Split charge systems and relays

Online resource for 12 volt and 24 volt split charge relays, systems and wiring kits. Your leisure/auxiliary battery bank split charging requirements made simple.

 

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Split Charge Systems

Why do I need a split charge relay?

 

Not only will the split charge relay/system recharge the leisure battery while the engine is running it will also stop current being drawn from the starter battery when the engine is switched off (ensuring you will be able to start your vehicle) should the leisure/auxiliary bank run out of power.

How do I fit a split charge relay?

 

The Smartcom relay doesn't require an alternator connection, you simply wire it from your starter battery to the leisure battery and a separate wire to the fridge if required (either via the 12S towing socket on caravans, or direct to the leisure battery/fridge on campers and motorhomes)

If your vehicle is relatively new and has a complicated engine management system we would recommend using the voltage sensing split charge relay which is easy to fit and requires no connection to the vehicle electrics. Simply wire the relay from your starter battery to your leisure battery. For older vehicles where the split charge relay has a trigger wire (usually the alternator warning light).

Always fit suitably rated fuses close the both the starter battery and the leisure battery.

Split charge relays/systems FAQ’s

What size leisure battery do I need?

 

The Amp hour rating denotes the amount of energy that can be taken from a battery before the terminal voltage falls below 10.8 volts. This test is usually carried out over a 20 hour period (20 hour rate). Thus a 50 Amp hour battery can be discharged at 2.5 amps for 20 hours before the voltage drops below 10.8 volts (i.e. 20 x 2.5 = 50). With leisure batteries Amp hours is often abbreviated to amps (e.g. 85 amp leisure battery). For further explanation of volts, watts and amps click here.

What’s a battery to battery (DC to DC) split charger?

 

Battery to battery split charging systems are easy to fit and will ensure that the vehicle's starter battery system is at full charge before switching to fast charge the leisure/auxiliary battery system while the engine is running. Ideal for those who use a lot of battery power where no electric hook-up is available.
They are also very simple to fit as these units only needs wiring from the starter battery to the leisure battery. No connection to the alternator is required.

How do I choose the right split charger?

 

If your battery power consumption is light and your leisure battery is around 80Ah or less choose a split charge relay of, say, 30 - 70 amps. For medium battery power consumption and leisure batteries of up to 120Ah go 70 - 100 amps and for high consumption and larger leisure battery banks go a 100 amps +. Alternatively, you could choose from one of our range of Ctek D250S, Ctek D250S Dual and Durite micro-processor controlled battery to battery chargers which work differently to conventional split charge relays.

What does voltage sensing/sensitive relay mean?

 

Voltage sensing split charge relays are is easy to fit and require no connection to the vehicle alternator or other electrics. The relays sense when the starter battery is at full charge and then switch to charge the leisure battery. Simply wire the relay from your starter battery to your leisure battery. This also avoids any vehicle warranty issues.

The relays cut in at 13.7 volts, making sure the starter battery is at full charge first, and cut out at 12.8 volts ensuring that the starter battery cannot be discharged when the leisure battery is out of power and that your vehicle will always start!

Why do I need a split charge relay?

How do I choose the right split charger?

What does voltage sensing/sensitive relay mean?

What’s a battery to battery (DC to DC) split charger?

What size leisure battery do I need?

How do I fit a split charge relay?

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