Ancient single phase electric motor - reversing the rotation

[Marvo]

Lol, I though there might be a cap somewhere, you don't often get motors that size that are split phase.

Firstly the two capacitors are wired to the same terminals so they're in parallel which means they're acting as just one big 40uF start cap, not as two individual 20uF caps.

There's almost certainly a centrifugal switch in there somewhere which will have 2 wires coming off it. Can you see where they go?

 

[PEG]

Hi dude,so it looks like a capacitor start motor,your capacitors seem to be paralleled up. Can you confirm a functioning switch? Was an audible "click" heard,on run up or down? It should be noticeable,on one that vintage.

If so,Mykeys drawing should be your way out.

 

[PEG]

Too slow...:dead:

 

[AndrewB]

Right...... I can see the switch - or parts of it - but I don't remember hearing it click when the motor started.
I can't see which wires go to it without taking the other end cap off. That will have to wait till tomorrow although I've just noticed that of the 4 wires which disappear through the hole in the casting at the top of the photo the black goes into the windings. As the red and blue are connected on the board the brown must be one side of the switch and the blue or the red must be on the other. Which means sod all to me but it might help you guys ?

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.

Still don't understand where A, Z and Z1 are on my board.

 

[Besoeker]

Correct, I've never stripped one of the VSD's down. But I'd imagine they have one built in.

Not as a rule on standard offerings.

 

[Barry White]

At a guess its the blue and yellow (did you call it brown) but need more info. remove the other cover please

 

[AndrewB]

Sorry Mykey, now I've just re read your original post and watched the youtube clip I understand your diagram. I'll finish dismantling tomorrow and once I can see the switch and identify the 2 different size windings I think it will all become clear.

One other question - once converted I'll be running it on the 'starter' winding. Presumably this won't be a problem on a pillar drill but would be on something like a lathe where it runs continuously for sustained periods ?

 

[Barry White]

The start winding just starts it running then is switched off by the centrifugal switch if done correctly the motor will run at full power.
If the start winding was not there you could spin the shaft forward and it would run forward or conversly spin in reverse and it will run in reverse. The start winding just starts it spinning.
please post back before altering wiring as the caps if shorted will go off like a shotgun.

 

[telectrix]

the start winding only runs on start up to provide a phase rotation. . then the centrifugal switch kicks it out.

 

[Lucien Nunes]

To clarify, what you need to achieve is to reverse the polarity of one winding relative to the other. It does not matter which one you reverse because their polarity relative to the mains supply is immaterial. All you need to do is identify the two leads belonging to one of the windings and interchange them.

If you can identify four leads from the windings, by disconnecting them and checking for continuity between them you can make them up into pairs. E.g. if you call them 1,2,3 & 4, and you have continuity from 1 to 2 (one winding) and from 3 to 4 (other winding), then reconnect leads 1 & 2 whence they came but interchange 3 with 4. I would expect Red/Black to be the run winding, and Yellow/Blue to be the start winding, with the starting switch internally connected in series with one of those leads. In this case, interchanging blue and yellow will reverse the motor, but you should do the continuity check and try to follow the leads in case my assumption is wrong.

The start winding and run winding retain their original functions, but the phasing of their currents is inverted so as to produce a magnetic field that revolves in the opposite direction. Once up to speed and the centrifugal switch opens, the motor carries on running in whichever direction it is already running.

E2A: Have you looked inside the covers you have removed? There is often a wiring diagram stuck on the inside.

 

[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.