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
