Date: Fri, 9 May 1997 14:59:46 -0500 (EST) From: "John S. Dyson" <toor@dyson.iquest.net> To: steve@visint.co.uk (Stephen Roome) Cc: freebsd-questions@FreeBSD.ORG Subject: Re: catching a powerfail NMI Message-ID: <199705091959.OAA00252@dyson.iquest.net> In-Reply-To: <Pine.BSF.3.91.970509195840.16810A-100000@bagpuss.visint.co.uk> from Stephen Roome at "May 9, 97 08:02:03 pm"
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> > (This is serious) > > I'm looking at the possibilty of using the powerfail NMI > which seems to already have some code for it in > /sys/i386/i386/trap.c > > Basically, with a bunch of capacitors and a monostable we think we can > make a very cheap UPS, which gives long enough to get the system to do > little more than just fasthalt or somesuch. :-). 1 Farad == 1V drop per amp every second. Say that you have .5 Farads (500 000 Microfarads), and a 15 Amp load, then you will have 1/30 of a second before you loose a Volt. .5 Farads is a lot of capacitance. (The little low-current supercaps notwithstanding.) I guess that you do have a lot of capacitors!!! John
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