If you have a campervan then in all likelihood you are going to want a second / leisure battery to run lights, fridge, TV (some people watch TV when camping… don’t get it myself but there you go), charge phones, laptops, cameras, radios, torches… the list is never ending!
There are few different types of battery charging systems such as diode charging, split charging or the one I am going for Voltage Sensing Relay. VSR charging is fairly straight forward, you connect your crank/starter battery to your leisure battery through the VSR. When the starter battery is up to 13.3V then the relay is opened and the leisure battery starts charging. When it drops to 12.8V the relay is closed and the two batteries isolated.
12V Batteries have a voltage profile and give out a high voltage the more charge they have so the voltage varies between 11v – 14v (exaggerated but you get the idea!).
Having done a little research, you can do this cheaply or well! The cheap option you can get set up for around £25 but it will take a long time to charge your second battery or you can splash out a poo load of money and get a high amp system with bells and whistles. Such as bidirectional charging, this is useful as if you have a Solar Panel charging your leisure battery a Bi Directional VSR will allow the Starter battery to be charged once the leisure battery is topped up.
In either case make sure you use the fattest DC cable you can get! 6mm auto cable isn’t good enough.
This is a UK kit version I have found for sale… £74 seems OK, but I stress that I don’t currently own one so can’t confirm. It seems to have everything although is it not bi-directional.
A little more looking and Simply Split Charge keep popping up as a recommended supplier….
I’ve decided to put this on hold… a solar power system would come first as I tend to go from home and park up somewhere for a weekend or week and then come home. If the leisure battery is charged before I leave then I gain no advantage from charging off the alternator. A solar system would keep me topped up while stationary at a campsite or festival.