Converting a single voltage 415v 3ph motor to 240v 3ph?

[Andy RV]

Good afternoon,

I have just got an old wadkin woodturning lathe which is fitted with a brookes 1hp 3ph 415v motor, from what I've found so far to run this motor using a 3ph 240v inverter / vfd I will need to change the voltage to 240v.

The problem is this motor is not dual voltage, it lists just 415 on the plate and has 4 wires within the terminal box, I have read that you can open up the motor and bring out the additional wires to allow the motor to be wired as 240v delta, is this true and is it worthwhile?
If so do you know of any tutorials on this process as I don't know where to start. :? Or is this a common modification that a motor rewind shop would offer for a reasonable price?

I feel that it might be easier and more cost effective to just fit a single phase motor and switch gear.

Thanks, Andy.

 

[kirkpoore1]

I bet the answer is "maybe". I know it can be done on some 480V motors over here--but not all of them. Another option would be to find an appropriately sized used 3ph transformer ( or three 1ph transformers) and step up the voltage between the motor and the inverter. Or, if you already have the inverter, look for a used 3hp 240V motor of the same frame size and swap the original out.

You will probably have to open up the motor and pull out the windings to be sure.

Kirk

 

[9fingers]

UK motors are easier to work on than most US motors as they only have three windings.
In your motor Andy, one end of each winding will be brought out to a terminal block of some sort and the remaining three ends are brazed together and tucked into the lacing inside the motor.
With extreme care, this point can be teased out and the three ends brought out via separate wires. Any breakage of a wire or damage to the insulation will result in a dead motor.
You MUST use high temperature wire and insulated sleeving and lace the wires back in to keep them well away from the rotor.
Once you have six wires these can be delta connected and the motor will run on 240v ac three phase.

Alternatively, I can supply you with a voltage converting inverter, 240 single phase input, 415v three phase output which will run the unmodified motor with variable speed and controlled acceleration and braking. PM me if you are wanting to take up this option.

Bob

 

[Andy RV]

Thanks for the advice.
I've found a motor rewire / repair service locally so i'll call them tomorrow and see what they say as I don't feel confident in carrying out the procedure without making a mess of the motor.

 

[Andy RV]

Just posting an update to this problem.

I ended up buying a new dual voltage 3 phase motor and a digital inverter to use on my lathe and this is working well, the old motor off the lathe has sat under my bench since it was removed.

I'm currently using a single motor to power my p/t, if I could fit another motor this would give me a more refined system and allow a wider range of feed speeds. With this in mind I dug out the old motor and started to do some research, I also bought Jim Cox's Electric Motors in the Home Workshop book which has a small section on converter single voltage motors.

With this new found knowledge and knowing that if I don't attempt it the motor will probably never be used again I pulled the end bells and rotor out leaving me with the windings and motor body. Using a pair of snips and stanley knife I cut away at the shellac like coating to release the 3 wires that lead up the terminal box, underneath these was the star point where the ends of each winding are connected, this join is broken and 3 additional wires are soldered on and brought out to the terminal box, I used heat shrink sleeving to insulate the joins.
After this the 6 wires are floating around the inside of the motor, these are then secured to the end of the windings using string to secure and then epoxy resin to ensure nothing moves.
The 6 wires are brought out into the terminal box, each pair from each winding can be identified with a multimeter, these wires can then be connected to give a delta wiring configuration by connecting the start of one winding to the end of another giving you 3 pairs of wires which can then be connected to a 3 phase converter.

The process is very simple although care must be taken to ensure you don't damage the motor, it allows almost any 3 phase motor to be run from a 240v supply without having to boost the voltage with a transformer, Jim Cox's book contains plans to build inexpensive phase converters if you do not wish to use a digital unit.

Here is a quick video showing the motor and digital inverter unit in action.

http://www.youtube.com/watch?v=DTSo22NYhao&feature=youtu.be

 

[wallace]

Andy that has just given me a cracken idea. Do you know the problem I have with the feed on my suttcliffe pt going too fast. I'm sure I have a VFD of sorts tucked away from another project. Are you planning on haveing a separate motor for the feed which you can control to give differant quality's of planeing.
Mark

 

[kinsella]

Hi chaps,
Probably a stupid reply, but I've had the opertunity over the years to be offered 3Phase equip and i've stupidly turned it all down as i'm a weekend DIY'r. I looked into converters etc, but only recently i realise that most 3phase equipment (the items i was offered were bandsaw, morticer and a few others i actually can't remember) are sometimes belt driven. Am i missing something or can't the motor be replace with single phase belt motor. And even with a little Heath Robinson approach can't other direct drive kit be powered by a belt using single phase. The bandsaw probably could easily converted, but not sure about the moticer. i did a quick search to see if a topic exists on this topic and i cant see one. A lathe must be a prime candidate to using a single phase to belt power the shaft.
Anyone done anything like this? Why spend loads of money on convertor and other kit which loses power etc in conversion. Just ignore if i'm talking BS.

 

[kinsella]

PS i should have added i have a 3phase Wadkin radial arm saw (3HP) which the motor was rewound professionally by an electrican and i would imagine is now 1HP or less. I have to take my time cutting chunks of Oak. But as a machine which is easily older than me, its my favorite machine in the workshop and is as realiable as the day it was bought.

 

[Andy RV]

Yes mark that's what I plan on doing, I'll fit a taperlock pulley to the machine in place of the flat belt pulleys then mount the motor to the floor and run a vee belt between them.

Kinsella, yes you can and that is what I did with the first couple of 3 phase machines I bought, however this normally will require fabricating mounting plates to fit the motor to the original fixings and buying new pulleys to fit the new motor shaft, this can be easy in some cases or a pita in others.

By using the original motor you don't have to deal with any mounting and pulley problems, for a small motor such as mine at 1hp the cost of a new single phase motor and starter is more than the cost of a digital inverter. As the hp increases the price of the digital converter increases to more than the alternate single phase motor so this is where i'd be looking to build my own rotary phase converter to run it off.
Digital inverters also give much more operating options such as variable speed, braking ram up and down times ect.