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

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  • jong kung
    Kerry, ... I didn t think of the CB, etc.  The old PSU I have uses screw type connectors.  So I was thinking of them as lab PSU.  So why would lab PSU be
    Message 1 of 45 , Jun 3 9:41 AM
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      Kerry,


      > It's so you can run your car electronics on AC. (CB

      > radio, for example)

      I didn't think of the CB, etc.  The old PSU I have uses screw type connectors.  So I was thinking of them as lab PSU.  So why would lab PSU be 13.8v ??  This just didn't make sense to me.

      But if I was running CB, 8-track, etc. that makes sense.  These car electronics probably have another built-in voltage regulator so they need MORE than 12v (to overcome the regulator's drop out voltage).

      =====

      Sometimes I look at a simple problem from just one POV so long, it becomes impossible to think in a different way.  For me I was always thinking:

      ****   LAB PSU with 13.8V output.  ****


      Jong

      P.S. Sort of embarrassingly simple - ain't it. 

      :-)
















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    • 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 9:18 AM
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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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