Testing power supply
Testing power supply
(OP)
Hey Guys, Got a question about a switching supply I'm testing. The environment it will be used in is typically at 158 degrees F. So I'm testing it in an oven with a load on it to pull max power non stop. How long do I need to test it to determine if these will work for our needs? I could run it around the clock if need be. Is there any standard for this? Thanks





RE: Testing power supply
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RE: Testing power supply
MIL-STD-810G, Method 501.5, Procedure II (Operational), 55ºC for 2 hours after temperature stabilization.
In other words, monitor the temperature of the Unut Under Test somewhere sensible (perhaps on the hotest heat sink?), and after it stabilizes then give it at least two more hours.
RE: Testing power supply
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RE: Testing power supply
RE: Testing power supply
It'll lead into the topic.
Temperature is typically an input to the calculations. Keep in mind the true meaning of words such as 'prediction' and 'estimate'. The real world MTBF can easily be in a different order of magnitude than the calculation (sometimes for good reasons not included in the model).
RE: Testing power supply
RE: Testing power supply
That is still correct, however, which is why the Arhenius equation is so widely used for electronics. Also in answer to the OP's question, you need to perform an accelerated life test, assuming you want to spend the money. You'd need to run at least two batches of parts at different temperatures to failure, and the failure rates as a function of temperature can then be determined, as well as identifying which components are the weakest. There are a series of military standards that describe how life testing is performed.
160ºF = 71ºC, which is already at the upper limit of commercial component temperature ratings; when you factor in the thermal resistance of the components within the supply to that ambient temperature, you could be easily at 85ºC. which is the temperature limit for many industrial temperature range components. Given that, you definitely need to run a few supplies at a minimum of 85ºC ambient, with instrumentation on the components to determine what the induced case temperatures are. I suggest the higher ambient temperature because it's almost invariably true that a "measured" ambient temperature is taken where it's convenient, and may not reflect the true thermal environment. We once ran a life test in an oven with 125ºC ambient temperatures, but the test engineer didn't do any thermal calculations to predict that the 1.5 kW being dissipated by the components might raise the local ambient temperatures above 180ºC, resulting in junction temperatures in excess of 200ºC. Naturally, we got failures almost immediately.
As far as the duration is concerned, therefore, if the part is truly that susceptible, you might try three supplies at 70ºC, 85ºC, and 100ºC, and run them to failure, since that's the actual objective, to determine the weakest component(s) within the power supply. This may become and iterative process, as you may have multiple weak links. As a first step, though, you may need to revisit the parts list of the supply and determine whether all the components are rated for at least 85ºC ambient. Note, also, your supplies may not necessarily have permanent failures,; they may just be operating outside of the design conditions and may regain operability when cooled down.
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RE: Testing power supply
RE: Testing power supply
Perhaps these approaches are not possible.