I wonder if there is a very simple way to control one or two light bulbs in a box that are providing heat for my Tomato seed Propagator sitting on top ... i.e. I need the heat underneath...It would be wonderful if I could get a static 80 degrees ???..I am not an electrical person and I live in New Zealand which is a drawback in many ways for trying to find off the shelf items...I would be sincerely grateful for any tips on how I could do this.


I found this on the NZ online auction. Would this be what one requires?

  • \$\begingroup\$ Buy from a supermarket? \$\endgroup\$ – Andy aka Aug 14 '15 at 23:22
  • \$\begingroup\$ Consider a "Heating Pad" thermostat combination. A "Variac" may adjust the temp. enough. \$\endgroup\$ – Optionparty Aug 15 '15 at 15:33
  • \$\begingroup\$ Re Update: That certainly looks like it would do the job at a price that would be hard to beat. \$\endgroup\$ – Charles Cowie Aug 15 '15 at 16:56

I just built something like this, actually it was for a much larger heat box to test some servers but the concept is the same. I bought one of these cheapo ($27) pid controllers on amazon. I think this one requires you to get the equally cheap AC relay a little further down the page but there is also another model that has a relay built in.

enter image description here

Notice it comes with a nice thermocouple you can place where you want to monitor the temperature. Then I grabbed some ceramic light bulb fixtures from lowes, and wired everything together.

It's pretty simple this controller has a relay output and it has a built in PID loop to get to and maintain whatever temperature you set it to. I've found them really useful for all sorts of little projects.

Here's a page with the manual, some useful information, and more pics.

As usual be careful playing with AC it can kill you.


The very simple way to do this is to put a thermostat in the box and connect the power to the bulbs through that. You will need the type of thermostat that is used for electric baseboard heaters or electric heating elements that are built into the floor of a room. They would probably be called "mains voltage" or "line voltage" thermostats. If you have that type of heating available in New Zealand, the thermostats should be available.


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