So we are heading on a 5200km round trip and want to use a 12v cooler. Any ideas for constant power? It would be great to be able to turn the car off and have the cooler keep running.

I know, it wont REALLY be needed as the cooler should stay cold for a few hours without the vehicle running. But in the sun and so on you never know.


Ideas?

 

DO NOT DO THIS!

Open the hood and look at your battery, tiny tiny little battery. Look at the amp draw on
that cooler. No way will this work

Buy a high quality ice-chest (Yeti or equal) and your stuff will stay cold and the car will start.

 

It is a 12v cooler designed for a vehicle. Its not a FRIDGE....

it pulls 3amps at most

 

Don't do this!!! The small starter battery cannot handle the amp discharge for very long, assuming you have a thermo electric peltier cooler. While thermally efficient they are electrically inefficient. Even at 3 amps the starter battery has very little reserve time and will be damaged after a certain time.

If you REALLY wanted/needed to have constant 12VDC then get a group 24, 27, or 29 deep cycle battery to run the fridge with the engine off. You can make an acc lighter adapter to go directly to the deep cycle battery. It will be in parallel with the starter battery and charge it. Be sure to disconnect it before shutting off the car as you do not want to backfeed the aux fuse panel once its relay stops powering its components as you will likely pop the 20A fuse to the accessory outlet.

The internal fuse of the cigarette lighter adapter will prevent you from burning up anything. Ive done this before camping and no problems.

The simpler method is buy a large group 29dc bat and a charger, run the fridge then charge it up when you stop overnight. More than one way to accomplish what you seek.

 

Group 51 battery has an RC rating between 75-85. It will take 75 minutes for the battery to drain down to 10.5V with a 25 amp load. I would not let it drain that low, but at 3 amps you are using about 1/8th of that 25 amps so your time is about 600 minutes until the battery reaches 10.5 amps. Seems long enough!?!

How long are you planing on leaving it plugged in?

 

i didnt know GKs use a 51 battery now?

 

Keep in mind that a group 51 battery is not a deep cycle battery. The plates inside are way thinner in comparison. Cycles below 80% DOC will most certainly have a noticable shorter life expectancy of the battery, seen it first hand. Also there is likely a chemistry difference, for example lead-calcium or lead-antimony, all of which have different properties for electrical potential storage, discharge, and charge.

You need the right rig for the gig, and a deep cycle battery is the way to go. Tasking a starter battery to use its reserve time, no matter how much of it is like driving down the highway with bald tires and hoping against hope you won't have a blowout. My 0.02 cents

 

^ I agree deep cycle is the way to go. Starter battery is going to build up sulfation quickly and won't last as long. If OP wants to keep his starter battery in tip top shape using it run the fridge is not the way to do it. He may be ok with the shortened life span.

Diode isolating the fridge circuit from the rest of the car would protect against back feed.

It's a 151 not 51. RC=55 so 440 min discharge time to 10.5 volts.

 

Agreed on the diode, forgot to mention that. The accessory outlet is fused at 20A, so naturally the diode has be able to accommodate that amperage as well. Though the fuse is a fast blow and will likely pop around ~15-16A roughly

I'd go with something like this: the pckage size is more than enough to ahndle 20A current if needed. You would need to build a small project box to house it and a heat sink with thermal paste.

DHG20I1200HA IXYS | Mouser

 

don't do it. the battery is small, u will drain it and prematurely wear it out.
unless ofcourse, you run a deep cycle battery.