control valve or speed controller

[Maxflow]

If I use a motor speed controller on my bench do I still need
my flow control valve. I am going to make my bench single
direction flow. If I only need motor speed control how many motors do I need to control, just 1 or 2 or ? My plan is to
use a router speed controller.

Thanks.

[200cfm]

On my bench I went with 5 motors with electrical control on two motors. My motors are not all identical. Some are stronger than others. But the depression control is very good at 28" wc as long as I don't run them to long. My goal was up to 200 cfm capacity and higher capacity benches are going to require more motors but I would think at a minium two controlled motors for a start to see if it can give you the depression control you need. Everytime you change the lift or make a port flow change improvement the depression will shift and you will need to make an adjustment back up to a 28" wc test depression. I used standard 600 watt light dimmer switches. No issues so far and I like the on/off variable control on the two motors. My stategy is: Power up the motors necessary for 28" wc test. Mark or read the incline rise point down to the milimeter. Confirm that both manometer are stable and shut down the motors. I then use math to zero in on the cfm flow. Then I will adjust to the next lift valve and start the motors again. This reduces the heat on the motors. Allows cool down and time for my head to think apart from the noise.

[Maxflow]

200 cfm did you eliminate the flow control valve(mercdog syle bench)or was yours designed for motor control from the start.
My thinking on the router controller is that it is designed
for motor use.

Thanks for the info.

[dragv6]

My moter supplier steered me away from speed control with varying voltage due to motor getting to hot especialy when left on with prolonged use. Instead will use a water globe valve that came from the original stuska dyno control valve.

[Tony]

It is not really possible for a motor "to get too hot" with a speed controller.

Running a motor flat out with completely blocked internal cooling flow most likely will burn it out, regardless of which method is actually used to control flow.

But remember, motor drive power rises hugely with the flow and pressure requirement. Reducing motor rpm to half will roughly reduce flow to half, and pressure to one quarter, and motor drive power requirement to one eighth.

A motor running at only one eighth of full power that still has maybe half the full maximum cooling airflow passing through it, is definitely not going to run hot.

A motor speed controller will use less electrical power, and the motors will run cooler and make a LOT less noise, and probably last a lot longer as well.

[racehead]

Tony, from Terry Terezakis calculations." a motor should not be operated below 25 cfm each, in the order to not overheat the motors, as the working air provides the colling".

According to him to change the variable speed should be obtained by use of a variac, the second option is the triac, solid state control and the least preferable vfd.

Where can I find a triac or router speed control for 220 volts.

[Tony]

[1960flh]

Look for some historical posts, I posted a link to Payne Engineering they make several solid state units even with remote pot for easy install and the price is reasonable.

Rick

[dragv6]

Would this work?

[Tony]

[Tony]

I still believe your money would be best spent on an e-bay variac.

Just make sure that it works smoothly over the whole adjustment range with a light bulb attached to the output. There should be no flickering or sudden jumps in brightness anywhere, and it should feel smooth to turn.

*Hint* A large variac is a very handy thing to have for slowing down really big electric drills. Especially for honing cylinder blocks, or drilling very large diameter holes. These drills typically have a slow range speed of 250 to 350 rpm which is often miles too fast for some jobs.

[racehead]

Tony, I just wanted to point out that a motor operating below 25cfm is also bad because it will overheat. Your point of view is also right.The triac as a speed controller, it clips a A.C. signal and it is not good for the motors. In Europe as you know the 220-240 volt triac speed control are too expensive, in the United States they are cheaper. I went to the eBay they have the variac but they are kind of heavy to send it to Europe, anyway they are the best to control the speed of brush type motors because those motors like to see the resistance. I wanted to buy the 16-1234 surplus center vacuum mototrs but they are one stage motors and in a flowbench they recomend the two stage motors. Can you or anybody else explain to me the difference in detail if possible.

[Tony]

One stage vacuum motors have the motor driving a single rotor centrifugal blower mounted directly on the end of the motor.

With two stage vacuum motors there are two centrifugal blowers mounted on the same shaft, one behind the other. The air passes first through one, then the other, and this greatly increases the maximum available developed air pressure, (or vacuum).

The whole thing is usually built into a common round pressed metal outer housing. It is usually not very obvious just by looking, if a vacuum motor has one or two stages.

At higher developed pressures two stage vacuum motors can operate more efficiently, but they also have the unfortunate characteristic, that pressure falls off faster with increasing flow, and pressure rises far more steeply as flow is restricted.

That is not a very desirable characteristic for us, but it is deliberately designed into a vacuum cleaner to give greater suction against the floor, but not allow the motor to be overloaded too much with full unrestricted open airflow. The vacuum cleaner manufacturers build in this characteristic deliberately. For us it is an absolute curse. It means your bench may be likely to implode or burst from overpressure if flow is accidentally restricted, and both pressure and flow die off at a disappointingly high rate when you are trying to flow something particularly large on your bench.

That is the main reason I much prefer a large single stage industrial blower to multi vacuum cleaner motors. The pressure stays much more constant over the whole flow range. It is structurally a lot safer for the bench too.

Everything is cheaper in the US, particularly as the US dollar continues to sink lower. But just as you say, shipping stuff overseas from the US often costs far more than the part is worth, and not just for heavy objects either.

A triac controller will certainly never hurt the motor, it is far more likely that the motor will blow up the triac !

The beauty of a variac is that it is just a simple transformer, and is completely immune to the damaging effects of very high voltage transients or high electrical interference.

I am not familiar with the situation in Europe, but in Australia we have weekly papers published that are full of nothing else but second hand goods advertised by private individuals. There are some other on line secondhand websites like e-bay too. E-bay is probably the most famous, but surely Europe must have some similar if less well known secondhand websites ??

[Maxflow]

I sounds like speed control is the way to go. Is there any reason to keep the flow control valve in place. I plan on single direction flow. One more ? what type is a router speed controller, and will it work?

[racehead]

The router speed cotrol that I know of are triac. Try : www.rockler.com. They have one for 120 volts, 20 amp.