I've got my self an English lathe after patiently looking for around 7~8 months.

The motor is 1/2 hp 3 phase and is wired to a suitable inverter and all works fine. I found the coolant pump in the base and it hadn't seen day light in over 20 years. I've given it a good clean up, its 1/8hp and on a second inverter it works just fine.

Problem.... Both together instantly trip the 30ma Rcd in the house consumer unit. Having done some reading this is pretty common with these inverters due to the capacitors leaking to earth and I am lucky to get away with one. But my reading hasn't offered any real solution some say a type B rcd will do the job some say it wont. My house is on the market so I don't want to be playing with the electric supply. And I doubt I would get it signed of with out a 30ma rcd anyway .

I could sell the pump and inverter and get a single phase pump but A) I always loose out B) the reading of done says its frowned upon mixing voltages on the one machine.

Any ideas or help ?

Cheap 12v (or 240v) pump with a PSU.

ETA 12v or 240v submersable fountain pumps work OK as do 12v caravan type pumps.

[Edited on 24/4/14 by owelly]

Windscreen washer pump from breakers

Are you using the inverter to vary the motor speed or just running it at 50hz? .If running at set speed then I would wire the pump in parallel with the lathe motor, ideally you would need to fit a separate overload for the lower rated pump but I personally would just link it across the motor or terminals.
What inverters are you using ? some are better than others for Leakage. Central heating pumps are quite good for coolant pumps if you want to change the pump.
Paul

Quite often you can't run the coolant pump alongside the main motor when using an inverter - I certainly can't with my Colchester Student lathe. The inverter is matched to the size of the lathe's drive motor, and adding the 1/8th HP coolant pump motor throws out the inverter and can result in mayhem - throwing trips, or burning stuff out.

Apparently the solution is to use another 3-phase motor across the output of the inverter to 'condition' the output so that it's as near as possible the same as a regular 3-phase supply (the inverter isn't, being 1 real phase + 2 artificially created phases that only work when matched to the size of the lathe motor). IIRC, this extra motor is called a pilot motor. This pilot motor doesn't drive anything - it just runs without a load. The combination of an inverter and a pilot motor allows you to run various sizes of 3-phase motor without messing up the phases from the inverter.

I didn't bother, simply because I don't need a coolant pump for the sort of work I do - I just use a hand spray of diluted coolant, or a spray can of cutting oil. I've heard of some people suspending a bottle of coolant over the lathe, running a hose down to the work and using a tap of some sort to regulate the flow.

This isn't going to help you with the rcd problem but the motor should be on a c type breaker not the normal b type.
We had a roller door on a b type and the breaker burnt out. They are so cheap to replace and easy to do (or when you move house)

I would look at the main motor as the pilot motor, I have come across a few motors wired in parallel with no ill effects, it is not ideal but I think most inverters will tolerate being used like this nowadays. Having said that I also have never bothered with a coolant pump as a squirty bottle does the job for most things and if using tipped tools there is not usually any need for coolant on a small lathe.
Paul

quote:

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Originally posted by David Jenkins
Quite often you can't run the coolant pump alongside the main motor when using an inverter - I certainly can't with my Colchester Student lathe. The inverter is matched to the size of the lathe's drive motor, and adding the 1/8th HP coolant pump motor throws out the inverter and can result in mayhem - throwing trips, or burning stuff out.

Apparently the solution is to use another 3-phase motor across the output of the inverter to 'condition' the output so that it's as near as possible the same as a regular 3-phase supply (the inverter isn't, being 1 real phase + 2 artificially created phases that only work when matched to the size of the lathe motor). IIRC, this extra motor is called a pilot motor. This pilot motor doesn't drive anything - it just runs without a load. The combination of an inverter and a pilot motor allows you to run various sizes of 3-phase motor without messing up the phases from the inverter.

I didn't bother, simply because I don't need a coolant pump for the sort of work I do - I just use a hand spray of diluted coolant, or a spray can of cutting oil. I've heard of some people suspending a bottle of coolant over the lathe, running a hose down to the work and using a tap of some sort to regulate the flow.

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