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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.
Sometimes, 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 15A. A 2000 watts 240V 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 the SSR, the power can be switched at high speed with no noise and
no life time limitation. However, compared to electromechanical relays, the SSR has one
drawback. It generates heat when passing the current. SSRs are made of semiconductors that
have 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 12 Amp is passing through
the controller, 16 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 other 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 10A continuously without worry of the temperature of the controller. At
12A, the temperature of the controller will increase with time. The bottom of the controller where
the heat sink is located can rise by 63 °F (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.