Electrickery

[twentysix by twentyfive]

Not sure this is on the correct forum page. Apols @Mods if I've put it in the wrong place.

Problem with single phase relay switch gear for motor start/stop. Help please.

The wood turning lathe won't turn on now. Previous problem was down to the surge capacitor failing but I've tried new ones with no joy. So I guess it might be the switch gear. So pulled it out of the housing with the following photographs taken to assist in remote diagnosis.

So I've only got as far as checking the green and red buttons. Both seem to be open circuit whether pressed in or not. From Googling I expected (rightly or wrongly) that the on switch would normally be open and the off switch would normally be on. Since neither are behaving as I thought I'm in a quandary. Am I doing something silly as I wouldn't expect both switches to fail simultaneously (or would I?).

As far as I can see the (two only) relay contacts inside are open and the two tube like things on the outside on one side (I think may be thermal fuses operated by bitmetal strip?) are closed.

So what next please - I'm at a loss.

 

[presta]

Not something I have any direct experience of, but it's simple, so I'd be inclined to draw the circuit diagram so you can see the wood for the trees. The buttons don't sound right, but they might be momentary contact ones - worth another check. From the poor quality soldering, dry joints are a possibility. Have you checked the continuity of the relay coil? Does the motor run if you connect the mains to it directly?

 

[twentysix by twentyfive]

Does the motor run if you connect the mains to it directly?

I did wonder if that was safe. I assume the few on/offs for testing won't knacker the switch on the wall?

Thanks for your thoughts. The coil I haven't investigated. Need to work out which contacts they are on the circuit board so I guess a circuit diagram is a good idea.

 

[slowmotion]

Looking at the fourth photo, the second and third soldered joints (from the left) at the top of the relay PCB look like they might be shorted together. It may just be the camera angle, of course.

 

[Low Gear Guy]

I Don't think those devices next to the relay are cut-outs. They look like magnetic reed switches which are activated by the relay coil.

It is not clear why these are present.

 

[Tenkaykev]

Hello. How many capacitors are fitted to the motor. If two, then one will be the “ Start “ capacitor about 100-200 Mfd depending on motor power, and the other will be the “ Run” capacitor typically 8 - 25 ish Mfd.
Most single phase motors have a centrifugal switch on the shaft at the non drive end which disconnects the start capacitor and start windings once the motor is at about 75% of full speed. This is to protect the motor “ start “ windings and capacitor which will burn out if left connected for more than a few seconds. If it is a cheapie machine then they may be using the relay as a bimetallic strip to take the start windings out of circuit.

 

[twentysix by twentyfive]

Looking at the fourth photo, the second and third soldered joints (from the left) at the top of the relay PCB look like they might be shorted together. It may just be the camera angle, of course.

They are and I assume intended to be as that's what I found when I took it out

I Don't think those devices next to the relay are cut-outs. They look like magnetic reed switches which are activated by the relay coil.

It is not clear why these are present.

Hmmmph - I don't know either but they don't lie along the axis of the coil which suggests that they aren't magnetically coupled

I’d expect, in this type of setup, for the “ON” switch to close when pressed applying power to the relay. The relay would then close, both powering the device and providing feedback to itself to hold it on. The “OFF” switch would break the feedback loop thus shutting on the system.

That was my expectation having Googled

Hello. How many capacitors are fitted to the motor. If two, then one will be the “ Start “ capacitor about 100-200 Mfd depending on motor power, and the other will be the “ Run” capacitor typically 8 - 25 ish Mfd.

Most single phase motors have a centrifugal switch on the shaft at the non drive end which disconnects the start capacitor and start windings once the motor is at about 75% of full speed. This is to protect the motor “ start “ windings and capacitor which will burn out if left connected for more than a few seconds. If it is a cheapie machine then they may be using the relay as a bimetallic strip to take the start windings out of circuit.

I've only found one capacitor (100uF) which is disconnected by a centrifugal shaft switch as you mention. That 100uF failed a while ago and I replaced it with 80uF and all was well again until now when replacing the 80uF with others of same value didn't achieve the required result.

 

[Tenkaykev]

As it’s an AC motor the capacitor‘s sole purpose is to ensure the motor turns in the correct direction when power is applied

The capacitor puts the start windings out of phase with the main windings. The start windings are also physically displaced with regard to the main windings. If you swap either the run winding leads or the start winding leads then the motor will run in the opposite direction. There are several types of switch / starters that allow you to do this. With a " Shaded Pole" motor the start windings are replaced by a solid loop of copper offset to one side of the windings. These typically have low starting torque but don't require a capacitor. They are a fixed rotation but often physically reversible by dismantling and reassembling with the main body reversed.

 

[MrGrumpy]

Not sure this is on the correct forum page. Apols @Mods if I've put it in the wrong place.

Problem with single phase relay switch gear for motor start/stop. Help please.

The wood turning lathe won't turn on now. Previous problem was down to the surge capacitor failing but I've tried new ones with no joy. So I guess it might be the switch gear. So pulled it out of the housing with the following photographs taken to assist in remote diagnosis.

So I've only got as far as checking the green and red buttons. Both seem to be open circuit whether pressed in or not. From Googling I expected (rightly or wrongly) that the on switch would normally be open and the off switch would normally be on. Since neither are behaving as I thought I'm in a quandary. Am I doing something silly as I wouldn't expect both switches to fail simultaneously (or would I?).

As far as I can see the (two only) relay contacts inside are open and the two tube like things on the outside on one side (I think may be thermal fuses operated by bitmetal strip?) are closed.

So what next please - I'm at a loss.

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The switches will be momentary , can you push the coil in on the contactor ? Be careful as need the mains on. It should start if motor is ok , after which check you have 24v or 12v on the relay coil of contactor ? If coil working you should have 0v across the coil .

 

[twentysix by twentyfive]

The switches will be momentary , can you push the coil in on the contactor ? Be careful as need the mains on. It should start if motor is ok , after which check you have 24v or 12v on the relay coil of contactor ? If coil working you should have 0v across the coil .

Are the switches momentary when no power applied?? I've used my multimeter on ohms setting and only see open circuit whether pushed in or not. No access (physically) to the coil. I'm yet to identify which contacts (on the outside) are at the ends of the coil. I'm guessing an "on the bench apply mains power" test is next best. Got to sort out the safety aspects before I try that. Thanks.

 

[twentysix by twentyfive]

One of the booooogers with all this is that there are no part numbers on anything

 

[MrGrumpy]

Are the switches momentary when no power applied?? I've used my multimeter on ohms setting and only see open circuit whether pushed in or not. No access (physically) to the coil. I'm yet to identify which contacts (on the outside) are at the ends of the coil. I'm guessing an "on the bench apply mains power" test is next best. Got to sort out the safety aspects before I try that. Thanks.

When pressed in they should make a contact across the switch, even if just when pressed ? I need to look at the pictures you posted. A set of contacts on the contactor maybe acting as the holding circuit to keep the coil in. You stop switch will drop that out. Need to get a look at them ?

Where do the wires come from/go to that have white tape wrapped round them ?

 

[Tenkaykev]

You should be able to see the fine wires that go from the contactor coil to the pins. Put a multimeter on them and check continuity.
Is there a manufacturers name on the Lathe?

 

[twentysix by twentyfive]

Where do the wires come from/go to that have white tape wrapped round them ?

Those wires are the input cable to the mains plug and the output to the motor

Is there a manufacturers name on the Lathe?

There is and I've checked. Very old model it is and no spares.

I put mains directly on the input wires and pressed Green. Nothing. I was expecting to maybe hear the relay clunk over and maybe see some volts at the output. But nothing.

My next move is to bypass the Green button to see if that's any better. And maybe try to test the coil continuity.

 

[Tenkaykev]

Those wires are the input cable to the mains plug and the output to the motor

There is and I've checked. Very old model it is and no spares.

I put mains directly on the input wires and pressed Green. Nothing. I was expecting to maybe hear the relay clunk over and maybe see some volts at the output. But nothing.

My next move is to bypass the Green button to see if that's any better. And maybe try to test the coil continuity.

What make is it and how old is “ very old “ ? ( I’ve worked on Electric motors that are getting on for 100 years old )