Linear speed fan control for a smoker

[Saison]

Hello there, I'm so rusty at this stuff I squeak. Quick into, I graduated from a CET about 20 years ago. Back then, I could build circuits in my sleep. Since then, I've moved onto industrial instrumentation, and my circuit level electronics knowledge is long gone.

The project I need help with is a smoker temperature controller for my Primo XL. The simplest and most well known option is a small fan (around 10 cfm) to provide the intake draft, with feedback and control provided by a PID temperature controller.

Generally, the 12 Vdc fan is run in the on/off mode, but this presents a few issues. I would prefer a linear control, but that has problems as well. I just need some sort of offset adjustment on an amplifier circuit, I guess, to account for the fan start-up voltage probably not being 0V dc. I would like to be a able to adjust that bottom voltage so that the 0% output from the controller (4mA, 1Vdc or 2.4vdc to the amplifier input) is 0Vdc out of the amp, and 1% becomes a voltage of 3-6 Vdc (or whatever the startup voltage for the fan is). And 100% is 12vDC.

Thanks.

 

[MikeMl]

Google PID and PWM

 

[Saison]

Yeah, I'd rather try to find an analog solution before going that route.

 

[Dragon Tamer]

If analog is what you want, then try using an op-amp based controller. Depending on the temperatures involved, you may need to pick between a thermistor and a temperature sensor. If the circuit is going to be connected to anything else, you may want to include a PWM controller to turn the op-amp DC into a signal that would not cause any ripple in the line. If not just boost the output power of the op-amp with an appropriate transistor. This is a pretty nice little fan controller that should have no trouble operating your fan on PWM: TC649BEPA Microchip Technology Motor / Motion / Ignition Controllers & Drivers

 

[Saison]

The control for the op amp will come from the PID, which will get it's feedback from a TC. I'll just use a resistor to convert the 4-20 mA out to 1-5vCD or 2.4-12 Vdc into an op-amp.