Motors are sized to standards, have a look at the motor and it should have a frame size such as D112 as a metric or a Nema size such as 48. Metric sizes relate to shaft height. Depends how old the machine is but metric motors have been in use in the UK for most of my working life, 50+ years. With the details you can then look at motor manufacturers sheets to choose a motor. Alternatively as some will say get an inverter.

Mine came with a 1ph motor fitted (3kw !!). It had been fitted by someone drilling mounting holes in the column about 5 1/2" down from the top mounting holes and I am guessing they must be tapped. Spacers are used to align with the pad. Otherwise I would have thought an adaptor plate would suffice.

Edited By AStroud on 19/12/2020 15:51:05

Matt, if you can, much the best approach is to fit a VFD and use the existing motor. It is presumably connected in "Star" for 380-420 V but to use a standard low cost inverter it needs to be changed to Delta. If the motor star connection point, where the three windings are connected together at one end, is brought out to the terminals, this is very easy. You should find that the cable enters the motor at a junction box with a screwed on cover – remove this and take some photos of what is inside, showing the terminals and the existing wiring. Also take a photo of the rating plate on the motor which states the voltage, hp, current, speed and that sort of stuff. If we are lucky it will also indicate if a delta connection is possible. When you have photos post them here and we can advise if the conversion is straightforward.

Generally speaking it is easy to go from Star to Delta, its often shown on the back of the terminal box lid. There was a very good article on "here" a few years ago, with lots of pictures, clearly showing how to locate and bring out the extra three leads required. I'm sure a rewind shop would soon do it for you and then fit an inverter via the net for £50 or so, no need to buy an expensive one with all bells and whistles for the home workshop. John

Hello again Matt, I have also replied to you on your other query.

Brian

I have a Mk3 BCA with its original two speed 3 phase motor which unfortunately is specially wound and can only be operated on 440 volts.

Not having 3 phase available and also wanting the machine to have the capability of variable speed I have fitted it with a 440 volt inverter powered from the domestic mains through a 240v to 440V auto-transformer. I have fixed the motor in its low speed configuration and configured the inverter to provide 100Hz at max speed to recover the higher speeds. The original motor is quite capable and has all the necessary guards so unless it is faulty I saw no reason to change it and although the auto-transformer/VFD kit is more complicated it does transform the machine and enable less belt changing. There are VFDs available that produce 440v output from 240v but these are less common and can be much more expensive if fitted with the more capable Power Factor Correction (PFC) front booster stage.

If one doesn't want variable speed or the complication that goes with it then a static converter can provide the 440v 3 phase.

Clive

Hi Guys,

I don't know if you are aware that there are 240 volt single phase input VFD's with 380/440 three phase outputs available.

https://www.aliexpress.com/item/4000976184024.html

HTH.

Matt –

It's simple to fit a new motor to the original mounting, by interposing an adaptor:

I have just traipsed down the garden to remind myself what I did for my BCA.

I bought it from one of our regular second-hand machinery dealers, who said it came from a university who had also made the somewhat functional-looking inverter dangling from the original motor, with a plug that might have been for a 16A or 32A mains – certainly not regular 13A household type.

The dealer had nowhere in his warehouse to plug it in, so I had to buy it on sight. (I think I had been advised that would be so.) The machine itself was in good condition, despite a couple of small drill dimples in the table.

I was not prepared to risk the electrics, so contacted Newton-Tesla.

They were understandably worried about me sticking one of their nice new inverters and controllers on a motor of known type but unknown history, and equally understandably, keen to sell a nice new motor too.

I had no problems fitting the replacement motor, entailing 2 items : –

– An adaptor-plate. I used 20mm thick PVC in near-BCA Grey. You could use aluminium, or as Michael G, says above, plywood! Four clearance holes match the original mounting, and 4 tapped M8 match the smaller new motor's feet. (Use screws with their heads in counter-bores if in plywood, of course.) I turned a broad but shallow central recess from each side to stiffen the plate – possibly needlessly, but PVC is fairly flexible.

– A bush to fit the original pulley on the smaller, new spindle. The important point of course was concentricity. Plus a new key, or the original modified, to pass through the bush wall and fit its new home.

So all quite straightforwards, helped by the machine's open layout.

The tapped / counter-bored holes are necessary to set the plate flush against the pad on the column, which with the plate's thickness help put the pulley in about the right place.

Oops! I made a significant omission in my first reply – the guard over the motor-pulley!

The location of my jig-borer in a tight corner probably makes it less necessary but it ought still be fitted.

It was deigned to fit the original motor but I think it would be fairly easy to make for it an adaptor-plate screwed to the tapped holes provided in the face of the motor.

The voltage has little or no influence on the speed of an induction motor, speed is controlled by frequency and number of poles – hence VFD = Variable Frequency Drive. From John's post above it looks like that VFD does convert 220 V single phase to 380V 3 phase, so is a voltage doubling inverter. So that should do the job fine with the current motor. It looks like the motor must switch from 2 pole to 4 pole for speed control. With the VFD you would simply set to the high speed parallel star connection (which presumably needs no change to the wiring) and do all the speed control through the VFD.

What power is your motor? But a 0.75 kW VFD should be ok I think.