I forgot that I already have a great measurement device, very recently acquired! <slaps self on head> Namely, a Danfysik "Ultrastab" 867-700I current transducer. DC to 100 KHz bandwidth, maximum current 700 amps, runs on +/- 15 volt supplies. Puts out max 400 mA into a 2.5 ohm burden resistor, or down to 0 ohm if desired.. at present, it's hooked up to a handy 2 ohm 3% power resistor, and a 500 uA panel meter with appropriate series resistor, so it now reads 500 A full scale. For smaller currents I can wrap multiple turns of the conductor through the center hole, but there's no practical way to read larger than 700.
So I could just put my scope on the Ultrastab's output and look at the waveform directly. As long as it's less than 700 amps, of course. That is not necessarily the case for the single half-cycle inrush, even with the primary-side NTC limiter. It won't hurt the transducer even so, and it should be obvious if the pulse is flat-topped.
Ross, regarding the AC line issues, don't worry I have thought of all that. I'm running it off a 240 volt 20 amp outlet (normally runs a 1.5-2 KW electric baseboard heater), and as noted I have an inrush limiter. Also Heinemann panel breakers in the supply itself, both AC and DC sides. It's all in good condition (I've re-done most of the wiring in this old house myself. No permits or inspections out here in the country, which is definitely a double-edged sword). Tomorrow I'm running the Romex for a separate 240V, 20A outlet in this room. My ham shack takes up two spare bedrooms upstairs ;)
The surge drawn from the 28V when I start the inverter, read on the meter, is just over 400 amps, the output is hauled down to around 16 volts! then rapidly dropping to 250 in about 2 seconds. Then the inverter's regulators kick in and it idles at "only" 35 amps. It doesn't trip any of the breakers because I used ones with motor-start curves, intended for just such an application :) No sign of any heating or magic smoke on numerous starts and runs, including a 525 watt heat gun element. About 60 amps drawn at that load.
