[TriLUG] UPS (was linksys stuff)

[Jeremy Portzer]

On Wed, 2004-07-28 at 13:55, Aaron S. Joyner wrote:

> The small margin of error enters if your computer is unable to actively 
> turn off the UPS (for various possible reasons).  If that's the case, 
> the best you can do is approximate how long a shutdown takes, instruct 
> the computer to try to stay up as long as possible on battery and 
> initiate a shutdown with only the required amount of battery-time 
> remaining (plus a marginal grace period, of course).  Do not send the 
> appropriate ACPI signals to power down the machine.  This will cause the 
> machine to safely shut down, and then remain on, thus depleting the 
> battery and turning off the UPS.  The UPS then comes back on when the 
> power comes back on, and the machine with it.  Of course, the obvious 
> danger is if the power comes back right after you finish your shutdown, 
> before the UPS has given up and turned off due to lack of juice.  Then 
> your box is sitting there, turned off, and unhappy.  Such is the dangers 
> inherent in that setup.

Another danger is that the power could go off for a long time, then come
on for a minute or two, and then go back off again. This minute or two
of power would be enough to power on both the UPS and computer, but not
enough time to recharge the batteries.  Therefore, the computer might
start up, but then be shutdown uncleanly if the power goes off again. 
The UPS might not have enough battery power to give the computer time to
do a safe shutdown.

A good way to avoid this is to have the UPS monitoring software initiate
a full shutdown and poweroff of the computer when battery level reaches,
say 40%.  This gives you plenty of extra battery power if you have a
series of startup/shutdown sequences.   

Also, note that the if the computer is the only device on the UPS, and
it powers itself off completely, you don't necessarily need to shutdown
the UPS itself. Nothing will be drawing any current, and therefore the
batteries won't die*.  This doesn't apply if you have other devices on
the UPS (such as network routers, monitors that don't shutdown
automatically, etc.)

Hope this helps,
Jeremy

* actually, computers with ATX and similar power supplies do still draw
a small amount of current when turned "off" but still plugged
in...however this shouldn't be enough to affect battery life
signficantly unless it's a really small UPS or really long power outage.
-- 
/---------------------------------------------------------------------\
| Jeremy Portzer        jeremyp at pobox.com      trilug.org/~jeremy     |
| GPG Fingerprint: 712D 77C7 AB2D 2130 989F  E135 6F9F F7BC CC1A 7B92 |
\---------------------------------------------------------------------/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
URL: <http://www.trilug.org/pipermail/trilug/attachments/20040728/9b77d312/attachment.pgp>