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When UPS was disconnected from power source and 25W desk lamp was connected to it, all was normal:

enter image description here

But as soon as i have unplugged it and plugged in 95W fan, AVR "Normal" changed to up arrow:

enter image description here

Can somebody explain what does up arrow mean?

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up vote 7 down vote accepted

I have UPS with that same software and the AVR mode stands for automatic voltage regulation.

Basically the UPS has internal regulator which is supposed to provide stable voltage when the input voltage does out of a specified range.

The only reason I can think of now that could be causing the AVR to turn on is if somehow the inverter is producing too low voltage at the output so that it needs to pass through AVR. The UP arrow means that AVR is increasing voltage while the DOWN arrow means that AVR is decreasing voltage.

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Well my fan was made here like my lamp and any other appliances. I don't know why would its voltage be different. – Boris_yo Nov 21 '11 at 13:58
@Boris_yo I haven't mentioned the input voltage of the fan at all in my answer and the behavior of the UPS shouldn't depends on it. The point that I'm making is that for some strange reason when the fan is connected, the UPS's inverter isn't producing right voltage so the AVR needs to correct the inverter output. The only logical reason for that which comes to my mind right now is the one Shaun provided. – AndrejaKo Nov 21 '11 at 17:32

There's a high chance this is related to motors being inductive loads, which can be difficult for an inverter without any form of correction. Your lamp is a perfect example of a resistive load, so no power-factor correction is required at all. Devices with transformers (most the equipment you'd usually run on a UPS) start leaning into inductive, but a motor is the textbook example of a difficult load.

I must admit I've little idea why this is manifesting as AVR; usually AVR is used to correct for brownouts (undervoltages) in the supply, so shouldn't be required at all when running on battery.

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Your answer is very good and complements the accepted answer. Thanks! – Boris_yo Nov 21 '11 at 18:43

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