Caravan Current draw????

My own personal preference is 8 B&S but that is not going to fit into the 5 large pins in the 12 pin plug, you will need to use 6mm auto for that. A 30 amp breaker would suit the 6mm.

A better alternative would be an anderson plug.

"if I run a 40 amp breaker and 50 amp cable that should do the job..... "

This will ensure that you prized posssession doesn't go up in smoke - but it doesn't help ensure that you get adequate voltage at the far end at 40 amps.

It's not question of how long is a piece of string . . . BUT, a question of how long is the TOTAL wire run from battery to fridge etc.

Then you can decide what size wire you will need.

goodday mr F
i bought an adaptor to suit the 12pin plug and ran 6 mm to the power line for fridge on car (not that it matters )and 10mm to an anderson plug which goes to the battery both car and van direct, brake wires 6mm on car also to other pin and 7 core cable so that it all works fridge should just come from van battery or have van and car in paralel

steve

"figuring that if I run a 40 amp breaker and 50 amp cable that should do the job"

Forget the current rating on Auto cable. If your cable is over 1/2 metre long and you are running more than 1/2 the rated current through the cable you will be experiencing too much voltage drop. All the current rating refers to is the current that will heat the cable unacceptably. You do not want that sort of voltage drop.

Do not purchase auto cable looking at the size in mm either. This figure is just the minimum diameter of the hole that the cable will pass through. The Australian standard for quoting cable sizes is mm2 (millimetres squared.) Auto cables for a given mm size comes in various mm2 amounts of copper.

To work out the size of copper you require you need to know the length of cable to be employed and the maximum current draw (work on 15 A for a Dometic fridge if you do not know the exact figure.) The suggested maximum voltage drop for designing a circuit is 3% - this applies to any voltage including 240 V. To find out how much voltage drop there will be in a circuit, use the following formula:

Voltage drop equals (cable length (in metres) X current (in amps) X 0.017) divided by cable cross-section in mm2.

For more on this subject see Site Link

PeterD

Was going to post reply but NN in 4 seems to have covered it, especially the link!! Would only add; be very wary of plug connections carrying 15 amps, and when all is complete, take a multi meter and put one probe on the battery +ve and one probe on the closest +ve point you can access to your operating fridge. If the vehicles running, substitute alternator +ve.
Once you've done that, repeat process on the -ve side. On 12/24V systems, voltage drop is a far bigger issue than ultimate capacity!

Thanks for that info guys.... I'm pleased you did not do what the cretin at Dick Smiths just told me.... "Sir you need OFC (oxygen free copper) to stop current loss".....
I suspect that voltage drop is going to be the main problem and the diode protecting the van battery will also give a volt or so drop but I am not sure of how the van battery is charged, if it's just in parrallel with the car batteries with a diode the voltage may never get high enough to charge the battery completley....
I'v sent a rather unambiguous Email to the manufacturer asking for complete details, I await their response. How dare they fob me off....

Go an Anderson Plug.
Most vanners do. Mine is supplied by a 40amp relay worked off the ign switch.
Most van 3 way fridges draw approx 150watt or 13amps continously. Plus whatever your charging unit uses.
I built in an Arid twin charge unit in the van which charges the van battery at max of 20amps. So total draw for mine is a max of 33amps. However I find that the charger usually only charges around the 6 amps as the in house van batt is usually not that low as it is an 110amp AGM type. So my draw is somewhere near 19 amps and as the batt comes up the charging rate reduces to a pulse charge when fully charged.