variable heat-mat

Hi everyone,

I would like to make a system which would permit to maintain constant temperature (28 degrees Celcius)in my terrarium.
For this I would use a sensor and make a program that would lower the mat power if temp is too high (and the other way around). The problem is that those heat mats are adapted for 220V (5W), so I can't use a mofset, which would have permited to use analogWrite. I thought of using a relay, but I think they only have ON/OFF positions, while I would like to regulate the intensity.

Do you know any solution?
Any relay have adjustable (progessive) intensity?
Or do you know any decent heating mat that would work under 100V?

Thank you

Suggest you use several of these:

Suggest you have several on all the time and modulate several as needed.

A normal heater, oven, refrigerator, etc., cycles on & off. You'd make the heat com-on when the temperature is below 28 degrees and off when it's above 28 degrees. There is usually some hysteresis or "swing" do it might come on at 27.9 degrees and shut-off at 28.1, etc.

Heaters are regulated by low-frequency PWM, in effect. The cycle time might be 1 minute or more, the duty cycle sets the average heating rate, the high thermal inertia of most situations smooths the temperature fluctuations.

An SSR might be useful for silent switching of a mains heater element.

If you want to use a 220 VAC % Watt heater pad I would suggest, as mentioned, using a SSR (Solid State Relay) and use your uC for control. One potential problem is the SSR leakage current. Your 5 Watt 220 VAC heating pad only draws 5 Watts / 220 Volts = 22.7 mA. Not very much current at all. Should you choose a SSR solution I suggest you look at the data sheets in detail and understand leakage current.

Next you will need some sort of sensor placed at the point where you want temperature control to happen. Have you given any thought to a sensor? You may wish to consider a DS18B20 for simplicity and easy compatibility with a uC like an Arduino.

Finally the actual control which can be as simple as ON/Off or more complex like using PID (Proportional Integral Derivative). The latter will afford much tighter temperature control but requires working with it a little. A Google of Arduino Temperature Control should get you going and a Google of Arduino PID Control should get you some examples of PID control loops.

Also as mentioned there are low DC voltage heater mats available and easily controlled with a simple MOSFET circuit. I have seen 12 VDC mats for keeping coffee cups warm in automotive applications in addition to those linked to. A simple Google of heater mats should find you plenty.

A heater mat really doesn't care if you apply AC or DC as long as it is just a heater element.

So now you have some decisions to make.

Ron

Hi,
GOOGLE

usb coffee warmer

Tom... :slight_smile:

You know... the BED heaters for 3D printers are not a bad idea...

Amazon Bed Heater

Common Parts can be used... copy design from open source REPRAP even. 12V Power Supply... can use mosfet...

Those look nice.