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I have a 3 way cigarette lighter splitter that says:

Input: 12VDC, 8A Output 3 Ports: 12VDC up to 8A Fuse: 8A, 250V

Does this mean it outputs 8A per port or, does it mean if the load of all 3 ports combined exceeds 8A then the fuse will blow? (i.e. the 8A is divided between the 3 ports depending on the load from each device).

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  • +1 for a reasonable question. It means that if the sum of any combination of currents out of the splitter is greater than 8 amperes, then the fuse will blow in the time specified on the fuse's data sheet.
    – EM Fields
    Commented Dec 5, 2015 at 20:34
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    Why would this be migrated from electronics? this really has almost nothing to do with cars.
    – JPhi1618
    Commented Dec 7, 2015 at 15:18
  • @JPhi1618 it was marked as off-topic, likely due to a mix of newbie hate, "question on consumer electronic use and not electronic design", and that it's even dared mentioned an auto or consumer product. That said, it is still tangentially on topic here.
    – cde
    Commented Dec 9, 2015 at 3:40

2 Answers 2

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Typical auto cigarette splitters are simply three connectors in parallel. Nothing but wire and the connectors. Zero circuitry aside from maybe the fuse. The 8A is shared between the three.

Hopefully you have one that's much better quality than the one seen below. It has undersized cabling, and no fuse. The white wire is heat protection as that connector is supposed to be used for a cigarette light. enter image description here

Here is a teardown of a fancier splitter, that has individual on/off buttons, and a cheap 12V to 5V "usb" converter builtin. They explain the circuit pretty well:

http://www.youtube.com/watch?v=TaoLlMw40Rc

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  • No embedded youtube videos on this stack yet? Shame.
    – cde
    Commented Dec 5, 2015 at 21:58
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The maximum total current that the splitter can supply is 8 Amps (provided your car cigarette lighter socket is fused and wired to be able to provide at least 8 amps). Some examples to help:

  • CB radio into plug 1 uses 1 amp and peaks at 4 amps (when transmitting)
  • GPS into plug 2 uses 1 amp
  • Inverter into plug 3 uses 5 amps

Each one is less than 8 amps, but the total when you don't talk on your CB radio is 7 amps so okay, but not okay when you talk on your CB because then the total is 10 amps.

So while it says each one can do up to 8 amps, the whole thing can only do 8 amps.

Hope this helps you understand :)

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