Ancient single phase electric motor - reversing the rotation

[Marvo]

.......The more I look at those wires the less I like them - that insulation must be 50,60 .....? years old. It's not old enough to be rubber but it doesn't look like healthy plastic. I may replace it all when (if !) I do the swap - if that's possible without interfering with the windings at all....

Don't worry about the insulation, it's normal for it to look tatty and go hard because the heat from the motor takes its toll over the years. Don't try to replace the wires, just use a couple of layers of heat shrink sleeving if there's areas where it's cracking.

As lucien says the name of the game now is to figure out the 3 pairs of wires for the start winding, run winding and centrifugal switch. If you separate out all the wires and measure the resistances I'd expect the start winding to be around 15 ohms, the run winding maybe about 5 ohms and the switch will either be infinite or zero resistance depending if it's open or closed but I'd expect the latter if the motor is stationary unless it's sticking. Please note the values given are a very rough guide and could even be 50% out.

 

[AndrewB]

Thanks Lucien - you are correct.



I removed the armature, the board and the two capacitors and I then get continuity across red and black but nothing across yellow and blue until I close the switch - which is hidden behind the casting.

I've sketched out the circuit as it was so I think I can now work out the rest. I'll check on here first though before I blow myself up.

Thanks again.

Edit - Marvo - heatshrink ! Thanks, hadn't thought of that.

 

[Barry White]

Thanks Lucien - you are correct.


I removed the armature, the board and the two capacitors and I then get continuity across red and black but nothing across yellow and blue until I close the switch - which is hidden behind the casting.

I've sketched out the circuit as it was so I think I can now work out the rest. I'll check on here first though before I blow myself up.

Thanks again.

Edit - Marvo - heatshrink ! Thanks, hadn't thought of that.

Looks like its plain sailing now rebuild it but swap the positions of the blue and yellow over. Do let us know how it drills.

 

[AndrewB]

swap the positions of the blue and yellow over.

Aaaahh the penny has finally dropped - this will change the direction of the current through the starter winding and the corkscrew rule thingy - or is it Flemings Right hand Rule (??? ...A Level physics was a long time ago) then means that the rotation is in the opposite direction, yes ? After that - as several people have said - the run winding takes over.

OK, heatshrink, bit of cleaning up connections and then reassemble. Photos to follow.

 

[Lucien Nunes]

change the direction of the current through the starter winding and the corkscrew rule thingy (??? ...A Level physics was a long time ago) then means that the rotation is in the opposite direction, yes?

Sort-of. The winding current is AC so it reverses 50 times a second anyway, what you are changing is the timing of the reversal of the start winding current relative to the run. The different characteristics of the two windings, and the presence of the capacitors, mean that when they are both connected to the same supply their currents will differ in phase by about 1/2 pi electrical radians, corresponding to their electrical angular displacement in the stator slots (on a 4-pole motor that's half the mechanical angle). Over one mains cycle you might get in sequence S- R+, S+, R- so a notional + seeking point on the rotor will follow from R to S around the stator. Reversing S will give S+, R+, S-, R- so the same point will now follow from S to R, developing torque in the other direction.

 

[Marvo]

Thanks Lucien - you are correct.

View attachment 31530

I removed the armature, the board and the two capacitors and I then get continuity across red and black but nothing across yellow and blue until I close the switch - which is hidden behind the casting.

Did you test each wire to every other wire? What was the resistance you saw yellow-blue?

When you removed the termination block where were the two power wires connected to underneath?

From the info so far your circuit should be something like this I think.

 

[AndrewB]

Did you test each wire to every other wire? Yes - no continuity except those above.

What was the resistance you saw yellow-blue? 29.5 Ohms, Red Black was 5.5 Ohms.

When you removed the termination block where were the two power wires connected to underneath?
The one at A4 went to A3 (the red/blue stud) and the black went to the bottom left stud - the one with the black going off to the winding.

From the info so far your circuit should be something like this I think.

View attachment 31534

You blokes are too clever ! I think that's what I've got - but clearer !

 

[AndrewB]

Sort-of.

You're too kind Lucien. At first your explanation went way over my head but after a couple of goes I think I understand the principle if not the detail.

 

[Marvo]

Did you test each wire to every other wire? Yes - no continuity except those above.

What was the resistance you saw yellow-blue? 29.5 Ohms, Red Black was 5.5 Ohms.

When you removed the termination block where were the two power wires connected to underneath?
The one at A4 went to A3 (the red/blue stud) and the black went to the bottom left stud - the one with the black going off to the winding.

From the info so far your circuit should be something like this I think.

View attachment 31534

You blokes are too clever ! I think that's what I've got - but clearer !

From the info you've given the drawing I did should be correct.

The end is in sight, you should be able to reassemble it exactly as it came apart and just reverse the black and the red wires that go to the windings to achieve reverse rotation. Obviously sleeve any wiring that needs it and check the terminations are all good , tight and none are frayed. Make sure you don't trap any wires, it's a common issue when reassembling motors. Using cable straps to truss everything up nicely helps avoid this.

When you test it some things to watch for;

• Start up of the motor should be crisp and you'll probably hear the centrifugal switch operate with a click almost instantaneously. If it's slow to start or there's humming/buzzing then disconnect immediately.
• When power is disconnected it should coast slowly to a stop and you'll hear the centrifugal switch operate when the rotation speed gets low.
• If the motor has a running current marked on it check the supply with the motor running using a clamp on ammeter. I'd think the running current should be around 50% of the stated value if there's no load on the motor. If the actual run current is greater than or almost equal to the current stated on the motor there's a problem and disconnect quickly before the windings get burned.

I'd strongly recommend you test the motor using a supply from a socket that's fed from an RCD in the consumer unit. If your CU doesn't have an RCD then maybe invest in a piggyback type RCCB that plugs into the socket first. Make sure the earth wire of the supply is connected to the steel frame of the motor and don't manually hold the motor whilst testing. Be safe.

 

[AndrewB]

Right Gents, wires swapped and re-assembled up to this stage.

Photos show before and after - hard to get it wrong really (famous last words) with all the excellent instructions.
I've not wired the capacitors back in exactly the same way as before - is it significant ? They're still in parallel.



If you're all happy I'll finish off tomorrow.

Thanks and regards.

BTW - there weren't any wiring diags inside the end covers.

 

[Barry White]

looks good to me do bear in mind Marvos advice

Quote "

• Start up of the motor should be crisp and you'll probably hear the centrifugal switch operate with a click almost instantaneously. If it's slow to start or there's humming/buzzing then disconnect immediately.
• When power is disconnected it should coast slowly to a stop and you'll hear the centrifugal switch operate when the rotation speed gets low.
• If the motor has a running current marked on it check the supply with the motor running using a clamp on ammeter. I'd think the running current should be around 50% of the stated value if there's no load on the motor. If the actual run current is greater than or almost equal to the current stated on the motor there's a problem and disconnect quickly before the windings get burned. "

 

[AndrewB]

reassemble it exactly as it came apart and just reverse the black and the red wires that go to the windings to achieve reverse rotation.

Hang on - I'm confused now. Mykey said swap blue and yellow - the circuit with the switch in it. ?
What have I misunderstood ?

 

[Barry White]

No Marvo said move the main winding (red and black) I said move the start winding (yellow and blue ) only one needs to be done or the motor will not reverse But any one swap should work

So both are correct just choose any one pair to swap looking at the picture you swapped yellow and blue so it will be ok to try now

 

[AndrewB]

Phew ! OK cheers. And I'll follow Marvo's safety advice as well.

 

[AndrewB]

Sorted ! Purrs like a kitten. And clockwise.
Mykey, Marvo and Lucien thanks for your help. If there was such a thing as a virtual pint I'd buy you one each.

if only I could remember what it was I wanted to drill.