1 Jan
2022
1 Jan
'22
11:44 a.m.
On Jan 1, 2022, at 2:38 PM, Grant Taylor via cctalk
<cctalk at classiccmp.org> wrote:
On 1/1/22 12:33 PM, Paul Koning via cctalk wrote:
Could be. For the CDC case, I see actual 3-phase DC supplies, i.e., 3 phase bridge
rectifiers fed by 3-phase transformers. If you run those off one phase the ripple would
be a lot larger. And of course 400 Hz gave them an additional advantage in reduced
transformer size and reduced ripple (for a given filter capacitor).
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".
paul
And mainframes may use 3-phase power supplies;
CDC 6000 mainframes do, though with those it's 3 phase 400 Hz produced by
motor-generators (which in turn run off 3-phase mains power).
I know that some IBM mainframes prefer 3? power but I know of multiple people that have
re-wired their CECs to use 1? power. They too are largely independent 1? supplies on
different phases to jointly power a common internal bus. So re-wiring the necessary
supplies to the same phase is mostly not a big deal.
Apparently even IBM sold and supported some systems in this configuration. The only down
side is that it put an upper cap on the amount of power that you could draw and thus
things that you could run in this configuration. But for smaller installations, it's
perfectly fine.