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reversing a single phase motor

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vic newey15/01/2022 14:24:59
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148 forum posts
77 photos

A motor that came with a south Bend lathe is running backwards, I think it requires two wires to be swapped round but just checking first.

Live power in goes to the central pair in Blue, which do I switch to make the motor go clockwise?wiring.jpg

Ady115/01/2022 14:33:53
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5065 forum posts
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There's a more recent post as well if you use the search function

Edited By Ady1 on 15/01/2022 14:39:18

Les Jones 115/01/2022 14:59:39
2255 forum posts
156 photos

Most motors have a diagram stuck to the cover plate on the terminal box showing how to reverse it.

My guess would be that the red and black wires connected to terminals A and Z are the main winding. If I am right then swapping them over so that the black wire goes to Z and the red wire to A should work. To find out properly you would have to partly disassemble the motor to trace the wires and do some resistance tests.

Les.

J Hancock15/01/2022 15:05:16
832 forum posts

Is the rest of the motor as dirty as the bit we can see ?

vic newey15/01/2022 17:36:17
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148 forum posts
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Thanks for the replies, I've sorted it now but some of the advice on those links is somewhat confusing

One says :- Myford suggest that "AZ" terminal is connected to the AC live and the "A" terminal is connected to the AC neutral (if they are exchanged, then the motor would simply go in reverse). As mine is already in reverse I swapped the leads back AZ to neutral and A to live but it still ran in reverse.

The fix is to simply swap the blue & yellow wires which not only made it run clockwise but also it seems to run better as it seemed slow & sluggish before.

Phil Whitley15/01/2022 17:57:08
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1437 forum posts
147 photos

I will put this here for future reference for anyone searching on this topic. To reverse a single phase motor, you reverse the polarity of the start winding. In a properly marked motor, the run winding is A1 and A2 and the start winding is Z1 and Z2. You simply swap over Z1 and Z2 connections. The problem is identifying the leads if they or the terminals are not marked up properly. If the motor has a centrifugal switch, it switches the start winding out of circuit, so if you have one lead marked Z and another going to the centrifugal switch, they are the start winding. The start winding will have a higher resistance than the run winding when checked with a multimeter. Sometimes other letters are used (thanks to EU harmonisation) if in doubt check the windings resistance. If your motor is as full of swarf as the op's, best strip it and clean it out, as the centrifugal switch has bare live contacts on it, which will set oil filled swarf on fire in seconds, doing the lathe and the workshop a lot of no good!!

Phil

Edited By Phil Whitley on 15/01/2022 18:00:33

john fletcher 115/01/2022 18:36:31
783 forum posts

It would appear that the electric supply is via the two BLUE crimp on terminals, and I see there are two bare copper wire links, which is OK. So, lift up the BLUE crimp supply wires, and swop over the two wires which are below them, the RED and the BLUE. Then replace the two BLUEs supply crimps back in their original positions/locations.as shown in your picture. John

old mart15/01/2022 19:27:26
3717 forum posts
233 photos

I would swap the incoming live and neutral wires from the mains lead, brown to A and blue to 7.

vic newey15/01/2022 20:05:35
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148 forum posts
77 photos
Posted by old mart on 15/01/2022 19:27:26:

I would swap the incoming live and neutral wires from the mains lead, brown to A and blue to 7.

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Doing that makes no difference

 

Edited By vic newey on 15/01/2022 20:05:59

vic newey15/01/2022 20:08:52
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148 forum posts
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Posted by J Hancock on 15/01/2022 15:05:16:

Is the rest of the motor as dirty as the bit we can see ?

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The motor is very clean, what you see inside the wire terminal box was a thin layer of sawdust which I have now brushed out

Steviegtr15/01/2022 21:03:34
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2421 forum posts
336 photos

Glad you got it sorted out Vic.

Steve.

Brian Morehen16/01/2022 18:56:52
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189 forum posts
11 photos

Swapping Your Brown and Blue led roun has only reversed the incomeing polarity on motor. You earthe is blocking the view of motor leads . To reverse the motor you need toreverse the start windings This looks like the Blue and Yellow leads that need to be changed round . The earth lead is restricking view;

Bee.M

vic newey16/01/2022 19:51:39
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148 forum posts
77 photos
Posted by Brian Morehen on 16/01/2022 18:56:52:

Swapping Your Brown and Blue led roun has only reversed the incomeing polarity on motor. You earthe is blocking the view of motor leads . To reverse the motor you need toreverse the start windings This looks like the Blue and Yellow leads that need to be changed round . The earth lead is restricking view;

Bee.M

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You haven't read my post properly Brian, the fifth one down from the top where I have written :-

The fix is to simply swap the blue & yellow wires which not only made it run clockwise but also it seems to run better as it seemed slow & sluggish before.

Brian Morehen16/01/2022 21:05:11
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189 forum posts
11 photos

Missed your 5 letter Pleased it is now running o/k

Bee .M

Circlip17/01/2022 10:13:59
1499 forum posts

How can a single phase AC motor be expected to run in reverse by changing over the mains input connections? Does the sine wave become anti phased?

Regards Ian.

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