Derating a Powerflex 70 25hp

[G_man62]

I am working at a company doing an install and they want to use a 25hp Powerflex 70 on a 2 hp agitator. I was wondering 1 if this is even feasible and 2 how low can I even take this down?

 

[alan_505]

Rule of thumb is only use a motor that is greater than 50% of VSD rated current.

 

[PLC Pie Guy]

Why?? Sell the 25 HP drive and buy 4, 2 HP drives. It doesn't make sense. It could be a fun experiment though to twist a motor shaft apart.

 

[pturmel]

Yeah, no. I'm ok with maybe 4x oversize. 12x oversize is giving up too much resolution in the drive's current sensing circuits.

 

[Jim3846]

Do not most manufacturers offer a normal duty versus a heavy duty version for the same horsepower?
Just select the heavy duty option.

 

[jdbrandt]

Rule of thumb is only use a motor that is greater than 50% of VSD rated current.

I've seen numbers as low as 30% of rated, but 50 is a good general rule.

I normally only see this where the designer is expecting to slow down really really fast, and needs the capacity of the oversized drive to do it.

 

[thingstodo]

I am working at a company doing an install and they want to use a 25hp Powerflex 70 on a 2 hp agitator. I was wondering 1 if this is even feasible and 2 how low can I even take this down?

We use 5 HP minimum because some of the VFD vendors have very small terminals on smaller VFDs. We have used 5 HP VFDs on 0.5 HP motors. The parameters for motor protection likely don't have great resolution that low - but the motor is a throw-away when it fails.


Besides being a bit of a waste ... I don't believe it is dangerous.



If you are running in vector mode instead of V/Hz ... the 25 HP VFD may not accept the measured values for the smaller motor as valid. I don't have that type of in-depth knowledge on the PF 70.