I've got a 21 inch CRT monitor, a 1.80 dual core, Intel 946 motherboard, 256mb Geforce 7600GS, five hard disks, a 500w power supply, and a dvd burner.
If I want a UPS that can power the computer for at least 20 minutes, how powerful does the UPS need to be? I need to know what I would need, both for the computer+monitor, and then just for the computer.

I've posted awhile back regarding the UPS, you can have a read there. http://www.astahost.com/index.php?showtopi...l=backup+power#

Quite a lengthy topic.

Just a quick calculation for your case, assuming the power consume by your system is 400W max(500W power supply doesn't mean it will consume as much), 21" CRT is normally 150 to 200W, correct me if i'm wrong. You can see the rating at the back of the monitor. That equate to 600W. So you need a 600VA and above UPS. Battery current will be 600/12 = 50A. Hmm, a car battery will last you 1 hour. A standard UPS battery is only 7Ah, which in this case will be 7/50 * 60mins = 8mins 24secs. To get 20mins, you'll need 20/60 * 50 = 16.67Ah. So a UPS will a pack of 3 standard battery will do. Some UPS comes with bigger battery, so you might only need 1 battery.

But most UPS will not disclose much information. From the size of the UPS, you might be able to guess the size of the battery. If you look at this link, http://en.wikipedia.org/wiki/Uninterruptible_power_supply

In the first picture, that size of UPS can normally house 2 x 12V 7Ah battery. The right picture under Outdoor UPS, You see the black color battery there, it's 4Ah, half standard size battery.

One thing to note though, you need to get a rating higher that calculated, at least a factor of 1.25 in order to safely achieve your 20min mark, plus overcoming battery deterioration over time.

Thanks for the info. I did read the other thread you mentioned, but wanted to get taliored specifics, as anything I'm looking at seems to cost close to $150. So i didn't want to make a stupid investment. Though my power supply is rated for 500w, it outputs around 480w as it's a proper ASUS one. So I need to get something, maybe even more powerful than just 20 min. I really should have looked it up on wikipedia though. As the first thing that pooped out at me when i looked at that link was the online or backup versions. And I realize that all this time all I've been looking at are backup models when i should have been on the prowl for a good online UPS. Thanks.

You're welcome.

One thing to take note. Online vs Backup UPS. Backup one is only to supply power during power outage. It's more efficient in a way that it's only charging the battery when there's power. Online UPS, the power is feed through the battery, charging it, at the same time, AC is generated back. It act as a shield, so at the same time it can also regulate the voltage, and take over if there's power outage.Therefore Online UPS is less efficient, cause it need to use it DC to AC converter all the time. The advantage is that it's power output is clean, glitch less, so most of the time use for sensitive equipment.

Btw, Backup UPS can only power non inductive load, like PC, monitor. It can't power fan and motor alike.

If you really want more power and longer backup time, consider those that can connect using car battery.

I've got a 500W PSU (usually under heavy load) with my 2x 19" LCDs running on an APC 1500VA unit, and I have plenty of time to shut things down.

I've got my router (an old linux box) and all my networking gear (switches, APs,) running off a separate 500VA one by belkin or something...that one works fine too.

Well I guess either one would work for me then. I wanted an online one to get the full protection range, but they don't really have them available here. I found lead acid batteries, but they're almost just a crate with a car battery inside, so won't do for my office. I got a 1000w backup UPS. It came in 800w and 1000w versions, and the price difference was $20, so I figure if I want a bit more life and also add a little printer and external hard disk to the UPS load, the 200w wouldn't be a bad idea. It wasn't cheap, though, or at least not as cheap as I had thought... $130 for the 800w and $150 for the 1000w. Though with an average of 5 power cuts a day, not counting freezing up times due to low voltage, I'll easily recoup the investment in time saved.

There are also very cheap devices that can measure the power usage of electronic equipment. One such device I know of is called Kill-a-watt and goes for like $20. You plug the equipment you want to check power usage for into the device, plug the device into the wall, and it will tell you the power consumption. This can be useful for getting an estimate on how much power you need, then you can round up to figure out how powerful a UPS you need.

~Viz

Where do you live? So bad !!!

For the low voltage situation, it would be good if you can get the online one. If not, just add a voltage stabilizer (voltage regulator, AVR) before your UPS. Those should be cheap. Same wattage rules applies.

The battery you saw in those normal UPS are sealed lead acid. Not exactly like car battery. The electrolyte is in gel form. So you can put it in anyway you like. Car's lead acid, you'll have to keep it up right.

In Karachi.... Half the time it's "scheduled" loadshedding and the other half is unannounced power cuts. I may not have the terminology down correctly, but from what I know, Karachi uses around 750MW but the power grid only can produce 450MW. I do have a stabilizer sitting around somewhere, so I could add that. But someone told me not to stick a UPS after a stabilizer because if the UPS has a built-in stabilizer then the other stabilizer drains it. Is that true?

A backup UPS would not have a built in stabilizer. Only the Online version has it. And the draining only happen if you connect the stabilizer after the UPS. If you have online UPS, why would you still need a stabilizer in the first place.