# Choosing the right DC-DC converter for a computer

I am looking at converting a computer to run off of a 12V battery, which means replacing its PSU with a DC-DC converter.

So, assuming that the computer is currently using 600 Watt PSU, then I assume that rating applies to the INPUT side of the PSU, which is a 120V. So, that would mean its max rated load is approximately 600W/120V = 5 Amps. Is that right?

If the DC-DC converter takes a 12V input, then it would seem the equivalent the rated load for the converter would be 5 Amps x 12 Volts = 60W. So, I would apparently need only a 60 Watt DC-DC converter.

However, when I look at typical catalog listings of DC-DC ATX converters, they seem to offer WAY more power than this. For example, if you look at PowerStream's DC-DC converters, the smallest one they have is listed as 320W and seems to have the same form factor as a typical small AC-DC ATX power supply. That does not really seem possible. So, is PowerStream listing their converter wattage as a 120V equivalent, not as a true 12V wattage? In other words is their "320W" PSU actually a 32 Watt PSU, and they are just calling it 320W to imply that it can replace a 320W 120V AC-based PSU?

• Are you trolling or actually asking? ”So, I would apparently need only a 60 Watt DC-DC converter.” That would violate the laws of physics. To replace a 600 W whatever input voltage PSU will require a 600 W 12 V PSU. – winny Nov 1 '20 at 8:50
• Does this answer your question? Choosing power supply, how to get the voltage and current ratings? – winny Nov 1 '20 at 8:52
• A switch mode computer power supply isn't some linear regulator. current in != current out. 600W in means 510W out, assuming a reasonable 85% efficiency. If that is all 12V it would make over 42A. – Unimportant Nov 1 '20 at 8:55