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My PC’s configuration is as follows: Pentium D Processor (Dual Core), Mercury 945 Mother board with Intel chip, 512 MB ddr2 ram with LCD display. For this system, I am using offline UPS 2.00 K.V. To the same UPS, another system of similar configuration is also connected (in all, two systems are connected).

The problem I face is that when there is no power, one system gets booted. Once power is restored, the other system boots. Why is this happening? Please suggest a solution. The two systems work perfectly under online 2.00 k.v UPS.

Munikrishna Reddy

There are different types of UPS (Uninterrupted Power Supply) Offline, Line Interactive and Online UPS. In Offline UPS, the power for the output load is given from the input supply with some power conditioning.

When the input supply fails, the power is fed from the battery through a switch. When again the input supply resumes, the output is given from the input disconnecting from the battery

As long as the input supply is present, the battery will be charging. There will be a break in output supply for a small duration, say, milliseconds, whenever the input supply fails and is restored.

The offline UPS is highly efficient and low-cost. In Online UPS, the output is always supplied from battery.

The battery gets charged from the input supply. Even when the input supply fails, the output will be supplied. There is no break of output supply during power failure and resumption. The online UPS is not that efficient. The output power is well conditioned without any noise and voltage fluctuations.

Line Interactive UPS works the same way as the offline UPS except that there is no break in the output supply whenever the input supply is cut and restored. In the Line interactive UPS, there is a charger to charge the battery, the input supply is converted to DC, this DC is again converted to AC for the output. When the input supply fails, output is supplied from the battery. A small amount of energy will be stored internally to reduce the break in the output during switching from input mains supply to battery and also for the battery to input supply when the input supply resumes.

Any computer will be able to withstand a break in supply for a small duration, say 4 milliseconds.

The exact duration can be found in the computer manufacturer’s data sheet. In the Offline UPS, if the duration to switch between mains input and battery is more than the PC withstanding duration, the computer will boot.

This is the reason for the computer booting when the input supply fails and again when the input supply resumes.

Line Interactive UPS or Online UPS is the first choice for computers. The offline UPS can be used in cases where the break in output for small duration is acceptable.

Solution by P. Natarajan

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