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Battery Generalities
06
Generalities Concerning Batteries
• A battery is a container in which an electric power is stored in chemical form.
This energy is restored in the form of D.C. current.
• The application on its terminals of voltage produced by an alternator or by a
charger creates a current which modifies the composition of its elements by the
phenomenon of electrolysis: the battery accumulates energy.
• When the direction of the chemical reactions is reversed (when the energy
of the battery is consumed) the battery restores the accumulated charge,
functioning as a generator of D.C. current.
Operation of a Battery
HOW DOES IT FUNCTION?
• A 12V battery consists of 6 elements of 2V each assembled in series in a
“polypropylene container”. A 24V battery results from the connection in series
of 2 batteries of 12V or 4 batteries of 6V.
• In each element, 2 plates out of lead covered with active matter are put in
opposite polarity in an electrolytic solution containing sulphuric acid and
distilled water.
• This coupling of plates generates a potential difference of 2 Volts. The process
of charging/discharging consists of a migration of the “active matter” from the
lead plate towards the electrolyte and vice-versa.
3 Battery Families
3 FAMILIES OF BATTERIES FOR 3 TYPES Of USE:
• Starting Batteries: Classically used in automobiles (low price). They can
produce high intensities (100 to 1,000A) for short periods. These batteries do
not tolerate being discharged deeply.
• Stationary Batteries: Can undergo a great number of discharge cycles.
The discharge can be as much as 80% of the capacity. They are often used for
alarms, for example.
• Traction Batteries: for strong discharge currents, long and significant levels of
discharge (material handling equipment such as forklifts, for example).
Gel Batteries
2 BATTERY TYPES:
• Batteries with Liquid Electrolyte: Generally speaking, “open” batteries can
lose their electrolyte over time. They require maintenance and can release
acid in the event of reversal (corrosion!). These batteries now exist with
“maintenance free” stoppers which limit the losses of electrolyte.
• Gel Batteries (Maintenance Free): The electrolyte is fixed in a gel. They can
be turned upside down without any loss of liquid. These batteries are more
expensive and have lower performance than batteries with free electrolyte.
Preconditions to Charging
• Checking the Charge State: This is performed by measurement of the no-load
voltage of the battery. In order to do this the battery must not be used for
several hours prior. A battery having a no-load voltage of 12.8V is considered
as 100% charged. At 12V the battery is 90% discharged. Checking can also be
performed by weighing the density of the electrolyte using an “acid scale”. It is
a more difficult (due to the handling of the acid) but reliable method.
• Charge Intensity: The recommended charging current is approximately 1/10th
of the capacity of the battery (i.e. 10A for a battery of 100Ah). Beyond this level
the charger could deliver too much current, which does not ensure an effective
charge. It is not possible to completely charge a lead-acid battery in 1 hour!
Comparing Battery Chargers
• Automatic chargers guarantee the protection of the on-board electronics of
vehicle accessories when charging batteries still connected to the vehicle.
Traditional chargers do not!
• Average Current (Adc): This is the actual value officially and internationally
recognized by European standards (in EN 60335-2-29). This is not the effective
(RMS) value indicated on most chargers, including ABSAAR chargers. The RMS
value stated on most chargers is generally 1.414 times the Adc value, rounded
up or down with a margin of 10%. It does not make it possible to charge of the
more important batteries.
Charging Current Selection
• The nominal voltage of the battery charger must correspond to the nominal
voltage of the battery.
• The charging current must meet the requirements of the battery, because it is
a function of the capacity.
• The only important current for charging is the average value of the current, which
is also called Arithmetic Value, or Adc.
• It determines the amount of time required to charge the battery.
Short rule:
Charging current (AMPS DC) = Capacity of the battery (Ah)
10
Example:
Charging current for a battery of 60Ah is 60Ah = 6 Adc
10
Note : With a charger of this value (example 6Adc) a 50% empty battery
can be charged in 12 hours (also referred to as over-night charging).
6Adc * 1.414 = 8.48A RMS.
Comparing Jump Starters
•
Starting Current: In order to compare jump starters it is necessary to look
at the average current at the time of starting at 1V per element. For a 12V
battery that amounts to knowing the current at 6V. An automobile with a petrol
engine consumes approximately 300A at the time of starting (400A with a
diesel engine). For purpose of comparison, an agricultural tractor consumes
approximately 650A.
•
Short-Circuit Current: The value of the short-circuit starting current (under 0V
per element) is usually provided by the manufacturer. It is provided only as an
indication, because under 0V the car’s starter does not turn. For an ABSAAR
SL60 the starting current is 441A and the short-circuit current is 540A.