14 Jul
2021
14 Jul
'21
12:12 p.m.
On 7/14/21 11:33 AM, Guy Sotomayor via cctalk wrote:
On 7/14/21 6:21 AM, Paul Koning via cctalk wrote:
I've found 2 issues w.r.t. "rotary converters".
?* They *always* consume lots of power regardless of the
actual load
?* They typically don't have great frequency regulation as
they are
?? really designed for machine tools (which are pretty
tolerant) so if
?? the load varies, the frequency will vary until the
"mass" catches up
Frequency regulation comes from the single-phase mains, and
thus will be the same as the utility provides.
On Jul 13, 2021, at 11:34 PM, Chris Zach via
cctalk
<cctalk at classiccmp.org> wrote:
A number of the large disk drives use
3 phase motors;
RP04/5/6 are examples as well.
Three phase motors won't run on single phase power
without help from run capacitors.? (There is no such
thing as "two phase power" -- 220 volts is single phase,
balanced.)
If the issue is motors, a "variable frequency converter"
will do the job easily.? I have suggested in the past
that three phase power supplies could run from those, but
others have pointed out I overlooked some issues.? So
that's probably not a good idea.
If you need three phase power to feed power supplies or
other non-motor power consumers, the best answer is
probably a "rotary converter".? You can find those in
machine tool supply catalogs.? Basically they are a three
phase motor equipped with run capacitors so they can be
fed single phase power; the three phase power needed is
then taken off the three motor terminals. You can think
of these as rotary transformers -- dynamotors in a sense,
for those of you who remember electronics that old.? :-)
Don't look at "static converters" -- those are only for
motors, it seems they aren't much more than run
capacitors in a box. They won't help you for anything
other than a motor, and even for motors they aren't very
good.
????paul When we got an 8530 at work in the early 90s
(needed a
machine with a
Nautilus bus for specific hardware testing), it was
definitely a
3-phase machine and since we were in an industrial
setting, I just
tapped into our panel at the back of the warehouse and
wired up a
3-phase outlet for it.? It never sat on our datacenter
floor as a
result, but it really only ever had one purpose and
that wasn't a
daily driver.? Too much power, too much heat for so few
employees (at
that stage of the company).
Interesting. Were the power supplies 3 phase input?
Like
you I have noticed that most pdp and vax gear just pull
120 volt legs off the 3 phase to balance power loads. So
you can run them on a couple of 120 circuits. Outside of
say the RP07 (which is a real 3 phase motor) I did a fair amount of investigation of this in order
to
power the peripherals for my IBM 4331.? The peripherals in
total require on the order of 21KVA of 3-phase power and
with them (printer, card reader/punch and tape drives) the
load will vary *a lot) which would screw up the DASD
(string of 3340 drives and some 3350 clones).
I ended up looking at a solid state phase converter (takes
in 220v single phase and produces 208v 3-phase).? It has a
good (< 1% frequency regulation) and only consumed 100W at
idle.? Plus it's relatively small and quiet.? The downside
is cost (~$5000).