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
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
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!