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:cctalk@classiccmp.org]
Sent: 17 July 2025 14:42
To: Paul Koning via cctalk <cctalk(a)classiccmp.org>
Cc: Jon Elson <elson(a)pico-systems.com>
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 <cctalk(a)classiccmp.org> 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