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Adding switchable power for USB charger.

Discussion in 'XJ DIY How-To Instructions' started by Nuch, May 29, 2017.

  1. Polock

    Polock Well-Known Member

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    we have us apples and oranges. with that setup you can't measure what i measured. i measured voltage at the battery with the load, then current from the battery, with and without load.
     
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  2. Wintersdark

    Wintersdark Well-Known Member

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    Oh I know. In my may above I'm converting - note the 1.76A draw at 5v = 0.74A at 12v in my mathy post above.

    I should have just used watts for clarity, but yeah. You're still looking at 20 watts charging (not counting efficiency losses in the charger) draw with a modern phone, and the current spec allows up to 100 watts draw (though no current phones draw that).

    Still, it's not enough that it'll be a problem under normal circumstances I think(Again, not aware of how much you can discharge our batteries before starting becomes problematic), but it's definitely a non trivial draw, and it may be an issue when other factors contribute.
     
  3. Wintersdark

    Wintersdark Well-Known Member

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    Yeah, parasitic draw is a pretty minor concern. I know I've got two high current chargers in my truck unswitched, and together their parasitic draw is small compared to the basic truck electronics - so much so that it's irrelevant.

    I use the same sort of setup on my XJ as well, using the battery tender's hookup attached directly to the battery (of course fused) as a multipurpose 12v source.

    I'd only be concerned about it if I wasn't going to be riding for an extended period and not having my battery on a tender, but that's not going to happen.

    Mostly, just wanted to highlight the potential dangers in smartphone charging when you're not riding, as modern devices draw a substantial amount of power - way more than most people think they do.
     
  4. cgutz

    cgutz Well-Known Member

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    5 watts vs. 12 watts...
     
  5. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    How many amps of load are needed at 12V to get Naomi Watts?
     
    Last edited: Jul 23, 2017
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  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    more than I can supply
     
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