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Re: [toyota-prius] Re: $20 per gallon in NYC-Craigs list

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  • Peter Blackford
    Couple of points you re missing: With low voltage circuits, voltage drop becomes more of an issue (Vd is the same, regardless of circuit voltage, thus it
    Message 1 of 31 , Nov 13, 2012
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      Couple of points you're missing:
      With low voltage circuits, voltage drop becomes more of an issue (Vd is the
      same, regardless of circuit voltage, thus it becomes an increasing
      percentage and more of a problem with 12V than 120V). Also, there's no
      such thing as 'magic wire' -- some 'published ampacities' of
      high-temperature wire are shockingly high, however one must read the 'fine
      print' and realize what the operating (not ambient) temperature and
      commensurate Vd would be at those currents. Thirdly, draws of most audio
      systems are ragged (not continuous) in nature, thus a transient condition
      might want to be 'handled' by a larger fuse, but not generally a great idea
      for continuous loads.
      There too, the battery (i.e., a larger one) can act like a capacitor in
      handling transient loads, but for the emergency power application it should
      make little difference since the system will be 'running' off of the DC-DC
      converter. As always, Prius should be in 'ready' mode before using the
      inverter power.
      Bottom line: Use adequate wire size for the continuous load, and proper
      fusing (ditto) to avoid problems. No magic here.
      Pete (Wire guy)

      P.S. 40A is a bit much for #10 wire... it will get rather warm when you go
      over 30A continuous load.

      P.P.S. The 10A limit of the outlet is NOT set by the wire - the contact
      system in the basic design will toast the plug/jack if you exceed that
      rating for any amount of time. Did lab work on that, and it's the
      disappointing truth.

      On Mon, Nov 12, 2012 at 11:38 PM, Dan <hyattdj@...> wrote:

      >
      >> Yes you are correct, but there is some critical information.
      >
      > The amperage the circuit can draw is dependant on the source, the gauge of
      > the wire, the length of the wire, and the limits of the components.
      >
      > http://www.engineeringtoolbox.**com/amps-wire-gauge-d_730.html<http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html>
      >
      > For instance, on my jeep, I had a 6' run of 10 or 12 gauge wire from the
      > battery to an overhead fuse block. I think we calculated we could draw 40
      > amps of 12v, or 360 watts of power.
      > I am trying to figure out how the fuse blocks on the cars can be rated at
      > so many amps max capacity with 10 gauge wires.
      >
      > The big problem with the power ports is that they still use 18 guage wire,
      > designed for 5 second duty cycles. You use a 5minute or 1 hour duty cycle
      > and you can (I have) burn the wire.
      >
      > A much debated limit for the Prius is the OE 12v battery, by the factory
      > manual, is woefully low on reserve capacity. While the Optima will have
      > lots of reserve capacity for your deep draws.
      >
      > Radio operators also have a tendacy to use anderson connectors, which have
      > excellant capacity and often have thier own wire to the main block.
      >
      >


      [Non-text portions of this message have been removed]
    • David Kelly
      ... I think you are trying to over think it. If the inverter can really put out 80W (most are sold by liars) then we know the input draw must be at least 80W.
      Message 31 of 31 , Nov 13, 2012
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        On Nov 13, 2012, at 6:19 AM, Walter Lee wrote:

        > David,
        >
        > I'd really am interested in this scenario and what my options are.
        > I messed up last time - I don't want to mess up twice. (9_9)Can you confirm whether I am getting the basics correctly. (9_9)
        >
        > The Peter's reasoning goes as follows: the power loss from the input circuityr (fuse) to the actual power adapter is 30W ( 150w-120w) or 20% power loss in the adapter circuitry.

        I think you are trying to over think it.

        If the inverter can really put out 80W (most are sold by liars) then we know the input draw must be at least 80W. The Prius outlet is rated 120W. There is a conversion loss somewhere in your 80W inverter. So we say that an 80W inverter is about the limit of what one can safely use on a 120W supply. Perhaps you could get by with a 100W unit.

        Truth be told 119W isn't going to be safe when 121W is a sure kill. These things are not that predictable. Gut feel from experience says 80W should be safe, 100W might be safe, and 120W rated inverter is certainly not safe at its full capacity because it will be drawing more than 120W.

        --
        David Kelly N4HHE, dkelly@...
        ========================================================================
        Whom computers would destroy, they must first drive mad.
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