PTS Flowbench Forum

Just thought I'd let some of know what I found with having phase controllers on your bench.
First if your running a regular depression of 28' to 48' then you will be fine. But if you decide to start testing at higher depressions then you may start to discover motor fluctuations or a chopping sound. I found this started to occur at around 80"WC.
Not that anyone is testing at that depression with an orifice type bench but I just thought I'd let everyone know. I guess a Variac would be the solution to this problem, but not cheap

Are you sure this is a affect of the phase control or is it that the motors cant move enough air and begin cavitation between motors.

At 80" how many motors and how much flow, if i read into your other posts in this testing it should only be 1 motor.

Rick

I ran it with three different tests. First I ran both motors with the controller and they started failing at the lowest depression. Then I ran one motor with the the mains and one with the controller, this gave me more depression but then the chopping noise started and it was coming from the motor with the controller . I could also feel the air pulsations coming out of the back of this controlled motor. Finally I just ran both from the mains and this gave me the highest depression before the motors started to stall.
With both motors controlled it was around 80"WC . Running straight from the mains gave me around 115"WC. I guess killing the power to a motors under high vacuum is not a good idea.

What controller were/are you using?

I have seen little to no loss of flow with my solid state relay/phase angle control?

Quite possible the controlled motor was being over powered (un-even flow) by the non-controlled motor? Not sure how you have them hooked together in your flow path?

I'm using an SSR 25AVA. I also have a triac based controller that is around 15 amps.
Motors are wired in parallel and bolted next to each other on the back of the test rig.
What is the max depression you have run your bench at?
Also I'm not that sure it's a good idea to run vac motors at really high depression with little to no airflow to cool them.

Vacuum motors run at full power, and almost blocked flow in the original vacuum cleaner application they were designed for, and should have a much easier life in a flow bench, especially at reduced voltage.

One test I suggest you try is placing a light bulb across the supply to your motors. If it flickers, then there is a good chance your Triac is misfiring.
There is nothing wrong with phase control, but for an inductive motor load, back to back SCRs will be far more predictable and offer much better control completely free of the misfires and surging that sometimes plague Triacs in this application.

I would try the light bulb but it does the same thing without the controllers.
I think the motors are competing for the small amount of available air and I don't think anyone here has run this high a depression to test the effects of it on two or more motors.