For a small filter like this one an inline type fan could work just fine.
Inline type fans are so different than squirrel cage blowers that a squirrel cage blower with no static pressure will burn up very quickly because they are designed to operate at load at a certain speed and without that load they overspin. Inline type fans have no such requirement. So dialing a squirrel cage blower by adding to the static pressure is no problem. Inline fans are utterly worthless in the face of static pressure.
Inline type fans use DC motors, squirrel cage blowers use AC induction motors. It's all a little complicated to explain but they require a certain voltage and frequency and when you adjust the voltage things get really weird on them.
- Changing Applied Voltage: This method, even though easiest, it is rarely used. The reasons are (a) for a small change in speed, there must be a large variation in voltage. (b) This large change in voltage will result in large change in flux density, thereby seriously disturbing the magnetic distribution/condition of the motor.
Now I used to use a speed controller for my old flowhood once upon a time. No problem at all. Everything was grand.
Then I built a new hood with a new slightly larger blower but still way under the rated 15 amps of the controller.
I was running the hood for a few hours testing it out. Went to turn it off and the controller looked funny.
It was half melted. Turned it off. Touched the motor of the blower. It was around 350 degrees...
Researched why this is happening, turns out you cant speed control most of these motors with a simple tool speed controller.
I assume the blower that worked fine with the controller only needed a small adjustment in speed but the bigger one needed a little more adjustment that exasperated the problem.
So then I made a post apologizing for advocating speed controllers and telling bout it.
Anyone can google all about this. It even says specifically NOT FOR SPEED CONTROL in plain English on most of the dayton blowers from grainger.
SO DONT PUT A CHEAP TOOL SPEED CONTROLLER ON YOUR SQUIRREL CAGE BLOWERS! YOU COULD BURN YOUR HOUSE DOWN.
Please if you could refrain from telling people to add a speed controller to their flowhoods now that you also know.
I think I was the first one to advocate for the router speed controllers many many years ago, after noticing that they looked identical to the more expensive "fan speed controllers" and they indeed are the same things. They just aren't good to use for squirrel cage blowers.
Edited by sandman, 10 March 2021 - 06:39 AM.