A customer has an existing application using 2 off, 4 pole contactor/relays of Brook Crompton make, model HR1310 and 3 capacitors of 200, 60 and 20 microfarads. The 3 phase motor is an English Electric, 4 pole with nameplate details - 2 HP, 400/440, star connected, (but the motor may be delta connected for 240 volts). This motor is on a lathe and the controls are inside a metalclad box with a start and a stop pushbutton. The supply is at 240V single phase from a 13A plug.

The fact that the relays are of Brook Crompton make, suggests that this was a proprietary method of this application.

I realise that this setup using discrete relays for the control is out of date, but has anyone got a wiring diagram for this unit?. One of the relays is immediately energised when power is switched on, and I think the other relay should briefly switch on the start capacitor (the 200 microfard, I think), to start the motor from the start pushbutton, i.e. this relay is not retained.

The owner has replaced the relay for running, since it "was always energised" and the motor could only be stopped by switching off at the 13A plug. It appears that he has miswired the relay, since that relay energises but nothing else works!.

An inverter is an option, I haven't pursued this route but they are expensive, as is a single phase motor.

Regards

Brooks Crompton Park (does that date us Jaymack) had exactly that set up available as an "off the shelf" arrangement.

You will have a running cap permanently connected (perhaps about 50 muF per kW with a starting cap about 4 times that size just to get it all going round - ie the two contactors are start and run, the run being permanently energised via the stop and start buttons - pressing start should close an hold the contactor with the lower value caps and also momentarily close the start cap - it usually stays closed as long as the start button is depressed and requires a degree of operator knowledge to gauge when the motor is running up to speed

I think it was originally sold to be able to start what was effectively an idler motor - from there you generated 3 phase to run the other motors. It could of course run a single motor (but usually you needed a bigger motor for a given driven load - negative sequence currents etc)

I don't have a wiring diagram to hand (there used to be an example in the old brooks crompton motor handbook - the little pocket book).

Perhaps a google for "idler motor" or similar.

failing that, bin the bloody thing thing and get a small single to 3 phase invertor unit - particularly if this is "trade" rather than "hobby"

Regards

OMS

-------------------------
Failure is always an option

That little book has saved my proverbial on a number of occasions! i'll have a look it to see if I can find what you are looking for. sounds like a capacitive phase shifter for single to 3 phase conversion. It works, but really a decent inverter set is so much better. Pretty cheap now too.

I appreciate that a modern inverter is more efficient .... and more expensive. The customer is a retired engineer, who passes the time in the garage cum workshop, to get away from 'er inside.

Regards

An update to say that the customer has seen sense and ordered a 230V motor! Positive though, I have enough knowledge for the next one.

Regards