VFD reversing
VFD reversing
(OP)
I cannot get an answer from the mfr, nor does a search produce an answer....but I have a VFD controlling a 3HP 208v motor. I need to occasionally reverse the direction somewhat immediately. I've hooked it up and have been playing with it and it seems to work, but without actually telling it to STOP between direction changing, am I overworking the VFD (and/or motor) by switching directions on the fly? I realize the frequency will ramp up/down based on my VFD settings, I just want to be sure that I'm not going to do any harm by not stopping it between changes.





RE: VFD reversing
What you can do is decrease the ramp time and keep an eye on the resulting current draw. Keep decreasing ramp time until your current draw approaches the limits of the supply circuit.
Good luck!
RE: VFD reversing
The drive will not, however, change direction instantaneously. It will follow the deceleration ramp to zero speed, then acceleration ramp upto commanded speed in the opposite direction.
RE: VFD reversing
RE: VFD reversing
If you want to increase the slow-down speed, or do it very often, you need to install an external resistor rated for the energy dissipation.
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD reversing
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RE: VFD reversing
RE: VFD reversing
If you are using a controlled ramp time, then I see no reason why this should cause problems with the motor if the ramp times are correct for the load inertia. It is only the same effect if you were stopping/starting in the same direction.
If the ramp down time is too short then the drive will typically trip on overvoltage due to the regenerative energy. If the ramp up time is too short then it will typically hit current limit.
Either way, if the drive is constantly tripping and you ignore all these trips then, as jraef points out, it has the potential to damage the drive (eventually) but before that time happens, I'm quite sure you would be so tired of resetting trips that you would have increased the ramp times.
RE: VFD reversing
Another question I've got, and I'm kind of surprised how little info I can get on it...there's NO mention of it in the installation and operation manual (Leeson 174279)...there are B- and B+ terminals on the unit. My guess would be that's where I would install a resistor if necessary. After reading up on it several months ago, I seem to remember that I would most likely not need to worry about it at the time.
RE: VFD reversing
Leeson are usually quite good with tech support questions, have you asked them?