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Inverter for 3 phase supply

Inverter recomendations.

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Me.14/01/2022 13:25:04
138 forum posts
30 photos

Hi All

I can only apologies for this thread as I am assuming that this topic has been covered before - but my ability to do a search on this forum never works out for me.

I have a Harrison 140 with a 3 motor and a proper 3 phase supply. I thinking of changing the original motor to a 2 speed type for the advantage of the higher turning speeds.

I want to then control the motor with a Inverter (VFD) what should I be looking for ?

Anyone recommend a supplier or a type/make to look out for.

Clive Foster14/01/2022 13:51:00
3103 forum posts
107 photos


Simple answer.

Just buy a VFD from a reputable supplier like Inverter Drive Supermarket and try. You may decide your motor works well enough. Even if you end up changing the pulleys to improve low speed grunt it will still go fast enough.

Boring details.

No need for a two speed motor. A 6 pole single speed motor will work fine with a VFD and give essentially the same power characteristics. Vector drive would be best. You may decide to up the power a little over standard but I can't see the gain being worthwhile. If you need more torque at low speeds consider adjusting pulley sizes a little. Top speed should still be more than enough.

A standard 1,400 rpm motor needs a smaller motor pulley to help compensate for power reduction at lower speeds when driven by the VFD which will be operating in constant torque mode . In general over ± 1/3 rd of motor nameplate speed you will not notice any motor power issues from the VFD. Once you start dropping below 2/3 rds nameplate you may notice if working hard on large jobs. A 6 pole motor pushes the "you may notice" speed down sufficiently that a home shop worker is virtually certain never to be affected. Lots of folk do just fine with a 1400 rpm motor though.

Theoretically an 8 pole motor will be a closer match but again the extra cost isn't worthwhile.

Two speed motors are expensive and don't play well with vector drive VFD boxes. Although a basic voltage / frequency drive can work well enough its impossible to set the internal parameters to match both speeds. So you end up with a compromise that suits neither. In particular you can't get a maximum current setting that suits both speeds so there is a potential safety hazard.


Edited By Clive Foster on 14/01/2022 13:53:49

SillyOldDuffer14/01/2022 14:05:18
8469 forum posts
1885 photos

Not sure the topic has been covered before: someone with a 3-phase supply wanting a VFD. Most of us second-class citizens only have single phase electricity.

Wait for the experts to comment, but my advice:

  • Don't change the motor. It spends money, requires a somewhat complicated rewiring job, and is unnecessary because the VFD controls motor speed by varying frequency. At 50Hz, the motor runs at normal speed, fewer Hz slow it down and more Hz speed it up.
  • I'd fit a three-phase to 3-phase VFD. Plenty of them about, this WEG is an example. They work the same way as a 1phase to 3phase VFD, adding a pot, direction and stop switches, and using the keypad interface to set parameters to match.

I'm in deep water when it comes changing the lathe's existing wiring, if needed. For example, I suspect the Harrison probably connects and disconnects power from it's motor with a contactor. If the contactor is retained, it must be before the VFD, not after it. VFD outputs must always be connected directly to the motor, because switching a VFD's output is likely to damage the motor and the VFD by generating vicious voltage spikes. The machines wiring is changed so the VFD controls On/Off, Speed and Reverse, not the existing control system.

Let's hope someone knows more about it than I do!


Henry Brown14/01/2022 14:52:38
548 forum posts
117 photos

Another thumbs up for Inverter Supermarket, brilliant technical help from their engineer if you ask and branded product.

There are loads of post on here if you search..

Brian H14/01/2022 15:09:00
2312 forum posts
112 photos

I needed to supply 3 ph from 1 ph mains for an Alexander 3D mill and engraver and found company just of M1 Jtn 28 called ;

They were excellent in supplying a VFD with a remote controller and advising me how to wire it up.

I have no connection with them apart from being a very satisfied customer.


old mart14/01/2022 16:49:38
3717 forum posts
233 photos

Clive Foster covers all the requirements. I also recommend the Inverter Drive Supermarket, for both the motor and the VFD. Have a look at the VFD'S in the same power range as the motor that you choose and find one which includes a printable pdf of their "quick start guide". That guide is worth its weight in gold if you intend to do the wiring yourself. One thing to know that if the existing motor is old, it may not have an exact match for the mounts, and the spindle diameter might not match the motor pulley. You loose power when running slower, half frequency, 25Hz will halve the power, but most motors will run at full power up to double their rated speed. Running between 25 and 100Hz will give you a 4:1 speed range which is pretty good, but you will still benefit from mechanical speed changes.

Me.16/01/2022 14:09:00
138 forum posts
30 photos

Thanks for the replies. I should have said I do have plenty of motors I can use, even the correct 2 speed motor for the Harrison 140 - I was only after the inverter.

I will have a look at the Inverter drive supermarket and the Transwave site.

Robert Atkinson 216/01/2022 14:47:59
1195 forum posts
20 photos

Ideally you would add the 3 PH to 3 PH VFD between the existing control gear but connect the stop /start and reverse control signals to the VFD control instead of the control contactors. You only need one power contactor connected to the main ON/OFF switch and emergency stop. Any reversing contactor(s) can be bypassed (ideal) or left in the power circuit with coil disconnected (not ideal, operating the contactors "cleans" the contacts. Leaving them in one position permanently can lead it failure in the long tern) The emergency stop signal should be connected to the VFD as well s the power contactor. This reduces the stopping time.
This arrangement will allow you to preset the required speed and make full use of the drives speed ramps and torque control. You can put a remote speed control potentiometer in the existing control panel.

Make sure to follow the drive manufacturer's instructions for enclosing the drive and EMC filters. Just screwing it to the wall, connecting it directly before the motor and using the buttons on the front of the drive is not good practice or safe.

Robert G8RPI.

old mart16/01/2022 22:12:29
3717 forum posts
233 photos

If you have a 2 hp motor and want to save money when buying a VFD, then get one that has a standard single phase 230V supply. The inverters which have a three phase input cost quite a lot more. As I said in my earlier post, look for the "IDS quick start guide" , not all of the VFD'S that the Inverter Drive Supermarket sell have it. Having remote controls is better than relying on the ones on the VFD, which are only intended for setting up a motor from scratch.

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