This discussion centers on calculating the number of AA batteries required to power a PC with a 750W power supply unit (PSU). It is established that 8 AA batteries can deliver 1 Watt, and to power a 750W PSU for one hour, approximately 480 AA batteries would be needed, assuming each battery can deliver 2400 mAh at 1.5 Volts. The calculations clarify that 750 Watts translates to 6.25 Amperes at 120 Volts, necessitating multiple sets of batteries in parallel to meet the current demand. The conversation also emphasizes that actual power consumption of a PC is typically lower than its peak rating.
PREREQUISITESThis discussion is beneficial for electronics enthusiasts, hobbyists experimenting with battery-powered devices, and anyone interested in understanding power requirements for computing hardware.
!Well, I wasn't expecting that response! Still taking it in, but thanks! :DBvU said:Hello Dougie, welcome to PF
I would have guessed one AA battery would already be capable of delivering one Watt, but never mind.
The calculations go as follows: Delivering one Ampere of current at a voltage of 1 Volt over the load is one Watt of power.
One Watt of power is one Joule of energy per second. So for Watts given you never have to wonder whether that is per hour or per fortnight: it is one Joule per second.
To answer you rhetorical question, you would need to know for how long your battery can hold up this one Watt. Usually the makers don't tell you on the package. For rechargeable batteries you often find the capacity expressed in mAh -- milliAmps times hours. I have some that say 2500 mAh, meaning that they can deliver 1 Ampere for a period of 2.5 hours (when fully charged and in good condition, at reasonable temperature, etcetera etcetera. I wouldn't bet on it too heavily...). Or one half amp for 5 hours. 2.5 Amp for one hour is asking an awful lot (they heat up internally, a waste of ... yes, energy).
Suppose an AA battery can deliver 2400 mAh at 1.5 Volt. With 80 AA batteries you would get 120 Volt. 750 Watt at 120 Volt means about 6.25 Ampere. So with six sets in parallel of these sets of 80 AA batteries, each set would have to cough up 1.04 Ampere. Still with me ? Each and every one of these 480 batteries can claim (in theory) to be able to keep up this 1.04 Ampere for a time of around 2.4 Ampere hour / 1.04 Ampere = 2 hours and 20 minutes.
Pretty expensive experiment ! In reality you'll be a lot better off, because on average your PC doesn't gobble up these 750 Watts at all. It is boasting 750 W peak but it would be a room heater if it did that continuously.
How about that for a verbose answer to a simple rhetorical question !
--
AA batteries are 1.5 Volt, yes.