1 Jan
2022
1 Jan
'22
12:27 p.m.
On Jan 1, 2022, at 3:08 PM, Grant Taylor via cctalk
<cctalk at classiccmp.org> wrote:
On 1/1/22 12:44 PM, Paul Koning via cctalk wrote:
The impedance of a capacitor is inversely proportional to the frequency. Given a desired
ripple for a given load, you get the needed capacitor impedance, so if you increase the
freqency you'd end up with smaller capacitors. You see this, big time, in modern
switching supplies, where the frequency may into the many kHz or sometimes even a MHz or
so, resulting in tiny filter capacitors.
...
And of course 400 Hz gave them an additional advantage in reduced transformer size and
reduced ripple (for a given filter capacitor).
I was going to ask how the frequency altered the size of the ripple, but "for a
given filter capacitor" makes sense. You are messing with the ratio and having a
fixed value "for a given filter capacitor". -- If I'm even remotely
understanding correctly. They'd do
this even in devices that don't draw large amounts of power, for example the DD60
console display gets its power (other than fans which are single phase mains power) from
the 400 Hz 3-phase supply feeding the mainframe. I'd be surprised if it uses even a
kW, so this was probably a case of "why not since it's there to be used".
My understanding is that some of the special power requirements had more to do with
isolation and cleanliness / quality of the power. Meaning don't try to power the
equipment off of the same circuit(s) that motors and the likes are on which will induce
lots of noise on the line, some of which might make it into the computer and adversely
effect things. The motor / generator provides a quite strong
isolation for things like that. Probably more so than just a normal transformer.
Way more because of inertia. Not quite a UPS, but short power glitches enough to blink
the computer room lights are not going to be seen by the mainframe.
paul