Motor Problems

My lathe (a Portass PD5) has a Brook Crompton single phase induction motor. I have two problems with it:

1. It won't start itself. When I turn it on nothing happens (except a faint humming noise). I can start it by hand, in either direction, but it would be nice if it would start itself. Is this likely to be the starter winding burnt out, or open circuit? Or is it likely to be a problem with the centrifugal switch? Or something else? If it's the winding, can I find the break and fix it, or rewind it myself, or get someone to do it for me? Who?

2. After a few mintues running, it shuts off. It's like it has overheated. After a few minutes it will start again. Is there some kind of thermal shutoff with these motors? If so, where is it? I'm not overloading the motor, it's very lightly loaded with the jobs I am doing at present. If it's not that, what could it be?

Thank you - Rowan

Is there a capacitor attached to the side of the motor? They are a common source of not self starting when they have failed. The other suspect is the centrifugal starter switch used on many single phase motors. The motor would have to be dismantled to see the switch. Thermal safety switches/cutouts are also commonly fitted, you may well have two faults at the same time. Spare parts should be easy to get hold of by googling the motor name.

Edited By old mart on 21/05/2023 19:06:57

Edited By old mart on 21/05/2023 19:09:54

1/ Yes. An open circuit in the start circuit. Either switch, winding or wiring.
2/ Yes many have a thermal cut out. But it could be many things.

Probably time to get a new motor. Or consider a 3 phase motor and VFD.

Robert.

Thermal cutout. in the end cap

BTW if the motor is too hot to put your hand on it's scrap.

Edited By Dave Halford on 21/05/2023 20:15:09

Thermal cut-out switches were also fitted into the terminal cover, a red coloured push button resets the switch after a cooling off period.

Emgee

Is the lathe new to you or has this problem just occured ? Hand starting is rather dangerous and may not reach a proper running speed ! Start windings open circuit is possible due to a wiring fault, broken wire may be repairable depending on where it has broken. Re winding is a job for a specialist, it's not a DIY job and costly ! Centrifugal switch faulty, this will require the motor to be dismantled, again it may be repairable. The start capacitor may have failed, this will need testing and or replacing. Yes they were fitted with thermal overload switches, normally in the end casting. If the motor is popping that then a test of the current draw will show if repair is possible and an insulation test will show if there is any point. The full load amps FLA should be on the spec plate. I trust you have competance to deal with mains voltages that could KILL ? If not then enlist the help of someone who knows what their doing ! Good luck Noel.

I have a Brook 1/2 hp single phase motor,my father bought it for his wood lathe combined with a saw bench around 1950/3 I inherited it and it now drives my rapidor hack saw,it has a centrifugal starter and no capacitor,some years back it refused to start,so I striped it and found it was very dirty inside as its a motor casing with vent slots.A good clean and making sure the governor mechanism was clean and freely moving and it then worked ok ever since,a good bit of uk engineering. Last week on the tele i watched a heavy haulage programme, a transformer built somwhere on the continent had to go from the docks up to Lancashire,carried on a Dutch trailer and a Swedish lorry,60 years ago this would have been a uk built transformer,on a a uk built trailer probably hauled by a Watford built Scammel. where did the UK go wrong?

Unlikely its a non-starter because of the over-heat trip - unless the faint humming noise is not coming from the motor.

Could be a trip after running if the switch is dud or there is a an overload (or short circuit within the windings).

It’s likely that the motor is toast.

Another scenario that you may not be aware of is if the motor is not actually achieving its operating speed. Usually it would slow until being once again accelerated by the start winding, only to repeat the cycle.

My recommendation would be as per Robert. I would most certainly take his second suggestion.

(Industrialists were more interested in lining their own pockets, and decided it would be cheaper to import cheaper components and commodities from abroad than invest in modern factories in the UK. Cheaper for individual companies, that is, and bigger profits and salaries for the bosses, but much more expensive for the country in the long run). Apologies for thread drift.