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Re: [Electronics_101] Why are some PSU 13.8 v instead of 12v ??

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  • Reese
    ... Picking a nit: 13.8 volts is what a standard automotive alternator will produce when it is excited and is in its charging mode. The 6 cells in a healthy
    Message 1 of 45 , Jun 3, 2010
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      On 03-Jun-10 10:52, jong kung wrote:
      > Kerry Wentworth,
      >
      >
      >> 13.8V is what your 12V car battery is at when the car is running.
      >
      >
      > I was guessing this but I don't know for a fact. Is it that simple?

      Picking a nit:

      13.8 volts is what a standard automotive alternator will produce when
      it is "excited" and is in its charging mode. The 6 cells in a healthy
      12 volt automotive battery will never give a 13.8 volt reading when the
      battery is isolated from the charging system - unless maybe the battery
      has been overcharged in which case, it will die in short order.

      Reese
    • Donald H Locker
      I get it now! When the copper is positive at the panel connection the corrosive potential is reduced by any voltage drop rather than increased. (I did figure
      Message 45 of 45 , Jun 8, 2010
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        I get it now! When the copper is positive at the panel connection the corrosive potential is reduced by any voltage drop rather than increased.

        (I did figure out quite quickly after other posts that the ignition coil can be easily redesigned to deliver correct polarity despite the battery polarity; thanks to all for pointing that out. In the words of a famous philosopher, "D'Oh!")

        Thanks much.
        Donald.

        ----- "lists" <Stuartlists@...> wrote:

        > In article
        > <1636128660.4807421275619439843.JavaMail.root@...>,
        > Donald H Locker <dhlocker@...> wrote:
        > > More because in a negative ground system, the center electrode of
        > the
        > > sparking plug goes negative and ionises the gap more readily because
        > it
        > > is hotter then the side electrode. Result is a lower spark gap
        > voltage
        > > requirement.
        >
        > When a copper wire is connected to a steel car body and it gets wet
        > (normal in a car) there is an electrolytic action set up which
        > corrodes
        > the steel. When you apply a voltage such that there is an electron
        > flow
        > through the connection it will either accelerate or reduce the
        > corrosion.
        > Negative earth reduces corrosion of the steel
        >
        > --
        > Midlands Midsummer Mug show, for all things RISC OS, July 10th 2010.
        > Stuart Winsor
        >
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