Voltage on negative side

Discussion in 'General Electronics Chat' started by Webby, Jul 24, 2014.

  1. Webby

    Thread Starter Active Member

    Jun 15, 2008
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    What does a loss of voltage on the negative side of a circuit mean with a 12v circuit? How can there be voltage on the negative side of the circuit?
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi webby,
    Sorry I do not not understand your question.

    Could you please rephrase it or give an example.?

    E
     
  3. shell.albert

    New Member

    Jul 23, 2014
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    confused question.
     
  4. inwo

    Well-Known Member

    Nov 7, 2013
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    Do you mean voltage drop in the negative lead of battery, or power supply?:confused:

    Same as positive side! The "negative" just refers to the polarity or direction of flow.

    Just as flow to a hydraulic motor can have pressure drop in either or both supply lines.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,034
    Like water, electricity flows from uphill (V+) to downhill (V-). (This is an arbitrary convention, the electrons actually move in the opposite direction.)

    Like a pond on a mountain, no electricity will flow unless there is a path to a lower voltage. So we label the higher voltage as positive, and the lower voltage as negative or zero. All that matters is the voltage difference between them, same as elevation change for water.

    On a power supply and in many schematics, a voltage labelled as negative may well be below some other reference point such as common or ground. Like a valley compared to the plains above.
     
  6. Webby

    Thread Starter Active Member

    Jun 15, 2008
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    What I mean is if the voltage is lost on the negative side of a 12v circuit how will this effect the consumer?
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    What do you mean by "voltage is lost"?

    What do you mean by "negative side of a 12v circuit"?

    What do you mean by "consumer"?

    You make no sense whatsoever to me.
     
  8. inwo

    Well-Known Member

    Nov 7, 2013
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    Same as voltage lost on the positive side.

    If enough voltage is lost or circuit is open the consumer will get less or no current.

    Draw a picture.
     
  9. Webby

    Thread Starter Active Member

    Jun 15, 2008
    66
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    Thanks inwo... On a 12volt circuit what determines the voltage drop to earth I.e when measuring with a meter what is the maximum you should see on a earth side of a circuit
     
  10. ian field

    Distinguished Member

    Oct 27, 2012
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    If you lose too much voltage on the supply cables - use thicker cables.
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    Still makes no sense. Why don't you draw a picture?

    Assume you have a circuit powered by a 12V battery.

    Scenario #1. You measure voltage with a voltmeter: RED lead connected to -VE battery terminal, BLACK lead connected to EARTH GROUND. Reading should be 0V. There is no connection to EARTH GROUND.

    Scenario #2. The -VE terminal of the battery is connected to EARTH GROUND.
    Reading on the voltmeter should be 0V. There is no difference in potential between the -VE terminal and EARTH GROUND.
     
  12. inwo

    Well-Known Member

    Nov 7, 2013
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    If by earth you mean a large metal structure used as a common for the negative connections, then the voltage from battery - to ground is determined by current draw and (- to ground) wire size.

    Generally from near zero to a fraction of a volt.
     
  13. MrChips

    Moderator

    Oct 2, 2009
    12,432
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    Gleaning from your other posts, maybe this is what you are referring to:

    Senario #3: You are working on a 12V automotive system.
    You connect the BLACK lead of a voltmeter to CHASSIS.
    You connect the RED lead to the RETURN side of a circuit.

    You should see no greater than 0.1V (I'm guessing, without actually testing this.)

    As others have said, you need thicker cables.
     
  14. bladerunner

    Member

    Apr 15, 2012
    83
    4
    It will be the same since you are measuring the voltage of a DC system which requires you to measure its voltage by connecting a meter between the positive and negative post of the same source.

    In other words, you cannot connect your meter between the positive post of the source and an earth ground (that is not connected to the negative side of that particular source) and get any type of reading.

    Example: Place your negative cable (connected to the negative post) into the ground (dirt). Place your meter on the positive post of the DC source and the other lead into the ground (dirt) next to the Negative cable (but not touching it). You will get no reading.

    I once has a boat sink. Yes the batteries were hooked up. Did they fry themselves, NO. In fact when I got the boat sides up out of the water, I turned on the bilge pump on and let it bail out the rest of the water without incident.
     
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