How much power does a 500w power supply actually use?

By DelbertPGH ·
I've been looking at "green" drives and other equipment with low power requirements, and it makes me wonder: when you have a power supply with a certain rating, say 500 watts, does it consume 500 watts all the time, regardless of processing load or how much equipment is actually being supported? If I have only 200w of demand on a 500w unit, is it still burning all 500w?

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No & ...

by OldER Mycroft In reply to How much power does a 500 ...


Less text, less screen wattage! :^0

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The 500w is the capacity

by robo_dev In reply to How much power does a 500 ...

such that if the PC is on standby, the actual current draw is less than ten watts, versus if you're burning a DVD while calculating PI to the 40th digit, you're probably using something like 200 watts.

Think of it like an engine. A 500 horsepower engine only provides that power when you nail the throttle.

Most power supplies are over-rated in order to satisfy the 'worst case scenario' (somebody with five hard drives and five DVD drives) and also for the 'marketing factor' since 500 watts sounds more sexy than 325 watts.

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"PC Power Supply Efficiency", in more detail. :)

by Peconet Tietokoneet In reply to How much power does a 500 ...
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You might consider

by Brenton Keegan In reply to How much power does a 500 ...

You might consider using a UPS unit to improve your power efficiency. I've never purchased one for this reason so I don't know for sure if it's actually beneficial, but if you get a UPS that's energy efficient it could provide efficient power to a number of power-inefficient devices.

I could be wrong though, it might actually be more costly.

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Less Efficient

by TheChas In reply to You might consider

While it is true that a modern UPS is more efficient than an older UPS, a UPS does nothing to improve energy efficiency.

Just because there is a power supply and running electronics inside a UPS means that it will always draw some power. Even when the connected equipment is turned off.

Now, most UPS systems do have some level of surge suppressor built in which can help protect any equipment that is connected.

But, if energy efficiency is what you are after, a UPS is not the answer.


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by DelbertPGH In reply to How much power does a 500 ...

You've all been informative. Thank you.

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Some Thoughts

by TheChas In reply to How much power does a 500 ...

First, one of the benefits of a switch mode power supply is that it has a lower operating overhead than a linear power supply. This makes it more efficient to begin with.

Any power supply draws only the power it outputs plus it's overhead power.

In the case of a switching supply, that overhead is usually between 10% and 20% of the power produced.

The overhead power is at it's lowest as you approach the rated output power.

So, at 500 watts of supplied power, and efficient power supply will draw an additional 10% power and the total power in will be about 550 Watts.

Now, if you are looking to have your computer use the least amount of energy possible, you want to match the capacity of the power supply to no more than a safety margin above the maximum power the system could ever need. This is because the larger the power supply, the more power it consumes at idle.

If you calculate a peak demand of 300 watts, you want to add at least 10% for a safety margin. So you might want to use a 350 watt power supply to minimize any inefficiency when using less than maximum power.


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No it is not using 500W all of the time

by OH Smeg Moderator In reply to How much power does a 500 ...

That is a Value that the PS is capable of supplying at peek loads with most PS's but with some it is a Upper Limit on the Constant Power that it can feed into the system.

These PS's will consume some power producing the Supposedly Stable Voltages and Currents inside the case as they are a Switch Mode Supply which rely on Chopping Transistors to produce the DC Voltages from the AC input.

But in answer to your Hypothetical Question if you have a 200 W Load the PS will consume slightly more than the Load to provide the necessary power.


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