https://kikusuiamerica.com/products-index/ac/pcr-ma/ will oblige
I have a PCR500MA : good for 400 Hz synchro work, also 40/50/60 Hz induction motors - IIRC the wfm is much cleaner than the usu 12V -> ~ static inverter. The pricing reflects this. 3 phase (Op) VFD are wonderful for driving 3 phase machine tool motors, and can go slowly ie low frequency; eg https://uk.rs-online.com/web/p/inverter-drives/7858522 I have a 1 phase (Op) VFD on the shelf, boat anchor, cf PCR500 - wfm is ugly HtH B -----Original Message----- From: Jon Elson via cctalk [mailto:[email protected]] Sent: 17 July 2025 14:42 To: Paul Koning via cctalk <[email protected]> Cc: Jon Elson <[email protected]> Subject: [cctalk] Re: Ferroresonant transformer mystery On 7/17/25 08:45, Paul Koning via cctalk wrote: > >> On Jul 16, 2025, at 3:42 PM, Van Snyder via cctalk <[email protected]> >> wrote: >> >>> ... >> The Computer History Museum in Sunnyvale, CA has a working IBM 1401 >> computer from Germany. It has ferroresonant power supplies. They >> bought a converter to supply 50 Hz power because they were certain it >> wouldn't work at 60 Hz. And it has motors in the card reader, card >> punch, printer, and tape drives, that would all run at the wrong >> speed using >> 60 Hz power. > I wonder about "they were certain it would not work". That should be a > question of fact, not belief. > > As for the motors, that's an obvious issue (if they are induction motors > rather than universal motors). The modern solution is a VFC -- variable > frequency motor controller. Those are pretty cheap and work great with > motors. I've heard that they are not so good with power supply transformers, > not sure if that has been experimentally confirmed. For power supply > transformers, 50 vs. 60 Hz is unlikely to matter. People with CDC mainframes > that want 400 Hz power do need a solution, with motor-generators as the > traditional answer. I wonder if a VFC would work for that, perhaps with > post-VFC filtering to turn the waveform into something closer to a sine wave. > > VFDs (variable frequency drives) produce ~340 V PWM "square" waves, Given enough inductance in the motor windings, this causes roughly sinusoidal currents. But, feed this into a transformer, and you will get high frequency spikes. Now, MAYBE, due to the way a "Sola" transformer works, it might smooth out the square waves, but it is real hard to predict what will happen. Also, VFDs are usually designed for balanced 3-phase loads. Jon
