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Energy Monitor

Discussion in 'General Electronics Discussion' started by whiterabbott, Jun 4, 2010.

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  1. whiterabbott

    whiterabbott

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    May 13, 2010
    I am in the process of building an energy monitor, following the instructions from this website,http://openenergymonitor.org/emon/node/56. What I am confused about is the process of measuring the voltage. He put an ac-ac adapter into an outlet (this is not what is shown in the website) that was available by his circuit breaker. But it seems to me that this would only measure the components that are on that circuit and not the voltage for the whole house. From what I understand, appliances like air conditioners are on their own circuit and so these would definitely not be measured by the voltage circuit?

    Also, I am trying to understand residential wiring in general does anyone know of a good resource?

    Thanks.
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    I dont know what coountry you are from...

    As far as reading kW/hrs usage goes, most western world countries have a meter on the main switchboard ... its what the power utility guy reads so they know how much to bill you :)
    so you can also read it to find out comsumption over a day, a week etc

    As far as reading/monitoring the voltage goes, well that can be done on any power outlet with an appropriately rated AC voltmeter. the voltage shouldnt change throughout the building.

    just some thoughts :)

    Dave N
     
  3. whiterabbott

    whiterabbott

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    0
    May 13, 2010
    Thanks for your reply. I am in the US so I know that it is a three phase system. When you said "well that can be done on any power outlet with an appropriately rated AC voltmeter" that is what he is doing, but what I do not understand is how this works exactly. I thought that appliances such as air conditioners where on their own circuit.

    I was looking at some electronics sources. While one source had the outlets in series and the appliances in parallel because of the 240V and the circuit was connected another source talked about certain appliances having their own circuit. So I am a little confused on how the ac voltmeter can read the voltage from one outlet.

    I hope that is clear.

    Thanks,

    Dawn.
     
  4. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    I think you're confusing voltage with current.
    Like Dave says the voltage on one outlet is pretty much the same as on another, exept if they are connected to different phases of course.
    The current on one branch is of course not the same as on another. All branch currents gets summed in the main switchboard at the main switch/fuse/meter.
    So to measure the energy of the whole household you need to clamp the current sensor around one of the main wires there, and measure the voltage close by.
    With just one phase in the house you need just one energy meter kit, but with three phases you'll need three kits.
     
  5. whiterabbott

    whiterabbott

    6
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    May 13, 2010
    Still Confused

    I have two current transducer that go around the main wire from the breaker. Then, there is a step down ac-ac voltage adapter in the outlet next to it. Power = IV. From what I understand, it is a three phase circuit meaning two wires generate 120V out of phase with each other, third is a ground and when you measure the output form the outlet it is 120V unless something is on, like a light. Then the voltage drops because of the load but what about air conditioning and other appliances that are 240V. How would the voltage circuit in the energy monitor site be able to measure that?

    I am just not understanding how the circuitry works together in the house. I have been searching online but not really finding what I am looking for.

    Thanks.
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    no thats single phase

    3 phase is 3 lines of 120V plus a Neutral (earth is usually connected to neutral on a buss bar at the main switchboard

    cheers
    Dave N
     
  7. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    Like Dave says. Now, I don't know what may be practiced everywhere but in theory it's possible that only two wires plus neutral is introduced into the main switchboard.
    Leaving out the third phase could be called a rather minimalistic installation, just to get a dual voltage power system.
    Thus it could be possible to have 127V between neutral & either phase, and 220V between the phases. Notice the square-root of three relationship between voltages.

    Where you measure the voltages depends on what you want. You pay for the voltage at the switchboard, but the appliance gets some less power due to the wiring drop.
    If you really have two out of three phases plus neutral then you'll need two current sensor clamps as well as two voltage sensor transformers. The rest is mathemathics.
     
  8. whiterabbott

    whiterabbott

    6
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    May 13, 2010
    Dave

    You are right. I got it mixed up. It is a 120VAC 3-wire single phase system.
     
  9. davenn

    davenn Moderator

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    Sep 5, 2009
    thats cool mate, its all part of the learning process :) just be careful playing around the mains voltages dont want you bar-b-que'ing yourself.

    Dave
     
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