753 AB VFD

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JohnElect

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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
 
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.
 
petersonra said:
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.
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There are hundreds of parameters in that drive and pretty easy to mess up. Care to narrow things down?
 
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.
 
Jraef said:
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.
Click to expand...
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?
 
GoldDigger said:
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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Yep. Switching losses per switch operation are fairly constant, but more switching operations per second means more total losses.
 
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