silly question about power consumption 400 watt

[mark the sparki]

hi all
silly question but i have to ask as knowlage is a better understanding
i have a 400watt pc power supply powering leds as it is a 400watt is it consuming 400 watts?
it only needs 0.5 amps at 12 volt so if it is more cost efective to use a smaller power supply
thanks

 

[telectrix]

it will only use whatever wattage the load draws plus a little bit for losses. 0.5A@12v is 6watts.

 

[ackbarthestar]

I assume that the PC power supply is a SMP? If so they are very efficient. They only 'switch on' and draw current when there is an output load.
Just a thought, are you using this set up at the present?

 

[mark the sparki]

yes i'm using this setup at the moment and it is a SMP power supply its out of an old pc

 

[ackbarthestar]

As Tel says, the power consumption will be approximately the current drawn by the load. If you want to measure it then put a clamp meter around the LV supply Phase or neutral, measure the current and a voltmeter across the terminals and measure the voltage and do a quick sum.