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Appendix 1
Managing the heat generated by the controller
The heat dissipation of the controller is directly related to the electric current drawing
power of the heater. If your cooker consumes less than 10 ampere of current or your pot
is less than 5 gal (19 liters), you do not need to worry about the heat generated by the
controller.
Sometime, the AC current requirement might not be marked on the cooking appliance. To
find out how much current it will draw, divide the power (in wattage) by the line voltage,
for example, an 1800 watts 120V heater will draw 15 A. A 2000 watts 240 V heater will
draw 8.3 Ampere.
Why the heat becomes an issue?
The solid state relay (SSR) used in the controller is a critical component for the precision
temperature control. With SSR, the power can be switched at high speed with no noise
and no life time limitation. Compared with electromechanical relay, however, SSR has
one drawback. It generates heat when passing the current. SSR is made of
semiconductor that has a limited conductance. When passing current, the heat will be
produced from the resistance. Each ampere of current will produce about 1.3 watts of
heat. When 15 Amp is passing through the controller, 20 watt of heat is produced in the
controller. As more heat is produced, the temperature inside the controller will rise. If it
reaches to higher than 70 C, it can shorten the life or even damage some the components
in the controller. The temperature inside of the controller depends on the amplitude of the
current, how long the controller needs to run at full power and the ambient temperature.
The heat is only an issue during the start of the heating when the heater is running at full
power. Once the temperature is close to the set point, the controller will probably need
less than 50% of the power to maintain the temperature. Since the heat is directly related
to the current passing the controller, the heat produced at steady state will be insignificant
and can be ignored.
When the heat becomes an issue?
This controller can run at 12 A continuously without worry of the temperature of the
controller. At 15A, the temperature of the controller will increase with time. The bottom of
the controller where the heat sink is located can rise by 63F (35 C) from ambient if running
at full power continuously for 90 minutes. For this reason we don’t recommend running
the controller at full power for more than 90 minutes. For 120 VAC, 15 A for 90 minute will
provide enough energy to heat 10 gallon (38 liters) of water up by 108F (60 C). If you
