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VFD Not Increasing Frequency When in Increasing Setpoint

02/20/2013 8:39 AM

Hey all

I just want to know which parameter is taken into account when you are increasing drive frequency(speed of the motor). Like i give setpoint 100% from a pot. 100% of what ? Is it the base frequency or max rpm of the motor . I have 690 ssd drive connected to two motors .The base frequency is set to 50 hz ,the setpoint is already 100% percent but still the drive doesnt run at full speed. I checked the drive frequency on the display it is only 16 hz. Is it something wrong with the drive.

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#1

Re: VFD Not Increasing Frequency When in Increasing Setpoint

02/20/2013 10:19 AM

The 100% is 100% of what you tell it to be. Usually that is related to the max speed setting, but that depends on the programming and we cannot see your programming.

But another thing that can interfere is if the VFD is programmed for a current limit or a torque limit (sometimes called Stall Prevention). One mode of response to the load attempting to exceed that limit is to artificially drive down the frequency reference, overriding the set point command.

If I had to guess (and I do because I am not here), I'd suspect that you have put 2 motors on this one drive and the total load now exceeds the capacity of the drive, so it is smarter than you and is not allowing you to burn up the drive by stopping you from fully accelerating the motors. If you are sure that the motors are each less than 1/2 the rating of the drive, then I suggest you check the motor connections. You likely have the motors connected for the wrong voltage, which is just like creating an overload as far as the drive is concerned, because either the torque is too low so the motors stall (motor voltage > drive voltage) or the motor is saturating (drive voltage > motor voltage).

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#2

Re: VFD Not Increasing Frequency When in Increasing Setpoint

02/20/2013 1:42 PM

Have another read of the manual, you may have forgotten to set the analog input connecting the pot to the VFD as the manual speed control input (there can be a few parameters that need to be set that relate to this) and/or the base frequency (which is different to the min and max frequency).

All the information should be clearly indicated and explained in the manual applicable to your VFD and there are multiple parameters you need to change to get it to work.

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Power-User

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#3

Re: VFD Not Increasing Frequency When in Increasing Setpoint

02/20/2013 10:27 PM

Just check where are you crossing the limits of VFD for running two motors combined- Torque, current, speed. As they are not linear with frequency. No wonder both motors cant reach highest speed. torque, curremnt simultaneously. Limiting would be which ever comes first and corsses thereshold of VFD settings.

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#4

Re: VFD Not Increasing Frequency When in Increasing Setpoint

02/21/2013 2:48 AM

Rule of thumb... 1 motor = 1 VFD

You can however interlink two drives to work together, if you require both motors to operate at the same Hz.. etc!! But that would depend on the type and make of drive.

Take the one motor off and give it a try, you will probable find the motor & drive function as normal.

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#5

Re: VFD Not Increasing Frequency When in Increasing Setpoint

02/21/2013 5:52 PM

You can have as many motors down stream of a VFD as you want to (my record was 28), as long as you follow some basic rules and requirements:

1) Accept that they will all run at the same frequency all of the time.

2) Provide Short Citcuit and Overload protection for each motor individually, there is no way for the VFD to discrimiate one from another.

3) Do not turn motors on and off separately behind the VFD, the transistors are not made to handle that and you may damage them. If one trips on OL, it is better to shut down the etire VFD.

4) Size the drive for the total FLA of all of the motors, plus 10% to handle added harmonics issues.

5) You cannot use Sensorless Vector Control with multiple motors, the VFD cannot create an accurate motor model, so V/Hz mode only. If you don't know what that means, you should not be doing this.

#5 brings up another possibility for the problems the OP is having: someone was unaware of that rule and the VFD is in SVC mode, in which case it is very very confused about the motor model it is attempting to monitor. Since many drives now ship from the factory with the SVC mode enabled as the default, that is a real possibility.

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#6
In reply to #5

Re: VFD Not Increasing Frequency When in Increasing Setpoint

02/21/2013 7:03 PM

Looking at the manual for your drive, the factory default setting is for V/Hz control. But double check parameter #1105, it must be set to say "VOLTS / HZ". If it says "SENSORLESS VEC" then it will not work properly, reset it to V/Hz.

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Member

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#7

Re: VFD Not Increasing Frequency When in Increasing Setpoint

05/23/2016 4:36 AM

There are two ways: a. ask help from the technical support from the VFD supplier. b. checking the user manual to read the parameter setting steps. The analog may be forgotten. Learn more information about VFD drive.

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#8

Re: VFD Not Increasing Frequency When in Increasing Setpoint

12/17/2018 9:58 PM

Check your connections as per manual

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