rwdford wrote:
One thing I found is that the pot turns significantly before the motors just start to turn, probably over 1/8 turn, indicating the 470K resistance may be a little larger than needed, the sensitivity is a little too sharp even when adjusting 2 motors
The best solution to the sensitivity problem is fitting a ten turn potentiometer.
These are difficult to come by in values as high as 500K, but someone here at the Forum did discover a source of suitable 500K ten turn potentiometers, and its a good solution.
Fitting a larger diameter knob also helps a lot.
There are a few problems with any phase contol system. The first being that the motors typically require about 15v to 20v before they will begin to turn. So the first bit of potentiometer rotation nothing happens.
The other problem, especially with simple low cost modules such as the Kemo, is they just use a resistor/capacitor timing circuit to set the phase control timing range.
Any phase control system becomes erratic at the extreme ends of operation around the mains zero crossing points. So the range of adjustment MUST be deliberately limited to something less than 0% to 100% control range.
That, and component tolerances mean that a Kemo module might only go up to 92% or 95% or something (?) maximum, to keep out of the erratic triggering range right at the very top.
The more expensive phase control modules (such as those supplied by Bruce) use a microcontroller to set the firing angle.
The software is smart enough to allow full range adjustment from maybe 1% to 99% and its very linear in operation and reliable, and the control inputs are fully mains isolated.
Its also a lot more expensive than the Kemo, but also capable of a lot higher power.
I also like the idea of a 16A breaker rocker switch feeding the controller and a pressure switch to cut power to the motors if the bench reaches say 38" or 39" to save the DM and a switch having to be pressed to turn the motors on again.
That is a good idea for any flow bench where blocked flow can suddenly increase the pressure to dangerous levels.
It depends on the characteristics of the air blower, some hardly change pressure at all, others can spike incredibly high if flow is blocked.
Out of interest can the automatic motor control be used with this type of power controller if I was using 2 or 3 of them?
Kemo can supply an isolation module which replaces the potentiometer, and provides a fully isolated dc control voltage input to the Kemo power module. The automatic pressure control system can then be connected to the input of this isolation module. Its been done before, and definitely works.
I remember seeing a bench from Finland on here that was using 3 of them and automatic vacuum control but not sure how he has done this
He would have used three Kemo isolation modules, and three Kemo power modules to run three groups of motors off each of three phases.
There are now several three phase benches in operation around the world, and as far as I know, all have the automatic test pressure controller.
Also known as the infamous "Warpspeed" on some other Forums.
