Designing with SCR Power Controllers - Part 3: Environmental Conditions

SCR Design Checklist IconDownload the complete checklist here: Control Concepts SCR Design Checklist.PDF

Read Part 2: Fusing and Transformers

Environmental Conditions

Confirm adequate clearance around the controller for air flow.
A three inch clearance above and below the controller is required.
Check the temperature of the air surrounding the controller
Size enclosure and provide adequate cooling so that the air surrounding the controller does not exceed its thermal rating.  Use an enclosure heater if the environment can reach below 0 degrees C.  SCRs require more gate current as the temperature decreases and will eventually exceed the drive capability causing a misfire. 
Prevent radio interference
SCR power controllers are susceptible to radio interference from hand held radios and repeaters and can potentially misfire during radio transmissions.  Keep the controller in a metal enclosure to prevent radio interference.  Use grounded metal screen mesh over air louvers and cabinet openings to prevent radio signals from interfering with your equipment. 
Use a grounding rod in noisy environments
This may be beneficial if you have a bad system ground.
Use a sealed enclosure or alternative cooled power controllers for dirty and dusty environments
For heavy dirt or dusty environments, a sealed cabinet with air conditioning or filters is recommended.   Alternatively, select a SCR manufacturer that offers external mount or liquid cooled heatsinks to allow you to maintain a sealed environment in order to obtain maximum product life.
De-rate controller for installations above 6000 feet.
As the air thins at increased elevations, natural convection and forced air cooling becomes less efficient.  Follow the manufacturer’s recommendations for de-rating the SCR power controller above 6000 feet altitude.