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Testing Wattage consumption of your computer equipment
Making sure you’re not overloading your UPS or misc power source
By Red Squirrel

Did you ever wonder how many watts your equipment is using? Whether it is a PC with monitor, or a whole UD cluster setup with 100's of machines this article will let you know how to easily find out. Or perhaps you just want to know how much power you would need to build one of those clusters. You can estimate yourself since some appliances such as monitors show the rating on the back but some other things such as computer power supplies don't. And just because it's a 300W power supply does not mean it uses 300W of power. It all depends on how much of that power the components are using. Watts are usually the best measurement to know because it does not change. But volts and amps do. If you plug in a vacuum cleaner in an 80volt power source it will be using way more amps then if you plug it in a 120V power source.

Watts is equal to volts times amps. So basically the higher the voltage, the fewer amps being drawed. Amps are also the actual current and what decides on the power of the circuit. What I mean by that is, if there's not enough amps, you can't run much, even if the voltage is high. A static shock can have millions of volts passing through you but yet it's not enough to power a light bulb, because there are very little amps. Amps also cause wires to heat up, the more amps, the bigger wires you need since if they are too small they will melt. This explains why power cords for large equipment are thicker, while a small lamp is just a cheap cord that you can cut with a pair of scissors, since one uses more amps but same voltage, and this results in more watts as well. Because of this heat though, there is power loss, so this is why when power is delivered to far distances, it is sent in high voltages, so they can use smaller cabling (cheaper) and there's less loss of energy from heat. So it's more efficient. But just because of what I said about the static electricity, don't think you can go climb one of those poles and get a shock that tickles.

Enough theory, let's get started.

First this is what you will need:

  • A multi meter: One that can measure AC amps and AC voltages and should have a high enough rating. These can be purchased at a Radio Shack or similar store for about $100 and are very useful around the house.
  • Crocodile wires or other wires easy to manipulate and plug.
  • An old power cord with both ends open to connect the crocodile clips to it easily. (or equivalent, basically any thing that can easly be plugged and unplugged from the socket)
  • Calculator (everyone has at least one around the house)
  • Safety common sense (this can be hard to find in some households)

    Like mentioned earlier, Watts = Volts X Amps. So we need to know how much volts we are giving to the equipment, we know it's near 120 because that's the normal house voltage. But we want to be more exact, so set your meter to measure volts AC and

    put both ends in a socket that is on the same circuit as the equipment. For safety purposes, try to find a socket that is easy to access and has plenty of room to move quickly in case something happens. But if you have everything set correctly and don't short it out somehow, you're safe. Just make sure it's set to Volts AC and if your meter has different ranges, set the right range so you don't overload it. But most good meters will auto sense the range for you.

    shoving things in the mains is fun!

    Because my plug has too many wires near it at the PC, for this picture I'm measuring a different circuit but if your house is wired like mine there should only be 2 main circuits (two separate AC phases) so they should both be near anyway. I get the same reading here and in my room.

    The voltage tends to move a bit. In my case it was around 119 and 121 so let's just say 120.

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    29059 Hits Pages: [1] [2] 4 Comments

    Latest comments (newest first)
    Posted by Red Squirrel on August 08rd 2004 (19:26)
    lol. I knew this article would get lot of safety concerns. em320.gif

    If you use common sense, dangeraus situations can be made safe. wink.gif

    Posted by Red Squirrel on August 08rd 2004 (17:53)
    I've been zapped many ways and I can easly say from experience the most fatal is the heart thing like mentioned. By nature some people are forced to hold on tight to whatever they are being zapped by. Thankfully for me I'm the oposite. I got zapped with who knows how many amps from arm to arm, and I felt it for like an hour. It was only 120 volts. The zap might of lasted about a milisecond or 2 but enough to make me tempoarly black out and "wake up" 5 feet behind me. I was laughing though but it would of been fatal. Stupid guy put the ground wire in the live and I was holding the "grounded" device in one arm and went to unplug it with the other. Zap! lightbulb.gif
    Posted by Red Squirrel on August 08nd 2004 (18:49)
    Yeah I discovered that after, so I had added it at the end that it may not be very accurate. I'm not sure if mine is RMS or not, but I doubt it since I only paid about $100 for it. Later on I'll try to figure out a better way (low cost) to measure true RMS with any meter. (maybe plug the results in some formula or something but I doubt it's that easy)

    1.24 is pretty high for 240 bolts, do you have lot of high end stuff in it? Mine ran at about 1.2 (inacurate though) at 120 volts.

    Posted by Red Squirrel on August 08nd 2004 (13:21)
    QUOTE (Fin @ Aug 20 2004, 09:28 AM)
    First you say "I knew what I was doing" and then in next sentence "Please realize that this activity, especially with amp readings over 1 can be fatal!"

    There is a little conflict between what you say. Did you knew that dangerous currents are measured in tens of milliamps? Resistance of person is limitting current, so current in machine doesn't mean anything. Current depends of voltage and resistance so big voltage is the dangerous thing in these measurements.

    It's possible to do something dangeraus and still know what you're doing. wink.gif

    Look at those crazy stunt people like jackass. It's unsafe, but they know what they are doing so they (usually) don't get hurt.

    As for the accurcy, I sort of realized that afterwards, when I did more research, but this method will still give you at least an idea of wattage. If you can afford the fancy stuff that does it right good for you, but especially here in Canada it's not obvious to get the fancy stuff, sometimes it's too expensive, sometimes you can't even get it period.

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