Question : Problem: How do I size my UPS

I am British and had a UPS in the UK for the very rare occasions (maybe 2 times a year) when there would be a poewr cut for a couple of seconds.  Having had a spike when this happened that blew my LCD screen, I bought the UPS.  I bought an American APC device that served me well in the UK.

I have now moved to India and been here 2 years.  The APC blew up long ago (not sturdy enough).  Here I face power cuts for hours at a time several times a day.  Plus there are massive voltage fluctuations on the mains supply (mains drops to e.g. 80V from 220V).  I have a generator so the UPS equipment is just to cover the period from mains spike or power cut until generator kicks in - which is a couple of minutes.

I have installed stablisers everywhere on the sensitive equipment to cut power when the voltage spikes.  And I have mulitple UPS devices.  The problem is that I don't know how to size the UPSs that I have.  I have a lot of kit - e.g. right now, I am running 1 desktop, 4 laptops, 2 LCD screens, 1 wireless router, 1 wireless modem routers, 2 printers, 2 computer speaker systems and a free standing WD external hard drive and these are run off 4 UPS devices (2x 1KVA and 2x 500VA).

Whenever I talk to anyone here about sizing UPS I get answers I just don't believe - e.g. I've been told that for a single desktop machine with screen a 1KVA device should run the PC for an hour.  My stabilisers cut the power and keep it cut for about 2 minutes after power stabilises.  With my setup the UPS barely last long enough to cover the 2 minutes after the stabiliser allows mains power through again.

How do I work out what size UPS I need to run my computer equipment?

Answer : Problem: How do I size my UPS

250KVA UPS would weight a couple of tons and require more amps than a house in India could provide.  A diesel generator with that capacity would still cost a fortune, not to mention the batteries, power filters, switches, etc.

I think that was a typo?

If everything is in one location, you're better off consolidating your power into a larger UPS and using the network software from APC to notify all computers to shut down.  There is less loss and waste due to multiple units with excess capacity going unused.

If you really want to be protected, size your equipment per the  nominal watts on the manufacturer plate...this is the max draw.

Then, get two UPS units that can handle the load.  Probably 1500VA or 2kVA would work.  Add up your loads.

Then, get an automatic switch (also from APC) that will switch load from one UPS to the other in case of a failure on one UPS.

Runs a little more in cost than a half-dozen 750VA units, but much easier to maintain.

Also, do not put your printers on the UPS units.  They don't need it, and you will burn out the unit quickly.

To conserve power, also remove the computer speakers.