Overview 

When you’re ready to start out on your new campervan conversion, you’ll no doubt want to have electrically powered devices inside your camper van. You’ll also want to use these devices when you’re parked up with the engine turned off. 

These electrical items can be low consumption items; such as your LED lights, 12V power sockets through to the more power demanding things such as your 12V coolbox/fridge, laptop, inverter or water pump.

If you try to run these devices from your engine Battery without the engine running, sooner or later you’ll end up with a flat battery. If you do this, you run the risk of becoming stranded. 

That’s certainly not the best start to your epic VanLife Adventure now, is it!

So the standard solution is to fit one of more leisure batteries that are used to power all your devices that are not related to starting the engine.

But with installing these batteries, you will now need a way of keeping them topped up with that all-important juice.

This is campervan spit Charging comes in!

What is Split Charging in a Campervan?

Split charging is the terminology used to describe the simultaneous charging of the van starter battery (sometimes called the crank battery) and the leisure batteries, all from a common charging source.

On your camper van, the charging source will almost always be the vehicle alternator which is in turn powered by the engine when running.

There can also be other ways of charging up your leisure batteries not related to the van alternator. Alternate methods can be using a mains power charger, solar panel charging systems as well as portable fuel generators.

Split charging systems typically have a device that connects the engine starter battery and the leisure batteries together when the charging source (usually the engine) is running.

Split chargers can also isolate both batteries. This ensures that the use of one battery does not draw current from the other as it is essential to ensure that the engine starter battery is isolated so the engine can always be started. 

Also, you want to avoid the leisure battery to be accidentally used when starting the engine. Some dedicated leisure batteries are not designed for the high current draw used to turn the engine over.

A Few Words on Battery Charging

Before we take a look at connecting the batteries for split charging, it’s worth taking some time to learn how batteries obtain a charge from its charging source.

A typical 12v battery provides a voltage output in the region of 12-13 volts. 

Depending on the battery charge level, as well as when the charging source that is trying to deliver current to the battery it’s trying to recharge, the charging source has to provide a higher voltage that is higher than the output by the battery in order for the charge to flow into and be stored within the battery. 

Split Charger Methods/Technologies 

Campervan Manual Switch Charging

The simplest way to connect the engine starter battery to the leisure batteries is with a simple master ON/OFF switch. 

This method here uses a high current switch to manually connect the starter battery and leisure batteries in parallel once the engine is running. This will allow the charge to go to the leisure batteries. 

Once you turn the engine off, simply flick the switch back to the off position to now isolate the batteries. This will prevent you from flattening the main starter battery when drawing power from the leisure batteries.

Advantages of Using a Manual Switch Relay in a Campervan

• Cheap
• Simple to install and use
• Robust
• Quick and easy to combine both batteries together to start the vehicle in case of emergency (e.g. battery is flat)

Disadvantages of Using a Manual Switch Relay in a Campervan

• Inconvenient
• Installing a switch relies on the driver to manually connect and disconnect the batteries
• You risk leaving both batteries connected which could result in a flat battery and leave you stranded

Conclusion

Unfortunately, this is not the ‘smartest’ solution out there. You can easily forget to turn the switch back to the off position. This can then leave you vulnerable to flattening the starter battery. 

And we are sure you will agree that getting stranded with a flat battery can be a pain in the backside!

Campervan Split Charge Relay

A split charge relay system uses a heavy-duty version of a ‘make and break’ relay. The coil inside the split charge relay will energise once the relay receives a +12V signal. This signal is usually from the charge signal wire that connects to the alternator.

The split charge relay will only come on when the engine is running.

When energised, the split charge relay will instantly connect both batteries together. This will allow you to charge the leisure battery from the alternator. 

It will also disconnect both batteries once you turn the engine off as the +12V signal will disappear. 

You may also require a heavy-duty version of the relay. The relay will have to be able to handle the potentially large current that could pass through it by the alternator.

Advantages of Using a Split Charge Relay in a Campervan

• Simple Automatic operation
• Inexpensive compared to alternate methods
• Simple electro-mechanical construction
• Simple to replace

Disadvantages of Using a Split Charge Relay in a Campervan

• You will have to tap into factory wiring as this relay requires you to connect to other parts of the vehicle electrical system
• Over time, moving contacts can wear out which can lead to increased resistance and voltage drop
• You will not be able to combine your batteries for emergencies unless you install a bypass switch
• This relay is not really ‘intelligent’

Conclusion

Before the availability of the more intelligent and the now popular Voltage Sensing Relay came to market, this relay was the most common type of split charge relay used. 

Although this type of relay is still available today, many people are wary of tapping into their vehicles electrical system in case of damage or potentially affecting the warranty of the vehicle.

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