Date: Fri, 06 Mar 1998 20:13:26 -0800 From: Mike Smith <mike@smith.net.au> To: shimon@simon-shapiro.org Cc: Karl Denninger <karl@mcs.net>, lada@ws2301.gud.siemens.at, chat@FreeBSD.ORG, julian@whistle.com, wilko@yedi.iaf.nl, dmlb@ragnet.demon.co.uk, Terry Lambert <tlambert@primenet.com>, Chuck Robey <chuckr@glue.umd.edu> Subject: Old farts blathering (was Re: SCSI Bus redundancy... ) Message-ID: <199803070413.UAA02168@dingo.cdrom.com> In-Reply-To: Your message of "Fri, 06 Mar 1998 20:06:14 PST." <XFMail.980306200614.shimon@simon-shapiro.org>
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Where I come from we shoot people like this before they get started. The last time I had to put up with this, the geezer in question was busy trying to explain how resistors were more vulnerable to static electricity than capacitors. > On 07-Mar-98 Karl Denninger wrote: > > People discount lower-voltage circuits because they *think* they're > > safer. > > They're not really if there is what amounts to a near-infinite current > > source behind them. > > >From R/C car racing, a sub-c NiCd battery will put out 60 AMp for about 3.5 > minutes. That's 3.5Ah, which is substantially beyond the capacity of a "sub-c" NiCd cell (usually around 1.1Ah until quite recently). In reality, that sort of discharge rate will cause electrolyte depletion and self-regulation after a few seconds, although even then in older cells there's room for the sucker to pop on you. > A telephone man older than I am (yes, there is such a thing), claimed that > Union rules had as much to do with telephony voltages as pure engineering. > The DC thing dates back to the days that DC/AC converters used mechanical > vibrators and were less than efficient or reliable (yes, I used these on FM > two-way radios) These old days were NOT good. DC-is-better-than-AC is a comfortable myth with a grounding in FUD and a fertile ground in the not-so-well-informed minds of Telco engineers. Some contributing factors to this have historical validity, but most are overwhelmed by the drawbacks of low-voltage DC. IIR is not your friend. And just harking back to Karl's earlier comments inre: AC:DC vs. DC:DC conversion - AC:DC conversion these days *is* DC:DC conversion, and a TL437 and some garden-variety magnetics will give you better power than you might want to believe. You have to be outrageously stingy to produce rotten DC these days, or just obsessed with doing it the hard way. (Of course, PC manufacturers are typically outrageously stingy...) -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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