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Old 11-10-2011, 12:05 AM   #1
ahave
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Default dual purpose pwm controller

I will be putting together the well known pwm controller box project. The goal is to have this controller be multifunctional in that I would like to be able to use it as a stir plate controller before brew day and use it as a heating element controller on brew day.

Could someone with experience building pwm controllers tell me if it is possible to have this much range in the controller to function in either mode with one design? Or will I need to figure out a way to set a toggle switch to use different caps in order to adjust the duty cycle.

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Old 11-10-2011, 12:16 AM   #2
shortyjacobs
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I feel like you'll want a switching frequency in the 10+ Hz, at a minimum, for a motor, (better if it was much higher), and <1 Hz for sure for a heating element controller, (unless you really wanna kill your SSR quick). "Range" in the controller doesn't matter. The frequency does not change as you turn the potentiometer...only the % the circuit is "on" for each cycle. (So with a 1 Hz PWM, 50% means it's on for 0.5 seconds, off for 0.5 seconds. 25% means on for 0.25 seconds, off for 0.75 seconds).

A switch to switch caps would be easy peasy....a DPDT switch, low voltage, low current, would do the trick.

Really though, they cost ~$10 max to build...why not make two dedicated ones, so you're not having to switch outputs between the SSR for the element and the motor?

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Old 11-10-2011, 01:28 AM   #3
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I suggest the 'bakatronics' board, then rig up a DPDT switch with one set of contacts to change capacitor from standard one to a 2.2uf (for heating element) and one set of contacts to send output from transistor to external SSR(for heating element)...

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