Thread: converting 3 phase lathe to single phase

I would favor the convertor as it can give you variable speed.

Use of a converter (VFD) sounds like the best option.

BUT

The motor needs to be compatible with the use of a single phase (240V) to 3 phase (240) VFD.

3Phase motors come it 2 connection modes, STAR (Y) and DELTA (∆).

Chances are the motor is a 3Phase Y connected 415V motor,
If a single phase (240V) to 3 phase (240) VFD. is connected to this it will only ever develop half the power.

To be compatible with a standard single to 3 phase VFD the motor has to be configurable to become a 3Phase Y connected 240V motor.
Sometimes this can be done by swapping around connections inside the motor terminal box.
If it cannot be done this way then motor surgery may be required and this can be done by a motor rewinder for about $100.
Usually the 3phase switches are replaced with simpler switches.

Connection of all the bits and by a sparky can be a gamble
- just finding a spark to do the job is not that easy
- because they are all different, (even if you can find one) the sparky will most likely prefer to install a brand of VFD that he/she is familiar with - I would allow ~$150 for this
- a cheap controller costs about $140 BUT chances are the sparky will want to work with one that costs perhaps $250 or more.

So all up (unless you can do some of these things yourself) it may cost around $500.
This is why, apart from folks who are comfortable and capable of doing it all themselves, it is not that common a thing to do

Replacement of the 3 phase with a used single phase motor is the other alternative is usually cheaper however this is not always as straight forward as it sounds either
Upgrading can vary from easy to a PITA depending on the machine and the motor.

a) Enough space to mount the replacement motor.
Not all motors are the same size and may not physically fit in the space provided.
The easiest arrangement is where the motor is on the outside of the machine so space is not as critical.
If the motor location position has to be moved longer (or shorter) belt(s) may be needed and belt tensioning arrangements allowed for.

b) The motor mounting holes to match
If not, new holes may need to be drilled in the machined motor mounting plate or an adapter plate to be constructed .
Motors that use "feet" are much easier to swap out than motors that are flange mounted although it's possible to make adapters.

c) The old pulley to match the new motor shaft.
1HP motors tend to use 16/19 mm shafts, 2HP motors tend to use 19/24 mm shafts and 3HP tend to use 24/28 mm shafts.
It's not always possible to bore out the holes in pulleys as it may leave too little material especially if new keyways need to be cut (i.e. not easy)
A simpler alternative is to purchase a new pulley but this may not always be possible e.g. pulley is specialised such as on a DP or BS.

d) Switches will also need to be changed.

Originally Posted by BobL

Use of a converter (VFD) sounds like the best option.


Chances are the motor is a 3Phase Y connected 415V motor,
If a single phase (240V) to 3 phase (240) VFD. is connected to this it will only ever develop half the power.

To be compatible with a standard single to 3 phase VFD the motor has to be configurable to become a 3Phase Y connected 240V motor.

Bob, can you please clarify. Is the VFD star or delta? The above is somewhat confusing.

Green lathe motor details.jpgother lathe motor details.jpg
Thanks BobL I have been reading a few others posts on this forum and your comments bobble( up!
I think the variable speed idea is better than using the belt to change speeds so if I could use a VFD instead of changing the the motor then this is the way to go. So many things to understand and learn to begin with!
From the labels on the engines I cannot tell if they are delta or star configured, maybe someone here can?
And I was asked if they were 2 or 4 pole engines which I can also am not find out without some advice?

Cheers

Originally Posted by Yanis

Bob, can you please clarify. Is the VFD star or delta? The above is somewhat confusing.

Sorry - its the motor that comes in Y or ∆ (or configurable between both) configurations

AC power comes in single (SP) or 3 phase(3P) - there's also 2 phase, or multiphase but lets not concern ourselves with these.
AND
All manner of different voltages

VFDs are voltage specific 240V SP -240v 3P, 240v SP - 415V 3P (rare) and 415V 3P - 415V 3P plus many more
The small VFDs that convert single 240V to 3P 240V will drive a motor that is either Y or ∆ connected, and 3P 240V or 3P 415V.
BUT
the 415V motors wiil only run at half power.

Now it just so happens that if a 3phase (415V) motor that is Y connected, is converted to ∆, it becomes a 3 Phase 240V motor that runs at full power.
The conversion is often able to be performed in the motor junction box - this is done so the motor can move easily between e.g. North American (240V 3 phase) and European (415V) markets.

Just to round things off - connecting a 240V 3P to a 425V 3P will let the smoke out.

the motor will be wired star (Y) for 3 phase, many can be changed to delta.

If you take the little cover of the wiring you would see 3 posts down left and 3 down right, there will be brass straps in there joining left posts to right posts.
Check inside that cover and it may display how to move the straps for star and delta (thats where it was written for me in my woodfast motor), then at least you know you have a motor that can be changed.
Thats probably your first step.

Then a VFD can be got to drive the 415 volt motor in delta configuration using 240 volts.

I just did my woodfast 3 phase lathe and put in VFD, all goes well.
I got one of these http://www.ebay.com.au/itm/0-75KW-1H...item41889ef3d9
But I think I got one that was 1.5 HP seeing my motor was only 1 HP, I didn't get one for the same size.

If you can take a picture of the metal ID plate on the motor.
They usually list the setting for both.

My motor was made in czechoslovakia, and actually has Y415/<>240 (for want of a delta symbol)

Originally Posted by wolfbunny

I think the variable speed idea is better than using the belt to change speeds so if I could use a VFD instead of changing the the motor then this is the way to go.

DOn't get your hopes up too high about not needing to change belts.
This is possible if all you do for example is spindle work, but if you range across bowls and platters to pens you will find that a VFD will not provide the speed range required.

Between 0 and 50Hz (full power), unless you purchase a Vector Drive (i.e. expensive) VFD the power between 0 and 50Hz is proportional to the frequency.
For example at 25Hz the power is half the 50Hz power, for 12.5Hz the power is 3/4 etc
Between 50 and about 100 Hz the power is ~constant or full power and above that the power drops off slowly but you cannot go too fast or the bearings/motor will overheat.

If the motor is of reasonable quality and designed to run in the north american market the bearings should at least cope with 3600 rpm but most will cope with ~4500 rpm above that the motor might get too hot.

For a motor that is 1440 rpm at 50Hz 4500 rpm translates to a max frequency of ~150Hz. Even prior to this you might find the motor makes noises that don't sound right.
At the low end you cannot go much lower than about 25Hz for long periods without compromising motor cooling i.e. the fan doesn't run fast enough to cool the motor.
This gives you a speed range of about 6 which is not usually enough for the full range of wood turning and you may need to change belts.

From the labels on the engines I cannot tell if they are delta or star configured, maybe someone here can?

The GMF cadet motor is definitely a Y connection - its says so on the label under the Voltage rating.

I know this motor and have converted about 4 of these to ∆.
The Y point has to be dug out of the motor coils and if you cannot do it yourself (not a job for the faint hearted) it would need to be taken to a motor rewinder.

The second (WEG) motor is almost certainly a Y connected motor.
Now it does show connection diagrams at the bottom of the label that it MAY be a convertible to ∆s.
However, it does not show the ∆ voltage rating on the label so it may be one of those motors that was originally designed as switchable between Y and ∆ but they only made it in Y format.
To check if it is switchable you have to open up the connection box and see if there are 6 contacts and brass strips between pairs of contacts - photos will help

And I was asked if they were 2 or 4 pole engines which I can also am not find out without some advice?

They are both 4 pole motors

you can see on the right picture at the bottom the way the straps need to be for delta and star Y.
if you move the straps to across the posts instead of along the posts then it becomes a delta motor.

Then you can put a vfd on it to drive the motor, you cannot just connect it to 240 it has to go thru the vfd.

The only number I can see missing from the red tag is the current draw, it says 2 Amp for 415.
Mine has 1.9 for 415 and 3.5 for 240 delta config.

Bob will be a better guide on that though.

You will need the numbers off that plate to enter into the VFD, it needs all them to know what the motor is that it is driving.

Originally Posted by BobL

Now it just so happens that if a 3phase (415V) motor that is Y connected, is converted to ∆, it becomes a 3 Phase 240V motor that runs at full power.
The conversion is often able to be performed in the motor junction box - this is done so the motor can move easily between e.g. North American (240V 3 phase) and European (415V) markets.

Thanks - that clears it up. So rewire the motor (if possible) to ∆, connect up your 240v 3P VFD and you are on the home straight.

So when you buy the machine check that it has the plate for the internal connections to make it easier for connecting it to a VFD.

John

Originally Posted by Yanis

Thanks - that clears it up.
So rewire the motor (if possible) to ∆, connect up your 240v 3P VFD and you are on the home straight.

So when you buy the machine check that it has the plate for the internal connections to make it easier for connecting it to a VFD.

John

Just checking the motor plate to see if it Y-∆ convertible is a good guide but no guarantee and I have been caught out several times.

Some motors show the Y and ∆ connections on the name plate and one even had it stamped with the Y and ∆ Voltages and currents on the name plate but when I opened up the terminal box it only had 3 connections and they were Y only motors.

Even if it has 6 connections this is no guarantee that it is ∆ convertible - it could be a two speed motor with both speeds running under Y.

A better way to tell is if it configurable is if there are 6 connections and 3 of them are connected together (usually by metal straps) and 3 are connected to 2 wires each.
Like this - the top 3 connectors are connected together by metal straps.
Conversion from 415V Y to 240V ∆ usually involves removing the straps and using the straps to connect each of the top terminals with its corresponding partner terminal below

Hi Guys
other lathe wiring pic.jpg
heres a photo of the wiring of the WEG motor.
I think it suggests it's set up for delta?

Yeah not getting my hopes up re in not having to changing belts but if I get a little more flexibility in speed then that is a bonus.

Originally Posted by wolfbunny

Hi Guys
other lathe wiring pic.jpg
heres a photo of the wiring of the WEG motor.
I think it suggests it's set up for delta?

The setup in the photo is Y.
To make make it ∆ follow the instructions on the motor label..

Yeah not getting my hopes up re in not having to changing belts but if I get a little more flexibility in speed then that is a bonus.

Yes you will have more flexibility.

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Gee David
I'm not sure why you post that crap (that should remain in the forum rules and therefore absolve you and this forum of any liability!)
I'm very aware of my obligations and responsibilities in life hence why I'm still alive!
I don't plan to do any of this myself but so I can make informed decision one must first understand some the workings of this problem that has come my way and why great forums like this exist!
So if you can't add any worthy insight to my problem, please refrain from your unsolicited comments, thanks