Sorry to waffle on but this is as short as I could to explain it
Vehicle battery to van battery / fridge would usually be 4mtrs or more of cable length. Over this distance cable size and voltage drop becomes a very important factor. Without doing all the calculations I can tell you my previous van (we won’t mention the brand) using what is commonly referred to as 50amp cable (big stuff)I could only just get the correct voltage to the fridge to run it. The other big factor is the fridge will pull 12–16 amps constant… this is a BIG load when constant. Travel for 4 hours with fridge on 12v that is 4 X 13amps = 52amps used. That’s a lot of power.
Let’s start with Voltage drop, if you want to see this effect then while connected to the car, connect a volt meter to the fridge terminals behind vent(fridge off) if you’re lucky it will read 12V or more BUT, its most likely voltage drop will already be at play and you will get <11.5.
Now turn on the fridge and watch the proverbial backside drop out of the voltage to well below 11V. You may even find that the wire starts to noticeably warm up…
If you expect to do ANY charging to a battery this voltage must be 13V+ to charge or 12.5V to maintain, while the fridge is ON. Anything below these figures is a draw not a charge. Sorry these are the facts.
Unless you prepare for this, connecting your house battery (van) to this cable will only serve to flatten your house battery.
Let’s go back to the usage of the fridge for 4 hours travel, 52amps. Most house batteries will be around 100amp hr. and shouldn’t be drawn below 50% without damaging the battery. Do the math….we is losing the battle here
This is why the manufacturers wire the fridge separately. MOST vehicles can only JUST run fridge, if that.
IN short don’t do it !! Sounds like a great idea but it is MOST likely going to cause headaches. If you still want to proceed then read on.
If you have a solar system that is correctly installed then you don’t need power from your car to charge house batteries, the solar should look after it. If not or you wish to assist this charging method then you need to buy a dc to dc charger. This will bump the voltage up for vehicle so as to be an effective charge to house batteries and not a drain.
With either of the above unless you understand what is happening here I again strongly suggest you DON’T connect your fridge to your house battery. I did it, undid it, re did it, re re did it….. and learnt a lot about the real world and how to survive a bush camp with no power.
ON my latest van Expanda 20.63.1OB I have installed a 320W solar with 30amp charger. This system does produce (in full flight, 10am-3pm, full sun) 14.5 amps of charge. The fridge when on 12v draws 15 amps even.
I have connected the fridge to the house battery BUT it has a Low Voltage Disconnect (LVD) on this line. SO if the fridge starts to draw too much from the house battery it will disconnect to protect the house system. This line is supplemented by the “hot wire” from the car but this only assists house battery to run the fridge while traveling or on LVD will only run the fridge, best it can. I don’t get or expect the car (hot wire) to do any charging, it won’t happen, that’s the solars job.
BUT to finish the easiest way to ensure happy camping is to NOT connect the ‘hot wire’ for van fridge to the house battery system. If you want to charge your house system install a solar panel(s).
Happy Camping
