However, I am confused by your term "dimmer switch". The dimmer will regulate the voltage (and therefore, the wattage) of your heater. So if you have a 300W heater, and put it on a dimmer, it might turn into a 100W heater. There is no "switch" part at all, and this would have nothing to do with a controller (as your title implies). If your heater thermostat fails, your tank will still overheat, just on a slower rate, and max out at a lower temperature.
"Dimmer Switch" isn't my term---its just what they are called. And You're right: There is no "Switch".
So if you have a 300W heater, and put it on a dimmer, it might turn into a 100W heater.
Right, so if a Tank has a 300w heater, but really only needs a 100w heater, set according to my description--it would become, say a 125w heater by the dimmer switch. When the heater kicks on by the heater thermostat--it will run at 125w. Then off again when the thermostat reads the cut-off temp. So, in theory, you would be running a 300w heater at 125w on a tank that only needs 100w to maintain your set-point temp. And the dimmer would restrict the wattage to the 125w.
My Theory is this:
My A. javanicus temp is set at 84F. I calibrate the heaters/dimmer switch with the heaters full on to 90F (the snake can handle 90F). Once I determine where the dimmer switch setting is that maintains a max temp of 90F with the heaters full-on--I secure that setting with a simple piece of scotch tape (done it with reptile dimmers many times before--works Great).
Than I leave the dimmer set and taped and reduce the heaters to 84F. They kick on and off normally as they are originally designed---until there is a full-on failure. At that time, the dimmer is still limiting the electric supply to output only enough energy to heat the tank to 90F.
The biggest problem here is setting the dimmer. It would be setup specific and would have to be calibrated in place on the system. I cannot use 400w of heaters in a 5g bucket and then transfer the "Calibrated" setup to the tank. It would have to be setup---in place. But I can raised the temps to 86-87F for calibration--NP. That would give me an even larger over-heat buffer.
Have ya got any links to some decent controllers in the $30 range, besides the Otto in the other thread? The ones I found were $50-$200+........
I have a controller for my reptiles that woud work. It works on a thermostat I guess you could set it to the MAX you wantthe tank to goto if the heater failed... I'm sure this is how the regular controllers work as stated above. I also have an industrial one made by "Ranco" (you have to do all the wiring.)that will do the same thing... Not sure how many tanks it could control though...
Thanx for the info. I have a couple of Helix proportional controllers left over from the reptile days. I am looking for something inexpensive and effective---key word being inexpensive. I can build a Dimmer module like above with a niffty sliding switch for probably $10--and I already have some from when I started building racks, because I was going to get back into reptile breeding about 3-4yrs ago. I also have the junction boxes, extension cords, etc. and I have a rotary dimmer module already setup not being used. There's lots of options, but it comes down to $$$$$$$
My Helix were about $100 each, not including options.....
BTW, a proportional controller is basically just a dimmer that is controlled by a microchip. It just adjusts the wattage up and down until the correct amount is located. When the environment changes in a way that affects the temp(summer/winter)---the PPC just adjusts the wattage up and down again until it locates the correct amount again.