# Erratic behavior from VFD



## mikegt4 (May 3, 2021)

I have a TECO VFD on my Millrite that has exhibited erratic behavior for the 15 years that I have owned this machine. It isn't a big problem, just annoying.

I use the original F-OFF-R drum switch to control the TECO (EV series 201-H1). Sometimes when I switch from OFF to FWD the spindle shutters and slowly moves about 30* in the proper direction then reverses and slowly runs backwards. The Millrite motor (GE 1hp 3ph 220V) doesn't sound very happy when that happens. If I immediately move the switch to OFF then back to FWD the motor will usually operate normally, sometimes it takes 2 or 3 tries. Once I switch the motor off/on several times during the course of milling a part the problem seems to go away.

Being electrically challenged I am clueless but I have tried different "acceleration time" settings in the TECO with no change in the problem. Reverse rotation always works as it is suppose to. I also have a TECO EV series vfd on my Weiler Matador lathe, it works flawlessly. Could it be the contacts in the drum switch? Any suggestions?


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## benmychree (May 3, 2021)

It should be east to check out the contacts on the drum switch, a bit of sanding / filing should take care of any problem there, otherwise, electronics are as much a mystery to me as you.


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## ttabbal (May 3, 2021)

Is the switch wired to the low voltage inputs on the VFD? 

You might try removing that switch and using the panel on the VFD if there is one. 

I had some odd behavior on a Bridgeport motor that was fixed by changing a parameter labeled "Rated motor frequency". The default was 400Hz. Dropping it to 60hz helped significantly. It's not the speed frequency, I think it has something to do with the internal switching frequency. My newer grinder motor didn't need it adjusted.


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## f350ca (May 3, 2021)

I'd check the drum switch. They're meant to carry high voltage and current, probably not making good contact and the low voltage control signal isn't going to arc the contacts closed. Have a similar problem with the on/off push buttons on my radial arm drill.

Greg


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## markba633csi (May 4, 2021)

Agree with Greg, could be contact resistance or contact bounce causing your problems- If the wires to the drum switch are long and unshielded that may also be a factor
I guess the simplest test would be to substitute a small electronic-type toggle switch for the drum switch and try it out for a while, see if the problem goes away.
-Mark


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## Ulma Doctor (May 4, 2021)

by the symptoms described, i would infer that the contacts in the drum switch have degraded or otherwise not engaging properly

a quick fix would be to run the switch opposite and swap 2 of the motor wires to reverse the direction of the motor
it would involve retraining yourself to switch the drum in the opposite direction for forward operation
but you'd only have the problem in the reverse direction now
or you could buy a new drum switch after reconnaissance deemed necessary


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## mikegt4 (May 5, 2021)

Thanks for the suggestions. The mill is 25 miles away so the next time I am there I will look at the drum switch.


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## Ischgl99 (May 6, 2021)

What you are describing is what happens if you use the wrong motor voltage or speed settings in the VFD.  What speed is your motor?  I believe mine has the 900 rpm motor, I think they supplied a 1200 rpm motor as well on some models.  Make sure in the motor data section that the entries there match your motor data plate.   Also, if it is a dual voltage motor, you need to make sure you are wired for the correct voltage at the motor.  The proper ratio of voltage to speed is important to the motor and if it is too far off, will give erratic performance.

Are you using the drum switch on the output of the VFD to the motor, or as control inputs into the VFD to control the direction and the VFD is wired directly to the motor?  If the contacts are dirty as already mentioned, the VFD might not be getting a consistent run signal from the switch, but if you have the drum switch on the output of the VFD and you are trying to control forward and reverse that way, that needs to be changed immediately, the VFD cannot be operated that way and you could have damaged it.


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## sdelivery (May 7, 2021)

I run one of my Bridgeport mills with the VFD output connected to the drum switch. I do not change the drum switch while the VFD is energized.


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## Ischgl99 (May 7, 2021)

If you switch when it is deenergized, then you should be fine.  How are you stopping and starting it?


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## rabler (May 7, 2021)

sdelivery said:


> I run one of my Bridgeport mills with the VFD output connected to the drum switch. I do not change the drum switch while the VFD is energized.


Why?  Does your VFD not provide a reverse function?


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## jwmelvin (May 7, 2021)

rabler said:


> Why? Does your VFD not provide a reverse function?



I do that to select the high/low windings (2- vs 4-poles) and switch the VFD parameters simultaneously.


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## rabler (May 7, 2021)

jwmelvin said:


> I do that to select the high/low windings (2- vs 4-poles) and switch the VFD parameters simultaneously.


Makes sense, didn’t think of two speed motors.


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## Ischgl99 (May 8, 2021)

jwmelvin said:


> I do that to select the high/low windings (2- vs 4-poles) and switch the VFD parameters simultaneously.


Are you using an input in the VFD to tell it whether you are on the 2 or 4 pole side of the switch?  My VFD does not have the option to change the motor parameters in the drive by use of a switch, you need to go into the programming mode and manually make the change.

The problem with using a two speed motor is the HP on the lower speed windings is usually significantly lower than the full speed option, so you are not gaining anything by switching to a lower speed instead of using a speed potentiometer and slowing the motor down with the VFD, and you are actually worse off.  Most two speed motors actually produce less HP than simply dialing the speed down in the VFD since they are meant for air handling or pumping applications that are variable torque instead of constant torque like machine tools.  A typical Baldor motor rated for 1 HP at full speed 2 pole operation only produces 0.25HP on the 4 pole setting, if using a VFD and changing the speed from 100% to 50%, you would have 0.5 HP, or double the two speed motor HP.


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## jwmelvin (May 8, 2021)

Ischgl99 said:


> Are you using an input in the VFD to tell it whether you are on the 2 or 4 pole side of the switch? My VFD does not have the option to change the motor parameters in the drive by use of a switch, you need to go into the programming mode and manually make the change.
> 
> The problem with using a two speed motor is the HP on the lower speed windings is usually significantly lower than the full speed option, so you are not gaining anything by switching to a lower speed instead of using a speed potentiometer and slowing the motor down with the VFD, and you are actually worse off.



My VFD, an Automation Direct GS20, does have the option to select motors with a digital input. I use an extra set of contacts on the H/L drum switch to do so, making the switchover a sub-second affair. 

I believe my motor has the same rated power for low and high speeds:


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## Ischgl99 (May 8, 2021)

Deleted, wrong info


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## mksj (May 8, 2021)

Not much reason for going that route, the motor is a constant Hp, so wiring it for 4P, 1700 RPM, 60Hz, 5.4A and then setting the VFD to go to 120 Hz (3400 RPM) will give the same performance with a lot less complexity.


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## strantor (May 8, 2021)

Ischgl99 said:


> What you are describing is what happens if you use the wrong motor voltage or speed settings in the VFD.


+1

(Assuming you're using low voltage digital input through the drum switch rather than reversing phases on the high voltage VFD output): If it were the contacts in your drum switch, then it would either work or not, or work intermittently. The drifting in reverse and grumbling noise from the motor are symptoms most would associate with a 3ph motor having single phase applied, but it can happen any time the wrong volts:hertz ratio is applied. Verify that the motor nameplate data is entered correctly in the VFD.


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## jwmelvin (May 8, 2021)

mksj said:


> Not much reason for going that route, the motor is a constant Hp, so wiring it for 4P, 1700 RPM, 60Hz, 5.4A and then setting the VFD to go to 120 Hz (3400 RPM) will give the same performance with a lot less complexity.



I thought there was reason not to push an older motor like this past 90 Hz or so? 

Mostly I did it because it was easier than removing the H/L switch and I thought it would be an enjoyable experiment to see the difference myself. 

With 4-poles vs. 2-poles, isn’t there a torque difference for the same current?


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## Ischgl99 (May 8, 2021)

mksj said:


> Not much reason for going that route, the motor is a constant Hp, so wiring it for 4P, 1700 RPM, 60Hz, 5.4A and then setting the VFD to go to 120 Hz (3400 RPM) will give the same performance with a lot less complexity.


Not exactly, he'll have constant torque and variable HP up to 60 hz, then constant HP above 60 hz, but the torque will decrease as the speed increases to maintain the constant HP as well as overcoming the inefficiencies of the worsening V/f ratio.  Running above nameplate speed could be useful for small cutters that need high speeds and low cutting forces, but not very good if you want to hog out material.

This is a good article on it.  http://pumped101.com/hp torque vfd.pdf


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## jwmelvin (May 8, 2021)

Wasn’t Mark’s point that running 4-pole at 120 Hz is the same as running 2-pole at 60 Hz? The torque from 4-pole decreases over 60 Hz but the torque from 2-pole is less to begin with, as there’s no other way the two configurations would have the same power (because power is rpm*torque).


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## rabler (May 8, 2021)

A drum switch that's rated for high voltage and current may be making erratic contact to the VFD also, which would cause the VFD to try to use the wrong parameters.

5.8 amps at 230 volts 3phase is about 2.3KW.    5.4 amps translates to about 2.15KW.   Both are believable figures at 746 watts per HP, if a little inefficient, for roughly 2HP output.  So I'd *guess* you're getting double the torque by running four pole.    

Motor temperature is a pretty good guide to how well it's handling different operating parameters.  I'd be tempted to try it 4 pole at 120Hz and see if it starts running hot.


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## Ischgl99 (May 8, 2021)

jwmelvin said:


> I thought there was reason not to push an older motor like this past 90 Hz or so?
> 
> Mostly I did it because it was easier than removing the H/L switch and I thought it would be an enjoyable experiment to see the difference myself.
> 
> With 4-poles vs. 2-poles, isn’t there a torque difference for the same current?


Usually you don’t want to overspeed a 2 pole motor too much due to vibration problems, but by running it on 4 pole, doubling the speed brings it back up to what it can mechanically handle on 2 pole operation.  However, given it’s age, and it has E class winding insulation and not F, the windings might not be able to handle the stress of VFD operation as well as a newer motor with better insulation.


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## rabler (May 8, 2021)

Ischgl99 said:


> Not exactly, he'll have constant torque and variable HP up to 60 hz, then constant HP above 60 hz, but the torque will decrease as the speed increases to maintain the constant HP as well as overcoming the inefficiencies of the worsening V/f ratio.  Running above nameplate speed could be useful for small cutters that need high speeds and low cutting forces, but not very good if you want to hog out material.
> 
> This is a good article on it.  http://pumped101.com/hp torque vfd.pdf


The problem with that article is that it totally ignores efficiency in there.  Motors are optimized for 60Hz, so the farther away from 60Hz you get, the less applicable the graph is.  Inverter motors are somewhat less optimized for 60Hz, and designed to maintain efficiency over a wider frequency range.  This gets into complex issues like how the laminations in electromagnets are designed, etc.

Ultimately what determines the life of a typical motor is heat.  Insulation breaks down faster, and bearings wear faster, when things run hotter.   Inefficiency means running hotter.    You can make up for inefficiency to some extent by improving the cooling.


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## Ischgl99 (May 8, 2021)

jwmelvin said:


> Wasn’t Mark’s point that running 4-pole at 120 Hz is the same as running 2-pole at 60 Hz? The torque from 4-pole decreases over 60 Hz but the torque from 2-pole is less to begin with, as there’s no other way the two configurations would have the same power (because power is rpm*torque).


No, torque on a 2 pole motor is only less than a 4 pole motor if they are the same HP.  Since the current on the nameplate of the motor above is similar for both 2 and 4 pole settings, the torque will be similar for both settings.  The current is actually a bit less on 4 pole, so the HP will actually be a bit less than half the 2 pole rating.

Two speed motors are also two HP motors unless the windings on the 4 pole setting can handle higher current than on 2 pole.  I don’t think I have ever seen a motor that can do that.


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## Ischgl99 (May 8, 2021)

rabler said:


> The problem with that article is that it totally ignores efficiency in there.  Motors are optimized for 60Hz, so the farther away from 60Hz you get, the less applicable the graph is.  Inverter motors are somewhat less optimized for 60Hz, and designed to maintain efficiency over a wider frequency range.  This gets into complex issues like how the laminations in electromagnets are designed, etc.
> 
> Ultimately what determines the life of a typical motor is heat.  Insulation breaks down faster, and bearings wear faster, when things run hotter.   Inefficiency means running hotter.    You can make up for inefficiency to some extent by improving the cooling.


You are completely correct, there are a lot of things that will reduce the actual performance.  The article is a generalization to explain what happens, it’s not meant to say that is what your actual torque will be when running at higher than nameplate speeds.


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## rabler (May 8, 2021)

Ischgl99 said:


> No, torque on a 2 pole motor is only less than a 4 pole motor if they are the same HP.  Since the current on the nameplate of the motor above is similar for both 2 and 4 pole settings, the torque will be similar for both settings.  The current is actually a bit less on 4 pole, so the HP will actually be a bit less than half the 2 pole rating.



To be blunt, that is wrong.   Torque is NOT directly related to current.  By that logic, a typical motor running on 460V would generate half the torque as the same motor running on 230V, since the nameplate current is about 1/2.

Current * voltage / 746 = horsepower.  Or current * voltage * sqrt(3)/746 if its is 3 phase.   Actual horsepower is related to that by efficiency, and if you want to really get complicated, you throw in power factor (phase angle).

Use the HP = RPM * torque/5252 to compute torque.

If you're comparing the same number of poles, same voltage, then yes, torque follows current, ignoring efficiency and power factor.


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## Ischgl99 (May 8, 2021)

rabler said:


> To be blunt, that is wrong.   Torque is NOT directly related to current.  By that logic, a typical motor running on 460V would generate half the torque as the same motor running on 230V, since the nameplate current is about 1/2.
> 
> Current * voltage / 746 = horsepower.  Or current * voltage * sqrt(3)/746 if its is 3 phase.   Actual horsepower is related to that by efficiency, and if you want to really get complicated, you throw in power factor (phase angle).
> 
> ...



We are not comparing different voltages, we are comparing different numbers of poles in the motor.


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## rabler (May 8, 2021)

Ischgl99 said:


> We are not comparing different voltages, we are comparing different numbers of poles in the motor.


I think you need to go back and read the very article you quoted.
HP = T * rpm/5252.

If you get the same torque for the same current, regardless of rpm (poles), why would anyone run anything other than 2 pole motors?  You could gear a 2 pole motor down by a 2:1 pulley and get double the torque of the motor using the same amount of electricity to run a 4 pole motor.


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## jwmelvin (May 8, 2021)

Ischgl99 said:


> No, torque on a 2 pole motor is only less than a 4 pole motor if they are the same HP. Since the current on the nameplate of the motor above is similar for both 2 and 4 pole settings, the torque will be similar for both settings. The current is actually a bit less on 4 pole, so the HP will actually be a bit less than half the 2 pole rating.



Thanks for clarifying. Some time I’ll try 3400 rpm in 2-pole vs. 4-pole config to see what difference I can detect.


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## Ischgl99 (May 8, 2021)

rabler said:


> I think you need to go back and read the very article you quoted.
> HP = T * rpm/5252.
> 
> If you get the same torque for the same current, regardless of rpm (poles), why would anyone run anything other than 2 pole motors?  You could gear a 2 pole motor down by a 2:1 pulley and get double the torque of the motor using the same amount of electricity to run a 4 pole motor.


The article is about overspeeding a motor on a VFD and has nothing to do with two speed motors.

I screwed up, that is a constant HP motor he has.  What I posted earlier only applies to two speed motors that are commonly used in air handling applications.


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## Ischgl99 (May 8, 2021)

jwmelvin said:


> Thanks for clarifying. Some time I’ll try 3400 rpm in 2-pole vs. 4-pole config to see what difference I can detect.


Ignore what I said, you have a constant HP motor so you shouldn’t see a decrease in performance, I confused myself with a different type of two speed motor that are commonly used in air handling applications where the power does decrease at the lower speed setting.


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## jwmelvin (May 8, 2021)

Ischgl99 said:


> Ignore what I said, you have a constant HP motor so you shouldn’t see a decrease in performance, I confused myself with a different type of two speed motor that are commonly used in air handling applications where the power does decrease at the lower speed setting.



So although my motor has similar current ratings in 2- and 4-pole configs, it will make about double torque as a 4-pole? (Each running at 60Hz)

Then, running the 4-pole at 120 Hz will reduce the torque to about the same level as the 2-pole config (meaning either way it will be 2hp at 3400 rpm)? Overdriving the frequency should be smoother torque but less efficient and potentially harmful to the motor?


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## Ischgl99 (May 8, 2021)

jwmelvin said:


> So although my motor has similar current ratings in 2- and 4-pole configs, it will make about double torque as a 4-pole? (Each running at 60Hz)
> 
> Then, running the 4-pole at 120 Hz will reduce the torque to about the same level as the 2-pole config (meaning either way it will be 2hp at 3400 rpm)? Overdriving the frequency should be smoother torque but less efficient and potentially harmful to the motor?


Yes, the torque should be about double in the 4 pole configuration, so overspeeding with the VFD should get you close to the 2 pole speed torque at the same hp.

Overspeeding the motor puts more stress on it, so you could reduce its life the more you run it at the higher speeds.  I chose to not overspeed the 900 rpm motor on my Millrite due to it not being an off the shelf motor and would likely be pricey to replace, but the benefits of a wider variable speed range might be worth that risk to others.


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## rabler (May 8, 2021)

jwmelvin said:


> So although my motor has similar current ratings in 2- and 4-pole configs, it will make about double torque as a 4-pole? (Each running at 60Hz)
> 
> Then, running the 4-pole at 120 Hz will reduce the torque to about the same level as the 2-pole config (meaning either way it will be 2hp at 3400 rpm)? Overdriving the frequency should be smoother torque but less efficient and potentially harmful to the motor?


More or less.  I expect over driving it all the way to 120Hz will reduce torque by a bit more than 1/2 due to inefficiency.  Without having detailed data from a manufacturer on the motors performance at 120Hz as you might get in an expensive inverter-rated motor, your best way to test that is by measuring heat buildup.    You're trading off wear on the motor vs risk to the VFD from what may be an erratic drum switch.


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## mksj (May 8, 2021)

You are technically not over speeding the motor running it on 4 pole and 120 Hz, the motor is running at its rated speed for 2 pole. I also have not seen any information to indicate the effect of 60Hz vs. 120Hz on either insulation or heating of the coils, the biggest factor is the carrier frequency and very long cables. Older motors sometimes people will use a dV/dT filter between the VFD and the motor. Dual voltage motors run on their lower voltage windings, typically do not have an issue with insulation breakdown.

Torques does fall off in a non-linear fashion above the base speed and also Hp may dip a bit in the 100-120Hz range, the difference between that and the 2 pole setting would most likely be small. Also an older motor would not have a wider CT ratio so the torques would probably start dropping off below 20-30 Hz, and also motor cooling becomes an issue below 15 Hz. Newish 2-speed motors that are constant Hp, I have always run on the higher pole setting and run them to 2X their base speed with no issues. The 2 speed motors that are constant torque, I have done several VFD installs and they did not perform well on either pole setting with all the parameters adjusted for either configuration. I ended up replacing them with single speed.


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## strantor (May 8, 2021)

mksj said:


> the biggest factor is the carrier frequency and very long cables.


Carrier frequency and cable length are both critical factors, so agreed on that. 


mksj said:


> You are technically not over speeding the motor running it on 4 pole and 120 Hz, the motor is running at its rated speed for 2 pole.


Also agreed on that, if we add the stipulation of "you aren't _*mechanically*_ overspeeding the motor..."



mksj said:


> I also have not seen any information to indicate the effect of 60Hz vs. 120Hz on either insulation or heating of the coils


For a better understanding of this, you may find documentation of 400Hz motors interesting. 400Hz was/is used on aircraft because you can achieve the same quantity of horsepower from a motor 15% (60Hz/400Hz) the size. 400Hz motors are also used for some industrial applications like concrete saws which are run from a special 400Hz generator, to allow the operator to get into tighter spaces with smaller and more powerful tools that would usually be much larger. If you look into the construction of 400Hz motors you'll find that their iron laminations are of a special alloy and much thinner (think < 1 thou shim stock) than 60Hz motor laminations. The reason is _reluctance_, the magnetic equivalent of electrical resistance. Alternating magnetic fields cannot alternate fast enough through typical 60Hz motor stator to run on 400Hz. If they could, then any old induction motor could be rewound for higher voltage and we could run them at the 400-500Hz and get 7x the nameplate horsepower from them. But it doesn't work, sadly. 

60Hz motor laminations are manufactured to meet the demands of 60Hz service. You can usually get away with running them a little higher, especially inverter duty motors which typically have a separate rating for "base frequency" and "maximum safe speed" and can usually be ran up to 120Hz, maybe a bit beyond, wil no issue. But for a motor made before the idea of VFDs were ever conceived, you can put money on them _not_ performing to expectations at 120Hz. I don't know exactly what that means as I've never tried it, maybe overheating, but I would be surprised to see it work reliably.

One other thing I've never tried, but should be possible per my understanding of things, is doubling the HP of a 240v/480v inverter duty motor by wiring for 240V but powering it with 480V @ 120Hz from a VFD. The HP drop-off as shown in the graphs in this thread so far is contingent upon an [unplotted but present] identical graph of V/Hz, where the V:Hz relationship is linear up to nameplate ratings but thereafter voltage remains constant as frequency continues to increase. But if instead, you continued to increase voltage as you increase Hz, the HP would continue its linear upward trend. The inverter duty motor, due to its "skookum" insulation designed with multi-kV spikes in mind, (I think) should easily withstand a doubling of its applied voltage without issue. I keep meaning to try this but never have... I figure if I keep dropping bread crumbs on the internet, maybe some day someone else will get intrigued and try it for me...


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## rabler (May 8, 2021)

strantor said:


> For a better understanding of this, you may find documentation of 400Hz motors interesting. 400Hz was/is used on aircraft because you can achieve the same quantity of horsepower from a motor 15% (60Hz/400Hz) the size. 400Hz motors are also used for some industrial applications like concrete saws which are run from a special 400Hz generator, to allow the operator to get into tighter spaces with smaller and more powerful tools that would usually be much larger. If you look into the construction of 400Hz motors you'll find that their iron laminations are of a special alloy and much thinner (think < 1 thou shim stock) than 60Hz motor laminations. The reason is _reluctance_, the magnetic equivalent of electrical resistance.



Being picky, the reason is eddy currents, not reluctance. Otherwise you are right. Higher frequencies cause loss unless the motor is designed for that frequency. Same with transformers.


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## Ischgl99 (May 8, 2021)

strantor said:


> One other thing I've never tried, but should be possible per my understanding of things, is doubling the HP of a 240v/480v inverter duty motor by wiring for 240V but powering it with 480V @ 120Hz from a VFD.


I believe I read somewhere that Haas runs their machines that way.

The centrifuge company I worked for ran one of the motors on the machine that way, but used a delta-wye motor wired for 230v and 50 hz (it was a European company) on a 400 volt design feed into the VFD.  Instead of typing it out, this article describes how it works.









						87Hz motor control for Delta Wye VFD operated motors
					

This article gives an overview of the 87hz motor operation for delta/wye motors. The trick allows a motor to be oversped while keeping the torque constant. Effectively increasing the available motor power.




					www.kebamerica.com


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## mksj (May 8, 2021)

I agree with you on all points, the caveat being that one rarely runs a motor on a manual mill at maximum speed. There have been a number of real world evaluations of running a "standard" motor (if I recall from Toshiba) above the base speed and typically the full performance is maintain to around 100 Hz on a 4 pole motor, and in some cases the torque was higher than predicted. Above 100 Hz and the motor characteristics play a more significant factor. The motor is not so old that I would have significant concerns about the insulation.

With regard to your discussion of wiring a dual voltage motor for low voltage (240) and running the motor in to 120Hz/480V, this are a number of postings over in the Practical Machinist where they have done that in industrial motors. It would require 480V 3 phase service, or the means to convert single phase to 3 phase, step it up to 480V and then run it into a VFD. Phase Perfect also offers voltage doubler models, but we are talking some serious $$$.

Learn how to push VFDs above 60 Hz to widen speed range, improve stability, and reduce cost:




__





						StackPath
					





					www.machinedesign.com


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## jwmelvin (May 8, 2021)

This is a super interesting discussion, thank you all for your contributions.


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## strantor (May 8, 2021)

rabler said:


> Being picky, the reason is eddy currents, not reluctance. Otherwise you are right. Higher frequencies cause loss unless the motor is designed for that frequency. Same with transformers.


Ah yes, Thank you. I forgot about eddy currents. Actually both are at play. The following article speaks of permeability, but that's just another (inverse) way of saying reluctance. 

"Explaining Core Losses In AC Electric Motors" https://www.horizontechnology.biz/blog/explaining-core-losses-in-ac-electric-motors?hs_amp=true


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## strantor (May 8, 2021)

Ischgl99 said:


> I believe I read somewhere that Haas runs their machines that way.
> 
> The centrifuge company I worked for ran one of the motors on the machine that way, but used a delta-wye motor wired for 230v and 50 hz (it was a European company) on a 400 volt design feed into the VFD.  Instead of typing it out, this article describes how it works.
> 
> ...


Interesting! Thanks for the link, I am glad to finally learn that it is "a thing." Now I _*really*_ want to try it. I am a little confused about the paragraph at the end where they apply the concept to American motors. They get the 1.74 factor from European mains voltages (400V/230V = 1.74) and then apply 1.74 to 60Hz, resulting in 104Hz. But our mains are 480V/240V, so our factor should be 2.00 not 1.74, unless I'm missing something.


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## mksj (May 9, 2021)

It is 2.0 (120Hz) for US motors with a base speed of 60 Hz. A previous similar discussion and real world application in the link. Just not practical in the hobbyist setting. Evidently cooling is not an issue, which was a concern I had and the motor needs to be capable of sustained higher speeds so I am figuring this is more applicable to inverter/vector motors which maintain full Hp up to their maximum speed of around 5-6K for motors 10Hp and under. In this case I still feel the 4 pole setting is the practical, one rarely is pushing the motor at maximum output for any period of time and one would be using smaller endmills at speed. It is more a matter of keeping it simple in my book, performance wise I do not feel it would be noticeable.





						Encoder requirements for new VFD system
					

Rebuilding P&W twin spindle gun drill and the next step is to replace the ancient spindle drive motors and the change pulley setup with dual VFD's.    Since these are basically spindle drives, I'd like the most precise RPM control.  I know it is only drilling, but we are just talking about...



					www.practicalmachinist.com


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## Ischgl99 (May 9, 2021)

strantor said:


> Interesting! Thanks for the link, I am glad to finally learn that it is "a thing." Now I _*really*_ want to try it. I am a little confused about the paragraph at the end where they apply the concept to American motors. They get the 1.74 factor from European mains voltages (400V/230V = 1.74) and then apply 1.74 to 60Hz, resulting in 104Hz. But our mains are 480V/240V, so our factor should be 2.00 not 1.74, unless I'm missing something.


They are referring to a delta-wye motor, the 1.74 ratio is the same between the wye and delta windings with a 50hz or 60hz motor, so in the US with our 60hz frequency, the motor would be 277/460v instead of 230/400v on 50hz.  With that kind of motor, you would need to program the VFD with a motor base voltage and frequency of 277/60hz and that would give you the maximum frequency of 104hz at 480v.  If you used a 230v motor with a rated 60hz frequency, then you could run that up to 120hz, but you can’t do that with a delta-wye motor without overspeeding it.


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## strantor (May 9, 2021)

Ischgl99 said:


> They are referring to a delta-wye motor, the 1.74 ratio is the same between the wye and delta windings with a 50hz or 60hz motor, so in the US with our 60hz frequency, the motor would be 277/460v instead of 230/400v on 50hz.  With that kind of motor, you would need to program the VFD with a motor base voltage and frequency of 277/60hz and that would give you the maximum frequency of 104hz at 480v.  If you used a 230v motor with a rated 60hz frequency, then you could run that up to 120hz, but you can’t do that with a delta-wye motor without overspeeding it.


Thank you, you revealed a blind spot in my knowledge and prompted me to go illuminate it. The crucial thing I never realized is that America is unique in having two different 3-phase supply voltages (or, "many," if you want to count all the variations on "low" voltage 3-ph). I was aware of the sqrt(3) factor between wye and delta but it never occurred to me to question why I've never needed to permanently wire an American motor for a "low" voltage of 138V, or a "high" voltage of 277V (apart from wye/delta start) despite 12-wire motors availing those options. Meanwhile working on European equipment I do have to choose 230V or 400V. Europe (broad brush, I know) only has one 3-ph supply voltage. So, back to the point, they don't have the option for anything over 1.74x.


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## mikegt4 (May 10, 2021)

*Update*, I took the drum switch apart and cleaned the contacts, no change. I did some milling today, as usual the motor acted up for 2 tries than ran flawlessly. When the motor acts up the VFD makes a bit of a hum and I immediately return the lever to N and wait for the hum to stop (a second or two) before moving the lever back to F, usually the motor will then go forward normally and will continue to operate normally. The motor has never acted up when the drum switch is turned to R.

Drum switch only supplies a signal (F-N-R) to the VFD which is wired directly to the motor. Wired per instructions. Motor is a GE 1hp, 1150 rpm, 220-440 3 phase, it is listed in the Millrite spec sheet at 1200 rpm with spindle speeds of 250, 430, 725, 1160, 2300, 3400 which matches the spindle speed tag on my machine.


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## strantor (May 10, 2021)

mikegt4 said:


> *Update*, I took the drum switch apart and cleaned the contacts, no change. I did some milling today, as usual the motor acted up for 2 tries than ran flawlessly. When the motor acts up the VFD makes a bit of a hum and I immediately return the lever to N and wait for the hum to stop (a second or two) before moving the lever back to F, usually the motor will then go forward normally and will continue to operate normally. The motor has never acted up when the drum switch is turned to R.
> 
> Drum switch only supplies a signal (F-N-R) to the VFD which is wired directly to the motor. Wired per instructions. Motor is a GE 1hp, 1150 rpm, 220-440 3 phase, it is listed in the Millrite spec sheet at 1200 rpm with spindle speeds of 250, 430, 725, 1160, 2300, 3400 which matches the spindle speed tag on my machine.


Ok then you need to compare the 220V (and 50Hz?) To the parameters that are entered in the drive.


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## mksj (May 10, 2021)

Not 50 Hz motor, I would post a picture of your motor name plate information. If it is a 1150 RPM motor then it would be a 6 pole. so maybe you entered the wrong motor data. Other things to check would be the speed pots can get flakey, and I still would not use a used drum switch even with the contacts cleaned. The VFD low voltage inputs are a few mA. Recheck all your connection to the VFD that everything is tight.


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## Ischgl99 (May 10, 2021)

I started using my Millrite by using the drum switch wired to the VFD until I built a control pendant for it, I agree with Mark that it is not a good long term solution for starting and stopping for low current control circuits, it was designed for motor rated current.  Another problem you have by using the drum switch is if you trip the VFD or have a power failure, the mill will start running when it regains power unless you remember to turn the switch to the off position.

You can build a pendant that you can move to where it is needed, or mount a control box with start/stop buttons and a switch for reverse.  You would program your VFD for the three wire control method, works great and is much safer with an interruption of power. 

It still sounds like a programming issue, or possibly a wiring issue with the motor.  Check and make sure you are actually on the 230v connections and not 460v, as well as all the wire connections are tight and the wires are making contact properly.  It’s strange that it works in one direction and not the other, but electrical problems can be weird that way.


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## mikegt4 (May 10, 2021)

here is the motor plate.


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## strantor (May 10, 2021)

mikegt4 said:


> here is the motor plate.


Ok, and the drive parameters are...?


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## mksj (May 11, 2021)

Suggestions below as to motor parameters to check. Make sure the motor is wired for 220V.
00-00 SLV mode = 1

Group 02 parameters should be:
02-01 Motor rated current = 4.0A
02-03 Motor rated speed = 1150
02-04 Motor rated voltage = 220V
02-05 Motor rated power = 0.75 kW
02-06 Motor rated frequency = 60 Hz

set 02-07 to 1 and run auto tuning

I would be conservative with this motor given the age and the insulation rating, so 60 or 70 Hz maximum and a carrier frequency in the 6-8 kHz range. Usable speed range is probably 20-60 Hz.


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## mikegt4 (May 11, 2021)

mksj said:


> Suggestions below as to motor parameters to check. Make sure the motor is wired for 220V.
> 00-00 SLV mode = 1
> 
> Group 02 parameters should be:
> ...



I went through the 54 functions today and recorded them. Almost everything is default values. External command source is correct for using the drum switch. Frequency settings are for 60hz, voltage is set for 220V. Didn't see anything listed as "SLV".

My motor settings show:
motor current = 3.4A, motor voltage = 220V, motor power= 0.8kw, motor frequency= 60hz
The motor speed is a little confusing to me, my setting is 17.0   The manual has this value range notation: "0-120 (* 100 rpm) * 8"
If I did the calculation correctly my motor speed rivals a jet engine, obviously I am not doing it correctly. I don't remember putting these values in but that was 15 years ago.

One interesting thing that I did find is the last function is "Latest 3 fault records", the display shows: "LUC". I didn't find that code listed in the manual. Tomorrow I will look at that function again and see if I can find more info.

I agree on the usable speed range, my experience has been that 20hz is the lowest, I usually work with 40-60hz or change the drive belt position.


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## Ischgl99 (May 11, 2021)

That is a strange way to specify the motor speed.  Every VFD I have commissioned had the actual speed as the value, or the number of poles, not some weird formula.  The way I read what you wrote, your value should be 12*8 =96, ie (1200/100 * 8) = 96. The (*100) notation means the number you use in the formula times 100 is your motor speed.  

Can you post a picture of that section of the manual?  I would like to see if there is something else we are missing.


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## mikegt4 (May 11, 2021)

https://www.tecowestinghouse.com/Manuals/ev_operating_manual.pdf
		


The parameters section starts on page 18, the motor speed formula is F47.


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## Ischgl99 (May 11, 2021)

That makes a lot more sense.  You should change F47 to 12.  That is enough of a difference to cause the problem you are seeing.


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## mksj (May 12, 2021)

Did not realize you were dealing with the Teco FM50 which was discontinued quite a few years ago, and per above F47 is 12. I would seriously look into upgrading your VFD, the newer models have sensorless vector control and auto-tuning, as well as many other adjustment parameters that will do a better job of matching the VF to the motor. You are currently running V/Hz, and takes a bit more tweaking if the motor is stalling out when starting, although I think there may be other issues going on. The capacitors also have a finite lifespan.


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## mikegt4 (May 17, 2021)

For what it's worth, I changed changed F47 to 12, no change the motor's behavior.


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