Cooling Requirements for Solid State Relays & Other Solid State Devices Such as Diodes, SCR's, IGBT's

In this blog we discuss general cooling requirements for Solid State Relays

Thermal Comparison to Mechanical Relays or Contactors.

A Mechanical Contactor dissipates very little heat per pole. At full load for a 25 Amp Contactor such as IKD225-20-24VAC/DC or FPC1-25-20C-230VAC. The maximum dissipation per pole is only 2 Watts

A Solid State Relay dissipates a proportional amount of heat depending on the load current. For 25 Amp Load, the dissipation will generally be 1.5 x 25 Amp = 37.5 Watts. 20 Times higher!

You need to allow for adequate cooling via ventilation or fan(s) in order to get the heat out. You also need to consider the ambient operating temperature. 

LM Photonics New Zealand have a handy little app for calculating cubicle ventilation requirement which is supported through donations. We encourage you to donate.         

In general 50/60W of heat can be dissipated through vents only. Anything higher should have a fan at the top.

Fan Mounting Position

Position the fan at the top front or side of the cubicle, that way of the fan is off, minimal dust will settle inside the cubicle. The bottom incoming air vent should be at the opposite side of the cubicle and if the cubicle is on the floor, have some clearance from the bottom in order to nut pull in any dust off the floor.

Spacing for SSR and De-rating

If Solid State Relay heatsink is mounted directly next to each other, there will be some derating. one example for DR22 Nova 22 Series Solid State Relays is shown below

               

To avoid de-rating please mount each Solid State Relay a minimum of 20m apart with 100mm space at top and bottom. 

Mounting directly next to each other will de-rate approximately 10% and without surrounding 100m spacing the rating can not be guaranteed.10% derating of each SSR.       

 

For any questions or further clarification feel free to contact our technical sales team