Product specifications

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There are different kinds of rechargeable batteries. The most
common and widespread type is the lead-acid battery. A less
familiar one is the nickel-cadmium (NiCad) battery, which can
still often be found in old emergency power systems. Due to the
complex charge method required by a NiCad battery, and the
fact that they are environmentally unsound, these batteries are
not suitable for use onboard a boat.
The principle of the lead-acid battery
A battery is a device that stores electric power in the form of
chemical energy. When necessary, the energy is again released as
electric power for DC consumers such as lighting and starter
motors. A battery consists of several galvanic cells with a voltage
of 2 Volt each. For a 12 Volt battery, six cells are linked in series
and fitted inside a single casing. To achieve 24 Volt, two 12 Volt
batteries are linked in series. Each cell has positive oxidised lead
plates and negative lead metal plates, and has an electrolyte con-
sisting of water and sulphuric acid. During discharging, the lead
oxide on the lead plates is converted into lead. The acid content
decreases because sulphuric acid is required for this process.
To recharge the battery, an external power source - such as a
battery charger, alternator or solar panel - with a voltage of
around 2.4 Volt per cell must be connected. The lead sulphate
will then be converted back into lead and lead oxide, and the
sulphuric acid content will rise. There are limits set for the
charge voltage to prevent the release of an excessive amount of
hydrogen. A charge voltage of more than 2.4 Volt per cell, for
instance, releases a lot of hydrogen gas, which can form a highly
explosive mixture with the oxygen in the air. The upper limit on
charge voltage for a 12 Volt battery is 14.4 Volt, and the corres-
ponding value for a 24 Volt battery is 28.8 Volt. The relationship
between how full a battery is and the specific gravity of the
water/sulphuric acid mixture is as follows:
Different types of battery - in terms of the thickness and number
of plates per cell - correspond to different applications. The
maximum current that can be delivered is determined by the
total plate surface. The number of times that a battery can be
discharged and recharged - the number of cycles - depends on
the thickness of the plates. A battery can feature either many
thin plates or a few thick ones.
The starter battery
A starter battery has many thin plates per cell, leading to a large
total plate surface. This type of battery is, therefore, suitable for
delivering a high level of current over a short period of time.
The number of times that a starter battery can be heavily dis-
charged is limited to around 50. But as starting the engine uses
only a small part of the energy stored (around 0.01%), the
battery lasts for many years. This type of battery is unsuitable for
cyclical use as a service battery. Mastervolt’s AGM and gel
batteries are suitable to be used as starter batteries.
The semi-traction battery
A semi-traction battery has fewer but thicker plates in each cell.
These batteries supply relatively less starter current, but can be
discharged more often and to a greater extent (approximately
300 full cycles). This kind of battery is highly appropriate for the
combined function of starter/service battery. Mastervolt
recommends to use maintenance free ‘deep cycle’ AGM or gel
batteries (see previous pages). It is important to charge the
batteries according to the appropriate charge characteristic.
The traction battery
This type of battery has even fewer, but very thick, flat or cylin-
drical plates. It can therefore be discharged many times and fairly
completely (1000 full cycles). This is why wet traction batteries
are often used in forklifts and industrial-grade cleaning machines.
But wet traction batteries require a special charge method.
Because these batteries are mostly tall, they are sensitive to the
accumulation of sulphuric acid at the bottom of the battery
container. This phenomenon is called stratification and occurs
because sulphuric acid is denser than water.
Your b a t tery as a p o w er sou r c e
Acid content increases in the lower part of the battery, locally
intensifying plate corrosion, and decreases in the upper part,
reducing capacity. The battery is discharged unevenly,
significantly reducing the life span. In order to spread out the acid
evenly again, the battery has to be purposefully overloaded using
excessive voltage. This generates a large amount of hydrogen gas,
which will form a dangerous mixture with oxygen in the air.
The voltage required to recharge these batteries is around 2.7V
per cell, or 16.2V for a 12V system and 32.4V for a 24V system.
These high levels of voltage are extremely dangerous for the
connected equipment and the large amount of gas generated
makes these batteries unsuitable for use on board boats.
Mastervolt recommends to install maintenance free 2 volt gel
cells. An appropriate charge protocol should be followed.
M
astervolt gel batteries.
percentage battery specific percentage
charged voltage gravity discharged
0% 11.64 Volt 1.100 100%
20% 11.88 Volt 1.140 80%
40% 12.09 Volt 1.175 60%
60% 12.30 Volt 1.210 40%
80% 12.51 Volt 1.245 20%
100% 12.72 Volt 1.280 0%
‘Sealed’ traction battery.
C Y C L I C V E R S U S L I F E S P A N
discharge in %
6
0% discharge at 800 cycli
Mastervolt gel starter battery
Parallel connection
Parallel coupling involves connecting the plus poles of multiple
batteries to each other and the same with the minus poles.
The plus of the first battery and the minus of the last battery are
then connected to the system. This type of arrangement is used
to increase capacity (in this case 400 Ah).
Series connection
Batteries are coupled in series to gain higher voltage, for instance
24 or even 48 Volt. The plus pole of each battery is connected to
the minus pole of the following one, with the minus pole of the
first battery and plus pole of the last battery connected to the
system.
Series/parallel connection
A combination of series and parallel connections is required if
you need for example a 24 Volt battery set with a higher capacity.
The battery should then be cross-wired to the system using the
plus pole of the first and minus pole of the last battery.
24 V/400 Ah series/parallel connection.
48 V/200 Ah series connection.
12 V/400 Ah parallel coupling.
24 V/200 Ah series connection.