ups with switchable power for monitor


Tested my UPS systems and found them wanting in Friday's 10 hour Cupertino blackout. Last week I wrote about my longtime desire for a PC power supply that let you plug in an external battery for a cheap, long lasting UPS. But here are some other ideas.

Generally you don't want to plug your monitor into your UPS, because it will drain it faster, which is pointless if you are not there. Better energy-conserving monitors with screen-blanking screen savers can do something about this, but why waste any power on a monitor you're not looking at. I've taken to leaving the monitor off of the UPS power, and then when I come to the computer to do something, plugged the monitor into the UPS. Of course that can require a flashlight and wastes precious time.

So let's have a plug on the UPS that is switched. By default it only takes mains power, even during a failure. But during a failure you can push a button and it switches to the backup power. Perhaps have more than one of these, and plug all your optional devices into them. (For workstations, for example, you may want to only power network hubs or DSL modems when you are there, though I usually go the reverse path.)

Of course, since often the computer has a data link to the UPS, you could even have the computer tell the UPS to power on the optional plugs if the person is at the keyboard.

One could also build a fancy switched plug to do this though I don't know if anybody makes such off the shelf. That might be a simpler product.
Of course, when the power failure lasts a long time, you may wish to switch to longer power sources. Most UPSs refuse to take power from the modified-sine wave cheap inverters we can now get so cost effectively. Some can be convinced. Most, more correctly, won't take from unregulated generators though they often won't even take from inverter-based generators which are regulated but put out non-clean modified sine waves. That, of course is a shame.

All this is wasteful if you have a battery, you would rather feed the 12v battery power right in. A jack to do this would be a nice addition. You could also just open up your UPS and connect it to a bigger battery or build such a jack, though there are some downsides. The UPS's charger may not really be able to handle your 85ah deep cycle battery ($42 from costco) if you left it connected after the power came on, even though that puppy could run your computer for 10 hours. And for liability reaons, they probably don't want to assure that their inverter is well enough cooled to generate power for that long.

But, with a relay, they can arrange so that the battery-in jack would only bring in power from the battery, not recharge it. The typical computer (but not big monitor) will take no more than 15 amps at 12 volts, which you could run over a heavy duty 115v extension cord to your car in a pinch, if you had adapters.

It would be nice if they just sold UPSs and batteries independently at the low end. They do this at the high end. The batteries are actually quite cheap -- an 18ah SLA can be had for under $20 and that's twice the battery typically found in a consumer 20-minute 300 watt UPS that costs under $100. Would cut the shipping cost if they did this, too.

But I'm going to pull out the battery in my UPS and leave the terminals exposed. In a long failure, I can clamp on think cables to that costco deep cycle and run the computer most of the day. Though of course a laptop (for which 12v power supplies are now cheaply available) is really the way to go for power failure computing. It will run for over 3 days straight on that $43 battery.

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