PID or Relay for Circulating Shower

[mess]

TL;DR Summary

I am making a closed loop circulating shower for my campervan, and I am trying to decide between PID and Relay.

I am considering using PID (autopid arduino lib), in order to control the heat, with PWM and a 50amp mosfet heating a 40amp 24v heating element in a 3litter tank, but I am thinking, that since the water is going to be circulating, and sometimes losing heat to a person, sometimes falling straight into the drain, it will be varying anyways between +/- a few degrees, does it even make sense to use PID? or should I just use a 50amp relay with a basic range cycle?

 

[Baluncore]

It will depend on the reservoir time constant. You might do better with a fixed thermal mass in contact with the water, maintained at the required temperature.

 

[DaveE]

I think you could do it either way. My preference would be to avoid relays, they wear out. However, relay circuits are easier to design. The switching device selection is, in general, a separate issue from the control method.

 

[Windadct]

A simple arduino set up may be best - even if just to make edits in the future. Look at an ATtiny85 - not "native" in Arduino IDE but can be done.

On the Recirculate point - if you are recirculating water from the show back to the heater - be wary, as the pollution ( oils, soap, organics, etc) can really make a mess of a heater.

 

[russ_watters]

Seems like overkill to me. A simple temperature switch and relay is probably sufficient. I would not use a pid controller.

 

[dlgoff]

IIRC my Neslav RTE-9B circulating water bath doesn't even use a PID temperature controller.