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Inverter advice

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Mark B22/06/2018 08:08:58
22 forum posts

I have an Emcomat lathe / mill which I'd very much like to use... only problem is that it is 3 phase and my house has 1!

I'm far from an expert in these conversions but I believe I'd like to use a Variable Frequency Drive as not only does this do the inverting, but gives me speed control too. They appear to be very reasonably priced:

Most of these devices appear to have 220V output, but this may not be suitable. Here is a picture of the motor plate for the Lathe:

There are 6 wires coming out of the motor, and an earth cable.

There is also the mill motor which is slightly smaller:

This motor has 3 cables + earth.

Is there any advice on choosing an inverter for these motors and would I need 2 inverters ideally, or could I have some switching arrangement to share one inverter with 2 motors?

Edited By Mark B on 22/06/2018 08:09:51

Edited By Mark B on 22/06/2018 08:12:43

Edited By Mark B on 22/06/2018 08:13:51

Brian H22/06/2018 08:23:28
1134 forum posts
85 photos

440v motors will not run on 240v supply. You will need a unit that supplies 440v 3 phase and these tend to be more expensive. Having said that you would only need one inverter for both motors but I'm not sure about the speed controls.

I've recently bought an inverter from Drives Direct ( and found them to be very helpful with solutions to problems.


Clive Brown 122/06/2018 08:37:29
234 forum posts
7 photos

Take care if thinking of buying on ebay from a non-EU supplier. The price may seem good, but if more than a few pounds, my understanding is that import duty, VAT and a Post Office fee might be added.

Can't really advise on an inverter for you, but I've found Inverter Drive Supermarket to offer good prices and service.

Edited By Clive Brown 1 on 22/06/2018 08:37:59

not done it yet22/06/2018 09:33:36
3028 forum posts
11 photos

Not an expert, but my take on it.

Lathe motor. Likely connected in star configuration at the connection point within the supply connection box fitted to the motor. These may well be altered to delta config. at thees terminals and thus fed with a 220V 3 phase supply.

Mill motor. This would need the star point separating, and these wires extended for connection as delta, so not so easy and may not be practicable, dependent on how the wiring is embedded in the insulation, etc. So it is only 440V at the present time. Connecting this motor to a 220V inverter would reduce its power very considerably.

As for the inverter - I don’t know what its quality might be and expect it is 220V 3 phase output (doesn’t actually say?). Running one or the other motor is a possibility from the one VFD but running both at the same time may not be a sensible option. There would be issues with VFD settings, as each motor would be different (for overload trips, etc), so not really a recommended option - it would be OK to run either one or the other if they were the same type and power.

mgnbuk22/06/2018 09:58:38
506 forum posts
10 photos

A further complication may be that some Emco machines used two speed motors - the first picture suggests that this is a two speed machine, as it show 1390 & 2700 rpm at different power ratings on a constant 440V supply. What exact model of Emco machine is this to check the specifications ?

The mill motor is single speed, but Star wound only & I know from (expensive) experience from an FB2 milling machine clone that the star point is not easily accessible to break out the other ends of the windings to rewire as Delta for 220V operation - the wires are very fine, the star point is made very close to the windings and covered by the impregnation, so almost impossible to dig out without breaking a wire off.

I would be looking at a static or rotary converter to supply a fixed 440V supply as the easiest way to get going - I seem to recall reading of people having problems with two speed motors on inverters, but have no direct experience. Or re-motor the lathe with a single speed motor & suitable inverter. The mill motor is a lillte more problematic to change IIRC - I think it is a non-standard frame or shaft size & the nominally "standard" nearest equivalent replacement either has a larger diameter shaft or housing & isn't a "drop-in" fit.

Nigel B

Edited By mgnbuk on 22/06/2018 09:59:28

Circlip22/06/2018 11:12:38
947 forum posts

Might be worth joining the Emco lathe group on Yahoo. Problem with using a VFD on the standard motor is overheating, partially solved by mounting a 120mm Dia. computer PSU fan onto the motor end casing as the built in fan doesn't rotate fast enough at low rotation speeds. One guy replaced std. motor with a servo motor and speed controller. Always a point of discussion on both the 4 speed(blue) and six speed(green) milling heads as to whether the windings for the single or three phase motor are the same but connected with a capacitor for S/P or star connected for T/F.

My Blue 3ph Maximat V10 has run for years with a static phase convertor. V10P main motor (Green) is more robust than original Blue one. Head wired with a capacitor (original) and run from a separate S/P supply.

Regards Ian.

Andrew Johnston22/06/2018 11:14:17
4699 forum posts
532 photos

I'd agree with NigelB, both motors are 440V only and the lathe motor is two speed; looks like pole switching only as the power drops by nearly half as the speed halves.

A 440V motor will run on a 240V output inverter, but the power will be down in proportion at 50Hz.

You can run a two speed motor on an inverter, but it's not a good idea to switch while the outputs are live. You're more than likely to blow the output stages, especially with the cheaper units. To run a two speed motor properly you may need two different switchable setups in the inverter, again not something that is likely to on low end units.

It is possible to buy 415V output inverters, but they're significantly more expensive. Again I'd agreed with NigelB, investigate static or rotary converters.


Ian Parkin22/06/2018 12:21:13
617 forum posts
168 photos

I would get new/used motors that are dual voltage

motors like that are generally less than £20 used and only £80 ish for new

then a small branded inverter for each at £30 or so SH on ebay

If you can post a picture of the motors removed from the machine i'll check my stock or suggest ones on the bay

john fletcher 122/06/2018 13:51:08
508 forum posts

I'll go along with Ian above. Exchange the motor and fit an inverter. Usually it easy to fit a capacitor arrangement to run the coolant pump on 240 volts, if that is to be considered, or leave it on the inverter. The inverter will do all the speed changes you need. Regarding running the main motor on slow speed and cooling, yes an ex computer fan will Ok. All I can say I have 3 pre owned inverts and have checked my motors many times out of interest when the motor is been run slow speed and non of them have overheated, or even got hot. Not saying it doesn't happen. I think people are making reference to industry where a motor failure is very important, loss of production. My friends have fitted Huanyang 2.2KW 10 amp inverters to their lathes, you can adjust the setting for small motors. Some came from Germany and others from Leicester, like many things we think they made in UK or Europe but are made to Europe standards in PRC.All paid within range £90.40 to £115 for the same thing, never heard any of the moaning, all happy swarf makers. Apparently you can buy 240 in and 415 volt out inverters but at a price, I am told its not to difficult to modify others as well, for 415 volts.John

Jon22/06/2018 15:52:51
988 forum posts
46 photos

Problem is lathe motor dual speed and VFD dont like running them.

Secondly even if lathe motor was dual voltage single speed you still need 2 VFD.

Only way out Static convertor, Rotary convertor or Digital Inverter all able to run 1pg input 240v to 3ph 400+v output 3ph.
They are dear and will need to at least double the highest motor motor rating. I ran a 3hp motor dubiously off a 4.5kw invertor, lasted 23 mins £650 down the pan before they doubled in price 8 yrs ago. Had to run a 7.5kw invertor touch wood 8yrs on its still going but can power anything all at the same time all hard wired in.

Mark B24/06/2018 10:18:57
22 forum posts

Thanks very much for all the replies, some good information here.

This is the lathe : **LINK**

So looking closely, it would appear that the motor is dual speed as some of you have seen from the information plate on the motor.

There isn't an easy solution here I can see. I've looked at the mill motor and you would indeed need to dig into the windings to change from star to delta.

On balance it's probably not worth bothering with the mill but as some have suggested I could get a 220V 3 phase with a VFD for the lathe (which is what I'm most interested in). This would be far more economical than going for a static inverter as they are very expensive!

This is probably a silly question, but if a motor is wired as delta, does it become 220V and if star it would be 440?

Thor24/06/2018 10:53:12
1088 forum posts
31 photos
Posted by Mark B on 24/06/2018 10:18:57:

This is probably a silly question, but if a motor is wired as delta, does it become 220V and if star it would be 440?


where I live 3-phase motors in delta configuration are for 240V 3-phase, star configuration for 400V (or 440V). Many 3-phase motors can easily be connected either as delta or star, two speed motor is another story as several has said before. Good luck with your Emco.


Muzzer24/06/2018 14:33:44
2904 forum posts
448 photos
Posted by Mark B on 24/06/2018 10:18:57:

This is probably a silly question, but if a motor is wired as delta, does it become 220V and if star it would be 440?

Essentially, yes. What we call "240V single phase" is just one phase of a "415V three phase supply". The Neutral is the centre point of the 3 phases, which is grounded back at the substation (so Neutral is pretty much at ground potential). Whether you connect a motor as 240V delta or 415V star, each of the 3 phase windings simply sees 240V across its ends. 415V = 240V x (square root of 3).

Nothing at all wrong with "running a 3HP motor off a 4.5kW inverter". Will work exactly the same, except there won't be any overload protection unless you correctly set up the current limits in the config. Either it was wired up incorrectly, the config parameters (most likely for voltage and frequency) were wildly wrong or the motor was crap. Even so, the protection features in a good quality inverter should prevent damage.


mgnbuk24/06/2018 14:46:42
506 forum posts
10 photos

On balance it's probably not worth bothering with the mill but as some have suggested I could get a 220V 3 phase with a VFD for the lathe (which is what I'm most interested in). This would be far more economical than going for a static inverter as they are very expensive!

Depends what you mean by "expensive". I bought one of these for a 415V only surface grinder & also use it on a 3 phase RF30 mill/drill :


Sign up for Machine Mart e-mails & two or three times a year they used to do "Vat free" promotions on Clarke products, which is how I bought mine. No hassle, no faffing with "wrong" motors & the mill will work too - plug & play.

Nigel B

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