Basic Rectifier Circuit

Discussion in 'General Electronics Chat' started by ectmlk, Jun 19, 2011.

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  1. ectmlk

    Thread Starter Member

    Feb 11, 2008
    I am trying to work out the following:
    If i connect my mains to a suitable full-wave rectifier, that is HOT and NEUTRAL to the AC input (for a 240vAC RMS supply) on the recitifier and connect the smoothing cap and a simple load on the DC side then what are the voltages/currents for the positive and negative circuit at the recitifer DC + and - pins?

    The reason i ask is that it my understanding that the nuetral is always 0v.

    So for the positive cycle the voltage from the top of my load (say a resistor) to the - pin of the recitifier will be about +340V and also from the top of my load to the Neutral/ground 0v reference will be +340V. The voltage from the -pin to the Neutral pin of the rectifier will be slightly above 0v (diode voltage .7)??

    Then on the negative cycle because Neutral is always 0V then from the top of my load to the - pin of the rectifier is again about +340V.
    What will the voltage be from the top of the load to the Neutral/ground 0v reference? (i suspect +340V)
    What will the voltage be from the -pin to the Neutral/Ground pin?

    Reason i ask also is that when i try to connect the shield crocidile clamp of my scope to the -pin of the rectifier i get a short, which blows a 3amp fuse. This is a bit confusing as i suspected that the -pin should be 0V, but yet i am confident that the rectifier is not damaged.

    Thanks for any answers.
    Last edited: Jun 19, 2011
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
    You MUST use an isolating transformer if you want to connect your supply to any grounded equipment. The circuit you describe is not isolated from the mains, and apart from being very unsafe is not allowed to be discussed within the rules of this forum.
  3. tom66

    Senior Member

    May 9, 2009
    You're wading into dodgy territory with regards to the ToS here.

    If you consider neutral to be 0V, then the connection to neutral reverses its position each cycle.

    e.g. with -325V in, the positive rail becomes 0V and the negative rail -325V, giving 325V

    with +325V in, the positive rail becomes +325V and the negative rail 0V, giving 325V.

    Please be careful with this kind of voltage, it can easily cause fibrillation of the heart during an electric shock, which can be fatal.

    That's a simple view, most people connect the negative rail to a ground reference. Sometimes to earth mains through a class Y capacitor.
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    By the way, given that the neutral connection is close to ground potential, trying to connect a grounded lead to the negative output effectively shorts out some of the rectifiers in the bridge.

    There is no identity between neutral and negative: after all, the supply ia AC, or you would not need a rectiifier in the first place.
  5. bertus


    Apr 5, 2008

    I am closing this thread as it violates AAC policy and/or safety issues.

    6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

    • Any kind of over-unity devices and systems
    • Automotive modifications
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    • LEDs to mains
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    • Rail guns and high-energy projectile devices
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