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VFD struggling to power on motor

Dan1900

Aluminum
Joined
Jul 29, 2017
I recently hooked up a new Fuji frenic mini VFD to an older 3/4hp motor. I input all the needed motor parameters and functions into the vfd but I am having a strange recurring issue. The first time I power on the VFD, it works fine. Then when I power it off, sometimes but not always, it will lock up the motor. When this happens, I have to go over and tug on the pulleys to get the motor shaft to move and this slowly unblocks the motor.

Again this doesnt happen every time but maybe 50% of the time. I thought I would bump the torque boost to +20% and it still locks up. I changed the parameters so it doesn't decelerate the motor so quick (I had it set to 1.5 or 2 seconds acceleration / deceleration).

Any one have any ideas what might be the issue?
 
Dan,

Often the clue is "sometimes, but not always"! This would lead one to believe it certainly isn't a programmed parameter that's doing it but rather a bad drive or possibly noise from nearby electric/electronic gear.

Do you have the motor tied to a common ground with the drive? Are you very sure it's not a mechanical issue..something on the driven side of the motor that's binding after a pretty quick 'brake' command?

Stuart
 
Dan,

Often the clue is "sometimes, but not always"! This would lead one to believe it certainly isn't a programmed parameter that's doing it but rather a bad drive or possibly noise from nearby electric/electronic gear.

Do you have the motor tied to a common ground with the drive? Are you very sure it's not a mechanical issue..something on the driven side of the motor that's binding after a pretty quick 'brake' command?

Stuart

The motor and drive are both tied to a common ground. As far as confirming whether or not it's a mechanical issue with the motor...that's harder to say. The motor shaft rotates freely when not hooked up to the vfd, so if the issue is something deeper with the motor I would have no idea how to even diagnose.
 
My suggestion would be to reset your drive to factory defaults. Set the motor parameters and look to see if you have an auto tune function.

Leave the default settings, and see how the motor performs at the default settings.

The used motor can be checked by connecting to a 3Φ source, as well as doing a resistance test on the winding's.

SAF Ω
 
Sounds like for some reason you are getting DC injection on braking. A DC current will cause the motor to lockup.

This is assuming that there are no mechanical problems but a bad parameter in the braking parameters can cause this symptom.
 
Especially if the unit has an option to "hold the brake". Then there will be a small current that acts during stopped condition.
 
I thought the OP said..."sometimes but not always, it will lock up the motor"! So I guess this means the 'hold the brake' feature works some of the time, but not all of the time!:nutter:

Stuart
 
I thought the OP said..."sometimes but not always, it will lock up the motor"! So I guess this means the 'hold the brake' feature works some of the time, but not all of the time!:nutter:

Stuart

The problem is that we don't know exactly what the OP has entered for parameters, how he actually wired the VFD up or what he exactly means by turning the VFD off and if he is actually doing the exact same procedure each time.

Big difference internally between commanding the VFD to stop or to just unplug it.

It should also be assumed that the OP probably has limited knowledge if he is playing with torque boost and the decel curve and that he is here asking for help.
 
I thought the OP said..."sometimes but not always, it will lock up the motor"! So I guess this means the 'hold the brake' feature works some of the time, but not all of the time!:nutter:

Stuart




Yep..... noisy environment may "set" something that is "enabled", but normally not triggered.... The "reset to factory default" followed by setting the required parameters should take care of that.
 
So I didn't do a complete reset, but I did go and double check the motor parameters. Hp was set to 1 so I lowered it to 3/4 and amps were set to 2 and I bumped it to 2.6. I also double checked DC braking and that was not enabled. Not sure if the slightly off parameters was the root issue but it hasn't locked up yet...fingers crossed that was it
 
If you have a 230V 3/4HP motor, your motor FLA should be somewhere around 3.2A. 2.6A still sounds way too low, so you are essentially robbing yourself of some torque and speed capability. A VFD will often artificially drive down the speed command in order to keep the current below the tripping threshold. With the drive set for 2.0A, that may explain what was happening; it was going into current limit.

Also take a look at A14, which is where you program the "Control Mode". The factory default setting is "0" which is V/Hz mode. If someone changed that to a "1" for "Dynamic torque vector control" mode, then you MUST also perform an Auto-tune procedure on the specific motor that you have, using A18. If that drive was set up for 1HP and the wrong FLA, that means that drive was previously used and never tuned to your motor. Using any kind of Vector Control without tuning to the motor results in erratic behavior.
 
So if I am running the motor on 120v input, would I set the FLA to 3.2A or 2.6A? It is currently wired for the 220v setup so I would assume to use 3.2A?

If you have a 230V 3/4HP motor, your motor FLA should be somewhere around 3.2A. 2.6A still sounds way too low, so you are essentially robbing yourself of some torque and speed capability. A VFD will often artificially drive down the speed command in order to keep the current below the tripping threshold. With the drive set for 2.0A, that may explain what was happening; it was going into current limit.

Also take a look at A14, which is where you program the "Control Mode". The factory default setting is "0" which is V/Hz mode. If someone changed that to a "1" for "Dynamic torque vector control" mode, then you MUST also perform an Auto-tune procedure on the specific motor that you have, using A18. If that drive was set up for 1HP and the wrong FLA, that means that drive was previously used and never tuned to your motor. Using any kind of Vector Control without tuning to the motor results in erratic behavior.
 








 
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