From owner-freebsd-hackers Fri Mar 6 17:36:28 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id RAA27159 for freebsd-hackers-outgoing; Fri, 6 Mar 1998 17:36:28 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from sendero.simon-shapiro.org (sendero-fddi.Simon-Shapiro.ORG [206.190.148.2]) by hub.freebsd.org (8.8.8/8.8.8) with SMTP id RAA27143 for ; Fri, 6 Mar 1998 17:36:05 -0800 (PST) (envelope-from shimon@sendero-fxp0.simon-shapiro.org) Received: (qmail 21240 invoked by uid 1000); 7 Mar 1998 01:44:27 -0000 Message-ID: X-Mailer: XFMail 1.3-alpha-021598 [p0] on FreeBSD X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit MIME-Version: 1.0 In-Reply-To: <19980306191749.01367@mcs.net> Date: Fri, 06 Mar 1998 17:44:27 -0800 (PST) Reply-To: shimon@simon-shapiro.org Organization: The Simon Shapiro Foundation From: Simon Shapiro To: Karl Denninger Subject: Re: SCSI Bus redundancy... Cc: Bob Bishop , dmlb@ragnet.demon.co.uk, wilko@yedi.iaf.nl, julian@whistle.com, hackers@FreeBSD.ORG, "marino.ladavac@siemens.at" Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On 07-Mar-98 Karl Denninger wrote: ... >> BTW, 48VDC P/S for a PC is about $50.00, where an AC one is $15.00. > > Yeah, well, that's because DC/DC conversion takes two forms - expensive > and > cheap but wasteful in terms of dissipation (ie: basic regulation). Yup. Many things in this earthly life tend to be that way. > AC/DC conversion by switching power supplies is so cheap now that it gets > rediculous. Of course, its also cheap enough that lots of folks don't > pay > attention to minor little things like the tolerances of the components > they > use either. Which quickly makes the cheap very expensive. > I used to be involved in Satellite Earth Station work (microcontrollers > for > same); a goodly amount of the stuff out there, particularly MCL's > Klystron > tuners and amplifiers, probably still has my code running around in them. > > The people who own these devices tend to be a bit anal about electricity. > They also eat huge gobs of it. This means generators and monster UPS > systems. Unfortunately, virtually all of *this* kind of equipment wants > 220 3-phase in rather serious amperage ratings (or worse, 480 V). > > Shutting off a hot klystron by removing power is a great way to buy a new > $25,000 tube; there is enough energy being dissipated in those things > that > if you shut them down without going through a clean power-down sequence > (ie: forced air cooling for a few minutes) almost insures that you will > damage the alignment of the plates in the tube (due to heat-related > warpage). > Given that under typical operation you have ~3KW *emitted* from the > business > end of these things in the form of a nice electron beam you really don't > want that to happen. And those are the "small" ones; some of the larger > ones had ~30KW rated outputs. Ugliest radio station I visited was a 1.8 MegaWatt short radio station. They had a direct feed from the power station down the mountain. I think they had their own set of generators at the power house. Same story. you do NOT shut these down. The desert installation I referred to was running a 2GHz microwave link at 1GW contineous. You should see what happened to seagulls who tried to fly in front of the dishes... We used the diesel-flywheel-generator-electric_motor arrangement. > What I've seen used is a monster online UPS installation with battery > room, > frequently comprised of open wet cells, and a big honking generator for > utility backup. Some of these are big enough to stand in. The amount of hydrogen boubling up classifies these rooms as explosives. > The batteries are basically there as a "smoothing" function - they keep > things going until the generator can start up, warm up somewhat, and get > to operating power. Yup. something between a filer and capacitor. They are very effective in that role. A bit too much for the typical FreeBSD server, but the lesson is the same. Have a battery somewhere in the loop, so your power input to the equipment never goes down. I do not remember the numbers, but somewhere around 6+ servers, it pays to put them in a rackmount and feed them DC. Simon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message