Powering and using 12V fans for cooling PID

I’m building an insulated cabinet that will break out a door-less mini fridge into 1) a slightly larger chamber at fridge temperatures (used for lagering) and 2) two temperature controlled fermentation chambers. I’d like to buy a Brewpi Spark 3 and use it to control the latter two chambers. The cooling PID would turn on a case fan that would send air from the fridge chamber through ducts into the fermentation chamber (with a passive return air duct). The heating PID would probably just control a reptile heating pad or some other small heater.

I have a couple of questions regarding how to use the Spark 3 to power and control the fans for cooling.

  1. Is it possible to power the fans using the 12V power supplied to the Spark 3 with the optional AC adaptor? I saw that there is a valve-control breakout board that appears to do this. Is it drawing 12V through the RJ12 ports?
  2. The control for most fans appears to be PWM, can brewpi use this for the cooling PID. It seems potentially a little different then just controlling a relay for a fridge compressor with a high/low signal.
  3. Would it be simpler to just use a DC blower fan on a DC/DC relay instead?

Thanks in advance for any advice!

I think would use a DC blower fan anyway, because they are much easier to mount and to connect to a tube to link both rooms.

The valve boards do not require much current. A decent fan will require a lot more. The 12V output is can supply only 1.5A.

Using a DC-DC relay will be a more robust and safer approach. It will have less change of causing instability or damage to the Spark.

The controller has ‘slow pwm’, with a period of at least a couple of seconds. This will not speed control the fan, but turn it on and off periodically. this should be fine for your setup I think. I have made provisions on the board to support fast pwm on some output pins in the future, but the current software version does not support it.

Thanks for the advice. I’m definitely leaning towards a blower fan at this point. The form factor will simplify my ductwork and it sounds like it will be simplest to just to wire up with a DC-DC relay.

How fussy is the Spark 3 regarding it’s power? Can it share 12V DC with the fans to further simplify my setup? I’m looking at getting a Meanwell MDR-60-12 which is rated for 5A whereas the fans I’ll be using are only rated for .7A and I would only be using 2-4 (and rarely all at the same time). If that would be cutting it close, the MDR-100-12 is rated for 7.5A, would that be safer?

Not fussy at all. Splitting of 12V before the spark is fine. It’s a better idea than splitting it off after the spark, because then all the power for the fans will have to run through the spark.

The MDR-60-12 should be plenty.