Single phase motor reverse rotation

[waigy]

Brook Crompton Parkinson single phase PD90S (from the 70s) 240v 11A 2850rpm 50hz
I'm using it for polishing metal with a tapered spindle adapter and buffing wheels.

I've got 2 questions.

1. (This photo was taken with all the wiring in its original position.)
I've managed to reverse the motor rotation by swapping the two black wires that are behind the copper connector, but after a few quick trials it is constantly blowing fuses.
Can you confirm that I have changed the correct wires to reverse the rotation?

2. The capacitor starts the motor with a massive jolt which forces the buffing wheel so far onto the tapered spindle that I need large pliers to loosen the buffing wheel.
If I fitted a smaller capacitor would it start more gently or is it possible to remove the capacitor and start the motor by hand by rotating the buffing wheel?

The white arrows point to the three wires that go inside to the motor.

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UPDATE.
I just sorted the problem of blowing fuses.
I fitted new bearings to the motor a couple of days ago and noticed straight away that the motor was more stiff to turn and wouldn't turn freely if twisted by hand.
I thought that was just the bearings being a tight fit, but I slackened the 3 long bolts that hold the whole casing together by just a touch and it loosened the shaft a lot and it now can spin freely by giving it a quick twist.
It now spins for a long time after the motor is switched off which it didn't do before.
So I've tightened the 3 bolts just enough to keep the motor spinning freely.

But I still have the problem of the capacitor starting the motor with too much force.
I have a metal tapered spindle slid onto the splined end of the shaft which is a fairly tight fit.
That is then held in position by a 6mm screw to stop it rotating on the shaft.
The capacitor starts the motor so violently that the 6mm screw can't hold the tapered spindle on.

I have managed a work around just now of spinning the buffing wheel by hand as fast as I can, then switching the motor on while the wheel is already spinning.
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And the motor is now spinning in the direction I want and working fine so my original question about what wires to swap seems to be answered too.

 

[Lucien Nunes]

I hear your comment that it is starting in the correct direction, however interchanging two leads that are connected together by the copper link won't change anything, as they are both still connected to the same place electrically speaking. You might have actually altered something else too.

A smaller capacitor can reduce starting torque. If there are two in parallel, maybe disconnect one. However, this will alter voltages and currents and I can't say what will be out of spec - the capacitor voltage might be higher than intended - and can't really recommend random experiments on a forum. More conventional methods of taming a start would be an autotransformer or resistance.

Whatever method, it's important that the motor starts promptly so that the centrifugal switch cuts the start winding out of circuit within the rated operation time of the capacitors (which will fail catastrophically if lefft energised for too long).

 

[waigy]

Are you sure this motor has a centrifugal switch as I can't remember seeing one when I took it apart to change the bearings.
It doesn't have one of those switches that acts like brakes when the motor has been switched off.

 

[westward10]

It looks like a two value capacitor motor or capacitor start and capacitor run motor. Some means of switching, normally centrifugal opens to take the start winding out of circuit.

 

[waigy]

I thought these motors has a start and run capacitor but I've checked the website and it says some have start and run capacitors and some have capacitor start and induction run.
I can live with it the way it is just now by hand spinning the wheel just before starting.

 

[telectrix]

what you need is a variac. you start it on a lower voltage then increase as it spins up. like here, but a 240V one.

View: https://www.youtube.com/watch?v=AEyPBFOhhHw

 

[westward10]

You shouldn't need to spin the wheel.
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what you need is a variac. you start it on a lower voltage then increase as it spins up.

This may prevent the start switch activating quick enough.

 

[waigy]

I'm only spinning the wheel to stop the sudden jolt from over tightening the buffing wheel.
The buffing wheel is on a threaded tapered rod and the wheel tightens onto the thread by itself.
This motor starts far too quickly which forces the buffing wheel very tightly onto the thread.
As I mentioned before, it also starts fast enough for the metal tapered spindle to come loose on the shaft.
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I got this motor for 20 quid so I don't fancy paying a fortune for a variac.
Is there a cheap way of gradually increasing the speed?

 

[telectrix]

You shouldn't need to spin the wheel.
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This may prevent the start switch activating quick enough.

years ago, when working i development of motors, we used this method to obtain the parameters for stalling, overvolts, and pull-out torque. was fun doing the "test to destruction" bits. forgot most of the tech. stuff now.

 

[Lucien Nunes]

Looks to me like two caps in parallel between two left terminals. Bottom left has line, 2 caps and run winding, top left has 2 caps and start winding. A picture of the rating plate would help clarify what kind of animal this is.

Yes, Variac start is good. 500W floodlight start is cheaper. Not keen to get involved with anything that might launch a polishing mop c/w taper spindle at its operator though!

 

[waigy]

The kw output part was badly scratched and I can't make out what it says but It has a 5 and maybe a 1 so I have assumed it is 1.5kw.
I emailed the company that makes them and they couldn't confirm the kw power as it's from the 70s.

I've spent a lot of time searching online and can't find an identical motor anywhere to double check the power output.
It's bloody powerful for polishing though, I can almost lift the motor off the ground pushing a part against the buffing wheel and it isn't even thinking about slowing the motor.
I reckon 1.5kw seems about right or 2hp.
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[Lucien Nunes]

Yes, the line current is correct for 2hp. If there's no centrifugal switch it's permanent split capacitor, hence the need for two large cap boxes (continuously rated run caps are bigger than start caps).

 

[waigy]

I'm pretty sure it doesn't have a centrifugal switch.
When I took the motor shaft out to change the bearings the casing inside was pretty much empty apart from the magnet/winding part.
And the shaft was just very basic like this with a bearing on each end.

 

[Lucien Nunes]

PSC it is then

 

[waigy]

Does PSC make it any easier or harder to make it gradually speed up or to have a speed controller?

 

[waigy]

This is one of the capacitors I think they are both the same.