Cbus current measurement unit

Discussion in 'C-Bus Wired Hardware' started by Hollywoodperth, Oct 13, 2018.

  1. Hollywoodperth

    Hollywoodperth

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    I've read some where that the CTs for the current measurement unit are not directional.

    Is there anyway to get around this? Or is there another CT that we can use that is directional?
     
    Hollywoodperth, Oct 13, 2018
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  2. Hollywoodperth

    Ashley

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    If you are measuring AC current then direction is meaningless. AC changes direction every 10mS (that's why it is called Alternating Current :)).

    I assume you want to measure the direction of Power flow. To do this you need to measure the phase angle between the voltage and the current. This is not trivial and requires a bi-directional Power meter.
     
    Ashley, Oct 13, 2018
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  3. Hollywoodperth

    Wonkey

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    Or are you trying to determine how much your total usage is because you have solar.
    If so then, when configuring PICED to view your power meters you can declare an input on the CMU as Power generator, the solar circuit. .
    Its probably better when asking a question to explain what you want to achieve, as you can see Ashley and I had different opinions on your requirements.
    Colin
     
    Wonkey, Oct 14, 2018
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  4. Hollywoodperth

    Hollywoodperth

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    Thanks the replies guys. All CTs I have ever used are directional with markings to show which way to install them.

    I want to meter the mains to determine when the solar energy exceeds local load and reverses the power flow. Then (since power is sold into the grid at a discounted rate to power purchased) send a start signal to the hot water unit. Without a negative signal on the power meter it simply won't work.

    The power meter needs to operate as both a load and a generator so defining as a generator won't work.
     
    Hollywoodperth, Oct 15, 2018
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  5. Hollywoodperth

    Ashley

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    Yes, this is if you are using multiple ct's (e.g. 3 phase) and are combining their outputs directly. With the cbus ct's it doesn't matter.

    Depending on how it is all wired, you may be able to put one CT on the output of the solar inverter (since power only goes out) and another on the input to the house (since power only goes in). Then whenever the solar CT is greater than the house ct you are generating spare power. If you search the forums for solar monitoring you will find a number of alternate solutions.
     
    Ashley, Oct 15, 2018
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  6. Hollywoodperth

    Hollywoodperth

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    1 phase CTs are typically directional as well.

    Solar will either be single phase or three phase (depending on the size of the inverter). I hope to pick this up with a serial connection to the inverter.

    Load will be three phase.

    Standard AC switchboard, so meter into main switch into chassis. PV goes into the load chassis. So that won't work.
     
    Hollywoodperth, Oct 15, 2018
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  7. Hollywoodperth

    Hollywoodperth

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    Was trying to use the c-bus module but seems it doesn't work that great.

    Might go with the iEM3155 power meter. Has modbus connection so should be OK.
     
    Hollywoodperth, Oct 15, 2018
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  8. Hollywoodperth

    Ashley

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    I have a Fronius 3 phase inverter with a Fronius Smart Meter. The inverter has a well documented api that allows you to read anything you would ever want via HTTP requests. I do this via logic in a touch screen. All very neat and works perfectly. Controls various loads depending on inverter output and lets you know if you are importing excessive power.
     
    Ashley, Oct 15, 2018
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  9. Hollywoodperth

    NickD Moderator

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    The direction is only important if you are looking a the phase. The phase is only interesting if you have something to compare it to.

    The CBus CMU just measures the magnitude... it doesn't have a voltage measurement to compare the current phase to, so the CTs are not polarity sensitive.

    Nick
     
    NickD, Oct 16, 2018
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  10. Hollywoodperth

    znelbok

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    I believe they also have modbus
     
    znelbok, Oct 18, 2018
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  11. Hollywoodperth

    Ashley

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    Currently the only supported way to pull data from the device is via network HTTP requests. The only supported use of the modbus interface I know of is for their Smart Meter.
     
    Ashley, Oct 18, 2018
    #11
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