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Thread: Convert kwh to amp.

  1. #1
    Join Date
    Jun 2007

    Cool Convert kwh to amp.

    Dumb question: if we have monthly demand kwh from power company, how do we convert this number to Amp? Thanks.

  2. #2
    Join Date
    Mar 2004
    Quote Originally Posted by anbm View Post
    Dumb question: if we have monthly demand kwh from power company, how do we convert this number to Amp? Thanks.
    This conversion can be done (in a couple steps) Understand that kWh is a measurement of work done in time. Where amps is a measurement of rate of flow of electric current. They are measuring two different things.

    If you have the TOTAL kW (not kilo-watt hour) usage then you can figure it this way:

    Kilowatts to amps conversion
    The current (I) in amps is equal to the 1000 times the power (P) in kilowatts, divided by the voltage (V) in volts:

    I = 1000 P / V

    So amps are equal to 1000 times kilowatts divided by volts.

    amps = 1000 kilowatts / volts


    A = 1000 kW / V

    Kilowatts to amps example
    What is the current in amps when the power consumption is 0.33 kilowatts and the voltage supply is 110 volts?

    I = 1000 0.33kW / 110V = 3A

    If you want to figure how much kW per Hour:

    Kilowatts to kilowatt-hour calculation formula
    The energy (E) in kilowatt-hour is equal to the power (P) in kilowatts, times the time period (t) in hours:

    E(kWh) = P(kW) t(h)


    kilowatt-hour = kilowatt hour


    kWh = kW h

    What is the energy consumption when the power consumption is 5 kilowatts and for time duration of 3 hours?

    E = 5kW 3h = 15 kWh

  3. #3
    Join Date
    Jul 2006
    San Francisco, CA, USA
    This has been discussed here many times now.

    No, it can't be done. Your kWh demand meter has absolutely no way of recording the power consumed at any given moment. Say for example you have a reading of 10,000 peak kWh and your peak demand window is 30 minutes. That could be 5,000 kW for 30 minutes continuously, or 600,000 kW for one minute, and the remainder of the 29 minutes it is considerably less (I'm too lazy to even try to figure out an appropriate level, but you get the general idea). The net effect on the total kW used during that 30 minute demand window is the only thing recorded, that has almost zero correlation to a peak amount of current at any particular instant.

    That by the way is why the idea of "saving on peak demand charges with soft starters" is a myth; unless a soft starter can stretch the ramp time out beyond the demand window, the effect is almost meaningless.

  4. #4
    Join Date
    May 2005
    Redmond, WA
    Good answers. A demand meter reading can help determine the present loading on transformers and other devices that take a while to heat up, providing the loads don't change much from day to day. The monthly KWH reading can only get you in the ballpark (or maybe close to the parking lot without a ticket.)

    It is like knowing how many gallons of gas you put in your truck last month and trying to calculate the your maximum speed. You could estimate your miles driven from typical
    miles per gallon figures and guess at the hours driven to come up with an average speed and get a good guess at the distribution of speeds in that block of time to estimate your maximum speed. You would have a bunch of calculations and charts backed up by hard evidence (your gas receipts) but I don't think the traffic judge would buy it as proof you were not speeding for that one 2 mintue period.

    The KWH meter or your bill is like your odometer, telling how far you've gone. Your speedometer is like a KW meter giving the instantaeneous speed (kW). If you assume the voltage and power factor are constant, you can translate the KW to instantaneous amps to get an amp reading. For constant loads and short periods of time it can be relatively accurate. Imagine estimating your freeway speed by timing how long it takes to go exactly a mile. Then do it for 100 miles. The one mile calculation may be pretty accurate if speed was relatively constant. The 100 mile calc can only be considered an average.
    Bob Wilson

  5. #5
    Join Date
    Oct 2009
    Austin, TX, USA
    Quote Originally Posted by anbm View Post
    Dumb question: if we have monthly demand kwh from power company, how do we convert this number to Amp? Thanks.
    Good answers, but more simply,you can convert kilowatt hours to amperes if you know the voltage at which your loads operate and assume a steady state load (a big assumption). If, for example you consume 100 kwh in a day at 240VAC and assume a steady state load, that's 100 kwh divided by 24 hours, or a 4.17 kw load. 4.17 kw divided by 240V is 17.36 A.

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