over current

Status
Not open for further replies.
1

1965mt

Member
Location
Virginia
I have a VFD on a pallet elevator that will trip on over-current when the motor is lowering the load.
Has anyone on this forum seen this behavior?

The drive is an AB, the motor/gearbox is SEW

Going up is no problem, only when the pallet is lowered. If the pallet is loaded by 1/2 then it does not trip.
 
1965mt said:
I have a VFD on a pallet elevator that will trip on over-current when the motor is lowering the load.
Has anyone on this forum seen this behavior?

The drive is an AB, the motor/gearbox is SEW

Going up is no problem, only when the pallet is lowered. If the pallet is loaded by 1/2 then it does not trip.
Click to expand...

Has this always been the case or something new? Not sure if it applies here, but since you say this only happens while lowering, I will assume it is drawing the excess current because it is trying to maintain a given speed while descending. The weight of the load is trying to pull the motor along faster than it's reference due to gravity and the VFD is counteracting this which causes excess heat and an O.L.

Just my guess based on what I've seen but someone else may have a better idea or be able to explain it better
 
MattS87 said:
Has this always been the case or something new? Not sure if it applies here, but since you say this only happens while lowering, I will assume it is drawing the excess current because it is trying to maintain a given speed while descending. The weight of the load is trying to pull the motor along faster than it's reference due to gravity and the VFD is counteracting this which causes excess heat and an O.L.

Just my guess based on what I've seen but someone else may have a better idea or be able to explain it better
Click to expand...

It is a new installation. I believe that the braking resistor is missing which would confirm what you are saying.
 
1965mt said:
I have a VFD on a pallet elevator that will trip on over-current when the motor is lowering the load.
Has anyone on this forum seen this behavior?

The drive is an AB, the motor/gearbox is SEW

Going up is no problem, only when the pallet is lowered. If the pallet is loaded by 1/2 then it does not trip.
Click to expand...
Does the VSD have regenerative braking?
 
Are you sure it is over CURRENT? Seems odd on a lowering operation, but Over Voltage would not be unusual if there is no braking resistor. But it COULD be OC depending on what drive it is. Some of the A-B PowerFlex drives can do what's called "Flux Braking" when used in Flux Vector Mode, and when using that, the Flux Braking operation is tracked by the VFD's motor protection circuit in order to avoid damaging the motor. Flux Braking is not a good thing to use on an elevator application though, so if that's what's going on, it's a bad design decision.

Please update us with details; VFD model and size, motor size, accurate trip code etc.
 
Status
Not open for further replies.
Top