EMI Filter Wiring


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Thread: EMI Filter Wiring

  1. #1
    Member Sterob's Avatar
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    Default EMI Filter Wiring

    I'm in the process of re-building my X61500GT Controller box and I have noticed that the EMI filter is wired on before the Mains is distributed to the power supplies and the VSD.
    All the info I can find, suggests the EMI Filter is wired on just the VSD Input.

    What is the best practice in this regard? Use the EMI fIlter to protect ALL of the power devices OR just the VSD ?

    Steve

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    Member john-100's Avatar
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    Default Re: EMI Filter Wiring

    It all depends on what you want the EMI filter to do
    some times EMI filters are added just to get CE approval for sale in the E.U .

    when a EMI filter is just after the mains inlet it will help to prevent external electrical interference entering the control box
    or interference from the VFD and power supplies escaping via the mains supply

    switch mode power supplies and Vfd's usually have an EMI filter built in

    If you had a VFD that produce too much electrical noise at the mains input terminals then adding a EMI filter to the VFD supply may be needed

    Depending on how good your mains supply is,
    it may be necessary to add a transient suppressor
    with varistors or VDR's (voltage dependent resistors) to clamp mains transient voltages
    due to lightning strikes or the switching of very large inductive loads

    John



  3. #3
    Member Sterob's Avatar
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    Default Re: EMI Filter Wiring

    Thanks for the great answer John.

    My goal is for bullet proof controller design to minimise the chanc of any errors caused by EMI.

    Steve

    Sent from my SM-G920I using Tapatalk



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    Member john-100's Avatar
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    Default Re: EMI Filter Wiring

    adding to my previous reply

    if you look at the circuit diagram of an ATX power supply like this for example
    EMI Filter Wiring-atxps-jpg

    you will see they have a EMI filter built in with VDR's added to protect against voltage transients on the supply
    note- VDR's are damaged by large transients

    one issue with multiple EMI filters is the leakage current that flows from live to earth (ground)
    due to capacitor C2 in this example
    EMI Filter Wiring-atxps-emi-filter-jpg

    very often the leakage causes a problem in an office with many PC's on one circuit
    tripping the 30mA RCD (GFI) circuit breaker


    some VFD's have a removable link to disable the EMI filter !

    John



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    Member mactec54's Avatar
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    Default Re: EMI Filter Wiring

    Quote Originally Posted by Sterob View Post
    Thanks for the great answer John.

    My goal is for bullet proof controller design to minimise the chanc of any errors caused by EMI.

    Steve

    Sent from my SM-G920I using Tapatalk
    The filter is in the right place if it is before the VFD, there is more to your wiring that will play a big part of noise control, and how you terminate the Cable Shields, and Grounds, is more to be concerned with than the filter

    You don't have a VSD, (Variable Speed Drive ) you have a VFD ( Variable Frequency Drive ) the 2 types of drive are very different

    Mactec54


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    Member Sterob's Avatar
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    Default Re: EMI Filter Wiring

    Thanks Mactec. I'll wire in the EMI filter on the input of the VFD and see how I go.
    I have plans to implement careful grounding and shielding on the all of the other wiring.
    I just wanted to make sure I got the EMI filter connection correct.



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