Grounding DC

Discussion in 'General Electronics Chat' started by edgetrigger, Dec 19, 2010.

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  1. edgetrigger

    Thread Starter Member

    Dec 19, 2010
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    Can the negative terminal of the bridge rectifier connected to an A/C mains(either 120v/220v) be grounded( connected to earth).
     
  2. nerdegutta

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    Dec 15, 2009
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    Don't think so.
    Not like that.
    Do you have a schematic?
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    It is not recommended. If there is a wiring fault, your DC ground could be the AC hot line.

    Leave the DC ground common to the DC circuit, but isolated from the AC line.
     
  4. edgetrigger

    Thread Starter Member

    Dec 19, 2010
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    Just a four diode bridge, with the negative output point of the bridge connected to earth pin of the mains.

    I think it will short the voltage during negative half cycle, am not sure.
     
  5. nerdegutta

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    Dec 15, 2009
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    I would do what thatoneguy said, isolated from the mains.

    Welcome to the forum, btw. :)
     
  6. edgetrigger

    Thread Starter Member

    Dec 19, 2010
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    thanks for welcoming.

    but not clear why is the isolation required. Not for the safety issue, can this be connected. Wont there be a substantial voltage during the negative half cycle of the A/C. wont the grounding short this negative half cycle. My oscilloscope is down, just was trying to be analytical.
     
  7. #12

    Expert

    Nov 30, 2010
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    Looking at the schematic in my mind, I say you will blow a fuse, instantly. Can we see the schematic that is presently in your mind?
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    You are using a transformer for isolation? If so, it should be utterly obvious that a connection to the primary side does away with that isolation.

    If this is simply rectifying the line voltage, it is a practice we are against, as it is so unsafe.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    You must use a transformer or some type of inductive coupling to isolate the output from the mains. Without such isolation, your circuit won't be safe.

    If your rectifier circuit is on the primary side of a switching regulator, you don't use the ground wire; you use the neutral wire. The secondary side and enclosure should be connected to the ground wire.
     
  10. PackratKing

    Well-Known Member

    Jul 13, 2008
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    I have repaired a number of professional-type floor polishing machines, that plug in to 120vac, hot lead through a switch to a-c inputs of a large 50 amp monolithic bridge rectifier - no heatsink other than the motor end-bell it is mounted to. This directly feeds the 4-brush commutated DC motor driving the machine. brushes and fields are series.

    I'll update this, 'cuz I need to observe [ and remind myself ]where the rectifier negative is connected, whether mains return, or chassis green wire.

    Standard fault calling for service, is a blown rectifier, likely caused by excessive start / stop operation, or lousy heatsinking.
     
    Last edited: Dec 19, 2010
  11. beenthere

    Retired Moderator

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    We are aware that rectifying the line is done. We do not support discussions of it as there is such a large readership, with vastly differing abilities and comprehensions of danger. Without some applied and intelligent effort, it is very easy to cause a lethal shock hazard.
     
  12. edgetrigger

    Thread Starter Member

    Dec 19, 2010
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    safety apart! will it be a dead short for the negative half cycle of the A/C?
     
  13. edgetrigger

    Thread Starter Member

    Dec 19, 2010
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    I bet in your product it will be connected to mains return. There is no point connecting to chassis ground when you have mains return. I wanted to know if it can be connected to ground(earth) after rectifying. I think it may just blow the supply fuse if in neutral path.
     
  14. #12

    Expert

    Nov 30, 2010
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    Putting a bridge rectifier across the mains voltage and grounding one output of the bridge rectifier will absolute, positively, be a short circuit.
     
  15. edgetrigger

    Thread Starter Member

    Dec 19, 2010
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    Grounding the bridge negative will not be a short for positive half cycle of the input, i suppose
     
  16. beenthere

    Retired Moderator

    Apr 20, 2004
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    This discussion is really going nowhere. Please refer to post #11.
     
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