Running a 4 kW motor

[dave1w]

I have a hp compressor equipped with a 4kW/5.5 HP 3 phase motor. Where I used to live (Indonesia) Inhad 3 phase to the garage, but not any longer.

In my house now, I am wanting to run it again, and am thinking of my options with only a single phase supply.

While wiring up my new kitchen, I have had the electricians also put in a 10mm 240 V feed into the built in garage.

I can, I guess for around £300 get a 4kW single phase motor to fit, which should work ok, but as the motor fitted is almost brand new, then could Inget it to work ?

I was wondering what is the latest state with inverters and VFDs at this sort of power, as that could make life easier. Does anyone have any thoughts?

 

[oldbutnotdead]

Best start trawling Ebay, Gumtree etc for preloved devices (either motor or inverter)- new price for inverters is about at your £300 mark.
Re your lump of 10mm- presumably it is a short run so no excessive volt drop? I have a suspicion that in the UK you are meant to notify your electrical supplier if you are operating large appliances on domestic premises- bit more research for you before you start spending. Any particular reason you need such a chunky compressor?

 

[ban-all-sheds]

I have a suspicion that in the UK you are meant to notify your electrical supplier if you are operating large appliances on domestic premises

Absolutely.

And they tend to take no prisoners if neighbours report problems caused by an unauthorised appliance.

 

[big-all]

dont forget start up currents may take nearer to 40amp than 17amp ish running current

 

[JohnW2]

dont forget start up currents may take nearer to 40amp than 17amp ish running current

If that were all, it would be less than a decent shower, so not really a problem. However, I fear that you could be being very optimistic with your 40A!

Kind Regards, John

 

[ericmark]

If the motor is wired star then wiring delta and supplying from an inverter is possible, however with a compressor we have the deloading to consider, the basic idea is a compressor starts with no air supplied to compressor or air allowed to vent, until the motor has reached full speed, at which point the deloading valve allows it to start compressing air.

So yes can be done, but not as simple as just adding an inverter.

 

[dave1w]

The compressor is for diving and I bought it to last me the next 20 odd years. It’s actually quieter then the little plug in sewing machine sounding smaller compressor I have, which itself isn’t too obtrusive, and the garage is away from any neighbours.

There’s probably around 4 metres from the main box through the wall into the garage. From looking into it in the past, a type C 40 amp circuit breaker is what people have used to handle the start up current on these.

I was hanging on the slim hope that technology would allow a way to utilise the existing almost brand new motor, but when I last looked into it, with an inverter there was something about losing power over 29 hz or something, and the minimum speed of the compressor is key for internal lubrication. Current motor speed is 2950 rpm

The unit is rated at 1250 rpm, pumping 200 litres a minute up to 330 bar, from the manufacturer, I could slow it down to a min of 900 rpm, which they tell me would need about 3.5 kW, also, would. It need to run it up to 330 bar, so another thought would be to reduce the pulley size slightly and go for a 3.7 kW single phase, which seems to be easier to get hold of.

 

[dave1w]

The compressor is for diving and I bought it to last me the next 20 odd years. It’s actually quieter then the little plug in sewing machine sounding smaller compressor I have.

There’s probably around 4 metres from the main box through the wall into the garage. From looking into it in the past, a 40 amp circuit breaker should handle it

this is the plate from my mates identical motor ( can’t find the picture that I took of mine).its already delta

 

[Jackrae]

It's a 400 Delta so you'll need a step-up inverter to run it off 240 single phase, to produce the 400 volt 3-phase necessary. The advantage of the inverter is that you get genuine soft start and you can control the run-up time. Most half-decent compressors are designed to blow off their loading system when stopped so it starts up without having to fight the residual tank of compressed air; if yours is so then that's another plus for single phase operation. I know it'd be cheaper but going for a 4kW single phase motor really isn't the way to go. If you can get hold of 400v star motor (readily available) with the facility to rejig the windings to 240v delta then the inverter will be cheaper than a step-up unit. Such motors usually have 6 terminals and 3 inter-connector strips in their terminal heads.

 

[Simon35]

It's a 400 Delta so you'll need a step-up inverter to run it off 240 single phase, to produce the 400 volt 3-phase necessary. The advantage of the inverter is that you get genuine soft start and you can control the run-up time. Most half-decent compressors are designed to blow off their loading system when stopped so it starts up without having to fight the residual tank of compressed air; if yours is so then that's another plus for single phase operation. I know it'd be cheaper but going for a 4kW single phase motor really isn't the way to go. If you can get hold of 400v star motor (readily available) with the facility to rejig the windings to 240v delta then the inverter will be cheaper than a step-up unit. Such motors usually have 6 terminals and 3 inter-connector strips in their terminal heads.

A single phase input, 3 phase 400V output inverter is very hard, if not impossible, to find. You could try a single phase 230V input, 3 phase 230V output inverter, and run it at 230V 50Hz but your motor will be under-fluxed, low on torque. May be OK if the motor is not fully loaded, but all a bit haphazard and expensive just to try.

Change the motor for a 230/400 wound version as suggested by Jackrae above, equivalent from Siemens is £480 but I'm sure you can get something cheaper.

 

[ban-all-sheds]

Where in the world do they have 230V 3-phase supplies, such that there would be motors made for it?

That's a single-phase voltage of 133V - I've never heard of a country with that.

 

[Jackrae]

Where in the world do they have 230V 3-phase supplies, such that there would be motors made for it?

That's a single-phase voltage of 133V - I've never heard of a country with that.

I'd imaging the OP doesn't really care where.
The point is that 230/400 motors are available and 230-3phase can be generated by an inverter

 

[dave1w]

I think the US has something like that, 220 or so as 3 phase, 110 single.

 

[dave1w]

I’ve seen a couple of used 230/400 motors on eBay for about £175, which I would guess would work.

 

[Simon35]

Where in the world do they have 230V 3-phase supplies, such that there would be motors made for it?

That's a single-phase voltage of 133V - I've never heard of a country with that.

Most small industrial motors are usually wound for 230 delta, 400 star.

Japan use 200V 3 phase, either 50 or 60Hz, depending on which part of the country you're in. Must use a lot of copper...

Currently working on a project destined for use in both Japan and USA, and have managed to buy a three phase motor wound such that it will work on all voltages and frequencies, connected in delta in Japan and star in USA.