From: stevek@banshee.ecn.uoknor.edu (Steve K) Subject: Re: how safe is minix filesystem in power failure? Date: Thu, 15 Apr 1993 21:02:53 GMT
jim@n5ial.mythical.com (Jim Graham) writes:
>actually, the way UPSs normally work is more along the same lines as the
>battery in a telephone central office (switching center). basically, the
>entire phone system (including your telephone, provided it isn't one of
>the ones, such as cordless phones, that wants external AC power) runs off
>of the battery the whole time, whether external power is there or not.
>the external power, when it exists, is used to keep the battery charged.
>(in the case of the telco, there are *MASSIVE* generators to take over
>the charging of the battery when power failure is sustained.)
>UPS systems for computers (and other devices, too, of course) work the
>same way. the computer/whatever runs off of the battery, and the AC power
>keeps the battery charged.
WRONG! I just bought an APC 400 UPS for my box. It explicitly states that
it only conditions the power except in the event of a power failure. It then
*switches* to the batteries and provides a reduced amplitude modified sine
wave for the computer power supply.
I was under the same impression you stated above until I spoke with a
representative from the *manufacturer*. He stated that the life of the
batteries used in such a manner is far too short for small scale
(i.e. PC) use. For the larger systems you mentioned, I would guess
that they have a maintenance cycle in which they disconnect one or more
cells from the battery array to replace them.
Steve