Battery Master - keeps engine battery safely topped up from leisure battery
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The Battery Master keeps your engine starter battery safely topped up by linking
it to the leisure battery. Its automatic one-way action will pass a
small trickle charge to the engine battery whenever its voltage becomes
less than a defined level below that of the leisure battery, so that
the engine battery is kept in the best condition for easy starting and
a long service life.
The Battery Master will not allow any charge to flow
in the other direction, from the engine battery to the leisure battery.
Battery Master addresses an issue which is inherent in the way that modern
motorhomes are often equipped and used: the leisure battery gets a lot
of attention (naturally since it plays a vital part in running the equipment
which keeps you comfortable in the living area) but the engine battery
is left to fend for itself when the vehicle is not running.
Your vehicle is likely to be equipped with a hookup, and maybe a solar panel
or generator, which keep your leisure battery charged, and you'll probably
have instrumentation which monitors the state of charge of the leisure
battery. So the leisure battery can cope with long periods when the vehicle
is 'parked up' and not being charged from the engine alternator.
On the other hand, the engine battery is quietly being drained by small loads
which are drawn by the vehicle's standard electrical system even when
the vehicle is not being used, and by self-discharge. If you
have added an alarm system for the motorhome then that increases the
drain and the battery can lose charge quite quickly to a level where
starting is jeopardised. Batteries which are allowed to become
too discharged without prompt recharging will be permanently damaged.
And usually there is nothing to warn you that this is happening, since
the vehicle most likely does not have instrumentation to display the
engine battery's state of charge.
Battery Master has a maximum charging current of 1.1 amps which is designed
to cope with these low-level losses from the starter battery.
Fully waterproof, British made and designed, Battery Master is easy to install
and comes complete with instructions, and for fixing it has a self adhesive / velcro-type pad and tie wraps. It also includes a selection of cable connectors but you might need something different depending on your own installation conditions.
On the edge you can see the LED which signals red or green, depending on whether or not the unit is passing charging current to the engine starter battery
We decided to install a Battery Master in our own motorhome because its function offers
just what we want. Our motorhome is fitted with a sophisticated alarm
system which adds to the starter battery drain; we have
monitored the battery voltages and we find that after less than a week
of the vehicle not being driven, the starter battery voltage will fall
below 12.7 volts - a level at which the deterioration of battery service
In cold weather the drain is worse and this effect is exacerbated in extreme
weather when the vehicle is likely to be laid up for longer - if it's
freezing the roads are likely to be salted and we prefer to avoid driving
the motorhome on salted roads ...
The motorhome is fitted with a smallish (40 watt) solar panel which is more
than enough to maintain the leisure battery when the vehicle is parked
up; by fitting the Battery Master we are using the surplus output from
the panel to ensure that the engine battery is also maintained in peak
condition, automatically, without any intervention from us. Ah, peace
Fitting was very simple. The unit has three short leads which connect to the starter battery positive; the leisure battery positive; and to the vehicle earth (negative). The instructions advise that the ideal way of achieving this is to make the connection at the relay which controls the output of alternator current to the leisure battery when the engine is running: this relay is necessarily already wired to the positive terminal of the engine battery and the output side of the relay is likewise already wired to the leisure battery.
Our relay was located inside the living area close to the leisure battery and was easy to get at; an earthing point also was availabe close by so no extra wiring was required. All we needed was three crimp-on ring connectors for the wire ends. We used a basic multimeter to test the voltages either side of the relay: by comparing these with the voltages of the leisure and engine batteries we could be sure which side was which on the relay, before attaching the wires.
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