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Figuring out current draw

inavitech

So I'm working on a project with an unknown and not sure how to figure out what I need to know. My customer wants new USB chargers and I'm trying to figure out if the circuit will handle the load of the new chargers. The current charger is a single USB A. Input is 28VDC, output is 5VDC at 3 AMPS, 15 WATTS. Not sure what formula to use to compute current draw on the input side. My new chargers consume 1.25AMPS each.

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  • That's the thing, just can't find any formulas to do the computations. Guess I'm going to have to wait until the aircraft comes in and pull one of the outlets they want to replace and see if the data plate has any good information to help determine what the circuit is drawing off the branch and go from there.

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  • That's the thing, just can't find any formulas to do the computations. Guess I'm going to have to wait until the aircraft comes in and pull one of the outlets they want to replace and see if the data plate has any good information to help determine what the circuit is drawing off the branch and go from there.

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  • in reply to inavitech

     Go the simpler route.  First:  Decide that you want the same output capacity as the existing system.  If the system that you are replacing is old, the odds are greatly in your favor that new switching supplies will be more efficient - unless you purchase them on Ali Express or eBay.  Buy a new one.  Load it.  Measure it.  Multiply that by the number of outlets you are relacing.  Determine if that draws less than the current system.

    If you are trying to incorporate that with a load demand analysis (what they really use), the only reliable method is a load study.  Whoo-hoo!  YOU get a data logger!  And YOU get a data logger. etc.

  • in reply to inavitech

    If this is on a plane won't it need the full certification stuff ?

    MK