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Adding 12V Cig Plug Directly to Battery?

Discussion in 'Gen 3 Prius Technical Discussion' started by AnneN, May 16, 2024.

  1. AnneN

    AnneN Junior Member

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    Hi.
    Would it be OK to attach a 12v Cig plug directly to the 12v battery using eyelets to the battery + post/ground?

    The reason for it is that I have a small 12v cooler box that I would like to power when the car is running and when car left in Ready Mode. As there is no on/off switch I would have to be sure to unplug the cooler male plug from the female socket but would there be a problem leaving the female plug permanently attached to the battery - is it still drawing enough power to damage/drain the battery?

    Are there any other issues it could cause to the car?

    Thank you.
    Screenshot 2024-05-16 at 12.58.23.png
     
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    The socket + fuse assembly won't pull any power at all until somebody plugs in the fridge or another load.

    I might take the time to mark it "BATTERY" to remove any doubt to future users.
     
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  3. Tombukt2

    Tombukt2 Senior Member

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    Make sure you use a quality socket and with heavy cord on it maybe 12 gauge which is quite thick but would be a good thing good connections directly to the battery..
     
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  4. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Looks to be a fuse in the positive (red) wire, which is good.

    IMG_4146.jpeg
     
  5. ChapmanF

    ChapmanF Senior Member

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    Some fridges come with a "battery protector" circuit; it monitors the voltage, and below a certain voltage, the fridge turns off, to leave you enough battery to start the car.

    In some fridges, the shut-off voltage is adjustable.

    If you are able to adjust the shut-off voltage to around 13.4 or so, you effectively have a fridge that only runs when the car is in READY, because the car's READY voltage is always above that, but resting battery voltage isn't.

    If the fridge's own voltage setting can't be adjusted that high, there are "low-voltage disconnects" available that do the same thing, and some of those are adjustable enough to be used that way.
     
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  6. AnneN

    AnneN Junior Member

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    Yes, 15A fuse on red wire.
     
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  7. AnneN

    AnneN Junior Member

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    Would you not recommend the one in the photo - 16 gauge? The coolbox runs at approx 50w constantly as it is not a compressor and draws approx 3.5A
     
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  8. AnneN

    AnneN Junior Member

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    This is just a very plain12v peltier coolbox - it is just on and off, no other settings. Runs at approx 50w/3.5A
     
  9. AnneN

    AnneN Junior Member

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    Good idea. Thank you.
     
  10. Tombukt2

    Tombukt2 Senior Member

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    You'll be fine with that Ford and fuse for what you're running etc.
     
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  11. Danno5060

    Danno5060 Active Member

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  12. BiomedO1

    BiomedO1 Senior Member

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    FWIW; I like to "stupid-proof" stuff. If I was hooking this up, I'd go thru a relay. Hot wire from battery into relay. Switch power to an accessory-on wire, then to that harness. That way when the car is on, the relay closes and powers your cooler. turn-off the car, power is cut-off from your cooler.
    You can avoid all this by just using your existing plug, which works the same way. It avoids forgetfulness and a dead battery out in no man's land, if you don't carry a jump pack.

    Just my 2 cents....
     
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  13. AnneN

    AnneN Junior Member

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    Thank you. I am trying to keep it as simple as possible - I know you are right about making it "stupid-proof" because of course one day I will forget to unplug it. I do carry a Noco Boost GB40 for an emergency start.
    Maybe you could help with this - I know the existing cig plug in the front of the car the label states a max 120W. If I did have have this secondary socket running directly from the battery do I need to stay within the 120W limit between the two plugs? I'm guessing I do but hoping I don't?!
     
  14. rjparker

    rjparker Tu Humilde Sirviente

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    I have a similar solid state cooler and it runs fine on the existing switched 12v outlet with the car running or in Ready.

    3.5 amps is not much from a wire size standpoint if an extension cord is needed. A 16 awg would work if needed.
     
  15. ChapmanF

    ChapmanF Senior Member

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    Each of the two "cig plug" outlets—the one up front and the one in the console box—has its own independent 120 W rating, ten amps at twelve volts. That reflects the specs of the car's wiring and the relays that control those outlets and the fuses that protect them.

    Your 50 watt coolbox would be quite comfortably within the limits of either existing outlet, and that would be inherently "stupid-proof" because those shut off when the car isn't in ACC, ON, or READY.

    (Well, "stupid-resistant", anyway. The outlets are live in ACC or ON, but the 12 volt battery would be quickly depleted that way. I prefer using a low-voltage disconnect set to detect only when the car is READY.)
     
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  16. AnneN

    AnneN Junior Member

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    I only have the one plug outlet at the front of the car, none in the console box, which is why another one would be handy to have.
    I'm just not sure if by adding the second directly to the battery that is fused, but not run through a relay. would I be overloading the system if I had the cooler box running at 50w in one plug and my solar generator in the other recharging at 100W whilst driving or stationary in Ready Mode?
     
  17. ChapmanF

    ChapmanF Senior Member

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    There are other threads about the capacity of the car's DC/DC converter, operating when the car is in READY. It is rated 120 amps, or 1440 watts at 12 volts.

    How much of that the car itself uses will vary greatly depending on use of the car's equipment. Sitting peacefully in READY with most built-in equipment turned off, the car itself consumes around 400 watts, leaving 1000+ watts extra for your accessorizing pleasure. Turn on the lights, heater (which has a 700 watt electric supplement when the engine isn't yet warm), seat heaters, defoggers, turn the steering wheel in a parking space, and roll windows up/down, and so on, and there may be ~ nothing extra; Toyota had no incentive to oversize the converter beyond the car's own foreseeable needs.

    If you have a solar generator putting 100 W back into the system, that's to your advantage. It still has to be within the 120 W rating of the outlet you plug it into (because the circuit must handle that current regardless of its direction), but in your overall power-balance picture it is in the credit column, whereas your 50 W coolbox is a debit. At any given moment, whatever you're getting from the solar is reducing the load on the converter.
     
  18. rjparker

    rjparker Tu Humilde Sirviente

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    The solar panel should go to the battery directly if you want to use it. It is only effective as a low amp battery maintainer. It will be too variable to run the cooler directly.

    The cooler should go to the switched 12v outlet.

    A second 12v battery and a rv style battery isolator is an alternate and recommended off the shelf solution if you want the cooler running when the the car is not in Ready. You run the cooler off of the second battery which will charge from the car when in Ready or slowly off the solar panel anytime the sun is strong.
     
  19. ChapmanF

    ChapmanF Senior Member

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    The panel will be too variable to run the cooler directly, but however much it is producing at any moment is that much less needed from a battery. If there is any excess, it will go toward charging the battery; if it (as it usually will) falls short, battery will make up the rest. This does not depend much on where in the system the panel is connected.

    It would be usual to attach the panel somewhere that is not switched, so you don't miss out on the sunbeams that arrive while the car is off.
     
  20. BiomedO1

    BiomedO1 Senior Member

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    If wired directly to the battery, your limitation is the wire gauge of that harness and it's inline fuse. People above has already given you the safety specification of the cars OEM wiring limitations.

    Good luck...

    FYI, there's some room under the rear seat and spare tire area to place a small, lawn mower style AGM battery. You can use a similar hook-up I described before using a relay in parallel to your 12VDC system. You tie that aux. harness directly to your parallel battery system. It'll recharge as your driving and disconnect when you turn-off. Kill your aux. battery, no harm no foul. Add a manual switch and you have a built-in jump start system - assuming there's juice left in that aux. battery bank. Just a thought....