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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 the SSR, the power can be switched at high speeds with no
noise and no life time limitation. Compared with electromechanical relays, however,
SSRs has one drawback. They generate 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 Amps is passing through the controller, 16 watts of heat is produced in
the controller. As more heat is produced, the temperature inside the controller will rise. If
it reaches higher than 70 °C, it can shorten the life or even damage some of 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 usually 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 10 A 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. For 120 VAC, 12 A for 90
