Berkeley CSUA MOTD:Entry 33766
Berkeley CSUA MOTD
2018/08/16 [General] UID:1000 Activity:popular

2004/9/26-27 [Science/Electric] UID:33766 Activity:high
9/26    I was kinda of curious how much the little light on my power strip
        costs me each month.    Does anyone know how I can figure it out?
        I assume it would depend on how many watts per second it uses, how
        can I find out such a thing?
        \_ Uhm, like less than a quarter a year. If you are that concerned
           you can ask a bum for some change...
                \_ That said, I read somewhere that the cumulative energy
                   usage of appliances on standby, plus all the "little
                   lights" in an average household is pretty high over any
                   given year.  Any facts about this?  -John
        \_ Measure the current and voltage.
        \_ For real-life power consumption measurement, I found the kill-a-watt
           incredibly useful:

        \_ Something like this:
           \- it would be interesting to learn: opening the
              fridge for 10 seconds = how much time for the "little light".
        \_ Related question, a watt is on Amp at 1 volt for what, one
           \_ a watt is a joule per second, and an amp is a coulomb per
              second.  a watt is also a volt times an amp.  you could think
              of it as a volt times a coulomb per second, which makes
              sense, since voltage times charge has units of energy,
              so it's still energy per time.
           \_ obGoogle:
           \_ A watt is one amp at one volt.  A joule is one amp at one volt
              for one second.
              \_ So a kilowatt-hour is exactly 3.6 MJ then.. interesting.
                 They should have just used MJs for reporting your monthly
                 power usage.  Less need for decimal pointage, and it's
                 not a stupid unit.
                 \_ KW is not a stupid unit.  KWH is not a great scientific
                    unit, but it makes a lot of sense in relation to electrical
                    appliances and the like.  c.f. "How much power does it take
                    to run this light bulb for 1000 hours?  60KWH."
        \_ Another related question, I just read that AC-DC adapters are
           constantly sucking power regaurdless ow wether they are on or
           not.  True?
           \_ Since they are warm even when the appliance is not in use, the
              answer should be "yes".  There is some new design that is
              supposedly much more efficient but I haven't heard about it
              for years.
        \_ Watt is joule per second.
2018/08/16 [General] UID:1000 Activity:popular

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2005/3/28-30 [Science/Electric] UID:36926 Activity:low
3/28    So I'm really confused about the DC to DC, car-to-laptop power adapter.
        How come most of them are "inverter" types, where you convert from
        DC to AC, and then AC to DC? Isn't that inefficient?
        \_ Using a resistor or transistor to do DC->DC also gives power loss.
           -not an EE.
        \_ It's easier to step up/down the voltage if the current is in the
2004/12/27-28 [Science/Electric] UID:35451 Activity:moderate
12/27   Anyone have experience with voltage regulators? Ie, it will
        correct under and over voltage back to 120v? I am trying to
        find one... Thanks.
        \_ Yes, they will do that. Is there anything more specific
           you wanted to knwo?
           \_ What particular ones have you used? How well does it work?
2004/9/11-12 [Science/Electric, Science/GlobalWarming] UID:33475 Activity:insanely high
9/11    Is it practical to have, say, a large portion of CA or AZ running
        on solar power? My coworker runs his entire household via solar
        and it got me to wondering what would happen if everyone did this.
        Obviously industrial plants need more power, but could we do away
        with a lot of our polluting plants if everyone went solar? If so,
        then why don't we? What are the technological obstacles, if any?
2003/7/14-16 [Science/Battery, Science/Electric] UID:29030 Activity:moderate
7/14    Do DC to AC power inverters cause any strain / damage to car batteries?
        Would the car battery wear out faster from continued use of the
        inverter?  Specifically, I'm looking at the Xantrex XPower 75 watt DC
        to AC inverter, available on at  If it
        does not damage the car battery or the device, is this a good price?
        \_ no, no, yes
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power button Ourselves, we never thought all that gear we keep shut off and plugged in really pulled that much off the grid while in standby, and who would? If you just told us that some 10% of our electricity came from gear in standby, we'd outright not believe you. But PC Mag's Bill Machrone was struck by the notion that small amounts of electricity in aggregate could quickly add up, so he rigged up an AC breakout system to meter the juice sucked up by his gadgets and electronics while not in use. We doubt most of America has as many electronic toys as he or we do, but even a little goes a long way when it comes to 280 million people. Looks like EnergyStar should start with some belt-tightening right quick. Also Posted Sep 20, 2004, 10:04 AM ET by Maikeru Keep in mind that anything that has a AC to DC adapter either in the plug unit/cord or built into the device sucks power unless there's a physical switch between it and the outlet. The conversion of AC to DC power usually is done via induction if I remember correctly. This means that energy runs through a wire coil and induces current in the wire that actually goes to the device. This means that the cicuit is always closed on the AC side of the adapter and thus is always drawing power. Posted Sep 20, 2004, 10:29 AM ET by Brian I admit this is anecdotal hearsay but I read from a reliable source that I can't remember that a TV uses 75% of its power while in standby mode. Alternative Energy News I just read an extended essay on easy ways to reduce power consumption and was about to add an entry on my blog on this topic, when I checked Engadget. As well as unplugging all gadgets when not in use it's worthwhile making sure your PC's processor is being put to use. My house glows at night Posted Sep 20, 2004, 11:47 AM ET by Mark Beckerman I can navigate through my house at night, in the dark, just from the glow of all the standby lights -- four monitors, three printers, one fax machine, one copier, 58GHz phone system (the base of each handset has a charging light), two vcr's, one tape deck, one dvd player, one home theater receiver, even my Gyration Ultra Mouse has a charging light. That's eighteen standby lights, and I did this list quickly, so I may have missed a few. Standby led's Posted Sep 20, 2004, 2:12 PM ET by M One of my DVD players has a standby LED. That is, an LED that glows when the device is *off*, and is off when the device is on. Energy Star to the rescue indeed Posted Sep 20, 2004, 2:51 PM ET by Wes Felter At one point there was a proposal for a new standard that would encourage devices to consume less than 1W when "off". Computers use more power when they're crunching something@HOME than when idle, so you're not necessarily putting wasted power to work by doing that. I guess they let you know that the device is plugged in. Vcr's are the worst Posted Sep 20, 2004, 9:10 PM ET by mike prevette there was a story on NPR last year that was about this. The reporter concluded that VCR's wore the worst culprits. Some of the cheaper brands consume almost as much off a on. In addition Posted Sep 20, 2004, 10:28 PM ET by Maikeru Anything that can be awoken by a signal (such as a VCR or TV and even a computer in standby) is obviously going to be drawing power for powering the sensors whilest waiting for that all important signal from the IR port or mouse/keyboard. Add your comments Please keep your comments relevant to this blog entry: inappropriate comments may be removed. To create a live link, simply type the URL (including http://) or email address and we will make it a live link for you. Line breaks and paragraphs are automatically converted -- no need to use <p> or <br> tags. Your name (required): Your email address (required, will not be shown to the public): Your site's URL (optional): Do you want us to remember your personal information for next time?
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Connect your appliances into the Kill A Watt(TM), and assess how efficient they are. A large LCD display counts consumption by the Kilowatt-hour just like utility companies. You can figure out your electrical expenses by the hour, day, week, month, even an entire year. Monitor the quality of your power by displaying Voltage, Line Frequency, and Power Factor. Model................................................................. Voltage............................................................... Current............................................................... Weight................................................................
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SI derived units Other quantities, called derived quantities, are defined in terms of the seven base quantities via a system of quantity equations. The SI derived units for these derived quantities are obtained from these equations and the seven SI base units. Examples of such SI derived units are given in Table 2, where it should be noted that the symbol 1 for quantities of dimension 1 such as mass fraction is generally omitted. some examples are given in Table 4 In practice, the symbols rad and sr are used where appropriate, but the derived unit "1" is generally omitted. In photometry, the unit name steradian and the unit symbol sr are usually retained in expressions for derived units. Other quantities expressed in sieverts are ambient dose equivalent, directional dose equivalent, personal dose equivalent, and organ equivalent dose. It follows from the definition of t that the degree Celsius is equal in magnitude to the kelvin, which in turn implies that the numerical value of a given temperature difference or temperature interval whose value is expressed in the unit degree Celsius (C) is equal to the numerical value of the same difference or interval when its value is expressed in the unit kelvin . Thus, temperature differences or temperature intervals may be expressed in either the degree Celsius or the kelvin using the same numerical value.
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It would seem that the volt-amp refers to the maximum power flow, while the Watt refers to a time-averaged power flow. Thus, a current of one amp in a wire means exactly 16 x 10 19 ... number of coulombs per second, and power is the number of joules per second (watts), we see ... SurgeX - The Leader in Power Conditioning Technology ... Current (expressed in units of amperes, or simply amps): Current is the electrical ... Energy (expressed as joules or watt-seconds): 1 joule = 1 watt-second.