This page is only to give a brief overview of charging
circuits for vehicle etc.
Whilst the drawings can be used
as working drawings to carry out an installation, they are
also intended to show the simplicity of some of the Sterling
Split charge relay
additional battery can be quite simple, however some people are
concerned about flattening their engine starter battery (vehicle
battery) as well as their auxiliary battery. Its quite
simple to safely keep batteries isolated from one another when the
engine is not running, thus preventing accidental draining of the
vehicle battery. This is done by using a relay that is activated from
the alternator. This simple circuit is commonly known as a 'split
charge relay circuit'
I have tried to make the following drawing as
simple as possible.
have coloured the main cable red which is most likely the same as your
vehicle, however the other vehicle cables will be a variety of colours.
The terminal numbers above are the standard numbers found on
automotive relays. Terminals 85 & 86 are the coil, which activates
the relay. Terminals 30 & 87 are the switch contact terminals.
all you need to do is identify the cable which runs from the
alternator to the warning light on the dash board. Rather than pull
your dash to bits, it may be easier to have a look at the cables on
the back of the alternator. You'll find one or two large cables which
will be the cables which run back to the battery. You will also find
one smaller cable which is the charge indicator cable (no doubt
someone will come up with some exceptions)
you've identified the charge light cable, its a simple mater of
connecting it to the one side of the coil on a 12 volt relay (assuming
your vehicle is 12 volts), the other side of the coil is then
connected to an earth point (which eventually goes back to the
negative terminal on the battery).
drawn the above with 30 amp fuses in line with the battery link cable
(do make sure the cable between the vehicle and auxiliary battery is
capable of handling 30 amps, otherwise you can quite easily create a
This size is normally sufficient, however if you have a really dead
flat second battery they may blow. Don't increase the fuse size unless
your cable and relay are rated for higher currents.
above is reasonably reliable, however some alternators don't like
additional loads being applied to its charge indicator circuit, in which
case the alternator not only fails to charge, but also fails to activate
the split charge relay. In this situation a voltage sensing relay could
We presently don't stock these relays
as split charge diodes are so much better, however we are looking at
another relay available which is more expensive than the above plain
relay, however it consists of some electronics to activate a relay to
connect the two batteries together.
relay input is basically connected to a live cable on the vehicle,
preferably the main battery feed. The relay output cables are then
connected up to your auxiliary battery (no need to run a cable to the
alternator charge indicator wire).
relay operates by sensing the vehicle voltage, as the voltage to the
vehicle battery will rise when the alternator is producing power, when
the relay senses an increase in voltage, it activates its contact to
allow power to the auxiliary battery.
We don't stock these relays
as split charge diodes are so much better
There is now another way to split the charging
of your batteries. Instead of using relays, its now possible to use a
split charge diode block. The first units produced did use actual
diodes, whilst the units worked, they were not efficient due to the
voltage drop of around 0.8 - 1.2volts, this doesn't sound a lot, but in
terms of charging batteries it is quite a drop. To overcome this
voltage drop, the modern units as supplied by Sterling use clever
circuitry with mosfets, the result is that the voltage drop is now
lowered to around 0.04volts
Split charge diode blocks any problems
associated with the above relays and provide a good positive supply to
both battery banks, whilst maintaining total isolation between them.
The split charge
diode blocks are incredibly easy to install, as shown in the following
The best way to install this unit,
and to avoid any changes to the vehicles wiring, is to disconnect the
main feed cable off the back of the alternator, thoroughly insulate it
and tie it out of harms way with something like cable ties. You can now
run a fresh cable from the alternator to the diode block, and two more
to the two batteries. Basically that's it.
using the above method, its very easy to remove the diode block an
re-instate the original wiring.
to our split diodes
Having now fitted the above split charge block, its a good idea to fit an
advanced regulator to the charging circuit. This extra (Smart Regulator) will
then give the optimum charge rates for your batteries and will also take
care of any voltage/power loss in your charging system.
This system does required the removal and
stripping the alternator to add additional cables. Yes its quite
technical to strip the alternator, but
the end result is worth the effort.
It is possible to fit the advanced
regulator and use a split charge relay, but could cause problems with
the voltage regulation, so not recommended.
combined wiring of the split charge block and advanced regulator is
Go to our Advanced Alternator Regulator
To Battery Charger (A2B Charger)
Obviously not everyone wants to get involved with stripping alternators, well there is a far
easier route which combines the benefits of a split charge diode and
advanced voltage regulation, by using Sterling's Alternator to Battery Charger.
The A2B unit combines all the
above circuits shown above devices into one tidy package, and the good thing is,
it only requires the installation of four cables (Three main cables,
plus an earth). If you were paying someone to install a system for you,
go for this combined unit as the extra cost would be set against the
time to install the unit. However if your doing the work yourself, the
previous systems would work out cheaper.
combined unit can easily be configured (using switches) to take account
of the types of batteries your using. Its capable of charging 5+ times
faster and put an extra 50% extra power in to your batteries. Think
about this for a moment, why buy extra batteries, which will take a
while to recharge, when you can fit this to reap long term benefits!
easiest way to install the A2B unit is the same as described
above to install the split charge diode block.
Go to our
Alternator To Battery Charger
to Battery Charger with Hook-up Charging
Using Sterling's Battery to Battery charger is
probably as simple as it gets. There's no need for anything additional, as the
B2B unit does it all. The unit detects when there is spare power (when the
engine/alternator is running), and uses that spare power to charge the
house/second battery at the correct voltage and rate. What could be
It's worth pointing out that the B2B unit will
not drain the starter battery, as it effectively relies on the surplus power of
the alternator to charge the second battery, so you'll always have power to
start your engine.
Having installed a B2B unit, then installing one
of Sterling's Pro Budget battery chargers to the main starter battery, will give
you dual battery charging capability. The mains battery charger will charge the
starter batter, the the B2B unit will detect spare charging capacity, and use
the spare capacity to charge the house/second battery. This set-up will also
allow you to use 12 volt appliances whilst on hook-up.
The B2B is quite and advanced unit and although
described in its simplist form above, its quite advanced. For a more in depth
description of the B2B unit click
Go to our
Battery To Battery Charger
The manufacturer (Sterling) have done a lot of research into
their products and their use with various batteries. Their recommendations
for batteries is to stick to standard lead acid batteries,
rather than gel, leisure, carbon fibre etc. as they have found
no benefit for the extra expense. The down side to them is
that they don't charge as quickly as standard batteries. They
recommend standard lorry batteries, we have found tractor
batteries to be as good. In fact we have found they are
dramatically cheaper than using ordinary vehicle batteries.