Adding 12V Cig Plug Directly to Battery?

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.

 

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..

 

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

 

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.

 

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

 

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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....

 

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.

 

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.)

 

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.

 

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.

 

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.

 

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....