Too much cooling air? (Power supply failures due to condensation)

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SUMMARY

The discussion centers on the failure of 36 AC to DC power supplies due to moisture-related issues, specifically condensation forming inside the enclosures. Despite environmental conditions of 30°C and 45% relative humidity, moisture indicators confirmed the presence of moisture. The negative pressure created by large cooling fans pulling air out of the cabinet is hypothesized to contribute to condensation by lowering the dew point. The user seeks clarification on the thermodynamic principles at play in this scenario.

PREREQUISITES
  • Understanding of thermodynamics and dew point calculations
  • Knowledge of AC to DC power supply operation
  • Familiarity with humidity measurement techniques
  • Experience with cooling systems and airflow dynamics
NEXT STEPS
  • Research thermodynamic principles related to condensation in electronic enclosures
  • Investigate the impact of negative pressure on dew point and moisture accumulation
  • Explore alternative cooling fan configurations for electronic equipment
  • Learn about moisture control solutions for sensitive electronic environments
USEFUL FOR

Electrical engineers, power supply designers, HVAC professionals, and anyone involved in the thermal management of electronic equipment.

powerelect
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TL;DR
condensation and dew point in electrical cabinet with high velocity air
I have a situation that I cannot explain so I need the assistance of someone with a good understanding of thermodynamics.

I have 36 AC to DC power supplies located in an equipment rack. These power supplies are failing after some time. The failures appear to be moisture related. We put moisture indicating labels in the power supply and their color changed indicating the presence of moisture.

We replaced the metal cover on the power supply with clear plexiglass and we also saw condensation form inside the enclosure after a number of hours. The environmental conditions were 30C and 45%RH. The dew point should be far below room temperature under these conditions. This was installed at a location close to sea level. There are large cooling fans on the cabinet door pulling air out of the cabinet.

So, the pressure inside the cabinet is negative. Could this large amount of airflow pulling through the unit cause the moisture in the air to condense? Could the negative pressure cause the dew point to drop? Can someone explain this? I have been designing power electronics for decades and have never seen this before.
 
Last edited by a moderator:
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Welcome, @powerelect ! :smile:

Is the room containing the panel conditioned?
If so, at what temperature?
Could you relocate the cooling fans to be blowing into the cabinet?
 

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