VFD setup help

Installed my ATC spindle finally after figuring out why it was overloading. It seems fine, except that it seems to not have the power it should. I assume I botched some settings with all the messing around I've been doing, but I'm not sure what.The spindle is 1.5kw, 0.24nm torque, 60,000rpm, 220vac. However my drive is restricted to 600hz or 36000rpm.As a result I have set the motor voltage to 132V which is 60% of 220v.At idle the spindle uses about 1.4 amps, which is roughly what is expected. Full rated amps is 5.132v at 5 amps is about 900w, which is a bit over 1 horsepower.However, at 5A, I am getting only 2 cubic inches a minute of cutting volume before the spindle begins to bog. Math says I should be getting 5 cubic inches per minute (machine rigidity notwithstanding). So I'm missing basically half my power it seems.What settings should I be looking for to rectify this? The drive is a durapulse G10, which is a stripped down verison of the delta MS300. It is running in vector control mode. The drive will not autotune for some reason, it overloads. I suspect there are some motor parameters I need to manually enter in for it to behave but I'm not sure. My other spindle (also a delta ms300 drive) just autotunes and works as expected no fuss.

Are you sure you're supposed to be reducing the motor voltage?

I don't think you need to drop the voltage due to your VFD not having the frequency to match the MAX frequency of the spindle.

Pretty sure if it's a 220V motor on the nameplate then that's what it should be set to in the VFD. The vfd will be making a bunch of calculations based on that value and so it should be the true value. It just will top out at 600Hz.

Putting the correct motor voltage in will probs allow it to do an auto-tune without failure too. Use all the data from the nameplate on the motor

The only time I have had to stray from nameplate ratings was when I had to up the current 0.5A over the nameplate rating a couple of times to get through some spindle run-in before putting it back to the correct value.

Every motor that is controlled by a Variable frequency drive...... Changes speed by frequency not voltage.... Hence the name!

It's not pwm like you see in small DC motors, universal motors, AC router speed controllers, etc

The drive coverts ac from the wall, into DC, then back into AC at a varying frequency to control the motor speed. Trying to keep voltage at name plate specs.

It makes sense that at ~half the voltage you have ~half the torque

Fix that quickly or you will fry that spindle.


Second thing to watch out for is endmill size. Too big and it won't have the torque to spin it even if it has power on tap (try loosening a rusty bolt with a stubby wrench... Same problem). Drop down an endmill size or two. I'd try in the 3-6mm range (1/8 to 1/4 in) for a spindle like that.

I was told to set the voltage by the manufacturer. This is mandatory or you fry the spindle. Spindle speed corresponds to voltage, hence the v/f curve. 220 is full speed, 110 is half. etc. I am at 60% so 132v.

The drive eventually autotuned itself, and it's much better now, but not perfect. Still bogs down and uses more current than it should. Still seems to be about half or a little more power than it should have. (at 36000rpm it should be 900w, and its bogging down on 400-500w cuts at 5A).

thanks

Is it possible that the manufacturer meant that its very important to set the voltage as per what was written on the side of the spindle? IE 220V. I ask because there could be a misunderstanding here. If that's what they meant then I agree, failing to do this could well destroy the motor and its one of the first params to get set along with rated current before even thinking of hitting the start button.

The spindle speed is linked to and linear with frequency, the output voltage and current limiting are managed by the vfd. It's a 220v wound motor regardless what speed / frequency you are trying to run it at.

Voltage/RPM is very tightly connected on a DC motor wound to hit a speed at a certain voltage - but AC motors just don't work this way. They are generally wound to run at a certain speed based on the HZ they rate you to be allowed to drive them at. Typically at 50 or 60HZ which is what we would, without a VFD, have available to supply it. The VFD will be converting your ac, to dc, and back to ac again, split over 3 phases shifted 120 degrees from each other at a frequency that it can vary depending on your desired RPM - it's not however rewiring your motor to adjust number of poles and so this is why I cannot understand why your manufacturer told you to lie to the VFD about the motors parameters.

Your motor is a dumb bunch of coils - the VFD just needs to know a few key bits of data about how they made this motor so it can do some amazing maths and organise things to run perfectly whilst also protecting your motor - I think the garbage in garbage out saying here is what you are seeing - lie to the VFD about the motor it has connected and it produces a sub-standard result in running it.

In any situation if you are attempting to make use of a certain wattage and you drop the voltage you will always see a rise in current. If you have told that vfd about the motors current rating then it would probably not allow the current to rise and hence not provide the required power which might show in an over-current error on the vfd or a spindle baulking in RPM and available power

Soooorta.

So the drive needs to be 135v or it will toast the spindle. BUT, you are 100% right in that lowering the voltage has some some sort of math and reduced the power.

After working with the drive support people, we did a few things. ! was to boost the carrier frequency to 16khz. this reduced current a lot (over an amp at load). Then we upped the voltage bit by bit until we found a compromise where it is no longer bogging down, but also not getting more than slightly warm. Idles at 2.1A now.

As a result, I have about 600w usable power at 5A draw, no bogging down, and it's "fine" for now, until I can wrangle a high speed drive.

Well, I better bow out, you sound quite sure that your motor speed is voltage-dependent not hz/poles like an AC induction motor.
Might be worth throwing some info on the motor up here - surely someone in the linuxcnc community has used a similar unit.

AC induction motor voltage is speed dependent in the same way as DC motors.
They are more complex because of things like field weakening in the the armature,
but the basic behaviour is the same.

That is if you took a 240V 60 Hz AC induction motor and ran it at 1/2 speed at 30 Hz
you would need to reduce the voltage to approximately 120 V to avoid overcurrent/saturation

Yes. But apparently setting a 220v 1000hz motor to 135v and 600hz on this drive is not the same as just moving down the VF curve on a 1000hz drive. The engineer was confused as much as me. It should "just work" but it doesn't.

And of course as I found out, faster drives are not easy to get so I'm stuck with this compromise we found for now.

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