Strostkovy
Titanium
- Joined
- Oct 29, 2017
Like many people, I hate the whine of VFDs. I have often thought of disconnecting the VFD after startup of an inertial load and connecting it to line voltage for the rest of the time it is running. I know VFD's don't like to contactors on their output, but that seems to be because they don't like loads being suddenly connected. I also am aware of line filters, but have heard varied results as far as quieting goes.
The main reason I have never attempted this (other than not having a reason to) is because of concerns with phase matching during the switch. But, we just got a compressor and dust collector with star-delta starters that connect the motor in a star configuration, disconnect it, then connect it in delta. I can hear the delay between the two and I know the motors slow down to at least be a half cycle out of phase, and while there is a slight current peak it really doesn't matter.
The reason I am revisiting this now is because I was considering making blower wheels for some dust collection/air purification/powder booth applications. Blower wheels like these have significant inertia, and would typically use a star delta starter. However, I also am considering two or more motor/blower pairs to run sets of filters so that one can blow off with the blower stopped while leaving the other filters uninterrupted. This would require less air and simpler to construct baffles.
So my question is, what is stopping me from having, say, four 2hp motors with heavy blower wheels, each with a contactor to a single VFD and a contactor to mains power (preferably interlocked)? A motor would connect to the VFD, start, switch to mains, and repeat until all motors have started, then individual motors could stop and start the same way for a blowoff cycle on their filter stack.
I know there would be some control circuitry but I see no reason a finite state machine or sequence of timers would have any issue controlling everything.
And of course there is extra complexity here, but star-delta starters aren't much simpler or surge current/motor friendly, and I'm far more electrically capable than I am slip-clutch or similar capable.
I will say I better implement a phase protection device, otherwise the first switchover from VFD to line with reversed phase would sound soul crushing at best.
The main reason I have never attempted this (other than not having a reason to) is because of concerns with phase matching during the switch. But, we just got a compressor and dust collector with star-delta starters that connect the motor in a star configuration, disconnect it, then connect it in delta. I can hear the delay between the two and I know the motors slow down to at least be a half cycle out of phase, and while there is a slight current peak it really doesn't matter.
The reason I am revisiting this now is because I was considering making blower wheels for some dust collection/air purification/powder booth applications. Blower wheels like these have significant inertia, and would typically use a star delta starter. However, I also am considering two or more motor/blower pairs to run sets of filters so that one can blow off with the blower stopped while leaving the other filters uninterrupted. This would require less air and simpler to construct baffles.
So my question is, what is stopping me from having, say, four 2hp motors with heavy blower wheels, each with a contactor to a single VFD and a contactor to mains power (preferably interlocked)? A motor would connect to the VFD, start, switch to mains, and repeat until all motors have started, then individual motors could stop and start the same way for a blowoff cycle on their filter stack.
I know there would be some control circuitry but I see no reason a finite state machine or sequence of timers would have any issue controlling everything.
And of course there is extra complexity here, but star-delta starters aren't much simpler or surge current/motor friendly, and I'm far more electrically capable than I am slip-clutch or similar capable.
I will say I better implement a phase protection device, otherwise the first switchover from VFD to line with reversed phase would sound soul crushing at best.