3 Phase Inverters


Help Support UKworkshop.co.uk:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Established Member
21 Jan 2021
Reaction score
Regina, Canada
This is a question for anyone here running a 3 phase inverter on a machine.

I am looking at getting a new Planer Thicknesser and a second hand one i am considering is 3 Phase and i was wondering if theres anything i should be taking into consideration or if I am good just to go ahead and get a inverter that is the right size to manage the machine i am looking to get? I already have 20 amp 240volts in my shop.
You need to look at the motor to establish whether it can be configured to to run in delta. On more modern motors the connections are in a terminal box on the outside of the motor casing and there should be 6 connection points plus earth. Older motors wound in star may have the star point ( where the 3 windings are joined inside the motor windings so you will only see 3 connections plus earth. It is possible to open a motor up and extract the star point but I have no experience of this.
Also be aware that some older machines will have 2 motors, 1 for the cutter block and 1 for the thicknesser drive. If this is the case you will need 2 inverters but on the plus side you will have variable speed on your thicknesser
As Hornbeam said you may need two. Also the invrter is not a plug socket that you plug the machine into it has to directly feed the motor, so you have to change/modify the switchgear as well.
I've only been told that there are folks on the metalwork forums site successfully running 400v "fixed star wound" motors with EcoGoo VFD's.
I haven't priced these to see if these are 50% more expensive, as is the case with
some other cheapo units, which I've not seen anyone use to power these kinda motors.

First thing first, should you be considering the machine right now,
making sure the motors are either two or four pole motors
Check RPM to find this,
i.e a two pole motor runs at 2840 to 3000 RPM
whilst a four pole motor runs at half the above.
Anything other than either of these, and the machine might not be suitable.
It's beyond anything I've read, (joe soap here)

ps always good to look inside the terminal cover, even if it says it's only 400v
as there might be schematics under the lid, or something similar to this, where you may see three brass tabs, or just seemingly two if wired for high star voltage,
these would be stacked to join three from one side.

Dual voltage motor tab coniguration.JPG


Make sure to follow myfordman's AKA bob 9 fingers article found on the woodhaven2
titled Induction motors volume 2 which has the necessary information you will need before you start shopping for units, as mistakes can be made,

i.e getting one which can de-rate motors, as some inverters don't have this option.

Everyone need be aware that these things can hold a lethal charge (with no fuse to save you) for quite some time after being unplugged.
No touching these terminals, nor the ones on the VFD until the unit has successfully drained off.

And no pressing start/run before the necessary parameters (motor control settings)
has been understood and set correctly.
Make a metal box for the VFD with no plug inbetween.

Read Bob's excellent write up, which is specifically written for folks in your shoes,
and going through the options of practically getting this running doing various options
It explains what you need to know,
Last edited:
An inverter is a perfectly sound way to power a P/T.
It has the advantage that it will reduce the startup power surge of the machine. This can be very high on a P/T (more than a tablesaw's) because their cutter block is a big heavy piece of metal that has to be accelerated while the motor is also spinning up it's own rotor.

You don't need variable speed on a P/T. The inverter can be wired for a simple start stop and programmed to soft start and ramp upto full, constant, speed. As mentioned. You will need to rewire the controls. The DOL starter and and any electronic brake are incompatible and need to be removed. Replace with start stop buttons or a run-stop switch.

Also check out digital phase converter on ebay. These are like a single to 3 phase VFD but
1. They make 400V 3 phase, not 240V, so no changes to motor required
2. They will drive multiple motors - subject to some constraints - so you could run a 12" PT with separate cutter and feed motors, or 3ph saw and extractor or a 3ph saw with main and scribe blades from one converter....
3. Your electrician just needs to wire it in and connect some red 3 phase outlets.


Used as a modern alternative to a rotary phase converter (for example) you get 400V 50Hz out. No speed control in this mode.

The ebay ones are optimistic in spec. You would be wise to buy a converter that is at least 2 sizes larger than you would hope from reading the headline power rating. If their total rating is (say) 3kW at a time, the largest individual motor that you should connect is (say) 2kW. Read the soecification and then size up.

The advantage is that you can then buy trade / industrial 3 phase machines, plug them in and just get on with it.

The cost saving of buying a good old 3 phase machine compared to a new Chinese single phase might well pay for the converter and then you are all set for the future.
Last edited:
An inverter is a perfectly sound way to power a P/T.
@ Sideways, do you mean a specific inverter like you've shown,
which gives out 400v and has the necessary parameters to de-rate motors...
(I got chastised about mentioning this, even though I'd mentioned it in Italic writing.)

If so, are most motors for the thicknesser feed 4 pole?
I would have thought it be slower again on these, and some wizardry were possibly involved, but perhaps they are geared down?

Hi Tom.
I only have a small workshop so my own PT is a Sedgewick 10"
This has a single motor powering the block and the feed rollers.
I chose a 3 phase model, swapped the controls out, changed it to delta in the motor terminal box and run it from as single VFD giving out 3ph 240V.
Kity and Axminsters in this same 10x8 or 10x7" size that I have used are the same - powering both the block and the feed from the one motor. The kity's are single phase. I don't know if Axy offer a 3 phase option.
It's a personal quirk that I much prefer a 3 phase motor and a VFD to a single phase motor. I had the Sedgwick 10x7 in single phase. Totally renovated it but sold it on to buy a lightly used 3 phase version of the identical machine. My TS, pillar drill, extractor and lathe are all powered by VFDs , their motors configured delta for 240v 3ph.

The 12" and 16" Sedgwicks that flow through ebay regularly have 2 motors. They are switched separately with 2 starters on the front of the machine. The 12" model is I think 2.2kW for the cutter and 1.1kW for the feed motor. The feed motor has a flange and is bolted directly to an oil filled gearbox to get the low speed high torque. For an old Sedgwick MB in 3ph, that would mean 2 VFDs and I can't remember if the stock feed motor is a dual voltage type that can run on 240V 3 phase. It is vital to check all the motor nameplates looking to see that both 415 and 240V (400 & 230V, or 380 and 220V) are stamped there if you want to use VFDs.

It's much easier and more versatile to buy a digital phase converter than it is to retrofit a 3 phase 2 motor Sedgwick with a pair of VFDs. Price comparison is a bit subjective. A DPC costs more than 2 cheap chinese VFDs, but less than a pair of European ones that are IP sealed and can be mounted directly on the machine.

I'd love an MB. Great machine but heavy. You need at least a double garage workshop for one of those so it's beyond me.

I renovated a single phase one with @deema and we wrote it up. Probably one of his threads. All the photos are there. You'll see the two motors in the base, starters on the front the gearbox and chain drive.
You have not mentioned the size of your workshop or any potential future machinery purchases and what your line of woodworking is. If you have the space and are looking at buying mostly big second hand machinery then three phase is what you want as it is cheaper and the heavy cast iron stuff is much better than most of the modern stuff so a great way to equip a workshop. In this case your want to buy a digital phase convertor as sideways has said and your available power will only be limited by your supply and you can use it to power multiple machines, ie unlike the invertor which has to be wired to just one machine and limited to 3Kw. Plus with the convertor you just wire the machine up without having to do any modifications and away you go.
This is a question for anyone here running a 3 phase inverter on a machine.

I am looking at getting a new Planer Thicknesser and a second hand one i am considering is 3 Phase and i was wondering if theres anything i should be taking into consideration or if I am good just to go ahead and get a inverter that is the right size to manage the machine i am looking to get? I already have 20 amp 240volts in my shop.
Why not look at phase converter, static or rotary, options to run more than one machine. I used a transwave 15hp.
just a question......
elsewhere here a chap has a 20amp x 240v supply...wanting a 3phase supply....
might be good to give a rough idea on max 3phase HP that supply could safely handle thru a DPC...
ta....hope that makes sence.....?

Latest posts