Basic Circuits

Apparently, calculating the resistivity of parallel elements is beyond the capability of a vendor to understand.

If you’re required by a spec to test an element to no less than 3.5 W/in^2, and you’re testing these elements in parallel so as to save on the number of power supplies you’re devoting to this burn-in, don’t you find the highest resistance in the parallel lot, then calculate the voltage needed to take that element to said energy density value, and then apply said voltage to all units?

Apparently not. These clowns just grabbed the first element they came to, checked resistance, ran the numbers, and went on with life.

:sigh: Any time you question these vendors on how they do their jobs, their first, defensive reply is, “We’ve been doing this for N years!” The reply going off in my head is always, “And you’re still in business?”

When an aerospace engineer who passed Circuits I only by the grace of the instructor—hey, I had the flu that semester and missed a midterm, and my “makeup” was just having the next midterm count twice, but of course, that was the midterm everyone bombed—can figure out that you’re fooling with the numbers, you’re in trouble.

Morons.

3 comments

  1. If I understood correctly, they tried to “burn-in” two assemblies (components, sub-assemblies, whatever) with different effective resistance values with one power supply, at the same time?

    Not being an Electrical Engineer, but having known several good ones, I would guess the lower resistance assembly is now a “crispy critter” and the higher resistance assembly was not really stressed.

    I would be interested to know what your double E buddies have to say.

  2. If I understand the statement, then I would agree that there is a good chance that following their method would lead to (if lucky) untested, but also undamaged hardware. Following you case, I think that you almost guarantee damaged hardware…. that or they or the lower resistance items are set to handle a higher power load than the spec requires.

    just my two cents as your local CPE (close enough, eh?)

  3. Well, these things can withstand >4 W/in^2, so frying these things isn’t the concern so much as meeting our SCD. Because these units are replacing failed units, we have high visibility on this, and our NASA customer moved us from 3.0 W/in^2 to 3.5.

    Suffice it to say that this morning’s meeting will be, um, interesting.

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