Lathe spindle VFD

Hi I would like help setting up a vfd to run the spindle motor for an Okuma lathe.
Motor Nameplate:

I have a few VFD options, but the one I would like to try is a 15hp Emerson Commander SK.
I have not seen a nameplate like this and I'm wondering what I have so I can enter parameters.
Is this a 7.5 KW motor? Motor rated Current??
Is this a 2 speed motor? (1500/6000) UVW coming from the Motor.
Can I assume 60HZ?
Any help appreciated, any red flags before I start?

Thanks, Paul

If I'm reading that name plate correctly its rated for 7.5 kW continuous. Google says 7.5 kW is hair over 10 Hp and 11 kW is a bit over 14, so a 15 HP drive (assuming that you're running on 3 phase and not derating for single phase operation) should work fine.

Rated current looks like 40A at 7.5 and 59 at 11 kW loads. If you only have 3 power leads coming off the motor its unlikely to be a dahlander wound motor (more info on them here: http://www.lmphotonics.com/InductionMotor/dahlander_motor.php). Could be that its an inverter duty motor (especially if this is on a CNC) and its listing upper and lower end of its RPM range. Normal 3 phase motors tend to run at 1800 or 3600 RPM at 60 Hz mains frequency.

Don't really understand why its listing those amp loads at 150 volts though, unless its a nonstandard voltage motor. You could always call an Okuma factory rep like Hartwig for clarification. This site will find your local Okuma rep: CNC Machine Tool Sales, CNC Machines, Sales and Support, CNC Support, Okuma Distributor, Okuma

It's hard to know for sure, because with foreign gear there is always the possibility of a mistake in translation. But with that voltage rating, it appears this is a custom motor designed to be run from a VFD so that it can be run over speed without loss of torque. So yes, you will need a good VFD that allows you to program in a custom V/Hz ratio by setting the maximum V at 150 when at base speed, which we have to assume is 50Hz (based on the 1500RPM lower speed).

Then if you want to be able to use it at the highest speed is is capable of, 6000RPM, you will need to have the Hz go to 200 and at that speed, the drive will need 600V input. So you would need a 600V source and a 600V rated drive capable of 59A to get the peak rated performance out of this motor of 11kW for 30min. If you don't need peak design power from it there are other options to explore, but start there and let us know what you want to do with it and what you have by way of voltage and phase for a power source.

Jraef said:

Then if you want to be able to use it at the highest speed is is capable of, 6000RPM, you will need to have the Hz go to 200 and at that speed, the drive will need 600V input. So you would need a 600V source and a 600V rated drive capable of 59A to get the peak rated performance out of this motor of 11kW for 30min. If you don't need peak design power from it there are other options to explore, but start there and let us know what you want to do with it and what you have by way of voltage and phase for a power source.

Click to expand...

Not saying you're wrong, just curious where you see 600V to run at peak performance. From what I see it says 150V at both kW outputs

Jraef said:

It's hard to know for sure, because with foreign gear there is always the possibility of a mistake in translation. But with that voltage rating, it appears this is a custom motor designed to be run from a VFD so that it can be run over speed without loss of torque. So yes, you will need a good VFD that allows you to program in a custom V/Hz ratio by setting the maximum V at 150 when at base speed, which we have to assume is 50Hz (based on the 1500RPM lower speed).

Then if you want to be able to use it at the highest speed is is capable of, 6000RPM, you will need to have the Hz go to 200 and at that speed, the drive will need 600V input. So you would need a 600V source and a 600V rated drive capable of 59A to get the peak rated performance out of this motor of 11kW for 30min. If you don't need peak design power from it there are other options to explore, but start there and let us know what you want to do with it and what you have by way of voltage and phase for a power source.

Click to expand...

Ok, I think with the emerson drive I can limit the V to 150 at 50 hz. I have 220(nominal)3ph input voltage, this will limit my top speed?
This motor is going to be used to power the lathe that it came on, original drive is fried and I don't want to replace. Lathe has a geared? headstock with high and low range.

Alternative solution would be to replace motor with conventional 15hp, but I would like to try original as I have nothing to lose but time.

Thanks

I follow Jraef's logic as apples to the tor data plate.

If I were to try to set this up using a 240V VFD for testing. (Sized to put out the AMPS!) I would set up the VFD with a custom V/h profile with the min frequency of 40 hz (1200 rpm) at 120V. And set the VFD max output frequency to 80hz (2400 rpm) at 240V.

Then I would run the combination between 50 and 80 hz watching the load amps on the VFD display.

If all went well, I might look for a 440 V VFD on ebay and a 240X480 transformer. just because they are quite common. Really I would look for the full 600 V gear if the testing proved out.

So yes, at 220 volts your speed range will be limited.

I think I do have a 15 hp 440v vfd would this be more appropriate? I was hoping to set this up without a transformer, as other motors in the machine are 208v

I just don't see how you can get the speed out of the motor without increasing the frequency, and if the frequency goes up, the applied voltage should follow or you will have little power. If you can get buy with "little power" at those speed, any voltage will work.
At some frequency, and voltage off the low side of the V/h curve, the motor won't have enough power to run it's self.
Then you end up with AC universal motor performance. self limiting. ;-)

That's a lot of machine to have a whimpy motor on. but how often do you plan to go fast ?

At 6000 rpm, the torque is less for the same power.....if the voltage went up with the rpm according to the V/Hz, so would the power .

If it can produce x kW at 150V and lower speed, then at 4x speed, and 1/4 current, it is still the same power. The TORQUE is lower, and current produced torque, so it does not NEED the current.

It's looking at "torque as equal to power" that makes the confusion. It ain't. power is proportional to torque x rpm. That's why gearboxes and belt drives work. Reduce speed to half with a lossless bet system, and torque doubles.

VFDs tend to be constant torque at slow speeds, because they are current limited, and constant POWER at high speeds where they are VOLTAGE limited. This assumes the actual current and voltage still adds up to the power, since you have to get the power into the motor, plus losses. Since the motor copper loss goes down, you do a little better and do not need as much voltage as it might seem, total motor power input can be a bit less.

Motor force causing rotation is proportional to the current in the windings, x length of wire x magnetic field strength. The diameter at which it is applied then gives the torque. So lower torque is lower current, but if matched by a speed increase, it gives constant POWER.

The 40A is not implying it is 40A at any speed, necessarily, it presumably means that is the most it needs for 7.5 kW, at 1500 rpm.

Now, the 150VAC and 40A is something over 10 kW. Easily enough for 7.5 kW shaft power. Actually way TOO MUCH, since it seems unlikely the motor should be happy with continuous losses of 3kW. To get the same power at 6000 rpm, the torque needs to be only 1/4 that at 1500 rpm, so the current needs only to be about 10A. But the POWER still needs to be about the same input, reduced for there being 1/16 the resistive losses.

The kicker here is that we DO NOT KNOW the back EMF curve of the motor. We are ASSUMING it takes 150V to run the motor at 1500 rpm and full power, but likely it does NOT. A more reasonable loss for the motor is several hundred watts, perhaps 800 watts. That's about 90% efficiency, maybe a little high, but we are just guessing here.

In that case, the 40A must occur at a lower voltage, more like 120V. That's 8300W input. Most losses are likely to be resistive, so the efficiency may be even better, with somewhat lower losses, because the 59A will double the losses, and it is safe at that current for 30 min..

We do NOT KNOW that the motor is limiting the current input....the drive may do that. We do not know the frequency for 1500 rpm. We can guess it must be at least 25 Hz for a 2 pole motor. All we do know is that 120V 40A puts in enough power to run the motor at rated output. The frequency is not that important.

So the motor COULD be set up to run 6000 rpm at 100 Hz, and might then take as much as 480VAC. That's pretty reasonable as far as available input voltages are concerned.

yep!

That's why I suggest to run the motor with the 240 V VFD and see what shakes out. Better would be to bump into someone who actually knew how these things were designed.

Theoretical guessing is still guessing.

Yabbut.... Theoretical guessing at least is putting limits on the possible performance and requirements based on whatever IS known.

it's quite common for spindle drives to use weird motors that are set up for odd voltages and have oddball back EMF curves just in order to get the high speed at an available voltage. Usually that means they are set up for LOW voltages.

Running at 240V will very possibly get 60 to 80% of the performance and not take special stuff. Could be good enough. Might even do better.

We are guessing about the currents, and where they occur. Good guesses, probably, but still guesses, based on how motors that are NOT these motors operate.

Problem is, we do not know enough about the motor. It can be found out with measurements, but I'd not want to try to tell someone how to do it at long range on the internet.......

JST You are on to something...;-)

What is the MACHINE input requirements? There must a placard somewhere! ;-)

Lots of good guesses guys. Only 3 items wrong are it says 46 amps rated, not 40 - look closer, and it certainly does not require or want 600v applied, and it certainly does require 46amps at 6000rpm too.

Stop reading magic into it.

It is 4 pole rated 50hz, 1500r0m, 46 amp continuos, 150v ac rms. It has a top speed of 6000rpm. It is designed at 150v base to reach 6000rpm WITH FULL 7.5KW RATING.

I am on silly phone so limited in reply word. Jst or jraef can run u a speed torque curve showing WHY it must be rated 150v to keep out of breakdown torque at 6000rpm.

This is very common design for hi speed spindle motors

Fortot to say this motor expects and requires 240v drive. Do not use 480 on it! If u only want 0-1500rpm, 150v is enough. If u want more than abt 2500rpm u need 240v or u will be in breakdown

Makes sense, even more than what I said.

Point being that this type motor tends to be low volts high amp. And goes high speed without needing as high a voltage as you might expect.

mike_kilroy said:

Fortot to say this motor expects and requires 240v drive. Do not use 480 on it! If u only want 0-1500rpm, 150v is enough. If u want more than abt 2500rpm u need 240v or u will be in breakdown

Click to expand...

Mike

Your information suggests, 0-1500 rpm needs 150 V, and then if more than 2500 rpm are wanted, the voltage requirement goes up to 240 V. At what frequency? Proportional to 50/1500?

And then, what if the full 6000 rpm are wanted ? No change of voltage above 240V? Is it not a linear relationship?

Forgive my innocence, I'm not familiar with these "spindle motors"?

CalG said:

Mike

Your information suggests, 0-1500 rpm needs 150 V, and then if more than 2500 rpm are wanted, the voltage requirement goes up to 240 V.

1) At what frequency? Proportional to 50/1500?
2) And then, what if the full 6000 rpm are wanted ? No change of voltage above 240V?
3) Is it not a linear relationship?

Forgive my innocence, I'm not familiar with these "spindle motors"?

Click to expand...

Good questions and you are close to spot on (I am at a computer keyboard this morning - it is world's largest hamvention (hamfest to you other oldies) going on this weekend in Dayton, Oh here and I need to get my mind off not going for first time in 25 years.... As Scarlet Ohare once said, "there is always tomorrow" or next year...

1) Spot on. Like you know, v/hz ratio is the same at any volts/freq to maintain constant torque (increasing HP as it goes up)
2) Right again. Above 'some mystery magic speed,' reached by using #1 to hit 240v, THEN no more increase in volts so now you are in the constant HP range of course - until you reach the breakdown torque speed and not enough torque left to keep going up at constant HP. During all this of course the voltage is 240v constant and so is the current - for constant HP.
3)See #1 & #2 and next post with nice picture.

Spindle motors are same as any other AC induction motor, just a bit unique in how they are rated; we want a zillion rpm so have to play this game. see next post for better explanation

Most folks know torque goes down LINEARLY with increase in speed when in constant voltage (v/hz ratio reducing) increasing freq range known as constant HP.

What most don't pay attention to - because they generally don't have to - is breakdown torque. THIS torque goes down BY THE SQUARE OF THE SPEED. This is the absolute MAX torque the motor can put out and can be graphed just like regular continuous rated output torque.

I did that here....

I plotted rated torque of a 10hp 4 pole 1800rpm motor. Typical breakdown torque (IEC spec for normal motors too) is 200% rated. So I also plotted this Tbd breakdown torque. You can see the square function on Tbd brings it down a lot faster that rated; If your motor is typical and rated 200% Tbd, then both torques WILL intersect at 2x base speed - 3600rpm in this case....

But you say, "I run my motor to 5400 rpm all the time and it works fine!" Sure - because you are not pushing it past its reduced available torque! You can see from this plot that at 3x base speed it still has 6.7#-ft of torque available - but NOT the 10 for 10hp still... If you keep going faster and faster, assuming you don't blow it up mechanically, you will quickly reach a max speed you cannot get beyond - because the available torque = your friction torque and nothing left to accelerate faster... but back to a spindle motor application...

So how to get this motor to go 6000rpm AND still have full rated torque? Cheat.

Wind it for 150v @ base speed 1500rpm and use it on a 240v supply! NOW the 'fake' base speed of 150v can REALLY be 1500*240/150 = 2400rpm... NOW 2x the 240v base speed where you REALLY run out of volts, is 4800rpm instead of only 3000rpm... Design it to have 230% breakdown and get a tad more again - if needed... But often that 6000rpm is derated in torque a bit to show the loss of torque and it is called a good design since MOST machine tools don't push it at max speed anyway.

So THIS OP spindle motor rated 1500/6000 will be setup in the vfd drive with a base speed of 2400rpm not 1500. It will run full 7.5kw upto 4800rpm and then the output HP will begin to drop off linearly to 6000rpm, where it will be rated (6000/2400)at this 2.5x base speed, per the plot attached, 9.6/12= 80% less, or 6kw.

Cheating? Maybe, but gets the job done swell. I work with a lot of 10-100hp spindle motors (on large industrial machine tools) where 1500rpm base speed voltage is 100-160v for just this reason. We often set corner freq (where we hit max volts) at 4700, 5500, 6700rpm.... These motors easily hit 10&12,000rpm for full HP cutting (many aerospace customers like to push them at 10&12000rpm to 110-120% rated load for long periods of time - they can with these lower voltage higher base speed designs. A lot of these motors were designed by Kreso at Reuland Electric for many many years. Many of us considered him on similar level to Tesla (from the same town too). Anyway, he was a hell of a teacher to us! Nowadays he playfully calls himself Zuess and has a wonderful winery (vinokletwines.com) in Cincinnati...

Good clear explanation....

It's not that bad of a cheat..... EVERY machine has less torque at the highest speed. That or less power at lower speeds.

Even with gear or belt drive, torque and speed are inverse. So having less at the highest speed is right in line with other machines, expected and understood.

Thank you Mike

I think the logic is going past me. What I see is a standard induction motor V/h with some "that's the way we do it in our business" at the high end of the frequency envelope.

If the motor is designed to spin 1500 at 150V and 50 hz it should spin 6K at 600V at 200hz without being in the breakdown regime.
Is there something else happening?
If the motor is mechanically sound at 6k rpm, is there a reason not to run it full power?

Just a note: On the 16 inch engine lathe I had fitted a 440V Toshiba VFD, configuring the motor windings 240 v. The base frequency was set to 120hz, with the 240V and 60 hz crossing point equal to the normal 240V VFD configuration. I got twice the rpm flexibility, and twice the available hp (potential, I never had need to run the motor past about 100hz. (noisy gear head!) It is a 1725 motor, so 3450 rpm is no biggie in regard to throwing windings or bearings. (not the same as 6K though!) The set up worked great until a lightening hit took out one of the sub cards on the controller. (I really should get a replacement board, it's a 22kVA device. All replaced with a std config 240 V unit of the same capacity, happy to have the 240X440 boost transformer off the shop floor.