Overkill?

Status
Not open for further replies.
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
A few weeks ago I started a thread VFD on 1PH . I got back there today for another project and thought I would check the input current on the VFD. Line current of the single phase input is 2 amps for 1 of the output. When the pump motor is at full speed, fully loaded @ 60Hz the amp draw was about 25.5 according to the VFD display. Input was 51. Fluke 337 true RMS.

The recommended VFD for this single to three phase conversion was rated 30 hp @ 230 v. Input amps of 98 put my supply @ 125 amp single phase.

Nothing like having a little to spare.
 
You lost me a little bit, but I think you are questioning if the drive size is overkill with these figures:

actual input current at full load = 51 amps

drive rated input current = 98 amps

supply branch circuit is rated 125 amps.

Is that correct?

I'm not a drive expert myself, but it seems it maybe could have been a smaller drive, but next question may be what is actual motor load compared to motor rated full load? Maybe the motor itself is a little overkill for the load also.
 
ptonsparky said:
The overkill IMO is the required 125% of the vfd nameplate for this installation. The drive was specd for working with the proposed motor. I don't have choice in that. I don't care for.the required 125A feeder for a load that at most draws 51A.
Click to expand...
I see what you are saying and agree with you.

Been quite a while now but I installed a 250 Hp drive on a 50 Hp motor once, only because they had the 250 Hp drive sitting there on a machine that is no longer used. New owners never used that part of the plant as they have no use for the set up in that part, although I don't know why they wont sell that equipment either, but that is another story, bottom line is a no cost 250 Hp drive is still less expensive than a new 50 Hp drive. We left the conductors and overcurrent device as is - already set up for 50 HP motor - and well below what the 250 HP drive lists as input, and have never had any problems. Been that way for at least 10 years now.
 
Status
Not open for further replies.
Top