Recharge 2 batteries, caravan at the campsite

[ordiman56]

hello have here is my father's project, we have a caravan, we redid all the eletriciter (12v and 220v) for the 220 is when we are camping so no problem, but the 12v is if we ever stops at the bort of the road or other, it neither will have no 220 socket so we put on the 12v light by a battery in the trunk of the caravan.
everything is in place and working, the only problem, the battery discharges (normal), we would like to connect it to the car's alternator to recharge it when we are driving. so my father started to pass these cables and everything to connect but I told him not to do it. because I think it will be the energy of the car battery that will go into that of the battery and caravan.
voila, do you have any idea how to do this?
we put 2,5² but the wires are heating, do you think we should put 6²?
thank you to those who answer.

[dirk pitt]

two possibilities:

either you don't put a battery in the caravan (that's what I do) and therefore, when you are stopped for the night, you take the current on the car battery.

either you add a second battery in parallel on the first (no other connection possible) and in this case, at night, you unplug the car to drain only the battery of the caravan.
when you leave, you start the engine and then you plug in the caravan, the current from the car (alternator + battery) will recharge your caravan battery.
if the cable heats it is that the current is too strong. that means the battery is too low.

[boubka]

hello ordiman56
if you double the capacity of the batteries, the alternator may be too tight.
if you consume on bat 2 you must disconnect bat 1 so as not to flatten the 2
for the charging cable you must put a large enough section to avoid loss of voltage
to be sure that the bat 2 loads when the one and full and not to overload the alternator here is a small electronic assembly that does this
http://pagesperso-orange.fr/deltajp/mon ... plein.html

[boubka]

and not to bring the batteries to their knees we can also add a threshold detector
http://pagesperso-orange.fr/deltajp/montages/aop.html

[boubka]

of course if you have the means this type of assembly exists all done at motorhome dealers.
but given the prices they charge I think that self-construction is very interesting as long as you know how to weld ....

[ordiman56]

thank you very much for your reply. So if I understood correctly, I start with the battery one, I roll in can to recharge it and after I remove the one and I put the two. from what I understand would be the simplest. but is there any problem if we change while the car is running?
with a switch his should do it.
to intensify it I will try to watch how much goes to recharge the battery.

[boubka]

problem if we change while the car is running

it depends on the car but with an assembly as you describe if it is a recent car then you will have problem ...

[ordiman56]

he is a chrysler traveler from 1998 i think

[boubka]

if it is a gasoline by cutting the bat the engine is going to stall, if it is a diesel maybe it will work. but I do not know the engine fct on this vehicle you have to try to disconnect the bat an instant and even if it does not stall
otherwise if the management is electronic it may be that you create a failure and then you have to take the procedure for resetting the electronics, battery change procedure
in any case I advise you against this mounting, you might also be able to damage the alternator

[ordiman56]

ok thank you i would say all that to my father tonight.