How to charge a leisure battery while driving?

There’s more than one way to charge a leisure battery while driving


Charge your leisure battery while driving

If you are converting a van into a campervan it is useful to charge your leisure battery while you drive. This ensures you are topped up for your next adventure.

Split charging devices are usually cheaper and easier to install than solar. They are also available in a couple of different varieties to meet all requirements.

The two main types of split charging devices are known as Voltage sensing relays (VSRs) and DC-DC chargers. 

We will explain how they both work and when you might want to use one over the other.

Charge your leisure battery while driving

How does split charging work?

Split charging works by connecting your starter battery to your leisure battery via a split charger. The split charger acts as a switch. When your engine is running it feeds the excess energy generated by your van’s alternator to your leisure batteries. This ensures you can keep the lights running for longer when you stop.

When you do stop and shut off the engine, the connection between the two batteries is disconnected and no charging can occur.

If we want to get a little more technical, when you start the engine the van’s alternator generates around 14.4v which is higher than your vans starter battery and therefore a current can flow to start charging. This voltage jump is also detected by the split charging device allowing charging.

Most Split chargers are fitted with an automatic switch to turn on once your starter battery is sufficiently charged. This ensures your starter battery always has enough power to start your van.

Different types of split charging

There are two main types of split chargers you need to consider :

Voltage sensing relays – A VSR starts to charge your leisure battery only when the started battery has reached a certain voltage. When the ignition is switched off the circuit is cut and it stops charging. VSR’s are a simple and effective technology to charge your leisure battery but they have some limitations. 

VSR’s are not recommended when charging lithium batteries due to the different charging cycles required. They are also incompatible when used with smart alternators. Do you have a smart alternator? Read our complete blog to find out.

DC-DC Charger – The most efficient way to charge your leisure battery while driving is to use a DC-DC charger. These are fast charging and usually have built-in safety mechanics to protect your batteries from overcharging. They are also compatible with vehicles fitted with smart alternators. The downside is that they are more expensive.

There is also a third type you might come across called Ignition Triggered relays. These devices use an electromagnetic coil to pull a set of contacts to make or break a circuit but only when the voltage is above 12v. This usually happens when the ignition is started. However, we do not recommend using these for split charging.

What type of split charger should I install?

The recommended split charging technology is based on the type of leisure battery installed and the type of alternator fitted in your vehicle. 

Lead acid/AGM Battery –  You can use either a VSR or a DC-DC Charger.

Lithium-ion Battery – You will be required to use a DC-DC charger to help protect your batteries.

Smart Alternator – You will be required to use a DC-DC charger.  The variable voltages of a smart alternator are not compatible with older voltage sensing relay (VSR) chargers. 

Traditional Alternator – You can use both types of split charging. VSRs are often the cheaper option.

You can do a quick test to find out if you have a smart alternator.

What type of split charger should i use?

How does a VSR work?

Voltage sensing relays are simply devices. When your starter battery voltage reaches 13.7V, the VSR engages. This allow your starter battery to charge while driving.

When the ignition is turned off your starter battery voltage will drop dis-engaging the VSR so no current can flow.

How does a DC-DC charger work

DC-DC chargers have a cut-in and cut-out voltage for when to charge your leisure battery. 

Unlike VSRs, the voltage delivered to your leisure battery can be finely tuned. This protects your battery from the variable voltage delivered by smart alternators. It also allows for lithium-ion batteries to be charged safely and to the correct voltage.


Complete DC-DC charger systems

Unsure sure exactly what you need for your DC-DC system? Look no further.

All our DC-DC charging systems come with all the wires, fuses, lugs and heat shrink you need to install in your campervan… 

Learn More

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