14-02-2013, 09:16 AM
A GUIDE TO BATTERY CHARGING
[attachment=50780]
Charging a Battery
There are many types of battery but batteries on boats are nearly always LEAD-ACID types -
similar to car batteries but heavier duty.
A BATTERY is made up of a number of CELLS.
A LEAD-ACID CELL generates around 2 volts. Small batteries contain 6 cells in a container
which add together to give 12 volts at the terminals. Larger cells are quite heavy and
individual CELLS are connected together 'in series' to make batteries of either 12 volt (6 cells)
or 24 volt (12 cells).
Although a battery is called a '12 volt' battery, its voltage varies from about 12.6 volts down to
10 volts when it is discharging and can rise to 15 or 16 volts during charging. It is very
important, however, to limit the maximum battery voltage during charging otherwise the
battery will be damaged. The battery voltage should not exceed 13.8 volts for long periods
and 14.4 volts for short periods (8 hours maximum).
Types of Charger
There are several types of electronic circuitry used within battery chargers for the marine
market
FERRO-RESONANT (or CVT)
These use a low-frequency MAGNETIC control system, which makes them very HEAVY, very
BULKY and are also only available with a poor FLOAT charge characteristic, therefore very
SLOW recharging. They can also generate a large magnetic field which can upset other
equipment on board. On the plus side, they are CHEAP and RELIABLE due to the low
number of components used and they tend to appeal to boat-builders who put price at the top
of their list of priorities.
LINEAR CHARGERS
These also use a low-frequency transformer to reduce the input voltage to a lower level, but
they then use transistors to control the current and voltage fed to the battery. This technique
can be used for either FLOAT or 3-STAGE chargers but is very IN-EFFICIENT and therefore
HOT, HEAVY and BULKY. The biggest drawback is a LIMITED INPUT VOLTAGE range - not
ideal for running from a generator or some marina supplies.
SWITCHED MODE CHARGERS
These are more complicated than the previous two types and use the techniques perfected
for and now universally used in computers and televisions. The AC input is first turned into
high-voltage DC. It is then turned into high-frequency AC using special types of transistor and
a high-frequency transformer (one thirtieth the weight of a low-frequency transformer!)
reduces the voltage to the exact level needed to charge the battery. A sophisticated control
circuit produces an overall design with HIGH-EFFICIENCY, SMALL SIZE and LIGHT
WEIGHT. The extra complexity adds to the initial cost but results in lower running costs and
the ability to run from a SMALLER (and cheaper) GENERATOR if required. Switched mode
chargers can be either FLOAT or 3-STAGE types.
VOLTAGE SENSING
The thickness of cables joining a charger to a battery should be chosen to keep the voltage
drop on the cable very low. However, any drop in the cable will increase the re-charging time
to some extent. For the ultimate performance, the charger should control the voltage at the
battery not at the charger. This is achieved by taking a thin cable from the battery positive
terminal to a remote voltage sense terminal on the charger. Some chargers have this feature,
others do not. It becomes increasing important at higher currents.
6. Power Factor Correction (PFC)
Although the AC mains voltage is a smoothly-changing waveform called a SINE-WAVE, the
current taken from the mains by most battery chargers, T.V.s and computers consists of
narrow peaks of current. This is inefficient for the power generating companies and, with the
proliferation of T.V.s and computers in particular, the EC have considered enforcing the
addition of an extra circuit called a POWER FACTOR CORRECTION circuit to smooth out the
peaks. The date for introduction of this has already been postponed twice but it will eventually
become compulsory. In the meantime, PFC is beneficial on a boat because it uses the mains
power very efficiently and will therefore run from a smaller generator or poor marina supplies
which non-PFC chargers might struggle with.
DC-DC Converters
Some equipment is only available for 12 volt operation. If the boat's main battery is 24 volt,
there are three options to run 12 volt equipment on board
1.Install a separate 12 volt battery with its own 12 volt mains battery charger.
2.Use a DC-DC converter to generate 12 volts using energy from the main 24 volt battery.
3.Install a separate 12 volt battery and charge it using a DC-DC converter from the main 24
volt battery. This requires a 13.8 volt output converter designed for the purpose.
For options 2 and 3 it is useful to have a remote on/off switch otherwise the DC-DC converter
could drain the 24 volt battery whenever the 24 volt battery is not being charged.
Battery Charger Installation
1. The INPUT to the charger is AC mains voltage and is capable of causing death. A circuit
breaker of suitable rating MUST be fitted between the charger and the shore power in
accordance with good marine installation practice. If the charger is replacing an existing
charger, then this should already be in place.
2. The BATTERY itself stores large amounts of energy and is quite capable of causing a fire
or explosion if the output terminals are shorted together. Extreme care must be taken when
wiring the charger to the battery. Cables should be of suitable thickness for the current rating
for the charger, cable runs should be kept as short as possible and all cables must be
securely held in place with cable fixings to prevent wear to the cable insulation.
3. The charger should be securely fixed to a vertical surface using ALL mounting hole
positions ( 3 for BCM, 4 for BCH and BCO).
4. At least 75mm clearance must be left all around the charger to allow the free flow of air over the
charger. The ventilation holes or slots must not be obstructed in any way.
5. The chargers should be protected from water and spray.
[attachment=50780]
Charging a Battery
There are many types of battery but batteries on boats are nearly always LEAD-ACID types -
similar to car batteries but heavier duty.
A BATTERY is made up of a number of CELLS.
A LEAD-ACID CELL generates around 2 volts. Small batteries contain 6 cells in a container
which add together to give 12 volts at the terminals. Larger cells are quite heavy and
individual CELLS are connected together 'in series' to make batteries of either 12 volt (6 cells)
or 24 volt (12 cells).
Although a battery is called a '12 volt' battery, its voltage varies from about 12.6 volts down to
10 volts when it is discharging and can rise to 15 or 16 volts during charging. It is very
important, however, to limit the maximum battery voltage during charging otherwise the
battery will be damaged. The battery voltage should not exceed 13.8 volts for long periods
and 14.4 volts for short periods (8 hours maximum).
Types of Charger
There are several types of electronic circuitry used within battery chargers for the marine
market
FERRO-RESONANT (or CVT)
These use a low-frequency MAGNETIC control system, which makes them very HEAVY, very
BULKY and are also only available with a poor FLOAT charge characteristic, therefore very
SLOW recharging. They can also generate a large magnetic field which can upset other
equipment on board. On the plus side, they are CHEAP and RELIABLE due to the low
number of components used and they tend to appeal to boat-builders who put price at the top
of their list of priorities.
LINEAR CHARGERS
These also use a low-frequency transformer to reduce the input voltage to a lower level, but
they then use transistors to control the current and voltage fed to the battery. This technique
can be used for either FLOAT or 3-STAGE chargers but is very IN-EFFICIENT and therefore
HOT, HEAVY and BULKY. The biggest drawback is a LIMITED INPUT VOLTAGE range - not
ideal for running from a generator or some marina supplies.
SWITCHED MODE CHARGERS
These are more complicated than the previous two types and use the techniques perfected
for and now universally used in computers and televisions. The AC input is first turned into
high-voltage DC. It is then turned into high-frequency AC using special types of transistor and
a high-frequency transformer (one thirtieth the weight of a low-frequency transformer!)
reduces the voltage to the exact level needed to charge the battery. A sophisticated control
circuit produces an overall design with HIGH-EFFICIENCY, SMALL SIZE and LIGHT
WEIGHT. The extra complexity adds to the initial cost but results in lower running costs and
the ability to run from a SMALLER (and cheaper) GENERATOR if required. Switched mode
chargers can be either FLOAT or 3-STAGE types.
VOLTAGE SENSING
The thickness of cables joining a charger to a battery should be chosen to keep the voltage
drop on the cable very low. However, any drop in the cable will increase the re-charging time
to some extent. For the ultimate performance, the charger should control the voltage at the
battery not at the charger. This is achieved by taking a thin cable from the battery positive
terminal to a remote voltage sense terminal on the charger. Some chargers have this feature,
others do not. It becomes increasing important at higher currents.
6. Power Factor Correction (PFC)
Although the AC mains voltage is a smoothly-changing waveform called a SINE-WAVE, the
current taken from the mains by most battery chargers, T.V.s and computers consists of
narrow peaks of current. This is inefficient for the power generating companies and, with the
proliferation of T.V.s and computers in particular, the EC have considered enforcing the
addition of an extra circuit called a POWER FACTOR CORRECTION circuit to smooth out the
peaks. The date for introduction of this has already been postponed twice but it will eventually
become compulsory. In the meantime, PFC is beneficial on a boat because it uses the mains
power very efficiently and will therefore run from a smaller generator or poor marina supplies
which non-PFC chargers might struggle with.
DC-DC Converters
Some equipment is only available for 12 volt operation. If the boat's main battery is 24 volt,
there are three options to run 12 volt equipment on board
1.Install a separate 12 volt battery with its own 12 volt mains battery charger.
2.Use a DC-DC converter to generate 12 volts using energy from the main 24 volt battery.
3.Install a separate 12 volt battery and charge it using a DC-DC converter from the main 24
volt battery. This requires a 13.8 volt output converter designed for the purpose.
For options 2 and 3 it is useful to have a remote on/off switch otherwise the DC-DC converter
could drain the 24 volt battery whenever the 24 volt battery is not being charged.
Battery Charger Installation
1. The INPUT to the charger is AC mains voltage and is capable of causing death. A circuit
breaker of suitable rating MUST be fitted between the charger and the shore power in
accordance with good marine installation practice. If the charger is replacing an existing
charger, then this should already be in place.
2. The BATTERY itself stores large amounts of energy and is quite capable of causing a fire
or explosion if the output terminals are shorted together. Extreme care must be taken when
wiring the charger to the battery. Cables should be of suitable thickness for the current rating
for the charger, cable runs should be kept as short as possible and all cables must be
securely held in place with cable fixings to prevent wear to the cable insulation.
3. The charger should be securely fixed to a vertical surface using ALL mounting hole
positions ( 3 for BCM, 4 for BCH and BCO).
4. At least 75mm clearance must be left all around the charger to allow the free flow of air over the
charger. The ventilation holes or slots must not be obstructed in any way.
5. The chargers should be protected from water and spray.