Hello,
Here are the facts:
VFD Drive
No Encoder
V/Hz Control mode
Load is Constant Torque, with high starting torque required
Motor = 1800RPM rated with 3% slip, 460V rated
V/Hz typically limited to 150% FLT at 3 Hz. Below 3Hz it get wishy washy and you need all sorts of voltage boost which you don't know if you will have enough torque to start the high inertia load.
Question:
I know the load is is at 0RPM (0Hz) at starting, but why can't I just have the drive in V/Hz send the signal to start the motor at 3Hz (87.5RPM). I am not too concerned with current inrush etc. I just need to make sure the load starts.This will put me in the portion of the Torque/speed curve for the capabilities of V/Hz that would allow 150% FLT. It seems like the drive will try to start at 0.001Hz (something arbitrarily close to 0 Hz) and work its way up with a possibility of the load not starting, but if the drive continues to increase the voltage and current without caring if the motor actually started or not eventually it would get to 100%Voltage (460V)and 60Hz at that point the motor would be able to be started at Full Load Torque and the 150% FLT.
What am I missing? Why is there such concern of using V/Hz at low speeds with high starting torque requirements.
Here are the facts:
VFD Drive
No Encoder
V/Hz Control mode
Load is Constant Torque, with high starting torque required
Motor = 1800RPM rated with 3% slip, 460V rated
V/Hz typically limited to 150% FLT at 3 Hz. Below 3Hz it get wishy washy and you need all sorts of voltage boost which you don't know if you will have enough torque to start the high inertia load.
Question:
I know the load is is at 0RPM (0Hz) at starting, but why can't I just have the drive in V/Hz send the signal to start the motor at 3Hz (87.5RPM). I am not too concerned with current inrush etc. I just need to make sure the load starts.This will put me in the portion of the Torque/speed curve for the capabilities of V/Hz that would allow 150% FLT. It seems like the drive will try to start at 0.001Hz (something arbitrarily close to 0 Hz) and work its way up with a possibility of the load not starting, but if the drive continues to increase the voltage and current without caring if the motor actually started or not eventually it would get to 100%Voltage (460V)and 60Hz at that point the motor would be able to be started at Full Load Torque and the 150% FLT.
What am I missing? Why is there such concern of using V/Hz at low speeds with high starting torque requirements.