Temperature and humidity control for an incubator using Reef-Pi

[Litserv]

I have an incubator that I use to incubate Testudo Hermanni eggs. For this I use a RPI with Reef-Pi.

While the temperature control works great for my aquarium, I have major problems with the incubator:
The temperature in the aquarium runs within the set hysteresis around the set point.
But the temperature in the incubator shows a fluctuation range of 2 - 3 degrees Celsius, although I have set 0.1 degrees Celsius as hysteresis.
A DS18B20 serves as temperature sensor.

I assume that the 'inertial mass' - air instead of water - is much too low and that is why the overshoots occur.

Therefore, I imagine a proportional control instead of a 2-point control for the temperature as a solution: The heating power adapts to the difference between the set temperature and the actual temperature. This can be done very well via PWM.

In Reef-Pi, a PWM connection should also be selectable under temperature control. Two parameters would be useful: offset and slope.

Can this be implemented in Reef-Pi?
Or is there another solution or a work-around?

I am grateful for any suggestion for a solution.

 

[Sral]

I think your analysis is correct: the thermal capacity of your air is much lower and the heater is therefore too powerful and/or has too much thermal capacity (so it heats far after it has been turned off).

Another possibility is that your sensor isn’t coupled well. If it’s designed for water, which has higher thermal conductivity if I’m not mistaken, it might heat up much slower than the air around it, switching off your heater much later. You could either try to remove the sensor’s shielding or improve its coupling with a kind of heatsink with fins and/or put it into the airflow of a fan.

 

[Ranjib]

This will require some development work (coding) but I am happy to incorporate such feature if its of common use. I had thought of this (variable control based on analog input, instead of just digital on/off) while building the control logic, but i could not find any such output equipment (e.g. heater or ato) where it will be useful. Do you have any heater in mind that can take pwm input?

 

[Litserv]

analysis is correct

Thanks!

a kind of heatsink with fins and/or put it into the airflow of a fan

Good idea: "... heatsink with fins..." I'll try it, because a fan is not enough.

Do you have any heater in mind that can take pwm input?

Yes, using a module between Reef-Pi (PWM) and any Heater:
Unfortunately this module will not be sold resp. shipped to Germany. I found similar modules, but out of stock for now.

Next solution: DIY with MOSFET: https://www.instructables.com/AC-PWM-Dimmer-for-Arduino/

This is what I go for. I don't recommend it everybody, but I'm familiar with AC 230V.

 

[Sral]

Good idea: "... heatsink with fins..." I'll try it, because a fan is not enough.

Oh, just try to keep the thermal mass of the heatsink down ^^

 

[Litserv]

using a module between Reef-Pi (PWM) and any Heater

I found others, available in Germany; e.g.:
I ordered 3 and will test the functionality over the weekend and report.

 

[Sral]

I found others, available in Germany; e.g.:
I ordered 3 and will test the functionality over the weekend and report.

Nice ! I might actually use that too ramp up my flow pump, or dimm it, if it is too strong.

When you have set them up, can you write whether that circuit will still output AC or if it reduces it to pulsed DC ? Not sure if the latter works with typical Aquarium pumps.