A what-hour?

JetMech
JetMech Solar Expert Posts: 71 ✭✭✭✭
in General Solar Power Topics #1
I finally got myself a Kill-a-watt a few days ago and what a mistake! I've only checked a few things and I'm already freaked out by how much power they're using! None of us had any idea. :confused:
Anyway, I put it on my clothes washer and saw how many watts it used at different cycles, but at the end it showed 0.23 watt/hours. What exactly does this mean? Is it as obvious as in an hour it uses 230 watts? Because the spin cycle alone used close to 480 watts.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: A what-hour?

    Sorry--but to make the units clear:

    230 watts for 1 hour is 230 Watt*Hours or 0.23 kWatt*Hours (kilo=1,000x)

    The typical power charge in the US is around $0.09 to $0.30 per kWhr...

    If your washer used 2,300 watts for 6 minutes, it would still use:

    Power Used = 2,300w * 6min/60minperhour = 230 watt*hours or 0.23 kWhrs

    Or, if you ran your washer for ~4-5 hours straight, it would have used around $0.10 to $0.30 of electricity...

    So, during some of the time it may have used 480 watts, other times 100 watts, but the overall usage was 230 Watt*Hours (if it was for 1 hour cycle, then it would have averaged 230 watts for 1 hour).

    Does that make it clear? Watt*hours and kWHrs is basically the equivalent to how may gallons (or 1,000 gallons) of gasoline you used--what your MPG and mileage driven was--is all added together at the "fuel pump".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: A what-hour?

    That would indicate that your washer for one complete cycle, beginning to end, would have used almost 1/4 KWH (not watt hours) That means it used the equivalent of a 1000 watt electric heater being on for almost 15 minutes. Probably about average for most washers.
    A 1000 watt load for one hour, uses one KWH, as does a 500 watt load on for 2 hours, or a 2000 watt load running for 1/2 hour.
    Got it?
    Cheers
    Wayne
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  • System2
    System2 Posts: 6,290 admin
    #4
    Re: A what-hour?

    Haha, BB got ahead of me, I'm too slow. :)
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  • JetMech
    JetMech Solar Expert Posts: 71 ✭✭✭✭
    #5
    Re: A what-hour?

    OK, now I get it. Thanks. I guess it isn't as bad as I thought. Still, I like those front-loading washers better...
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  • JetMech
    JetMech Solar Expert Posts: 71 ✭✭✭✭
    #6
    Re: A what-hour?

    Oh! So does that mean that a 60W bulb will burn 60 watts per hour?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: A what-hour?
    JetMech wrote: »
    Oh! So does that mean that a 60W bulb will burn 60 watts per hour?

    Sort of... Think of Miles per Hour (rate of speed) = Watts (rate of electrical work)... Everyone (including me), wants to call it watts/hour--but it is not.

    When you want to know how far you went in a car:

    (Miles/Hour) * Hours = Miles driven (note: hours in MPH is "canceled" by *hour)

    Watts * Hours = Watts*hours used (note: Here *hour is carried through because no /hour in the denominator)

    In reallity, Watts are already defined as a rate:

    Watt = 1 Joule per second (among other definitions)...

    It is sort of if well changed the name of "MPH" to "Bill" (hey, why not immortalize my name). :roll:

    So:

    Driving at "60 Bills for one hour" and you would have gone "60 Bill*Hours"...

    It is screwy--blame the guys who wanted to be immortalized forever more...

    More interesting use of "Watt"--I always capitalize because it is a proper name, but looking at the Wiki site:
    This SI unit is named after James Watt. As with all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (W). When an SI unit is spelled out in English, it should always begin with a lowercase letter (watt), except for at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because of the "d".

    — Based on The International System of Units, section 5.2
    Notice that in the case here, we should be using "seconds" as the unit of time, but because the proper term Watt*Seconds (you hear that in all the medical shows when they are going to fire up the defribulator), is a pretty small number... So for energy billing, the cobbled up Watt*Hours (excuse me watt*hours) as the unit (scaling factor of 3,600=60sec/min*60min/hr)

    Want another weired name for units... Kilo-Grams in metric system (Mass, not weight as everyone tends to use it--"Newton" is the correct unit for weight as it has been beaten into us in High School Physics class)... In the "English" system (used in the US), lbs (which is weight or force) is to "Slug" (measurement of mass).

    I guess my teachers have finally beaten units into my head--Keeping track of units makes conversions (between voltage, current, time, watts, ohms, amp, amp*hrs, etc.) much cleaner and easier to check for dumb mistakes.

    -Bill (inventor of the MPH unit named the "Bill"). :p
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #8
    Re: A what-hour?
    JetMech wrote: »
    Oh! So does that mean that a 60W bulb will burn 60 watts per hour?
    =======================================
    Yes, if it was on for one full hour, it would use 60 watt hours (.06 KWH). Likewise, if it's only on for 30 minutes, it would use 30 watt hours (.03) KWH.
    And, if you run that 60 watt bulb for 30 minutes, then change the bulb to 30 watts and run it for another 30 minutes, you would have used:
    60 watts X 1/2 hour = 30 watt hours
    30 watts X 1/2 hour = 15 watt hours
    For an overall total of 45 watt hours, or .045 KWH and if you were paying 11 cents per KWH, your cost would be .11 X .045 = 1/2 cent.
    Hope this clarifies.
    Cheers
    Wayne
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  • System2
    System2 Posts: 6,290 admin
    #9
    Re: A what-hour?

    Haha, I'm still slower than BB! Beginning too look like I always will be. :p
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: A what-hour?

    Ha Ha Wayne! O'l speedy fingers strikes again. :p

    Also, I should have just cut and paste this from the Wiki-Watt:
    Confusion of watts and watt-hours

    Power and energy are frequently confused in the general media, for instance, when a device is said to be rated at "100 watts per hour",[6] it makes little sense since a watt is already a rate, specifically representing 1 joule of energy per second. As such, a watt does not need to be followed by a time designation, unless one is talking about a change in power over time, analogous to an acceleration or deceleration.

    Because a joule as a quantity of energy does not have a readily imagined size to the layperson, the non-SI unit watt-hour, often in its multiples such the kilowatt-hour or higher prefixes, is frequently used as a unit of energy, especially by energy-supply companies (electricity and natural gas suppliers), which often quote charges by the kilowatt-hour. A kilowatt-hour is the amount of energy equivalent to a power of 1 kilowatt running for 1 hour:

    (1 kW·h)(1000 W/kW)(3600 s/h) = 3,600,000 W·s = 3,600,000 J = 3.6 MJ.
    -Bill (inventor of the MPH unit named the "Bill").
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • JetMech
    JetMech Solar Expert Posts: 71 ✭✭✭✭
    #11
    Re: A what-hour?

    Cool! Thanks again!
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