753 AB VFD

JohnElect

Member
Location
Keasby NJ
Occupation
Electrician
I'm currently changing VFD'S from a 70 to a 753 Series. When powered up the VFD runs Very Hot and the Current dances between 20 and 40. This is a 30 hp VFD as the 70 was and the Motor is a 25 hp Motor, I'm thinking its a Parameter setting Can You Help. Thanks John
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Did you leave the recommended clearance around the VFD?

In any case these drives tend to be a little bit warm but usually only if they're producing close to Max current. With a 25 horsepower motor on a 30 horsepower drive you should have a lot of leeway.

Did you go through the auto-tune procedure? Sometimes this can cause all kinds of grief if you don't do it.

Another very critical thing to do when you start up these drives is to reset the drive parameters to the default. This is so important that the Allen Bradley software for configuring drives called CCW, includes this as a step in the startup procedure.

Another problem I have had with these drives is that running them in sensorless vector mode can cause the exact issue that you are describing. Tech support has never been able to explain to me why it does this but there are some parameters that they can give you to tone down the oscillations. My solution is generally not to bother to run them in sensorless vector mode since there really isn't much in the way of advantage to doing so for the vast majority of our applications.
 

JohnElect

Member
Location
Keasby NJ
Occupation
Electrician
Did you leave the recommended clearance around the VFD?

In any case these drives tend to be a little bit warm but usually only if they're producing close to Max current. With a 25 horsepower motor on a 30 horsepower drive you should have a lot of leeway.

Did you go through the auto-tune procedure? Sometimes this can cause all kinds of grief if you don't do it.

Another very critical thing to do when you start up these drives is to reset the drive parameters to the default. This is so important that the Allen Bradley software for configuring drives called CCW, includes this as a step in the startup procedure.

Another problem I have had with these drives is that running them in sensorless vector mode can cause the exact issue that you are describing. Tech support has never been able to explain to me why it does this but there are some parameters that they can give you to tone down the oscillations. My solution is generally not to bother to run them in sensorless vector mode since there really isn't much in the way of advantage to doing so for the vast majority of our applications.
 

paulengr

Senior Member
There are hundreds of parameters in that drive and pretty easy to mess up. Care to narrow things down?
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Check the Carrier Frequency (PWM Frequency) in Parameter P38. The default setting should be 4kHz, which would have been the same as the PF70. If someone set that higher, the drive will run hotter. Raising the carrier frequency reduces the whining sound made by the motor, but some people don't understand the effect that has on the drive.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Check the Carrier Frequency (PWM Frequency) in Parameter P38. The default setting should be 4kHz, which would have been the same as the PF70. If someone set that higher, the drive will run hotter. Raising the carrier frequency reduces the whining sound made by the motor, but some people don't understand the effect that has on the drive.
I imagine the reason is that the lossy switching time of the pass elements becomes a proportionally longer fraction of the total time as the frequency increases?
 
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