Elevated Temperature Question
Elevated Temperature Question
(OP)
Hello all!
So let's say I have a power supply with a case temperature of max 90degC and placed in a 3/16" thick 16"x9"x5" die cast aluminum chamber, fully enclosed.
During normal operations, the case temperature was measured at 74degC at a 25degC ambient temperature (room temperature).
Suppose I can elevate the ambient temperature up to 50degC. What is the relationship between the ambient, aluminum chamber, and the power supply.
Would it reach its 90degC limit? Can you walk me through the steps of how to relate all factors together? Is there a possible solution to maintain a 90degC max case temperature by only increasing the thickness of the chamber? let me know your thoughts and thank you.
So let's say I have a power supply with a case temperature of max 90degC and placed in a 3/16" thick 16"x9"x5" die cast aluminum chamber, fully enclosed.
During normal operations, the case temperature was measured at 74degC at a 25degC ambient temperature (room temperature).
Suppose I can elevate the ambient temperature up to 50degC. What is the relationship between the ambient, aluminum chamber, and the power supply.
Would it reach its 90degC limit? Can you walk me through the steps of how to relate all factors together? Is there a possible solution to maintain a 90degC max case temperature by only increasing the thickness of the chamber? let me know your thoughts and thank you.





RE: Elevated Temperature Question
In general, thermal test chambers are insulated, rather than conductive, and the ambient temperature is controlled with heaters, etc., to maintain a specific ambient temperature to the unit under test.
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RE: Elevated Temperature Question
RE: Elevated Temperature Question
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RE: Elevated Temperature Question
Here's my answer based on how I read your question.
Assuming the heat output from the power supply is constant, first determine the case temperature as follows:
1) Current case temperature is limited by external convection by the formula Q=h*A*Delta(T).
2) You know A and Delta(T) for your current operating conditions. You know your case temperature, so find a convective heat transfer correlation, and calculate Q.
3) With Q now in hand, go back to Q=h*A*Delta(T). Guess a case temperature, calculate a new convective heat transfer coefficient, calculate Q.
4) Iterate for a new case temperature until Q matches that calculated in step 2.
First guess, I think you're going to have an issue. Assuming convective heat transfer coefficient is the same, the effective delta(T) would remain constant. So, the case temperature would likely rise to: 50C + (74C-25C)= 99C.
Cheers,
Marty
RE: Elevated Temperature Question
Its that simple and thats how testing agencies correct for elevated ambient specifications/requirements without having to be in that ambient for testing.
If you need to be 90 C @ 50 amb you will have to make changes to conduct more heat through the enclosure (or chamber as you called it).. or make changes to this power supply to increase its efficiency
Funny how the choice of the word "chamber" leads some to think you are talking about a "test chamber" where had you used "enclosure" or "chassis" or similar the confusion would not exist.
RE: Elevated Temperature Question
RE: Elevated Temperature Question
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