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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 12 amperes 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. As current flows, heat is generated as a
result of the resistance. Each ampere of current will produce about 1.3 watts of heat.
When 15 Amp is passing through the controller, 20 watts of heat are 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 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 12A continuously without concerning about the heat generated
in 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 do not
recommend running the controller at full power for more than 90 minutes. For 120 VAC,
15 A for 90 minutes will provide enough energy to heat 10 gallon (38 liters) of water up by
