Ahh, yes.  As I see it, the motor, at full load will suck up about a kW (746W/0.72).  But others may consider a 0.75kW inverter good enough.

A common chinese VFD is likely rated at 1.5kW and that would suffice for me – as long as the maximum current, before tripping, can be derated sufficiently for the motor.

Best to ask pertinent questions to the supplier, methinks.

At only a bit over a kW total power  (motor full load (746W) + inefficiency + inverter) 2.5mm^2 conductors are far more than adequate.  Personally, I have loads of 2.5mm^2 cable, so would use it.  1.5mm^2 would be more than adequate.

I’m no electrician, so take advice from proper electrician is my suggestion – if different to mine.

You are unlikely to operate your lathe at full power.  Indeed, the motor supplied with the lathe, may well have been less than 1HP.  Vendors often quote Watts as the supposed power rating (conveniently including the inefficiency of the device but hoping the purchaser doesn’t notice or knows no better).

When I decided on a VFD set up, after a lot of research I just went went with a package from Newton Tesla. On the basis of cry once at the price. Years later after no issues, I couldn’t be happier and would do the same in the future.

Jimb

While a 4 or even 6 pole motor would normall be recommended as a replacement for a AC induction motor your choice of a 2 pole is appropriate to replace a DC or Brushless DC such as the one on your SC2. Even then you may have to fit a larger pulley if you need the higher speed range.

A 0.75 kW VFD is the correct choice for a 0.75 kW motor. Those suppliers who recommend larger seem to be covering for the fact that their products are not well made.
The VFD you link to seems OK but a quick look didn’t locate a manual. Their comments on filters is a little wrong but the conclusion that you should use a VFD with a built in filter is correct.

1.5 mm2 cable is more than adequate.
Note that the VFD MUST be installed in an enclosure with external controls. Not doing so is UNSAFE.

Robert.

On 3 January 2026 at 08:44 Robert Atkinson 2 Said:

While a 4 or even 6 pole motor would normall be recommended as a replacement for a AC induction motor your choice of a 2 pole is appropriate to replace a DC or Brushless DC such as the one on your SC2.

Ah, of course. As the OP pointed out, it’s a DC motor running at a higher RPM.  Fair enough.

On 3 January 2026 at 09:51 Russell Eberhardt Said:

On 3 January 2026 at 08:44 Robert Atkinson 2 Said:

Note that the VFD MUST be installed in an enclosure with external controls. Not doing so is UNSAFE.

Robert.

Can you please explain why it is unsafe? I have VFDs installed on both the Mill and the lathe.  Both mounted on the wall behind and above the machine so well clear of any swarf and with remote controls on the machines.  I can’t see what is unsafe.

Russell

Hi Russell,

I don’t know what make  & model VFDs you have or seen pictures of the installation so can’t say for certain what the status of your setup is. However most VFDs including those indicated by the OP are designed to be installed in an enclosure. They are components not complete equipment. The terminals are not adequately protected against being touched or being exposed to swarf etc. They don’t have adequate strain relief or cable protection. Any conductors i.e. wires, carrying mains voltage must have two layers of insulation or be enclosed such that a tool or key is required to access them. That includes motor wiring. It is almost certain that a VFD will require placing inside a metallic enclosure with additional filtering in order to meet residential EMC regulations. This is true even for VFDs with built in filters as these generally only meet industrial standards at best.

Robert.

I bought and fitted an Inverter to my Super 7 fairly recently from “Inverter Super Market”, following on from what my friends had already done, as the setting up  procedure which is on line, is so clear. I mounted the inverter in a pre used sheet steel alarm box, I cut slots top and bottom of the box, 50 x 150, attached wire mesh over each slot, made 8, 15  x 20mm spacers which I used to fit a ROOF top and bottom, pagoda style. Whilst the inverter has an in built fan, I’ve fitted an ex computer 12 volt fan below the inverter, air in at the bottom out at the top. I made a small 12 volt power supply, it and the inverter is controlled by a 8 pole 240 volt relay, used as No Volt release with Large RED stop push. There is no isolation between main supply and Inverter. I had a some second hand SY cable and used it, motor to Inverter, ex computer multi core screened for control wiring. Reading some early Model Engineering Workshop magazine the third time Nov 2010, Arcuro were advertising Inverters and inline filters, the filter appeared to be very similar to ex washing machine in line filters, as I had several I’ve fitted one. Belts and braces. I hope a little or some of the above will be of use to you Andy.  John

On 3 January 2026 at 11:00 Dave Halford Said:

The only issue will be when you run the motor anywhere near the low frequency end unless you fit additional cooling….

A bigger problem is that at low rpm there is very little power output. One might have trouble pulling the skin off a rice pudding.

An induction motor running below base speed (usually 50Hz in the UK) will have constant torque. But, since power is torque times angular velocity, the output power will decrease in proportion to the decrease in speed. Looking at the numbers provided by the OP for part time use the torque from 50Hz down is constant, as one would expect. For continuous use the torque below 50Hz falls off. I assume this is due to heating in the motor rather than anything to do with the VFD, which should have no problem running full current at any frequency output.

Having variable speed by twiddling one knob is great, but it does come with some disadvantages. I think JasonB has published some notes on how to machine large items, like a flywheel, when the lathe has inadequate power at the low rpm normally used.

Julie

I’m not a luddite but the variable speed which is the main advantage of the VFD does come with some disadvantages. The main one is that when using a mechanical speed reduction be it gears or belts as the speed goes down so the torque goes up, this does NOT happen with a VFD. Cooling the motor at low speeds can be an issue, though being 3 Phase does give an improvement in smoothness of running.

If one needs to do large diameter work it is better to run the motor near it’s rated speed and use the belts or gears to get the speeds one needs rather than just turn down the frequency. Noel.

On 3 January 2026 at 06:47 andy198712 Said:

with ordinary fles…

 

 

BUT like you say your going to struggle hitting anywhere near max on a small lathe I think?!

Depends on how hard you drive it, or there’s a crash.  Do you know why two control boards popped?  Mini-lathes aren’t high speed metal-munchers so avoid long heavy handed sessions.  Another possibility is something nasty in the workshop that’s spiking the electronics – welder maybe?

thanks I do have both those cables but fancy a nice suple flex maybe?! My cables are solid core so might just order a couple meters or source it 🙂

Yes, use flexible cable rather than solid core when vibration is present because solid cores are prone to metal fatigue.

You might consider armoured cable colour coded Brown/Black/Grey to indicate 3-phase.   (Not expensive.)

Please don’t wire the motor Brown/Blue/Green-Yellow with ordinary flex.  You can strip the flex and wire it all Brown, or all Blue, just not the standard single phase colour scheme because that’s liable to confuse an electrician or future owner.  Or yourself!

Make sure all 3 wires are connected firmly at both ends before powering up.   If an end is left floating, the motor winding is liable to behave like a car-ignition coil, creating giant sparks that damage the motor and electronics.  No danger if all is secure, but sloppy wiring is punished!

Dave