> On Jul 17, 2025, at 10:41 AM, Jon Elson via cctalk <[email protected]>
> wrote:
>
> 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.
Yes, the question is whether the transformer could be made sufficiently happy.
As for 3-phase: the CDC mainframes (6000 series) in fact use 3 phase 400 Hz
power feeding their power supplies -- you're dealing with 3-phase transformers
and 6-diode rectifiers behind them.
paul
