Current limiting with VFD

[Mark Snodgrass]

Something else you have to consider with a larger motor. The no-load current of a larger motor will be higher. For example, a 100hp motor I looked up draws 28A no-load, while an identical motor but at 125hp draws 44A at no-load. That gives you 16 less amps of available power if both are limited at the same value. That would mean the larger motor would actually not be able to provide as much power to what it is driving as the smaller one would.

You may still get yourself out of a bind, but you may be limited as to true capacity.

BCS and DScott, I'm originally from St. Pete till the navy took me away and now in NC.

 

[Bering C Sparky]

BCS and DScott, I'm originally from St. Pete till the navy took me away and now in NC.

Hello Mark,
Good to hear from another Florida Salty Dog.

(We are not so Salty at the moment though, Broke down in Dutch Harbor with engine troubles)

They say that there is a beautiful women behind every tree in Dutch Harbor,..... What they dont tell you is that there are only about 4 trees on the entire island.

BCS

 

[Lancie1]

I saw no motor conductor allowances in the 590 Temporary Installation.

Scott would not have needed any conductor allowance. Because the feeder was oversized at 400 Amps, it could have legally been used for the larger motor.

The machine feeder is 400 Amps. This drive is fused for 200

For example, a 100hp motor I looked up draws 28A no-load, while an identical motor but at 125hp draws 44A at no-load. That gives you 16 less amps of available power if both are limited at the same value. That would mean the larger motor would actually not be able to provide as much power to what it is driving as the smaller one would.

Yes, good point, but in this case the drive had a top rating (according to the User Manual) of 142 Amps. So for the old motor the current limit was set at 127. Now the larger proposed motor needs 16 more no-load Amps. If you add that 16 to the old 127 setting, you get 143. That is still only 1 Amp above the range of the Powerflex, so it could have worked okay with the drive Current Limit Parameter set to 142.

The best solution was what Scott did - installed the proper motor for the situation.

 

[DScott]

Well the motor was a day late, but its in, its up , and running

Thanks everyone for the help, advise, and pointers Also nice to hear from a few people around the corner from the house

Scott