Speed controller

L

LazyElectrician

Member
Location
North Jersey
Occupation
Lead / Estimator
Hey everyone,

I wired up a metallurgical testing laboratory in North Jersey last year. After settling in, the lab staff realized they need speed control for a few of their exhaust hoods.

Currently, the hoods run at full speed 24/7, but overnight they’d like to slow them down—just enough to safely ventilate corrosive chemical vapors without wasting energy or wearing out the fans.

Each hood is powered by a 3-phase, 480V, 1.5HP motor. I’m looking to add a VFD to control fan speed, and I’d like to mount the drive near the existing contactors, with a remote speed control (potentiometer or auxiliary controller) installed near the hood for easy access.

Could anyone recommend:

  1. A suitable VFD model for this application, and
  2. A good remote speed control or potentiometer setup that pairs well with it?
For background — I’ve done control wiring before (conveyor belt systems, a while back), so I have a basic understanding of motor controls, but I’d appreciate any insight or product recommendations from folks who’ve done similar lab ventilation setups.
Thanks in advance!IMG_4936 Large.jpeg​
 
I had great tech support with Danfoss & Allen Bradley drives. Its has been years since I connected a speed pot on a drive. I have used two methods. Either used the pot value drive company recommends ( ones that I wired in were 5000 Ohm pots ) . Have used a switch with a pot for day time speed then the a pot that had a locking nut to set speed for nights. In our research 12 story buildings we has JCI & Siemens control the numerous exhaust hoods. BSO systems are not cheap but have the advantage that when I got called in on weekends the control company can have techs remotely access the system to see if problem was on their end. They had monitors that would adjust exhaust speed on roof top 40 to 75 HP motors depending on how many work stations had sliding glass doors open. On critical areas we had drives with bypasses . In the event a drive failure the drives with 3 contactors ( some only had two ) allow you to run motors at full speed while troubleshooting drives.
 
Fairly straightforward application, I would use a Rockwell PowerFlex 523 (unless you want Ethernet connectivity, in which case 525). Simple programming, very reliable. Has a built-in speed pot, but you can use any 10k ohm remote pot instead. You can also just set it up (called “Step Logic”) to run at up to 7 speeds on a built-in timer; so for example full speed all day, low speed at night, no need for a remote pot or for them to remember to turn it down. There are other brands that do this too, I just know that one really well.

You mention contactors: DO JOT wire a VFD downstream of a contactor, it will kill the VFD. Use the VFD to REPLACE the contactor.
 
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