To calculate the heat sinking requirements for your application, the internal power dissipation of the controller must be considered.

For the examples below, we will use the 5CX-140 Series controllers. The idle circuit power dissipation of a 5CX-140 Series controller under no load conditions is 2.5 watts for 120 VAC units and 4.0 watts for 208/230 VAC units. For each ampere of load current, an additional 1.4 watts of power is dissipated by the controller.

Example 1: Model 5C1-140 and a 250 watt heater.
Basic Controller Dissipation: 2.5 watts.
Load Current: 2.08 amperes or 52% of maximum power rating.
Total Controller Dissipation: 2.5 + (2.08 x 1.4) = 5.412 watts.
Base Plate Temperature: From the derating curve below, the base plate temperature may not exceed 75�C for 52% of power with the controller dissipating 5.412 watts.

Example 2: Model 5C1-144 and a 1000 watt heater.
Basic Controller Dissipation: 2.5 watts.
Load Current: 8.3 amperes or 83% of maximum power rating.
Total Controller Dissipation: 2.5 + (8.3 x 1.4) = 14.12 watts.
Base Plate Temperature: From the derating curve below, the base plate temperature may not exceed 65�C for 83% of power with the controller dissipating 14.12 watts.