A transformer works on A/C only, for one thing by being electromagnetically sensitive to the cyclic reversal of incoming voltage. The higher the number of wind

A transformer works on A/C only, for one thing by being electromagnetically sensitive to the cyclic reversal of incoming voltage. The higher the number of windings in the coil, and/or the amount of iron in the core, the greater the impedance to this constant polarity reversal. And the more sensitive to the lower frequencies. These are basically audio frequencies and the inductance presented by the transformer's primary winding acts almost as a low-pass filter whose effectiveness changes rapidly as frequency approaches zero. IOW a small transformer doesn't have as much frequency response to the "lows", and that sensitivity is what is needed before it can induce current into the secondary winding to begin with. All other tings being equal, bigger iron would respond stronger to the same more-gradual fluctuations in primary voltage. Now with the alternator as the source of the frequency, a physically smaller alternator running at higher RPM could produce as much power as a bigger one running at lower rpm. Found a couple worthwhile links: https://www.gohz.com/why-we-use-115v-400hz-power-supply-in-aircraft https://www.gohz.com/why-we-use-115v-400hz-power-supply-in-a... https://www.powerstream.com/400hz-tutorial.htm https://www.powerstream.com/400hz-tutorial.htm Edit: Also when you use the 115V/400Hz A/C elsewhere on the aircraft like to power a radio, when it it rectified to DC inside the radio it takes a lot smaller capacitors and stuff to filter out the 400Hz line noise than it would for the low hum of 115V/60Hz.