Caravan battery being charged by Tow-car

[Rubix]

How does the caravan battery get charged by the Tow-car ?

Is it simply via the alternator of the car, in other words is it simply (electrically via the 12S socket) connected across the car battery.

The reason I ask, is as a car battery and a leisure battery are built differently surely there should be a different charging method ?

There is the battery charger in the 'van itself, but this is for charging from 240V mains ?

Thanks for your help.

 

[Damian]

Rubix,

You are correct in your thinking, it is simply the car alternator which charges the van battery whilst driving.

Th evan onboard charger is only operational when connected to 240 volts (sorry 230v + or - 10%)

The difference between battery makeup is notreally significant in charging rates, except that the car will deliver up to 14 volts or thereabouts, whereas the van is limited to 13.5 to avoid gassing of the battery.

Getting a charge of 14 volts actually benefits the battery and keeps it in good condition, as long as it is only a relatively short time, ie, not on 24/7.

 

[rob_jax]

Hi Rubix,

Car engine-starter batteries and caravan leisure batteries are both lead-acid batteries, the internal cells produce almost exactly the same 2.1 volts (and hence a 12 volt battery has six cells), and have very similar characteristics, except:

The internal design and chemistry are very subtly different, and the leisure battery needs an extra 0.8V (14.4V is recommended) during the first phase of charging to completely charge the leisure battery.

Charging a leisure battery with a car alternator (13.4 to 13.6 Volt output) will charge a leisure battery to between 80% and 90%

However, voltage drop in the wires (simple resistance) between the alternator and the caravan battery will reduce the charge voltage and the maximum charge state. How much depends on the quality of the wire and the connector between the car and caravan (Euro 13 pin connector is much better than 12S - less voltage drop, better contact)

Some caravans (all European makes) have a battery charge booster (made by Schaudt - the WA1214 model) that lifts the car voltage to around 14.4 volts and then the battery is fully charges. UK caravan? haven't heard of the Schaudt devices being fitted.

Once the battery has been charged, the charge controller should reduce the applied voltage to a "maintenance" charge of just over 13 volts to avoid gassing and overcharge. You need to check your caravan electronics to confirm what charger you have fitted.

Robert

 

[Rubix]

Robert,

Thanks for your help.

I think my charger is a Zig X-7 (Crown Soverign - 1998) But looking at the wiring diagram it appears that it only has a 240V input and the "Car charging" is done straight from the car.