Power consumption by DC-DCs?

**amthar** · 02-09-2006, 04:42 PM

I have looked on Carnetix's website and tried to search the forums (model number + consumption, amps, wattage, etc leads to tons of results if you can imagine) and have not been able to find what the consumption of the DC-DC regulators are?

I'm specifically interested int he CNX-P1900 and CNX-P1290. Assuming there was no load on them, how much do they consume? I'm trying to add the total load I am placing on a given 12v feed. I have found the load of the devices being powered by the regulators, but not the regulators themselves. Is it negligable and that's why there is no mention?

Thanks all.

**meddler** · 02-09-2006, 05:18 PM

Let's see if I understand you correctly. You want to know what the power draw of the PSU is when it is not loaded? If this is the case, the current draw really quite small and not worth mentioning as you have said. What you should be worried about is the current load when the PSU is fully loaded. At 90W it will draw somewhere in the vicinity of 9A.

**mushin** · 02-09-2006, 06:07 PM

A PSUs power consumption is not constant, it varies with load. If you're really trying to nail down the number, what you want to find is the efficiency curve. You can then see what the current draw is going to be for your given load.

If you're just looking for ballpark estimates, DC-DC PSUs tend to be around 90% efficient.

**piabu** · 02-09-2006, 07:53 PM

The M2-ATX connected to my full-sized ATX board draws about 47mA when the system is fully shut down (i.e. with no voltage on the 5vSB line).

I know you were asking about the CNX series, but the figures should not differ by too much.

**amthar** · 02-10-2006, 09:05 AM

Originally Posted by mushin

A PSUs power consumption is not constant, it varies with load. If you're really trying to nail down the number, what you want to find is the efficiency curve. You can then see what the current draw is going to be for your given load.

If you're just looking for ballpark estimates, DC-DC PSUs tend to be around 90% efficient.

So going with the 90% estimation, a maxed CNX-1900 at 140 Watts would be... 14 amps???