Using 7.5 HP PowerFlex 525 for smaller motors , such as 3 HP and 5 HP.

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Aug 2016
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Virginia
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Good Morning ,

I know this is a higher expense , but I would like to keep 7.5 HP PowerFlex 525's in stock . I am doing a machine upgrade . I have 3 motors on this machine, 2 - 5Hp and 1 - 3Hp. I would like to purchase 3 - 7.5 HP Powerflex 525's . Is there any problem upsizing a drive ? You can fine tune the drive for a smaller motor , correct ? I also want to leave room in case we increase a size .

Thanks so much.
 
There is typically a limit on how small you can select things like FLC on motor etc. I've successfully used 60hp VFDs on 30HP motors (mechanical engineers could not even correctly tell me what hp they ordered). That said, the 30hp FLC was at the very bottom of the selectable range on the 60HP drive. You may want to check in the 7.5hp drive that you can select a low enough current.
 
It's going to depend on what you want to do with the motor. The recommended lower limit is 50% of the output Amp rating of the drive, so by that rule a 2HP motor would be too small for a 7-1/2HP VFD. This is because below that 50% rating aspect, ability of the current sensors when current is very low because that small motor is at low speeds begins to be too small to detect correctly when in SVC mode. If using it in V/Hz mode, it doesn't matter at all.
 
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It's going to depend on what you want to do with the motor. The recommended lower limit is 50% of the output Amp rating of the drive, so by that rule a 2HP motor would be too small for a 7-1/2HP VFD. This is because below that 50% rating aspect, ability of the current sensors when current is very low because that small motor is at low speeds begins to be too small to detect correctly when in SVC mode. If using it in V/Hz mode, it doesn't matter at all.

Even in V/Hz mode, isn't there going to be a limit to how low of current the drive will be able to provide overload protection for? If using V/Hz and a small motor, would you use an external overload to protect the motor?
 
P033 (Motor OL Current) "Sets the motor nameplate overload current. Used to determine motor overload conditions and can be set from 0.1 A to 200% of drive rated current."

Unless the motor FLA is lower than 0.1A then the OL protection is functional in V/Hz operating mode for any 'lesser' motor that the VFD rating.
 
P033 (Motor OL Current) "Sets the motor nameplate overload current. Used to determine motor overload conditions and can be set from 0.1 A to 200% of drive rated current."

Unless the motor FLA is lower than 0.1A then the OL protection is functional in V/Hz operating mode for any 'lesser' motor that the VFD rating.

My experience had been using a different manufactured drive (AD GS3 drive), so my experience was slighly different. It would appear that with these drives, in v/hz mode, running s 2-3hp motor should not be an issue.
 
Even in V/Hz mode, isn't there going to be a limit to how low of current the drive will be able to provide overload protection for? If using V/Hz and a small motor, would you use an external overload to protect the motor?
Technically, yes, but think about it; if the current is so low that the sensors have trouble being accurate with it, then what does that matter with regard to overload?

The issue is, if you have a drive rated for 11A (7.5HP @460V) on a motor of that size, at 1Hz (the lower limit of SVC accuracy) the current could be only .183A, so the sensors must have a range of accuracy that wide (60:1 ratio). But if you connect a 2HP 3.4FLA motor to that same drive, at 1Hz the current could be as low as 0.056A, it's virtually impossible to get a range that wide (195:1) in a current sensor with the kind of accuracy needed for SVC.

But yes, as I said, if in V/Hz mode, no issue.
 

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