Chain 12v fridge to aux batt to truck aux power to charge and power at same time?

[DaveM]

I have what is probably a very stupid question regarding 12v power supply and charging from an aux 12v plug in a truck.

I have the Doemtic CFX 35 portable fridge from Campingworld. I don't have the budget or expertise to set up a dual battery system, so I plan to run the fridge off an auxiliary 12v plug in the truck bed while driving and a portable battery box (like the one below) while at camp. I have the figures somewhere for determining what size batt I'll need to run the fridge for at least 2 days on the batt (need to re grok that though). Most of my trips will be 2 - 4 day out and back camping trips where a single charge up on the batt at home should get me through the trip while not plugged into the aux power. This July however I'm taking a much longer road trip where I won't have the opportunity to top of the portable batt.

So what I'm curious about here is if while driving I can chain the portable batt and the aux power together to provide both a recharge to the portable batt and power to the fridge? I have a single 12v aux outlet in the rear of the truck. My idea is to plug the fridge into the portable batt 12v aux socket, then use a male 12v plug with ring ends to connect the batt box terminal to the truck 12v aux. Will that work to both provide power to run the fridge while also charging the batt? Or do I need to add a separate charging circuit to the bed?

 

[Tazman]

Charging requires a lot of Amperage so you will need to wire accordingly. You should isolate the battery so you don't drain your vehicle battery down and you will want to fuse it properly. There is a ton of info on this site so do a search. Lots of experts here who have done the job correctly. If you take shortcuts you could have fires, vehicle problems, fridge problems and subpar charging at best.

 

[DaveM]

I should have included the details on the aux plug to the rear. It's a marine grade outlet on 12 awg wire to a blue sea fuse box. It's on a 30amp fuse (IIRC), and the blue sea is wired with 10 awg direct to the batt and fused inline (need to check fuse amp, 30 or 60). I would unplug the aux to the batt once in camp so the fridge can't drain the starting batt. And I always travel with a jump pack.

Edited to add: I've searched the forum in the past for this but most of what pops up deals with dual batt or solar set ups. I'll keep looking though.

 

[DaveM]

This is about the most specific I can find: http://www.exploroz.com/Forum/Topic/72953/Can_i_run_the_fridge_off_battery_whilst_charging_it.aspx

Everybody else is talking about charging from generator or solar panels while running the fridge. I'm looking specifically at charging via the alternator while running the fridge. My assumption is this is the same as running the fridge directly from the aux plug while driving. With the portable batt in0line it will just act as a throughput for the charge (either draining very slowly or topping off very slowly depending on the fridge draw and the alternator output).

 

[1Louder]

My ArkPak can do this. Not sure what type of powerbox you are planning on purchasing. It has a built in charge controller. They are on sale for a short time.

 

[DaveM]

What you propose wont satisify guys afflicted with battery charger OCD but will get by.
Depends how your aux system is set-up, but probably will do better if you run the fridge & charge the aux. separately whilst driving. "Chained" like you describe, might be letting 'fridge "steal power" what otherwise could go toward charging.

That's more or less what I'm unclear on, the chaining versus independent power for each. A second fused line to the rear won't be difficult so maybe that's the best option for now. Down the road, when I trade up to a newer rig I'll likely do a proper dual batt set up.

 

[jonyjoe101]

you should be able to do it, The portable 12 volt jump packs can be charged that way, most are 18 ah agm batteries. it has a male adapter to male adapter wire, that you plug in from the cigarette plug on vehicle to 12 volt plug on the jump pack. Your aux battery is just a larger jump pack.

You wont need any special equipment, your 12 volt battery is self limiting, you cant overcharge it as long as the voltage doesnt go over 15 volts. once the battery is full, it wont accept any more amps. Even if your alternator puts out 100 amps, if your aux battery or jump pack is full, it wont damage anything.

You only need the thick gauge wires to take power out of the battery, the battery is capable of releasing more amps in one second, than any alternator can produce, thats where wires get overheated. The 12 volt receptacle should have a 15 amp fuse on it.

The 12 volt fridge doesnt run constantly so it shouldnt affect charging of the battery.