power flex drive 753 allen bradlley

i have a problem in the drive 30 kw used with motor 4 pole (1770 rpm ) , and the motor used to run load with pulley ratio 2.3 so the load speed 3500 as nominal
i try to adjust the drive for the load speed but its max speed not exceed motor speed
the problem is output volt from the drive not increase WITH HZ in (VHZ) mode
so the motor start slowly and not going with freq

adam_eyad said:

i have a problem in the drive 30 kw used with motor 4 pole (1770 rpm ) , and the motor used to run load with pulley ratio 2.3 so the load speed 3500 as nominal
i try to adjust the drive for the load speed but its max speed not exceed motor speed
the problem is output volt from the drive not increase WITH HZ in (VHZ) mode
so the motor start slowly and not going with freq

Click to expand...

V/Hz is set up to start at 0V for 0 Hz and ramp up to full voltage at 60 Hz. It can't raise the voltage after that, since it is at full voltage.


Boost is the voltage that the drive puts out at 0 Hz to start the motor turning. There is another parameter .. I don't remember the name .. where the boost tapers off to 0. I think the default value is 20 Hz.


If you are turning at 3500 rpm with an 4 pole 1770 rpm motor the output voltage will not raise above 1770 rpm. It will stay constant as the frequency goes up. If the motor will not speed up and it used to, there is a mechanical problem with your load that is taking more horsepower than your motor can provide.


We have many VFDs and motors over-sized. It allows for over-speed operation during testing. If you are running at 2X speed normally, I would advise changing the gearbox, or the pulley sizes if it is belt driven, so that your motor can run at 1770 rpm instead. The motor can have some strange problems when run that fast. The gearbox may not be rated for the input shaft speed either ... and I'm told that speed is what kills bearings over the long run.

thingstodo said:

V/Hz is set up to start at 0V for 0 Hz and ramp up to full voltage at 60 Hz. It can't raise the voltage after that, since it is at full voltage.


Boost is the voltage that the drive puts out at 0 Hz to start the motor turning. There is another parameter .. I don't remember the name .. where the boost tapers off to 0. I think the default value is 20 Hz.


If you are turning at 3500 rpm with an 4 pole 1770 rpm motor the output voltage will not raise above 1770 rpm. It will stay constant as the frequency goes up. If the motor will not speed up and it used to, there is a mechanical problem with your load that is taking more horsepower than your motor can provide.


We have many VFDs and motors over-sized. It allows for over-speed operation during testing. If you are running at 2X speed normally, I would advise changing the gearbox, or the pulley sizes if it is belt driven, so that your motor can run at 1770 rpm instead. The motor can have some strange problems when run that fast. The gearbox may not be rated for the input shaft speed either ... and I'm told that speed is what kills bearings over the long run.

Click to expand...

dear engineer ,
thanks alot for your assistance
i raised the run boost parameter and acc boost but the max output voltage only comes to 100 v but frquency going up and the motor move slowly,where the SPEED ON THE DRIVE GO TO 400 RPM BUT THE ACTUAL SPEED OF MOTOR ABOUT 150 RPM
I SEE THAT OUTPUT VOLTAGE NOT CORRECT AND THE MOTOR SPEED NOT SAME SPEED ON THE DRIVE

adam_eyad said:

dear engineer ,
thanks alot for your assistance
i raised the run boost parameter and acc boost but the max output voltage only comes to 100 v but frquency going up and the motor move slowly,where the SPEED ON THE DRIVE GO TO 400 RPM BUT THE ACTUAL SPEED OF MOTOR ABOUT 150 RPM
I SEE THAT OUTPUT VOLTAGE NOT CORRECT AND THE MOTOR SPEED NOT SAME SPEED ON THE DRIVE

Click to expand...

Let me make sure that I understand what you are trying to solve .. apparently I missed on the last post.

You are trying to start your motor.

- you bumped the boost setting up
- you adjusted the acceleration boost

The drive normally starts the motor at a certain speed. With a motor rated for 1770 rpm, with an 1800 rpm 4 pole motor (nominal) that would be 30 rpm of slip, or about 0.5 Hz.

The drive starts the acceleration of the motor, increasing the frequency and the output voltage as it goes.

If you are showing 400 rpm on your motor output, but the motor is actually turning at 150 rpm, your slip is 400 - 150 = 250 rpm. 250 rpm is very high slip. That is over 4 Hz.

If you take a look at the torque versus speed curve for an induction motor ... here https://en.wikipedia.org/wiki/Induction_motor

Under the standard torque section you will see that there is a hump in the torque versus speed curve. It's in the range of 200% to 250% of rated torque for a high efficiency T frame motor, at somewhere in the range of 200 rpm of slip.

I think your VFD won't speed up because it is already putting out the maximum current that it can at the speed it is turning. But that's just a guess, based on what you are describing.

If this was a new install, I'd say your motor is not powerful enough. But you say this was running .. so it should still run ... so something is taking too much power. I'd suggest that your load is likely having some mechanical problems.

If the drive is being over loaded, and you have set the response to try to avoid shutting down, it will respond by altering (restricting) the maximum frequency that you can run at. In the PF753, this is handled in parameter 420. The factory default is for it to BOTH reduce the PWM frequency (which is the CARRIER frequency, not the speed) and to reduce the Current Limit value. But Current Limit (parameter 421) is accomplished by limiting the output (speed) frequency. So if your Current Limit setting is low, AND/OR your response to an Overload is set to either Current Limit or Both, the drive will end up artificially limiting the speed you can run at if it is overloaded.

So the next question would be; is what you are trying to do causing the drive to be overloaded?

The other thing that can artificially override the desired output speed is the DC Bus Regulation feature (parameter 372), but that is a more rare situation.

jraef said:

If the drive is being over loaded, and you have set the response to try to avoid shutting down, it will respond by altering (restricting) the maximum frequency that you can run at. In the PF753, this is handled in parameter 420. The factory default is for it to BOTH reduce the PWM frequency (which is the CARRIER frequency, not the speed) and to reduce the Current Limit value. But Current Limit (parameter 421) is accomplished by limiting the output (speed) frequency. So if your Current Limit setting is low, AND/OR your response to an Overload is set to either Current Limit or Both, the drive will end up artificially limiting the speed you can run at if it is overloaded.

So the next question would be; is what you are trying to do causing the drive to be overloaded?

The other thing that can artificially override the desired output speed is the DC Bus Regulation feature (parameter 372), but that is a more rare situation.

Click to expand...

dear engineer thanks alot for assistance
problem as follow
if i start the motor without load these reading obtained with (VHZ MODE )
at S: 200 RPM - OUT VOLT IS : 17 V AC -CURRENT : 4.3 - BUS volt : 550
at S: 700 RPM - OUT VOLT IS : 30 V AC -CURRENT : 5 - BUS volt : 550
at S: 900 RPM - OUT VOLT IS : 42 V AC -CURRENT : 6 - BUS volt : 550
at S: 1350 RPM - OUT VOLT IS : 80V AC -CURRENT : 8 - BUS volt : 550
at S: 1520 RPM - OUT VOLT IS : 98 V AC -CURRENT : 9 - BUS volt : 550
if you calculate the fequency f= ( speed* no of pole )/120
so at speed :1521 frquency : 25.4 HZ SO output voltage from dive should be equal to 168 volt but the drive give out voltage 98v this the problem i dont know how can i solve it
also WITH load the motor speed is slow than the speed from the drive and the output voltage also not correct
i modfied the slip speed to 30 rpm but same problem obtained

jraef said:

If the drive is being over loaded, and you have set the response to try to avoid shutting down, it will respond by altering (restricting) the maximum frequency that you can run at. In the PF753, this is handled in parameter 420. The factory default is for it to BOTH reduce the PWM frequency (which is the CARRIER frequency, not the speed) and to reduce the Current Limit value. But Current Limit (parameter 421) is accomplished by limiting the output (speed) frequency. So if your Current Limit setting is low, AND/OR your response to an Overload is set to either Current Limit or Both, the drive will end up artificially limiting the speed you can run at if it is overloaded.

So the next question would be; is what you are trying to do causing the drive to be overloaded?

The other thing that can artificially override the desired output speed is the DC Bus Regulation feature (parameter 372), but that is a more rare situation.

Click to expand...

dear engineer i changed the slip speed to 0.5 hz at 30rpm but same problem as follow
if i start the motor without load these reading obtained with (VHZ MODE )
at S: 200 RPM - OUT VOLT IS : 17 V AC -CURRENT : 4.3 - BUS volt : 550
at S: 700 RPM - OUT VOLT IS : 30 V AC -CURRENT : 5 - BUS volt : 550
at S: 900 RPM - OUT VOLT IS : 42 V AC -CURRENT : 6 - BUS volt : 550
at S: 1350 RPM - OUT VOLT IS : 80V AC -CURRENT : 8 - BUS volt : 550
at S: 1520 RPM - OUT VOLT IS : 98 V AC -CURRENT : 9 - BUS volt : 550
if you calculate the fequency f= ( speed* no of pole )/120
so at speed :1521 frquency : 25.4 HZ SO output voltage from dive should be equal to 168 volt but the drive give out voltage 98v this the problem i dont know how can i solve it
also WITH load the motor speed is slow than the speed from the drive and the output voltage also not correct
i modfied the slip speed to 30 rpm but same problem obtained

adam_eyad said:

dear engineer thanks alot for assistance
problem as follow
if i start the motor without load these reading obtained with (VHZ MODE )
at S: 200 RPM - OUT VOLT IS : 17 V AC -CURRENT : 4.3 - BUS volt : 550
at S: 700 RPM - OUT VOLT IS : 30 V AC -CURRENT : 5 - BUS volt : 550
at S: 900 RPM - OUT VOLT IS : 42 V AC -CURRENT : 6 - BUS volt : 550
at S: 1350 RPM - OUT VOLT IS : 80V AC -CURRENT : 8 - BUS volt : 550
at S: 1520 RPM - OUT VOLT IS : 98 V AC -CURRENT : 9 - BUS volt : 550
if you calculate the fequency f= ( speed* no of pole )/120
so at speed :1521 frquency : 25.4 HZ SO output voltage from dive should be equal to 168 volt but the drive give out voltage 98v this the problem i dont know how can i solve it
also WITH load the motor speed is slow than the speed from the drive and the output voltage also not correct
i modfied the slip speed to 30 rpm but same problem obtained

Click to expand...

Are you in V/Hz mode or in Induction SV Mode (parameter 35)? Because if you left it at the factory default you are in Induction SV Mode and the V/Hz pattern will be optimized to whatever is necessary for the load. Induction Econ Mode would also have a non-linear V/Hz ratio. And if it is in InductionSV Mode, you MUST perform the Autotune at setup, otherwise the VFD does not know what the motor parameters are and it guesses, usually wrong. In fact I recommend doing an Autotune even if using V/Hz now.

If you are in InductionVHz mode in P35, then what is the V/Hz Curve you have selected in P65? The factory default is "Custom", which is not a perfectly linear relationship. There is a diagram right above the instructions for P65 that shows you the default settings of that "curve". But more importantly, if someone set P65 to "Pump/Fan", then the machine is NOT a centrifugal (quadratic) load, the torque will be very low at lower frequencies.

jraef said:

Are you in V/Hz mode or in Induction SV Mode (parameter 35)? Because if you left it at the factory default you are in Induction SV Mode and the V/Hz pattern will be optimized to whatever is necessary for the load. Induction Econ Mode would also have a non-linear V/Hz ratio. And if it is in InductionSV Mode, you MUST perform the Autotune at setup, otherwise the VFD does not know what the motor parameters are and it guesses, usually wrong. In fact I recommend doing an Autotune even if using V/Hz now.

If you are in InductionVHz mode in P35, then what is the V/Hz Curve you have selected in P65? The factory default is "Custom", which is not a perfectly linear relationship. There is a diagram right above the instructions for P65 that shows you the default settings of that "curve". But more importantly, if someone set P65 to "Pump/Fan", then the machine is NOT a centrifugal (quadratic) load, the torque will be very low at lower frequencies.

Click to expand...

thanks alot for your helping
please enginner i try make auto tune as (rotate tune ) after 3 minute during tue drive give fault (code 79 ) ( motor did not come up to speed in the alotted time during autotune )
also this is my problem when i start the drive with load it move slowly and not reach to frequency refernce set value ( in every mode v/hz or SV mode )

adam_eyad said:

thanks alot for your helping
please enginner i try make auto tune as (rotate tune ) after 3 minute during tue drive give fault (code 79 ) ( motor did not come up to speed in the alotted time during autotune )
also this is my problem when i start the drive with load it move slowly and not reach to frequency refernce set value ( in every mode v/hz or SV mode )

Click to expand...

To perform a tune, it is best to decouple the motor from the load it is driving. Remove the coupler from the motor, or the belt from the belt drive, before doing the tune.

thingstodo said:

To perform a tune, it is best to decouple the motor from the load it is driving. Remove the coupler from the motor, or the belt from the belt drive, before doing the tune.

Click to expand...

i make decoupling load from the motor but give this error

please engineer sequence for autotune

make static tune frist or rotate tune also there is inertia tune
thanks alot for you

adam_eyad said:

i make decoupling load from the motor but give this error

please engineer sequence for autotune

make static tune frist or rotate tune also there is inertia tune
thanks alot for you

Click to expand...

Did you got this error with the rotating tune, with the motor uncoupled from the load?


If so, you may have a problem with your motor. Do you have a spare motor? If the static tune does not finish successfully, I'd say you need to change out your motor.



I don't know what inertia tune is. Maybe it's been too long since I have done a tune on a Rockwell drive.


You can do a static tune only, with the load connected. It's not quite as good for control, but it is better than the V/Hz control.