I have 700VA UPS which I had bought in 2009 to power my Desktop Computer.It can power desktop(17" CRT monitor,CPU cabinet ) for 5-6 minutes.It has 7Ah battery(only 1), charging and inverting circuit and a transformer inside. Now I want to modify it to power my Laptop Adapter whose specifications are:
100-240V~1.8A 50-60Hz 20V-3.25A 65W
The problem is, it only last for 15 minutes. Since the load is only 65 watt, I had expected hours instead of minutes.
So, what should I do to make it last for hours??
I searched for this on google and went through several sites and found some things regarding UPS:
UPS transformer is designed to power high power device(generally 400-500Watt) for short time(5-6minutes). At longer use , it may burn.
So, if I change the transformer inside with lower capacity trasformer( 100Watt), will I get backup for long time(1-2hours). Also, I have cooling fan from desktop CPU cabinet which I can use to cool the tranformer.
Please suggest me ways to modify it.( If you are wondering why I need UPS for Laptop, here in Nepal we have Load Shedding for 11 hours each day and Laptop battery last only for 2.30-3hrs and if I am able to modify a UPS(lying around) for 1-2hrs, it would be great!!)