Mate of mine is a pilot.. was telling me how many of his mates plug their phone/iPad chargers etc into the airplanes cockpit power - 115v @ 400hz. Apparently, they work fine, no damage - BUT, they do get pretty hot/warm - this is the only noticeable side effect.

These little power supplies would be switch mode I'm sure - is that normal for phone/ipad chargers these days - ie no old style transformer - assuming it is.

So the question is.... what would be going on to generate the added heat.? (specifically) .. and, if you wanted to mod the power supply to be fine with 400hz (only, no longer 50/60) what would you change.?

* Not after advice or commentary about how bad this practice is etc etc - just after the engineering on what is going on - thanks for respecting that. *

 

This is a total guess. But since the first thing to happen in a switch mode supply is the AC is rectified to DC, it may be the diodes in the rectifiers not having enough of an "off" period between pulses/waves. Even small off time, nonconducting times makes a difference on many components. As said a total guess.

 

Well, they use schottky diodes on the high frequency part of the PSU, because standard rectifier diodes have a reverse recovery time. During that small time, the diodes conduct in the reverse direction. If instead of 50 Hz you have 400, then that's 8 times the 0v crossings. I suppose that's what happens.

All that aeronautics regulations and requirements to turn off equipment because of EMI, and the pilots are connecting a 50/60 Hz cellphone charger to plane's 400 Hz system?

 

thanks guys - appreciate the knowledge