NimbUx wrote: ↑
Wed Jan 15, 2020 11:41 am
What I am going to do next time I shutdown the system is to fetch my cheapo multimeter & measure currents drawn by the fan in operation, and when starting and shutting down : I hope
the figures - that I'll be sure to report here for discussion - will be low enough to assure my and everyone's peace of mind ;=)
I would take any such multimeter readings with a pinch of salt. Multimeters tend to average readings and won't reveal the in-rush current, transient peaks or ripple. It is those transients which have the potential to cause issues even if a regulator is capable of providing the current needed to run a running fan. There's also the potential for back-EMF when the 3V3 rail is shutdown or clamped to 0V.
I am not sure how the professionals measure such things but I would imagine they put a resistor in series and then measure the voltage across that, capture with a high-speed digital scope and calculate current draw from that. With correct amplification and adjustment what is shown will be instantaneous current.
Unless soak-testing for a long period of time, it's not always clear how the characteristics will change as the fan is used, as bearings wear, friction increases, what happens if the fan jams.
I don't doubt it does work, but that doesn't mean it will keep working forever, or what the consequences will be when it's less than perfect.
I am not saying don't do it if prepared to take the risk, but the risk of using 3V3 seems quite high compared to the cost of avoiding that risk by using 5V.