Hoping for a bit of input here as my AC voltage knowledge is somewhat limited.
I have a 12 X 36 Lathe with a single phase 2HP motor. Today while running some parts I became aware that the reverse feature is no longer functioning.

It runs fine in the forward direction. When trying to start the motor in reverse i can see the fan blades move a little as though it's trying to start but then it stops and just hums. I tried giving it a spin to see it that might help and it did not.

Time for a new motor ??? 400.00 OUCH !!! Any input/ help appreciated
Tim

Look for start capacitors. Replace those exactly as they are now. Then try it...

Would there be different start capacitors for forward and reverse ???
the reason I ask is it starts and runs fine in the forward direction

I believe there is just a run capacitor. The motor needs the polarity reversed to turn it the opposite direction. Being 220 and reversible the motor may have 4 to 6 wires. The switch has multiple contacts and is should we say is the control or computer. If any contact is pitted the motor will try but not be able to spin. You could try to see if you can see into the switch. Contact cleaner and giving the switch a rapid work out may bring it to life. Also make sure a breaker is not popped. Some designs may let the motor run on one leg but not allow any direction changes.

thanks to both responders

I will do that first thing in the AM, Anybody else ?

Switch contacts dirty, run some Emory cloth over the contacts. Sounds like one leg of the 110 isn’t conectng.

Make sure you unplug it first

Switch contact(s) is(are) dirty or damaged. The wiring diagram below illustrates how the reversing function works by switching two of the motor leads. I would be careful of using common emery cloth to clean electrical contacts. True emery cloth leaves hard debris on the contacts that leads to future contact burning. If the contacts are large, I use a common point file. If they are small, I'll use aluminum oxide sheet or roll abrasive.

Thank you all very much, I will check and report back

Might be a bearing, I've had them work fine froward but in reverse the shaft jams.

Unfortunately as near as i can tell at this time it appears to be the motor . Getting to it to actually measure the Voltages is a royal PITA. But i will do so before replacing it once the new motor is here. I will report back
Thanks to all that responded

I'll keep you posted
thanks again

Well if it’s the switch (has nothing to do with motor) you’ll still have the problem and out money and time.

I'm not buying that. Forward and reverse use the same windings and the same caps. Only the polarity of the start winding gets reversed.

If its in the motor then its a connection issue. I suspect a bad connection in the wiring system, and as stated, most probably in the switch.

A single phase motor has no starting torque and has no idea which direction to rotate. A start capacitor is used in a start winding to electrically phase shift the start winding in respect to the run winding. This phase shift allows the motor to have starting torque and defines motor rotation direction. By reversing the polarity of the start winding the phase shift is now in the other direction and motor rotation is reversed.

There is always a chance it could be in the motor, but the chances are slim............

I agree too

Well i will find out when the new one arrives and I gain access to the motor and electrical panel. The forward / revervse switches that I was able to access are 24VAC. They control two contactors that send the power to the motor. This is all per their Tech guy and the schematic that I have which leaves a bit to be desired.
He claims in 25 years they have not had a contactor fail unless the coil went bad. This one is Audibly working. He also stated that if it were a switch problem the contactor would be not be audibly clicking nor would the motor be trying to start.
I understand DC pretty well but get lost real fast on the AC stuff.

I understand the part about 110V AC and it reversing direction 60 times a minute.
I understand that two legs of of 110 together make the 220. Beyond that is where I start getting lost. Especially when you guys start talking about reversing the polarity, my head goes into a tailspin

I sincerely appreciate everyone's assistance and trying to help. It would be a lot better if I could access the backside without the PITA it's going to be. i will definitely keep everyone posted

What's confusing you is that someone is using DC terms (polarity) when referring to AC.

there is no polarity in an AC circuit, there is phasing though. I suppose if you want to be real technical about it AC is constantly changing it polarity as a function of it's action, but talking about AC polarity is like saying water is wet and not relevant to how is makes a motor work.

Pure AC is a nice sine wave, you've seen them even if you don't know it. Single phase shown.



All phases will look the same, or near enough, in frequency and amplitude.

What changes in multiphase power is when the peaks occur in time in relation to each other. By shifting that peak in time you can reverse the motor and that's what starting caps do when starting a single phase motor.

Two phase sine wave shown.



In a three phase motor you just swap two of the phases as wired to the motor, this is done with a switch of some sorts.

So in the pic below, wired A, B, C runs one way, A, C, B runs the other way



You can have more than three phases, but the ones I talked about are the three most common setups you will see.

I hated to wade into the polarity discussion but Sniper is correct. What reversing the connections on the start winding does is change the phasing between the start and run windings. The two different configurations changes what direction the motor turns as the relative phasing between the two windings changes. Apparently you have two contactors for the reversing function rather than a full voltage reversing switch. All this means is that the switches controlling the contactors are functioning and one of the contactors is not. As to the comment from the vendor that a clicking contactor means it is working is pure bull. As to the motor trying to start, the slight movement you are seeing is pretty common with an open start winding. With the additional information, I'm still betting that you have a switching problem it's just now that it is a contactor rather than the switch itself.

So if I am interpreting what you are saying correctly, the problem is likely the one of the contacts in the contactor, or the Reverse starting capacitor which I'm assuming is inside one of the two large enclosures on top of the motor. Correct?

Thanks Again for all the help.

I’m certainly not as knowledgeable as the one guy but my pump motor would just hum not start and ended up being the capacitor. Over the years in my dusty shop (wood) I have cleaned every motors contacts (3 phase and single phase) many times (magnetic type) Today’s motors are tough cookies and never had one just stop other than an external problem. If they do fail it’s in a long overworked death type struggle.

I don't have the energy to argue why using polarity is acceptable terminology in this case. A current transformer (CT) is an AC device and yet it is marked with polarity. Same concept. I don't care if you call it phasing or polarity, I think we all agree on how it works.

Usually the forward and reverse capacitors are the same capacitor.

And contactors absolutely do fail............. Lots of times easily fixed.

OK, then you are saying likely the Reverse contactor ?

This is why I get a bit confused I understand the A/C portion of the sine wave and that the difference between the high and low peaks equal the V. If I remember correctly the high was considered Plus V while the low was the opposite or negative.

thanks again to all who are trying to make me understand what I long ago forgot due to not using it

Why does a CT have a polarity marking? because it refers to the direction of current flow and has nothing to do with voltage.

That's why I said I didn't want to wade into a discussion about polarity. If you understand AC circuits, polarity is fine. The problem is when car people used to dealing with automotive DC systems hear the term polarity they assume a DC circuit. But I agree that we all agree on how it works. As to capacitors, there is only one start capacitor on a capacitor start motor and more than one capacitor on a capacitor start/capacitor run motor. But I have never seen a dedicated capacitor for forward and another for reverse. As to the thinking that it is the reversing contactor (now that we know you don't have a simple switch) I think that's what everyone is saying. If you want to prove to yourself which is the case, swap the forward and reverse contactors, I'll bet your problem follows the contactor.

Exactly!

And yes, I would be looking at your reverse contactor.

Thanks again and i will keep you posted as to the outcome

I am more than ready to take my beating now l

Well much to no one's surprise, those of you that said it was a contactor issue are likely right. I say so as the new BALDOR motor arrived an was installed per their instructions that I found on the net dated 2018 with pictures and a table on converting existing connections to the new motor. They were wrong directional wise to my machine but that was easily corrected.
As predicted the unit still will not run in reverse, Unless of course I switch wires Z1 znd Z2 also known as 5 & 8 or T5 and T8 per Baldors instructions. Then it will happily run in reverse, but not forward, Once again as predicted.
My other concern at this time is the motor has a hum or slight vibration while running. I will try it with the belts disconnected to see if it may be due to an alignment issue. I will also verify that the line voltage is hooked up to the correctly.
meanwhile I found a replace contactor on ebay for a pretty reasonable price but before I blow my wad again I thought i might see if there was any further input.
I'm attaching a couple of pic's in case they might be helpful . I at this point am assuming U1 & U2 are the run windings and the Z1 or Z2 control the direction on start up yes ???

Thanks again for all the assistance

Page 8 should answer your questions.

Motor Connections

But to expound a bit, there is no such thing as a 'control' winding. There is start and there is run. The connection configuration determines the relative phasing between the two and they both determine rotation. The only reason the non-reversible single phase single voltage capacitor start motor has only two terminals is that the start winding is internally connected.


As to single phase capacitor start motors, I like (and buy) a TEFC enclosure. The point of failure on a single phase is typically the internal centrifugal starting switch and a TEFC prevents airborne crud getting into the motor that an open or open drip-proof enclosure will.

I don't see a problem here, I mean the unused one on the right looks new And the other one ??/ that's black conductive carbon meant to enhance the current capacity LOL
Thanks to ALL for the assistance