Date: Fri, 6 Mar 1998 19:17:49 -0600 From: Karl Denninger <karl@mcs.net> To: shimon@simon-shapiro.org Cc: Bob Bishop <rb@gid.co.uk>, dmlb@ragnet.demon.co.uk, wilko@yedi.iaf.nl, julian@whistle.com, hackers@FreeBSD.ORG, "marino.ladavac@siemens.at" <lada@ws2301.gud.siemens.at> Subject: Re: SCSI Bus redundancy... Message-ID: <19980306191749.01367@mcs.net> In-Reply-To: <XFMail.980306171427.shimon@simon-shapiro.org>; from Simon Shapiro on Fri, Mar 06, 1998 at 05:14:27PM -0800 References: <l03020903b12615386f92@[194.32.164.2]> <XFMail.980306171427.shimon@simon-shapiro.org>
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On Fri, Mar 06, 1998 at 05:14:27PM -0800, Simon Shapiro wrote: > > On 06-Mar-98 Bob Bishop wrote: > > At 6:02 pm +0000 6/3/98, Simon Shapiro wrote: > >>Wrong again. Diesel generators have a 15-180 seconds switch over time. > > > > True. It's also not widely realised that they aren't awfully reliable. > > They > > fail to start one time in N, regardless of how often you start them. N > > used > > to be about 15 last time I had anything much to do with them. > > I used to run a military radio station (along with telephony stuff, etc.) > Somewhere in the Sinai deserts some time ago. Needless to say, we tended > to want to keep electricity flowing regularly into our equipment. > > As the power company was not disposed to run lines to our part of the > desert and the enemy (of that time) tended to cut any lines they could see, > we used generators. We actually used diesels (from 5KW up to 200MW), but > they were arranged as a non-stop. They charged BIG batteries. The > microwave people used AC. We never had our radios out. They did. Our > system cost 1/5 of theirs. AC is great for many things, but they tend to > disappear within 2ms of disconnect from the power generator. > > 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). 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. 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. 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. 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. Most of these were diesel, but I *did* see one (big) gas turbine. The tests of these things (typically run once a week) were, uh, "interesting". -- -- Karl Denninger (karl@MCS.Net)| MCSNet - Serving Chicagoland and Wisconsin http://www.mcs.net/ | T1's from $600 monthly to FULL DS-3 Service | NEW! K56Flex support on ALL modems Voice: [+1 312 803-MCS1 x219]| EXCLUSIVE NEW FEATURE ON ALL PERSONAL ACCOUNTS Fax: [+1 312 803-4929] | *SPAMBLOCK* Technology now included at no cost To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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