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I recently purchased a new HP Pavilion desktop. It only came with a 250 watt power supply. I installed a secondary hard drive and eventually may want to install a pci express video card but don't know if the current power supply could handle it. Is there any way to determine how many watts your power supply is using maybe in the way of a utility or trick anyone knows? Thank you for your time.

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Try searching your favourite search engine for "computer power consumption calculator", and you'll find several website that allow you to make a rough estimate of how powerful a power supply has to be for a certain combination of hardware.

I won't give direct links, as several of them are on sites of power supply manufacturers, and I don't want to promote any of those, and you probably want to check the opinions of both "amateurs" & power supply vendors. ;)

Anyway, a quick check seems to indicate that a 250W PS is probably not going to supply enough peak power during boot (once your system is running, it might be enough).

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the only true way is measuring. The principle itself is not that hard: disconnect a wire which has current running through it, put an ampere meter in between, multiply measured value with measured voltage and you have the consumption in watt. Now here are a number of problems with doing that in a power supply:

  • there's tons of wires coming out, either measure all of them, or open up power supply to see if they have a common starting point and measure there
  • the wrires are not simply disconnectable, this will at least require soldering
  • there's 5V, 12V and -12V to be measuerd (I doubt these are drawn from a common point)
  • ideally you have to measure at peak consumption, ie max out cpu, hd and video; but since you want to replave your current video card you'd have to measure without it to know how much is left.

Now even if all of the above succeeds, you are nowhere Power Supply ratings are to be taken with a huge grain of salt, so suppose you figure out the current setup uses 150W, there's no way of telling if there is really 100W left, and there is the same uncertainty in the rating of your new video card. Apart from that, you say it's rated 250W. What watt? Peak? Average? RMS?

Long story short: there is no way you can measure this accurately, and even if you can it won't tell you much. Simplest option is to install the card, and buy a new power supply should the current one not handle it. This should be quite safe sine modern supplies will turn of automatically in case of overload.

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Chances are a 250 watt power supply will not handle it. When I was a bench tech we had to upgrade the power supply on emachines (came standard with 230 watt at the time) anytime an AGP video card was added to the system. Considering that video cards these days are more powerful, I'm sure you'll need a better power supply.

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Like fergNab mentioned, the easiest way is to get a device called a Kill-a-Watt and have it measure how much power is coming from the wall to your computer.

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that won't do it: it will measure what the power supply drwas from the net, not what power the internals draw from the power supply. – stijn Oct 25 '10 at 7:08

Its a little overkill, but you could use this

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You should include details about what it is , what these things are called, in your answer. For OBVIOUS reasons Like, what if the link goes down. Or, what if people already know what the thing is, why should you cause them to waste their time clicking a link. Just say what it is. Also, so people can find them on google. Energy/Power/Electricity/Electric Meter/Metre/Monitor plug. It's not overkill at all, considering that it's not expensive and it's brilliant, does what it says on the tin. I've used one. – barlop Oct 24 '10 at 23:24
Link doesn't work. What did it say? What was the gist? Repost it here. – random Oct 24 '10 at 23:47
I didn't say the link didn't work – barlop Oct 25 '10 at 0:20

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