Identifying Winding Pairs

[Baluncore]

In this case DC current and a magnetic compass are not needed, because the connections of these Dahlander motors is internal, so relative polarity of the coils cannot be reversed. When you look at a row or a column in the resistance table, the two lowest resistance wires identify the ends of the two closest coils. So for example, #7 is between #8 and #16. That process continues to fully identify the ring of six coils.

Since the two rings of six coils show no connection, we know that there could be at most, one wire shorted to the motor frame. You should check the insulation is good, from the motor frame to one wire on each of the two windings. Remember to protect the coil insulation, by earthing the motor frame.

The experiment comes when you connect power to the motor. You need a fast breaker in case there is something unexpected. Three filament lamps rated to the line voltage will limit fault currents if there is a problem. Equal lamp dimness will tell you if things are balanced. Then you can apply the full supply, without the lamps.

 

[gah]

If it’s any help, it looks like your two Dahlanders are:

1. 3600-1800 switching 2 to 4-pole
2. 1200-600 switching 6 to 12-pole.

I’ve also seen someone using a DC power supply to inject controlled current into winding ends, watching the behaviour of a compass needle to check the phasing is correct.

OK, that is almost what I just figured out.

But it is 3, 6, 12, and 24 pole. Being used to thinking about single phase motors, which need an even number of poles, but not for 3-phase.

So, the 12 and 24 pole version will use all pairs of consecutive poles.

And the 3 and 6 use groups of 8 poles. I was trying to figure out before why 16 and 8 are not divisible by 3, (or 6), but it works if you do it that way.

The effect is of 24, 12, 6, or 3 poles, and 600, 1200, 1800, and 3600 RPM.

If you follow the previous suggestion of a small DC current, and a compass, you should be able to figure out the pole polarity, with different windings.

 

[Guineafowl]

I’m not sure what you’re driving at there ^. Are you trying to equate the number of stator slots with pole number?

For three phase motors, the number of poles is given per phase, so a 2-pole version will have 6 poles overall. For the synchronous speed, you use the per phase (P) figure in this equation:
$$N_s = \frac {120f} {P}$$
Hence, the field of a 2-pole (per phase) 60 Hz three phase motor will spin at 3600 rpm.

As far as I know, there are no 3-pole induction motors. It has to be an even number.

 

[Guineafowl]

I’ve just re-read the thread. Sorry, Baluncore, I missed that you’d already mentioned the compass trick. I take your point about this not being useful when each of the 6 windings aren’t separate.

Each set of 6 wires comes from a series delta, and each wire is from two winding ends either at a vertex or a mid-point. The vertices are the ones commoned in the double-star mode.

- Can we assume that the lowest-numbered wire is a vertex, and that increasing numbers count round the delta in a direction that’s consistent between the two Dahlanders?

- if we muddle the vertices with mid-points, does it matter?

- For the OP, does the lathe have a reversing switch before the speed selector? This would be a useful feature for threadcutting.

 

[Grubbs1960]

I wired the lathe today and it seems to be running as expected, although I have not yet attempted any actual turning.

 

[Grubbs1960]

I’ve just re-read the thread. Sorry, Baluncore, I missed that you’d already mentioned the compass trick. I take your point about this not being useful when each of the 6 windings aren’t separate.

Each set of 6 wires comes from a series delta, and each wire is from two winding ends either at a vertex or a mid-point. The vertices are the ones commoned in the double-star mode.

- Can we assume that the lowest-numbered wire is a vertex, and that increasing numbers count round the delta in a direction that’s consistent between the two Dahlanders?

- if we muddle the vertices with mid-points, does it matter?

- For the OP, does the lathe have a reversing switch before the speed selector? This would be a useful feature for threadcutting.

No reversing switch. This is a wood lathe, so there is little likelihood of threadcutting.

 

[Guineafowl]

No reversing switch. This is a wood lathe, so there is little likelihood of threadcutting.

The four-speed motor is quite an impressive feature, given the more common pulley arrangement for speed changes. There’s a short article on Oliver’s UK arm (and another on their US metal lathes in the main archives) on this excellent site: https://www.lathes.co.uk/oliveruk/

They’re always looking for pictures and details of machines.

 

[Grubbs1960]

The four-speed motor is quite an impressive feature, given the more common pulley arrangement for speed changes. There’s a short article on Oliver’s UK arm (and another on their US metal lathes in the main archives) on this excellent site: https://www.lathes.co.uk/oliveruk/

They’re always looking for pictures and details of machines.

Thanks for that link. We have a couple of similar websites here in the USA: https://www.owwm.org/ and vintagemachinery.org.

 

[Grubbs1960]

I have done some additional testing of the motor and observed some things that are puzzling/concerning:

1. When wired in the 600 rpm configuration, the VFD limits the speed to ~300 rpm because the motor is drawing max amperage (2.3amps). This is with no load.

2. When wired in the 1800 rpm configuration, it will run at the full 1800 rpm, but is drawing max amperage with no load.

The motor turns freely when rotated by hand.

I should add that since my motor tag doesn’t specify FLA, I have set that parameter on the VFD to 2.3 amps, the default for a 1/2hp motor.

I talked with tech support at the VFD manufacturer. They had me auto tune the drive and then see what winding resistance the drive detected. It was 8.9 ohms, which matches what I measured via ohmmeter. The drive tech support said that the expected resistance should be around 5.6 ohms.

Resistance across the 600 rpm windings measured 12.0 ohms with my ohmmeter, so that probably explains why the rpms were limited to 1/2 the rated speed in that configuration.

What I would like to understand is whether these higher than expected resistance values are because:

a. those are to be expected for a Dahlander winding configuration.
b. back when these motors were built they “overbuilt” or couldn’t achieve the efficiency of modern motors.
c. there is something faulty or incorrect with this motor’s windings.

In the case of a or b, might it be feasible to run the motor using a higher hp rated VFD? When I mentioned that I had a 2 hp VFD, the tech suggested that I connect it to the motor and monitor the amperage to see what kind of draw occurs with the motor under load. It will be quite some time before I can do this as I have some additional refurbishing to do on tool rest and tailstock before I actually put the lathe into service. And it is likely that before I can get that accomplished I will be traveling for a couple of weeks. But I thought I’d throw this out there in case someone had some helpful advice.

 

[Guineafowl]

Re: windings, I’d be checking the insulation resistance, if you have access to a megger. Sanity check - does the VFD output voltage match the motor?

It’s normally one VFD per motor, and you technically have four. The Dahlander on my 1950s spindle moulder (wood shaper) acts as two motors, being 3hp in low speed and 4hp in high. There’s also not supposed to be any switchgear between the VFD and motor. That’s why Dahlanders are tricky to run, and somewhat redundant, with VFDs.

- Pick a medium speed configuration, and control the lathe’s speed with the VFD? You can then tune and fettle the VFD’s overload settings. Try bumping the overload setting 10% and trying some turning. There’s nothing wrong with using a bigger VFD than the motor - I’ve been doing this for years with a 1.5 kW unit running a 500W motor.

- I know of someone who uses a VFD with a small idler motor permanently connected, to make a more versatile phase converter which copes with switchgear. I can ask him for details if you like.

One thing I’ve not seen before is the speed/frequency limiting you describe with the 600 rpm configuration. Is there something about this in the manual?

 

[Grubbs1960]

Re: windings, I’d be checking the insulation resistance, if you have access to a megger. Sanity check - does the VFD output voltage match the motor?

I do not have access to a megger. But I would like to understand this better. My perhaps incorrect/incomplete understanding is that a megger induces a high enough voltage to the windings that if there was a small fault in the winding insulation, it could be detected even though a regular ohmeter would not be able to detect said fault. But if that were the case with my motor, why would that create high resistance in my windings? Seems it would be the opposite.

My motor is rated 230v, and that is what the voltage output parameter on the VFD is set at.

It’s normally one VFD per motor, and you technically have four. The Dahlander on my 1950s spindle moulder (wood shaper) acts as two motors, being 3hp in low speed and 4hp in high. There’s also not supposed to be any switchgear between the VFD and motor. That’s why Dahlanders are tricky to run, and somewhat redundant, with VFDs.

Well, this is one reason that I removed the switchgear and am wiring directly to one set of windings, wired in the low speed configuration. A second reason is my suspicion that the switchgear is faulty somehow.

- Pick a medium speed configuration, and control the lathe’s speed with the VFD? You can then tune and fettle the VFD’s overload settings. Try bumping the overload setting 10% and trying some turning. There’s nothing wrong with using a bigger VFD than the motor - I’ve been doing this for years with a 1.5 kW unit running a 500W motor.

I may indeed end up following this path.

- I know of someone who uses a VFD with a small idler motor permanently connected, to make a more versatile phase converter which copes with switchgear. I can ask him for details if you like.

Yes, I would be interested both in how to do this as well as the theory behind how it works. Perhaps it is as simple as even when the switchgear is operated, causing momentary break of main motor with VFD, the VFD is able to tolerate that because it still has a load from the idler motor?

One thing I’ve not seen before is the speed/frequency limiting you describe with the 600 rpm configuration. Is there something about this in the manual?

This was the explanation given by the VFD tech. It is my speculation that the amperage overload in this configuration at lower than rated rpm is caused by the higher than expected (for a 1/2hp motor) resistance of that winding configuration. I did not discuss this with the VFD tech but developed that hypothesis after our conversation ended.

I am most appreciative of you helping me try to understand this old and unusual motor.

 

[Guineafowl]

You’re right about the megger. I’d normally do a check as a general precaution on any old motor, especially if I’ve been fiddling with the wiring. It could be that the VFD is unhappy with the windings at working voltage, for a reason undetectable with a multimeter.

So the VFD is 1ph 230V in, 3ph 230V out, or AT1 type? Have you set the base Hz and rated speed, etc. in parameters for the 600 rpm mode? You might have to trawl through the parameter settings to find one that’s causing trouble.

Reply about whether the VFD/idler system would work for your motor:

“It should cope fine. Mine mainly powers my CNC lathe, but it used to fire up my old Harrison mill without any issue, and my old RPC setup would struggle to get that wound up in top gear, whereas the current setup had no issue.

My setup is an isolating transformer (had issues with the setup tripping the upstream RCD, which would have been very involved getting it changed), which feeds a boost VFD (aka 240V in/400V out), which then goes through a Sine Wave/sinusoidal Filter. I can't remember what side of the filter I have the 2.2 kW idler motor attached though!.
VFD is just left at default settings, although I do keep meaning to reduce the ramp up time. The pole number doesn't actually matter in terms of operation, as it's only use is to show the RPM on the VFD display. The VFD doesn't really care how many poles the motor has.

From memory, it's a 7.5kw VFD. Only things it's currently used for are the CNC lathe (5.5KW spindle, with 1.2kw servos and a 1kw sub spindle), and an old tyre changer.”

Picking up on the comment about pole number, if you’ve put in the wrong value, the VFD will display the wrong speed.

It would be nice to use this get your lathe going with the native speed-change system. You can buy adaptable, stackable switches to replace the old drum switch.

 

[Grubbs1960]

You’re right about the megger. I’d normally do a check as a general precaution on any old motor, especially if I’ve been fiddling with the wiring. It could be that the VFD is unhappy with the windings at working voltage, for a reason undetectable with a multimeter.

So the VFD is 1ph 230V in, 3ph 230V out, or AT1 type?

Yes to phase and voltage. I am not familiar with AT1 type designation.

Have you set the base Hz and rated speed, etc. in parameters for the 600 rpm mode?

Yes

You might have to trawl through the parameter settings to find one that’s causing trouble

Reply about whether the VFD/idler system would work for your motor:

“It should cope fine. Mine mainly powers my CNC lathe, but it used to fire up my old Harrison mill without any issue, and my old RPC setup would struggle to get that wound up in top gear, whereas the current setup had no issue.

My setup is an isolating transformer (had issues with the setup tripping the upstream RCD, which would have been very involved getting it changed), which feeds a boost VFD (aka 240V in/400V out), which then goes through a Sine Wave/sinusoidal Filter. I can't remember what side of the filter I have the 2.2 kW idler motor attached though!.
VFD is just left at default settings, although I do keep meaning to reduce the ramp up time. The pole number doesn't actually matter in terms of operation, as it's only use is to show the RPM on the VFD display. The VFD doesn't really care how many poles the motor has.

From memory, it's a 7.5kw VFD. Only things it's currently used for are the CNC lathe (5.5KW spindle, with 1.2kw servos and a 1kw sub spindle), and an old tyre changer.”

Thanks for this, although I still don’t have the understanding that I would like.

Picking up on the comment about pole number, if you’ve put in the wrong value, the VFD will display the wrong speed.

I don’t believe my VFD has a parameter that allows me to enter number of poles. Is that normally a user entered parameter?

It would be nice to use this get your lathe going with the native speed-change system. You can buy adaptable, stackable switches to replace the old drum switch.

This would be the ultimate goal.

 

[Baluncore]

1. When wired in the 600 rpm configuration, the VFD limits the speed to ~300 rpm because the motor is drawing max amperage (2.3amps). This is with no load.

Is that current reactive, or in phase wasting real energy as heat?
If it gets hot, one experiment would be to move all the wires around by one, in case that is important in the way windings cancel.
I assume the other set of six windings all remain open circuit, because they are wound on the same set of poles, it makes a transformer with a load on the secondary.

 

[Guineafowl]

Thanks for this, although I still don’t have the understanding that I would like.

You had it right here:

Perhaps it is as simple as even when the switchgear is operated, causing momentary break of main motor with VFD, the VFD is able to tolerate that because it still has a load from the idler motor?

This means a VFD should tolerate running a much smaller motor, so higher-resistance windings, than it’s configured for, making the behaviour of yours seem odd.

The idler also provides some inertia, to help start loaded motors.

I don’t believe my VFD has a parameter that allows me to enter number of poles. Is that normally a user entered parameter?

On the ones I have, yes, for the speed display. What’s the make and model? How are you measuring the 300 rpm?

 

[Grubbs1960]

Is that current reactive, or in phase wasting real energy as heat?
If it gets hot, one experiment would be to move all the wires around by one, in case that is important in the way windings cancel.

I have not noticed any wires getting hot, but I have not left it powered on for more than a minute or so. Would there be some other means of testing to answer this question definitively? I don’t understand what is meant by “reactive current “, but perhaps it has to do with your comment below about the transformer?

I assume the other set of six windings all remain open circuit, because they are wound on the same set of poles, it makes a transformer with a load on the secondary.

The other set of windings are unconnected. I am not sure what the implications of the transformer is, sorry.

 

[Baluncore]

Would there be some other means of testing to answer this question definitively?

Does the metal part, or the copper windings of the field windings get hot when 2.3 amps is flowing with no load?

I don’t understand what is meant by “reactive current “, ...

A voltage sinewave, across a resistor, causes a current sinewave to flow. The same voltage sinewave across a capacitor or inductor, causes a ±cosine wave of current to flow.
Power is the product of voltage and current, so resistors get hot, but the product of a sinewave and a cosine wave is a sinewave with twice the frequency, so energy comes and goes during every part of the cycle. Only the wires to the power source get hot, as energy circulates, the inductor and capacitor are "reactors" with reactive (unreal) power.
https://en.wikipedia.org/wiki/AC_power#Reactive_power_2

The other set of windings are unconnected. I am not sure what the implications of the transformer is, sorry.

The two sets of coils are isolated electrically, but magnetically coupled through shared poles. That means when one set of windings is driven, there can be voltages on the other set, like the secondary of a transformer. If two secondary connections touch, you may have big currents in the motor, a bit like a shorted turn in a faulty motor. You might also receive a shock from wires to the idle coils.

 

[Grubbs1960]

You had it right here:

Grubbs1960 said:
Perhaps it is as simple as even when the switchgear is operated, causing momentary break of main motor with VFD, the VFD is able to tolerate that because it still has a load from the idler motor?

Thanks for clarifying.

This means a VFD should tolerate running a much smaller motor, so higher-resistance windings, than it’s configured for, making the behaviour of yours seem odd.

The idler also provides some inertia, to help start loaded motors.

I don’t believe my VFD has a parameter that allows me to enter number of poles. Is that normally a user entered parameter?

On the ones I have, yes, for the speed display. What’s the make and model? How are you measuring the 300 rpm?

My VFD is an Invertek Optima E3. It will display speed as either Hz or RPM, which is how I determined the 600 rpm windings were maxing out at ~300 rpm. When it reached that speed, the display also flashed decimal points on every LED, which the Invertek technician said indicated max amperage draw.

 

[Grubbs1960]

Does the metal part, or the copper windings of the field windings get hot when 2.3 amps is flowing with no load?

I will try running a little longer while monitoring this. Thanks for the wiki link as well.

 

[Guineafowl]

If you haven’t input the number of poles (12), then the drive shouldn’t be able to display an accurate speed, so I assume the output frequency has been limited to 30 Hz in response to the near overload. I’m at a loss to explain how this would help much. For one thing, half speed would reduce fan cooling. VFDs are normally running, or tripped.

All I can say is, Invertek is a very good make and the manual should be intelligible. As well as investigating the motor, have a look at the quick start guide, and maybe the full parameter list, and check the settings are correct. If all is well in both cases, try increasing the current rating gradually.

It could well be that, as you suggested, the old motor draws more current than expected. This would be a combination of low efficiency and low power factor, which is a measure of reactive current draw. The motor plate might list this last quantity as pf, cosphi or cos$\phi$. Can you post details of the motor plate?

 

[Grubbs1960]

If you haven’t input the number of poles (12), then the drive shouldn’t be able to display an accurate speed, so I assume the output frequency has been limited to 30 Hz in response to the near overload. I’m at a loss to explain how this would help much. For one thing, half speed would reduce fan cooling. VFDs are normally running, or tripped.

I perused my manual again and found no input parameter that would allow me to enter the number of poles. Here’s a link to the manual:(https://admin.invertekdrives.com/as...IN_V1.05 E3 IP20 User Guide V1.04 ENGLISH.pdf)

But there are parameters to enter nameplate frequency and ROM, which I did enter. Perhaps the drive derives the number of poles from these parameters?

All I can say is, Invertek is a very good make and the manual should be intelligible. As well as investigating the motor, have a look at the quick start guide, and maybe the full parameter list, and check the settings are correct. If all is well in both cases, try increasing the current rating gradually.

It could well be that, as you suggested, the old motor draws more current than expected. This would be a combination of low efficiency and low power factor, which is a measure of reactive current draw. The motor plate might list this last quantity as pf, cosphi or cos$\phi$. Can you post details of the motor plate?

See picture of the plate below. None of those are specified.
View attachment 373850

 

[Grubbs1960]

Does the metal part, or the copper windings of the field windings get hot when 2.3 amps is flowing with no load?

After 7 minutes of continuous running at no load, the stator temp rose from 22.9C to 23.6C. At the end of this trial, the copper wire of the windings was 25C. This seems reasonable to me, but I have no other experience doing something like this.

I also measured voltage across each of the three terminals of the non-powered windings and got the following values:
19.8 vac across 6 & 14
23 vac across 6&9
4.4 vac across 14 & 9

I have no idea what to make of that or even if it was a meaningful test, but thought it might be indicative of reactive voltage.

 

[Baluncore]

I have no idea what to make of that or even if it was a meaningful test, but thought it might be indicative of reactive voltage.

That is transformer action. Magnetic coupling between the two independent Dahlander windings.

If 2.3 amps flowed in phase when 230v was applied, then crudely; 2.3*230 = over 500 watts. You would notice 500 watt of heat in the stator windings, so I assume it is a reactive current due to the inductance of the motor windings, which circulates, rather than dissipating energy as heat.