Whether you want to buy one PC or 100, a UPS has become a de facto need in this power-starved country of ours. So how do you go about buying one?

One or many?

If you run many PCs, then you’ll be faced with this question. Do you buy one central UPS for all of them, or do you put a separate UPS to each one of your machines? An associated question is—do you really need all the equipment to be provided with back-up power?

If you have many computers, you could go for one large UPS to power all of them, or you could have many smaller ones powering groups of computers—something like a different UPS for each workgroup. Or, you could choose a model where your critical systems such as servers are on a central backup, and the rest of the systems are on clustered backup.

How big?

UPSs are rated according to their VA rating and the backup time they provide. The VA rating determines the load, that is, the number of PCs, printers, etc, that the UPS will be able to handle. The backup time depends on the number of batteries and the connected load. That is, you could increase the backup time by either adding more batteries or by reducing the connected load on the UPS. In simpler terms, for the same VA rating, a UPS with more batteries will provide more backup time.

How much backup?

This is a crucial question. Do you need backup just to safely shutdown your systems or switch over to standby generator power and continue to work for, say, half-an-hour or one hour of no power? This is one question you need to answer in order to determine the backup you need.

You could also have only some of your systems running through the outage while the rest are shut down. In that case, the total backup time required, and hence the cost of the UPS, can be cut down, as you are reducing the connected load.

Online, offline, or line-interactive?

For a stand-alone PC, which you use at home, an online UPS is not the best buy. It would turn out to be too costly. You could go in for a line-interactive one, if not an offline. On the other hand, bigger systems are all online. The technical differences between these have been covered in detail in previous issues of PC Quest.

How much load do I have?

Typically, based on the wattages of PCs, a 500 VA UPS should be able to handle three PIII machines with 15" color monitors. But remember that most of the UPSs in the market are over-rated. So, lets say, if a vendor says that a 500 VA model will be able to handle a load of one PC, then the UPS is surely over-rated and would actually sustain load less than 500 VA. A 500 VA UPS is a good choice for any model of PC you have, plus the additional load of an inkjet or desktop laser printer, a set of amplified speakers, and your modem.

What else?

Ideally, the output voltage range of the UPS should be between 190-250 V. Check for a built-in AVR (Automatic Voltage Regulator). Also check for the input voltage range. The larger the range, the lesser the switchovers to battery, and lesser the drain on the battery. Another important factor is the switchover time. Ideally, it shouldn’t be more than 10 ms, or else the PC could reboot.

Apart from the technology, you should check for warranty. Many vendors have lower warranty periods for the batteries. You should clearly ask for the warranty on the batteries too. Also, check the type of batteries used. They should be SMF (sealed-maintenance-free) batteries.

Hope next time around you do not end up loosing a key project because there was no power back-up to finish the presentation without the KEB power.

Issue BG8 Nov01

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