Amp-hours, computer desktop power backup duration

[dsvillan]

I have a computer desktop which have an estimate consumption of 350 watts and I plan to get a Deep Cycle battery @ 120 amp-hours, for this type of battery, how many hours can it sustain power back up on my 350-watt computer?

 

[kellys_eye]

The battery alone won't work at all - I'm presuming (because you didn't mention) that the battery is to be used in a UPS device?

I'm also presuming you're referring to a 12V battery?

Such details are important!

A 350W PC power supply consumes 1.5A @240V (3A @120V) therefore will consume 30A at 12V (multiply the volts and amps and you get the watts - which are equal at all the stated voltages and currents).

A 120Ahr battery would in theory last 120/30 = 4 hours.

But the theory falls apart when you take into account all the losses in the system - the UPS conversion efficiency, the maximum rate/depth to which you can discharge the battery etc.

Assuming 75% efficiency in the UPS and discharging the battery to 50% of its capacity you reduce the working time accordingly - you'd be lucky to get 3 hours.

BUT you're assuming the PC takes 350W (most don't run at that level for much of the time - depends on what you're doing with it) and you're forgetting that a PC is useless without a monitor....

Rather than planning to RUN the PC for lengthy periods in power-out situations you should do as most people and use the power-out period to safely shut down the PC until power is restored. But that choice is up to you.

 

[WHONOES]

Buy a small generator. They are quite cheap these days.