by May 10, 2001 0 comments



This year, we tested UPS models of 1 kVA. These UPSs will be suitable for small office environments, or even branch offices of a large organization, because they can handle a load of more than one PC. We considered UPSs with a rating of 1 kVA with internal batteries and a price ceiling of Rs15,000. The UPSs were judged on their performance, features and price. Finally, the Brown-Gibson model was used for arriving at the weightages for all parameters. Let’s look at the various parameters under performance, features and price that we took into account for determining the winners.

Performance

Test Weights


Performance

Switchover Characteristics: 19
‘True’ VA Rating: 19
Maximum output voltage: 15
Minimum output voltage: 15
Maximum Switchover voltage: 10
Minimum Switchover voltage: 10
Backup time: 6
Cold Start: 4
Float Voltage: 2
Sum: 100


Features

Control Software: 36
Indicators: 27
Additional Features: 18
Compactness: 9
Documentation: 9
Sum: 100


Pricing

Price: 80
Warranty: 20
Sum: 100
For our final calculations, we used
the following weightages:
Performance: 200
Features: 100
Pricing: 50
Total: 35

‘True’ VA rating. This test is used to check for the true rating of a UPS; if it is rated at 1 kVA, we apply an equivalent load to it, and see whether it can sustain it for up to 30 seconds. Only UPSs that managed to sustain at least 80 percent of their rated load were ranked in the shootout. 

Switchover voltage. This gives us the maximum input voltage range over which a UPS doesn’t switchover to battery. The greater this range, the lesser a UPS will switch to battery, and hence lesser the drain on battery. So a voltage range of 20 percent above or below 220 V was considered best.

Voltage regulation. This is the maximum and minimum output voltage that a UPS can supply to the load. Ideally, it should keep its output within 10—15 percent above or below 220V.

Switchover characteristics. This is the characteristic that the UPS shows during switchover. A parameter called the Droop voltage is measured in this case. This measures the voltage drop experienced by a UPS when during the switchover to battery. We also captured the switchover waveform on an oscilloscope to see the switchover time. 

Backup time. Backup time for a UPS was measured at 80 percent of its rated load. For those that failed at 80 percent in the qualifier, a load of 70 percent was used.

Float voltage. This is the DC voltage across the terminals of the batteries inside the UPS. When fully charged, this should be between 2.25—2.30 V (DC) for each cell. This gives us an idea of the charger circuit of the UPS. It also determines the battery life.

Cold start. If there is no power and you still need to switch on your PC, say to take out a CD, then you do a cold start. The UPS needs to support a momentary high load in such cases. We checked each UPS for cold start at 80 percent of its rated load. For UPSs that failed at 80 percent, we used a starting load of 70 percent.

Features

Here, we considered indicators, documentation, control software, compactness, additional features (surge-protection port for telephone line, surge-protected power outlet for laser printers, and external battery support). Some line-interactive UPSs gave a sine wave output instead of quasi-sine wave. We considered this also in additional features. 

Pricing

As always, we considered two factors under pricing: price and warranty (for both battery and UPS).

USING BUYING TIPS

  • Load handling. Going by the actual load considerations, a 1 kVA UPS should ideally be able to take the load of around 5 PCs (P III machines with 15” color monitors). Check out if it can do so. 

  • Backup time. Check out the backup time a UPS can give to the load you are planning to connect to it. If you need longer backup, then ask for a UPS with more batteries.

  • Type of batteries. UPSs with Sealed Maintenance Free
    (SMF) batteries are the best.

  • Provision for extended backup. In a branch office with 4—5 PCs, it is always advisable to have external battery connection to handle long power cuts.

  • The front panel. Indicators on the front panel are essential to monitor the health of your UPS. Otherwise, you may not know whether the UPS has a battery fault, making your PC switch off during power failure.

  • Software. For small or branch offices, control software for saving your work and automatically shutting down your machines is necessary to protect you from data loss.

  • Warranty. Many times the batteries inside a UPS are not included in the warranty. This could be a problem if the batteries leak or don’t perform as they should.

  • Earthing. We normally tend to overlook this point. But in extreme cases, this may give you nasty shocks from the UPS or even send a bad spike down to the PC’s
    SMPS. So check that a UPS has this, else its plug could give you a shock even when it’s not plugged in. 

  • Surge protector for phone line. With a small or branch office, you are likely to use a shared dial-up Internet connection. It would be better to have a surge-protection port for the telephone line. 

Ashish Sharma

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