed before the main windings took over (if that is how they work) Or could the capacitor be of the wrong size? too big or too size. It is not original and the wires have been poorly (untidily) soldered on

What size capacitor should this motor be using ?

Here is a sketch of the wires going into the motor

My understanding is the starting winding is the one in series with the capacitor. And since measuring the resistance of this winding (not including the cap) iether produces no reading or something like 10megaohms. How is it even starting ?
If the centrifugal switch (which I haven't got to yet) is so dirty/pitted that it is not making contact. Then how is the motor even starting ??

I'm utterly bamboozled by this problem, its not making any sense

 

[Munroast]

beep - would love a bit of help and understanding of this problem

 

[Jackrae]

Show a photograph of the terminal block clearly showing the terminations and your connections as requested at #6

 

[Munroast]

A photo of the termination block shows little, hence my diagram.

The For/Rev switch is on another part of the machine and is just a mass of black wires. And I now believe all that is working properly, all I done was swap the wires from one side of the switch to the other, so that reverse is reverse. The problems have not changed, it still runs OKish anti clockwise, but set to forward, it will run Clockwise with no load, but as soon as the belts are fitted (giving a little resistance) it trips the fuse.

(I suspect the only wires interfered with by the previous owner are the ones I swapped back.)

here is a pic of the terminal block on the motor

 

[Munroast]

The plate on the motor suggest a 100µF cap. The Cap that is fitte is rated as 160µF and my multimeter measures the capacitance at 192µF
Could this be a problem.

 

[RandomGrinch]

The plate on the motor suggest a 100µF cap. The Cap that is fitte is rated as 160µF and my multimeter measures the capacitance at 192µF
Could this be a problem.

A larger capacitor will have a larger inrush current - it may be enough of a difference to cause a trip, if tolerances are tight?