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I am working on updating an existing product which uses a resistor network (with one potentiometer) and a phase controller (PHS230A6) to vary the speed of a blower. My goal in this redesign is to make it a more digital operation which would allow me to use one potentiometer (digital incremental encoder) to allow adjustment to the blower speed as well as other things (adjust settings on a display).

I have done a lot of research and have looked into PWM options which the lead engineer has ruled out due to the complexity of the snubber design and the fact that the existing PHS230A6 and resistor network have many years of trouble free experience.

Does anyone have any other ideas or suggestions on digital blower speed control? I have contacted the MFG of the PHS230A6 and they have no suggestions.

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  • \$\begingroup\$ Out of curiosity, and as something that stood out to me, how is the snubber going to be so much more complex than a resistive network + phase controller, it's a couple different diodes or caps to spec out. \$\endgroup\$ May 28 '13 at 17:32
  • \$\begingroup\$ Don't fix something that works unless of course there is another motivation like increasing profit/sales or reducing re-work/labour/failures - just a thought. \$\endgroup\$
    – Andy aka
    May 28 '13 at 18:12
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If you are worrying about the complexity/cost/lifecyle of the snubber design then I can only assume you're looking for the cheapest solution. If that's the case why bother going digital?

Digital controls on an AC motor are usually only employed for torque or fine speed controls. If you're just using this on a blower, your engineer is right. If you are trying to do fine control of some sort then the snubber is the least of your worries. Here's a good overview on PWM AC control techniques which might help.

As an aside if here is a link if you want to know bit more about snubbers. They do undergo a lot of stress and are often the failure point in PWM designs. The linked article also briefly discusses component selection and reliability.

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  • \$\begingroup\$ My thinking behind going digital is to allow one pot to do multiple things; to allow for ease of system setup and overall navagation through the product display (temp sensor readings etc..). Thank you for the feedback as well as the links provided. \$\endgroup\$
    – becjasl
    May 28 '13 at 18:01
  • \$\begingroup\$ If that's all you want then you could just sample the voltage on the analog pot with your microprocessor and make your own digital pot for your user interface using voltage ranges with hysteresis for settings. \$\endgroup\$
    – user6972
    May 29 '13 at 2:31
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Just an idea rather than the answer: http://www.galco.com/buy/SSAC/PHS230A6 - 230V, 6A solid state relay phase controller, analog out, variable resistance input. This seems a perfectly serviceable controller. Perhaps a way forward is to keep the PHS230A6 and figure out a way of replacing the input resistor/pot network so that it can be controlled digitally. (see below) enter image description here

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  • \$\begingroup\$ This is the route I want to go but the pot is varying 120V (1A). I do not believe I can interface to an IC. Correct me if I am wrong? I really like the idea \$\endgroup\$
    – becjasl
    May 28 '13 at 18:31
  • \$\begingroup\$ Not an answer. The blower speed controller is controlled by a variable resistance between two terminals, not a voltage. There aren't many good ways to electronically create a variable resistance that is isolated to full mains voltage. One that comes to mind is to simply attach a small servo to the control pot. \$\endgroup\$
    – Dave Tweed
    May 28 '13 at 21:37
  • \$\begingroup\$ I did open with "just an idea rather than an answer" If the internal circuit is a phase controlled diac/triac configuration then its a non starter. A rotary pot could be controlled by a servo or a worm/gear with stepper motor or change to a linear pot with a linear actuator - bit like a mixing desk with presets. \$\endgroup\$ May 29 '13 at 10:27

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