questionsany electrical engineers out there?

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If I'm not mistaken, that's the most power it can pull. You could tap it into a Belkin energy monitor to check, though.

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I have a kill-a-watt...Power supply number is the 'max' power it can draw.
Good question I had this argument with a UPS provider. He was telling me my 500w ps in my pc was drawing 500w at all times. I argued but it was pointless. I called back the next day with my Kill a watt and added enough devices to the UPS to draw the 500 watts he requested for our testing.

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No and no

The computer power supply can supply 450 watts @(probably)5&12 volts dc.
How much it draws @110 ac depends on load

The stereo can put out 700 watts of power at full volume but puts out far less 99.99% of the time

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Just to be a bit more precise here.

A 450 watt power supply should be (is is such an ideal word that rarely applies in the real world) capable of providing 450 watts of OUTPUT power continuously without overheating.

Since power supplies are not 100% efficient, the INPUT power (draw from the A/C line) will be greater than 450 watts when the supply is OUTPUTting 450 watts (the excess power is converted into heat).

However, it is unlikely that your computer is drawing the full 450 watts from the supply all the time, if ever. It depends on how many drives, cards, USB devices, etc. you are using at the moment.

Same thing for your stereo: max output of 700 watts (into your speakers)means max input (from the A/C line) of more than 700 watts.

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I got all excited since someone was calling for something I actually have. Just to add to the discussion, power supply as others have stated are what they can output and are safe maximum values. Now, most power supplies are very ineffective. All that heat you feel coming from the power supply is wasted electricity due to cheap design and parts being used. Your input, ie, electricity that you are charged for, is always going to be greater than the output of the device.

Also, depending on how they measure output, the outputs of the devices may not be the same. Same holds true with sound systems. There are some that are more powerful using 1000 watts then other that may also be rated at 1000 watts.

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I agree with @baqui63 and @videowallart:

Some small addendum for the specific devices.

1st: Let me offer a rough analogy.
Suppose you own a classic Mustang with a 410hp, 402CuIn engine.
It's parked, engine off.
What is the power produced or fuel used? -0-
Start it, let it idle. What's the power and fuel now? -tiny-
Putter along at 30 mph then gun it?

Each of the P/S examples have a maximum safe power, but they can exceed that for a limited time at risk. Typically they run at a small fraction of theoretical max. They'll draw and dissipate only as much as required, based on applied load and losses. However, both the computer P/S and audio amp have other limits, often ignored.

Example, the 700 watts total is the sum of the per channel limits. You can't exceed those without distortion or potential damage, even if it is a fraction of the 700 watts.

Ditto with computer power. You have separate current limits on each +5 vdc, +3.3 vdc, etc. You can't exceed individual or total limits.

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@videowallart: Watts are watts are watts, no matter what the voltage.

But to answer the original question - I have a UPS that tells me the actual load. My computer uses about 80 watts when idling and the monitor is off, and if something CPU intensive happens it goes way up.

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Thanks for the info! I've never seen so many ways to say the same thing. It's something I always wondered. Especially since the family leaves the AV receiver on all the time, and we leave our computers on 24/7.

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@tcayer: You really should try to turn off as many appliances as possible when not using them. The Mustang example is not entirely applicable here. Just because you are not using the AV system and not using your computer, they are still using power. Eve n turned off, most use a small fraction of power. Your TV off could be using 3 Watts, the AV sitting idle could still be using 80 Watts, your computer at idle could be using 50-150 Watts. Even the little wall warts can all be pulling 1/10 Watt when not in use. It all adds up. You should try a Kill-a-Watt if you're curious enough.

MrMucox
MSEE

P.S. I leave a couple computers on all the time, but I have since started to turn off my Surround sound system.

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@tsfisch: Thank you! I was going to say the same thing. Watts are watts, and can be compared no matter what.

Oh, and the MAX Wattage is just that, a MAX, you should NEVER go above that, and should only approach it for short periods of time. That is the point that the power supply actually starts to break down.

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@mrmucox:

You might want to unplug them as well.

I have a 16" stand fan with a remote control. I don't recall the actual wattages, so I'm making these numbers up, but they are relative:

Running on high, say it uses 60 watts, with 40 on medium and 30 on low.

However, when it is off, it uses 20 (a third of its usage on high).

I now leave it unplugged except when I'm using it. (Thanks, Kill-A-Watt.)