A couple of questions about a 3 phase motor

[sploo]

I've just acquired (another) Colchester Chipmaster lathe, and it was fitted with this motor:

The Chipmaster originally came with a mechanical CVT gearbox (so the motor runs at a constant speed, and the spindle speed is mechanically varied). In almost all used examples, the CVT is usually long gone; in favour of just a motor with a VFD.

This machine has no CVT, and was clearly being run from a 3 phase source. I'm assuming it must have been a variable frequency input (otherwise the lathe would be of limited use; fixed to only one speed).

My other Chipmaster has an Alpak II induction motor, and the datasheet shows that although it's a 50Hz motor, they can be run over a wide frequency range (anything from around 2.5 to 100Hz). I'm running it with a VFD, between around 10 and 70Hz to cover the lathe's speed range.

Is there any way I can determine if this motor can also be run across such a frequency range?

Also, it can be wired either star or delta (I need it in delta for 230v input). Usually the wiring diagram is on the inside of the lid, but unfortunately the lid is missing. Is it obvious to anyone (or is there a way of checking with a multimeter) whether the motor's currently in star or delta, and if it's in star, how to reconfigure it to delta? The bottom three connectors (yellow/blue/red) are UVW, with the connector on the bottom left being earth.

 

[deema]

Star, the yellow wires tie the three terminals together. Don’t mess with electrics if you do not know what you’re doing. By asking the question, it’s clear you don’t have the competence necessary to be tinkering with electrics.

 

[guineafowl21]

I agree with the above in principle, but I think we can guide you through it.

Take off the yellow link wires and use a multimeter on resistance setting to identify which of the top three terminals are connected to which of the bottom.

If you’re unsure how to do that, then yes, call an electrician.

 

[ChaiLatte]

By asking the question, it’s clear you don’t have the competence necessary to be tinkering with electrics.

The motor is slightly odd in that it has the yellow wires at the top in place of the standard link bars.

I do not think there is a robust logical connection between asking for clarification on an unusual situation and incompetence in a field.

To the OP: as you may know, a standard Chipmaster motor was a 1425 rpm item. The variator gave a 9:1 speed variation (from 1/3 input speed to 3x input speed). Again, you know that the Chipmaster has a two speed headstock, and the speed range of the machine is marketed (i.e. mathematically rounded) to 30-3000 rpm (30-300 in low and 300-3000 in high).

What this means is that to achieve the same speed range using a VFD, the frequency would need to vary from 50/3 = 17 Hz to 50 x 3 = 150 Hz, assuming the pulley ratio between motor and clutch input is kept the same as original.

You cannot easily change the clutch input pulley so you can juggle the motor pulley size and overall frequency range to see what speed range might be possible.

The only way to see if the motor is happy at any frequency is to try it under load. Listen to it, bring the cat in to listen to it (they can detect higher frequencies than us humans), sellotape a temperature probe to it. Adjust your performance expectations based on the results of that experiment.

 

[Dabop]

The motor is slightly odd in that it has the yellow wires at the top in place of the standard link bars.

Not that unusual to see in older motors...
(and yes its in star mode- currently...)

It's 'likely' that the pairs of windings are together ie one winding is the left top/bottom pair, another the middle pair, and the last the right pair- but its always wise to check that with a multimeter- and also megga it- ALWAYS do a insulation resistance check with a megga on old motors, plus a visual of the insulation to see what shape its in- many of those old motors had VIR cables (that possibly could have VIR in it- bit hard to tell)- the enameled wire of the coils is usually ok, but VIR on the connecting cables can be a deathtrap if it has decayed...

Also things like cleaning corrosion off the terminals with a wire minibrush wheel to ensure good connections...

 

[Sideways]

What year is your lathe out of curiousity ?
List of serial numbers by year given here :
https://www.lathes.co.uk/chipmaster/page2.html

You have a 4hp / 3kW motor. Possibly / probably not original.
Taking @ChaiLatte 's point, if you spin it with a vfd between 17 and 150 hz to replicate the range of the original mechanical CVT, you'll be down around the equivalent of 1kW at the low end. Probably not too bad. And you'll have 3kW everywhere above 50Hz, just with decreasing torque which shouldn't be too much of an issue.
You can tweak the drive pulley size to get it running best for you.

With newer motors, I don't have any great issue with driving a 4 pole upto 100Hz. I do this on my own lathe. With an older motor, I would be a little more careful over driving it upto 150Hz because of increased rotor heating at higher frequency. I haven't done it personally so I'd just want to keep an eye on the temperature in case there is an issue.

 

[sploo]

Star, the yellow wires tie the three terminals together. Don’t mess with electrics if you do not know what you’re doing. By asking the question, it’s clear you don’t have the competence necessary to be tinkering with electrics.

I don't think I've ever known what I'm doing; but I have changed probably 5 motors from star to delta and run them off VFDs over the years - but they'd all had the wiring diagram on the inside of the lid. So; following instructions: yes, winging it with electrics: no.

The motor is slightly odd in that it has the yellow wires at the top in place of the standard link bars.

I do not think there is a robust logical connection between asking for clarification on an unusual situation and incompetence in a field.

To the OP: as you may know, a standard Chipmaster motor was a 1425 rpm item. The variator gave a 9:1 speed variation (from 1/3 input speed to 3x input speed). Again, you know that the Chipmaster has a two speed headstock, and the speed range of the machine is marketed (i.e. mathematically rounded) to 30-3000 rpm (30-300 in low and 300-3000 in high).

What this means is that to achieve the same speed range using a VFD, the frequency would need to vary from 50/3 = 17 Hz to 50 x 3 = 150 Hz, assuming the pulley ratio between motor and clutch input is kept the same as original.

You cannot easily change the clutch input pulley so you can juggle the motor pulley size and overall frequency range to see what speed range might be possible.

The only way to see if the motor is happy at any frequency is to try it under load. Listen to it, bring the cat in to listen to it (they can detect higher frequencies than us humans), sellotape a temperature probe to it. Adjust your performance expectations based on the results of that experiment.

Yea - my current Chipmaster is running a similar ~8:1 VFD ratio (just under 10Hz to just over 70Hz, rather than 17Hz to 150Hz); as the Alpak datasheet indicated a max frequency of 100Hz, and with the pulleys I had the 10 to 70Hz range gives me the right spindle speeds.

If I could have used a smaller pulley on the motor I would have done that (trading max rpm for better low rpm torque, as I don't tend to run the lathe over 2000rpm). Unfortunately the motor pulley is already the smallest safe size for the belt.

What year is your lathe out of curiousity ?
List of serial numbers by year given here :
https://www.lathes.co.uk/chipmaster/page2.html

You have a 4hp / 3kW motor. Possibly / probably not original.
Taking @ChaiLatte 's point, if you spin it with a vfd between 17 and 150 hz to replicate the range of the original mechanical CVT, you'll be down around the equivalent of 1kW at the low end. Probably not too bad. And you'll have 3kW everywhere above 50Hz, just with decreasing torque which shouldn't be too much of an issue.
You can tweak the drive pulley size to get it running best for you.

With newer motors, I don't have any great issue with driving a 4 pole upto 100Hz. I do this on my own lathe. With an older motor, I would be a little more careful over driving it upto 150Hz because of increased rotor heating at higher frequency. I haven't done it personally so I'd just want to keep an eye on the temperature in case there is an issue.

The one I've been running for a few years is a 1969 model. This "new" one is 1974. I picked up the new one for a good price; with the intention of using it for spares; but it's arguably in better condition than the old one so I'm looking to get it fully running.

The current one (with the 3hp Alpak II motor) runs well, but if I try to take heavy cuts in the high ratio at anything under 1500rpm (about 36Hz on the VFD) then it does bog down a bit. Ideally I'd like to get hold of a variator, but if I could run this 4hp motor across a similar range then I'm hoping/assuming I'll get about 33% (4/3) more torque vs the 3hp motor in the other lathe.

 

[Sideways]

It is simple fact that as you dial down the speed of the motor with the VFD you are dialling down the power too.
With that alpak 2 motor, 2.2kw, at 36hz it's only making 1600W.
If I had to use a lathe with no gearbox just on a vfd I would buy a fairly powerful 4 pole version that will make much more torque than a 2 pole so it will remain more useful as you slow it down. At the fast end, you can run a 4 pole pole motor at 100Hz and it's only doing the same speed a 2 pole would do at 50Hz so no concerns about bearings and balance.

Yes you are into constant power once you are above 50Hz so as speed goes up, torque goes down, but higher speeds generally equate to smaller diameters so the loss of torque doesn't have so much impact.

Lastly, shifting to a 4 pole motor in place of a 2 pole means changing to a bigger motor pulley to compensate and get the correct spindle speed. Another win as long as you have room for the bigger pulley.

 

[guineafowl21]

I fitted a 3ph Tec motor and VFD to my mill, and added a speed control pot. It’s set to run between 5 and 200 Hz.

Pushing the frequency envelope like this comes down to a sort of duty cycle. There’s a big difference between 5 Hz for a few seconds, to tap a thread and back out, and running at 5 Hz all day long. A good quality VFD will also improve performance at low speeds.

I’ve set the pulley position such that 50 Hz equates to my most common milling speed. No problems in three years of regular use. If I do lots of tapping, I check the motor for heat regularly.

An auxiliary cooling fan for the motor might be an idea if you plan on lots of low-Hz work. You could even activate it with the VFD’s outputs.

 

[sploo]

It is simple fact that as you dial down the speed of the motor with the VFD you are dialling down the power too.
With that alpak 2 motor, 2.2kw, at 36hz it's only making 1600W.
If I had to use a lathe with no gearbox just on a vfd I would buy a fairly powerful 4 pole version that will make much more torque than a 2 pole so it will remain more useful as you slow it down. At the fast end, you can run a 4 pole pole motor at 100Hz and it's only doing the same speed a 2 pole would do at 50Hz so no concerns about bearings and balance.

Yes you are into constant power once you are above 50Hz so as speed goes up, torque goes down, but higher speeds generally equate to smaller diameters so the loss of torque doesn't have so much impact.

Lastly, shifting to a 4 pole motor in place of a 2 pole means changing to a bigger motor pulley to compensate and get the correct spindle speed. Another win as long as you have room for the bigger pulley.

The motor plate on that Brook motor indicates 1430rpm, so that should be a 4 pole motor? I think the Alpak II in the other lathe is too, but I'm not near it to check right now.

 

[Sideways]

3kW, 4 pole from your photos. A good candidate to experiment with.
I'd be tempted to set 20hz as my slowest speed and 150hz as absolute top, and look for a pulley to give you 400rpm at the chuck when the vfd is outputting 50hz / 1400 rpm.
That'll give you 160 through 1200 rpm.
It all depends on what parts you cut most often and how well balanced that motor is.
Maybe 600 rpm at the chuck for 50Hz and top out at 100Hz ?

 

[sploo]

I contacted Brook Crompton today about the old motor and they got back to me very quickly with wiring details for star vs delta. However, they advised that the motor is a late 1950s model, and (partly due to the age) they advised against using it with a VFD (and certainly not going over 60Hz). I think that probably means it's not an option for me.

Looking at the motor in my other Chipmaster (the Alpak II); it turns out it's actually a 2 pole motor (2800/3000rpm):

I guess that makes it slightly less attractive to keep (vs if it were a 4 pole motor).

Digging through some old kit, I remembered that I have a single phase 3hp motor, and it turns out it's 4 pole (i.e. the "correct" 1420 rpm for the Chipmaster):

I suppose the "best" option would be a 3 phase motor with the variator (the CVT gearbox); better motor, plus mechanical speed reduction.

But a single phase motor with the variator is probably preferable to a 3 phase motor with a VFD, as the latter reduces speed by losing power/torque?

 

[Sideways]

I like 3 phase motors with VFD drives better than single phase.
Single phase permanent capacitor motors are much more bulky than a 3 phase like for like, or lack torque.
Single phase with separate start and run capacitors have a centrifugal switch in them which is arguably the biggest single source of unreliability in induction motors.

So I'd opt for a 3 phase (4 pole) motor, add the variator but keep the VFD drive. I'd just reduce the range of variation on the VFD speed control to something like 35Hz to 70 Hz. I'd still have some super easy speed control at the twist of a knob but only over a 2:1 ratio and the mechanical variator to ensure I had max torque whenever I needed it.
It costs nothing to have the variable speed if you are using a VFD so why not.

An interesting trick I found facing 2" stainless bar this year, was to start low and dial up the vfd speed as the facing cut progressed toward the centre on power feed. This is a manual version of the Constant Linear Velocity feature on more advanced lathes. Doing this maintained a much better finish closer to the centre of the bar where the surface speed normally drops off as the radius reduces and the cut quality goes raggy. This was only possible because I had the VFD start stop and knob on a small pendant so that I could hold it and twist as I watched the cut.