3 phase

[les]

I would like an opinion from those who are more elecrically aware than myself, I have an elecrtic motor fitted to a lathe here that has been connected to a 3 phase supply, I was/am quite prepared to replace with a single phase motor to use on a domestic supply, but i notice that on the motor spec plate the voltage (220-240) amps (2.1) appears, also on the next line voltage (380-440) amps (1.2) Does this mean that if wired appropriately this motor could use a single phase suppy?

[aupickup]

or you can get a convertor box

[les]

Thanks I will have to look into that, if all else fails

[alanworland]

It has been noted by 'proper engineers' that a 3 phase lathe will run smoother than a single phase one, I have a single phase driven lathe which seems ok! but then I am not a 'proper engineer' (probably)

[alex_holden]

I don't suppose there's a wiring diagram on the motor plate?

I think the advantage of running a 3 phase motor from a converter instead of 3 phase mains is they usually allow you to control the speed and direction.

It has been noted by 'proper engineers' that a 3 phase lathe will run smoother than a single phase one

They also tend to be more powerful for a given size and have better low-speed torque I believe.

[les]

I will take the cover off and look for some info, but is it possible that a motor can be single or 3phase simply by using different internal connections?

[alex_holden]

Not that I know of. It is possible to connect a three phase motor to just one phase but it won't self-start and it'll be 1/3 less powerful.

[alanworland]

I don't think so, I thought 3 phase motors were wired for 'star' or 'delta' running? I only have experience (limited!) of single phase motors.

[bmcecosse]

That's it ! The two voltages are quoted - one for star connection - and one for delta connection. It does NOT mean it can run on single phase! I would fit a single phase motor. Can't see why it would be any less smooth ? And a 3 ph motor on single phase will be absolutely hopeless! IF you can manage to kick start it (on a lathe!) it will run pathetically - if at all!

[les]

That's the answer then, seeing the 250v made me jump to conclusions (wrong ones!) Thanks all.
Now what's this converter box Dennis mentioned, is that an option?

[nigelr2000]

Found these but they aint cheap starting at 500 quid for a 2hp supply

http://www.isomatic.co.uk/3phConverter.htm

However machine mart do one too and its a little cheaper.
http://www.machinemart.co.uk/shop/produ ... erters-sol

[alanworland]

Newton Tesslar is one manufacturer of 3 phase speed control units about £140, I have also seen similar on ebay (Drives Direct)

[Declan_Burns]

As Roy explained the two voltages relate to star and delta connection-the star being for the higher voltage. This means eg that a motor labelled 415V/240V can be connected to a three phase 415V system in star connection or a 240V three phase system (very rare) in delta. Do not attempt to connect that motor to single phase 240V. The normal way to run a three phase motor for household applications, where you normally only have a single phase 240V supply is either :
a) connect to a frequency inverter with a single phase input and three phase output or
b) use a starting capacitor-a so called Steinmetz connection. Very much standard procedure.
The capacitor rating is 60 ... 80 microfarad/kW. Google it. This is for single speed applications only and will work on your lathe. You can retrofit an inverter later if you want variable speed.
A lot of tools are out there on the market use standard three phase motors with a built in capacitor-eg pillar drills etc
I have my pillar drill connected like that for the last 25 years-no problem although every household here has a three phase supply. We even run our cookers and showers on three phase.
Regards

[les]

Thanks for all the useful information.

[bmcecosse]

3 phase at 240 volts is available in France. The factory I was involved in there - all the older machines ran on that voltage. Are you sure about that capacitor - on a 3 ph motor ???? Single ph motors have starting caps (or an additional 'starting' winding) - but not heard of 3 ph motor on single ph - with just a cap ??
Edit - Ok - just read about it! It doesn't sound very satisfactory, only works at given speed/load - and additional heating in the motor - but may be worth a 'go' !

[Alec]

Hello Les,

just had a quick look at Drives direct and their 1H.P. 240 single to 240 three phase converter is listed at £125. They also do 240 single to 415 three phase but I think they are more expensive. You may be able to get a single phase motor however for a similar price but will involve some wiring modifications.
Incidentally I have bought from Drives Direct and would recommend them.

Alec

[Declan_Burns]

Les,
That's the TECO frequency inverter. I have used and installed a lot of TECO (Taiwan) equipment in various industrial installations worldwide over the years and never had a problem with it. The price Alec has mentioned looks OK. The ABB ACS series is also excellent and is more or less plug and play. Try ebay and maybe you can pick one up at a reasonable price. I have an ACS on my lathe and it runs like a dream. They may or may not be a bit more expensive. Just keep away from the Siemens inverters as they are more difficult to set up. Danfoss inverters aren't bad either.
Regards

[les]

Again thanks. There's more to this than I first thought, if I decided to change to a single phase motor, should I up the hp rating from the 3phase rating? I have a spare single phase 3/4 hp motor that I keep as a stanby for my spray plant so I suppose I could put this to use if it suits.

[Alec]

Hello Les,

you didn't say what size is fitted but I calculated that it was about 1 h.p.
You can use a less powerful one but just don't load it too much.

Alec

[bmcecosse]

As long as the 3/4 HP motor is similar speed - just use it. Single ph motors above 1 HP tend to blow domestic fuses anyway!