Desktop PC power supply

I think it HAS to be that the Kill-a-Watt is not measuring a non-linear load properly. If the PS was burning 150 W internally, a small fan would NOT be able to cool the hot components effectively. Saying that 2 75 W bulbs in the housing would not burn up is not germane. There are several components in the PS that will be generating all the heat. Switching transistors, diodes and maybe transformers are what will get hot. Real Kill-a-Watt meters are SUPPOSED to properly measure non-linear loads up to some reasonable crest factor, like 10. Probably most non-PFC corrected power supplies won't be too much worse than a crest factor of 10 (I hope).

So, you might check this with a real electromagnetic wattmeter or a Kill-a- Watt that is known to handle non-linear loads accurately.

Or, if you want to go nuts, get a digital scope or other scope, digitize the current waveform and numerically integrate the true power draw.

Jon

Reply to
Jon Elson
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I checked my Kill-a-watt against my Fluke "True RMS" clamp-on. They read the same current, so that gives me a lot more confidence in the Kill-a-watt.

Now, for the "I'm feeling really stupid" part: in the maze of cables under my desk, I had put the Kill-a-watt on the wrong one! I was measuring the power on everything: PC, printer, modem, etc.

When I used the right cable & measured just the PC, the power was

155W+-. Versus the 200W previously. So my PSU efficiency is 33%+- (54/155). Better than the previous/wrong 25%, but not dramatically so.

Thanks to all the commenters.

Bob

Reply to
Bob Engelhardt

I had an older Pentium computer that came with a 100W PS. It worked fien until I added more RAM and an extra Harddrive. Then it would randomly crash or just do a reboot for no reason. Shortly afterwards, the PS just died. I bought a 350W PS and never had another problem with that computer. It's called RESERVE POWER. Under normal use, it only uses 54W, but add a few drives and run it real hard, and the power use demand rises.

This is about the same as an audio amplifier. You may have the output tubes or transistors that will pump out 100W, but if your power supply cant furnish the reserve power on high demand heavy bass loads, you will hear a lot of distortion, or lose power, or worse....

Reply to
oldschool

It's called 'Not using under rated parts'. That 100W was marginal, at best when the computer was built. That 350W rating may, or may not be the real power it can deliver.

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Reply to
Michael A. Terrell

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