Re: Temp controlled DIYS UG heating cables

Another problem John is the stability of the control loop. There would be a lag between
the time the heater switches on and when the controlling sensor sees a change in tank
temperature. By this time, we may have dumped quite a large quantity of heat into the
gravel which results in an overshoot and we end up with large oscillations in tank temperature.
To overcome this you could use some type of integrating controller as in process control
but this is more complicated than a thermally operated switch and would exceed the cost
of a simple conventional tank water heater. Would you put a temperature sensor in the gravel
next to the heating element? Again I wonder about the cost of this sensor and controller.
The conventional tank heaters are quite efficient, low cost and provide excellent temperature
control. It just wouldn't need to cycle on as long with a UG heater adding heat from underneath