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 [EMAIL PROTECTED] trilug.org/~jeremy | | GPG Fingerprint: 712D 77C7 AB2D 2130 989F E135 6F9F F7BC CC1A 7B92 | \---------------------------------------------------------------------/
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