Finding the watt rating of your computer?

[drfsupercenter]

Hi,

We have a generator, so I never really have to worry about losing power. However, it takes 20-30 seconds for the generator to kick in, which means I still lose all my work on the computer and stuff.

I figured, now that UPS units aren't too expensive, I can buy the cheapest one I can find (as it only needs to work for up to 30 seconds - I don't care how many minutes the battery lasts)... but I was a bit confused about the watt and volt-amp ratings.

After doing some Googling, I found out what the difference is.

However, I don't know what the actual Watt rating of my PC is. I have a 450W power supply unit, but I know it's not using all of it. I previously had a 200W unit that worked fine, and when I added another IDE hard drive it wouldn't start. Now, I don't know how many watts your average hard drive uses - but I doubt it'll knock it up to 450W

So what I need to know is, how do you find out how many watts your computer is actually using? CPU-Z didn't say, and I don't know if it's even possible.

I was looking at this unit (http://www.microcenter.com/single_product_results.phtml?product_id=0255535), but wasn't sure if it's powerful enough since it's only 230W.

On a side note - does anyone know how many watts your average clock radio uses? It would be nice to put that on a UPS as well so I don't have to keep resetting the time :)

[doctorhardware]

To calculate wattage the formula is W=IxV W=wattage, I=amperage, and V=voltage. I would guess that a clock radio would be around 2 watts or so. The only way to measure the current draw of your computer you will need a amp clamp to make the measurement.

[drfsupercenter]

I know how to measure watts... though obviously it's not just amps times volts, or VA and W would be the same thing.

So I could stick an ammeter into the power plug where my computer plugs in and use that?

[doctorhardware]

If it is an ac amp meter yes.

[drfsupercenter]

I think the one I have will do both, AC voltage/amps and DC.

So there's no way inside the computer to tell? I can probably find it written on the bottom of the clock... but obviously not for a computer.

[doctorhardware]

The rating that is usually on the label would be the max rating of the device. Since the computer is not using the full potential of the power supply hence it will not draw the same wattage.

[doctorhardware]

Va is a little bit different from wattage. http://www.newton.dep.anl.gov/askasci/phy00/phy00205.htm this link gives a better explaination of VA ratings for ups backups.

[copyless]

I'm not sure what you mean by "stick into the power plug" but if by this you mean the same as you would to measure voltage, the answer is no. An ammeter has to be placed in series with the load, although they do make clamp on ammeters, to use this you must separate the two wires and clamp around just one of them, the best meters use what is known as the hall effect to measure the magnetic field.

And yes, wattage is only V*A, but this measurement is usually defined in a DC circuit, a specific part of the circuitry, or a specific item, where the VA rating is given in AC. But it is a lot more complicated than could be discussed or explained in a short period.

When and if you do make a measurement make sure to have the computer drawing most of it's load, then add 10-20% for safety.

[drfsupercenter]

I get what volt-amps are... as I said I looked them up.

So how would I go about wiring an ammeter in series with the power plug? Would I need to have some other plug that I strip the ends off in order to tie the ammeter to? Or what?

[doctorhardware]

That is why I did not go into such great detail. I also figured that drfsupercenter also looked up how to connect an amp meter up also.

[copyless]

So I could stick an ammeter into the power plug where my computer plugs in and use that?

Well this question, made me question the fact of whether or not he knew how to use an ammeter.

I did not see where you said you looked them up, but only seen where you said, obviously it was more than V*A or VA and watts would be the same.

I guess I'll stay clear of the discussion, I was only trying to help.

[MilesAhead]

Hmmmmm more to it than I would've guessed. Just gave this article a quick glean. Pretty interesting as long as I don't spend more than 5 minutes. Don't want to put too big a drain on My power supply. :)

http://compreviews.about.com/od/cases/a/PSUWattage.htm

[doctorhardware]

No that is not what I was or is saying. No need to stay away from the post you are not steping on any toes.

[doctorhardware]

Miles that was a excellent article on power supplies. It also shows you the potential issues with using a under sized power supply, and how to size your power supply properly.

[burrell84601]

Okay guys, don't laugh as I am learning on this thread too. Would it not make sense to get a 450w one.

I mean if you have an outage and your UPS is underrated then it could fry it out?

Just curious and if someone could explain, (without algebra please, thanks)

[doctorhardware]

Most of the new UPS's will tell you that you are over drawn on the ups capacity. No it will not burn up the UPS. But if you are not over the ups capacity but very close it will not last that long.

[copyless]

Miles, I had originally posted an example, but decided to remove it because I thought it might cause too much confusion. As their are numerous factors as in your article to determine what your power supply will actually supply.

doc, it's fine, I read this thread this morning and was going to stay clear because I just worry about taking shortcuts, and skimping on certain things. As I am sure you well know, there are some things that should not be fudged on, and for me supplying power is one of the most important factors for any circuitry. I would not even consider trying to get away with the least amount I needed, or undercutting the supply I had.

Myself I would say forget all the testing, and buy at least a 500 watt UPS, 450+45=495 to me, this would be the least amount I would consider. I mean I think you will want to plug your modem and monitor in also.

This is an example of advertising, three manufacturers selling an amplifier. One says output is 300 watts, another says 600 watts, and the third shows 212 watts. But, yet all three are describing the exact same device. Are they lying, no, just giving different aspects. One is showing Peak, one P~P, and one RMS. I know this has nothing to do with the discussion, I just wanted to throw it in, because it's something that has always tee'd me off.

[doctorhardware]

Yes I know that is the biggest quagmires of audio amplifiers. I always hunt for the RMS ratings. IMHO is the only good rating to use to compare amplifiers. That is the biggest lie some manufactures use to make their equipment look better.

[admin]

For UPS's, you need to look at the VA rating and then look at the power load of your PC. This online calculator works well:

http://www.apc.com/tools/ups_selector/

[MilesAhead]

@copyless I gotcha'. I just posted that link since I happened across it and I thought it might be interesting to people like me who have some idea how stuff works but not really sure what all the numbers signify.