Starter batteries

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Starter batteries
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Starter batteries

• The battery is a chemical accumulator which
  stores the electricity generated by the
  alternator while the engine is running.
• The stored electricity is needed to start the
  engine and to supply the electrical equipment in
  the vehicle's electrical system.

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1. Battery design

• the vehicle electrical system comprises the
  alternator as energy generator, the battery as
  energy store, and the starter and other loads as
  consumers.
• Electrical load requirements
• Alternator current output
• Engine speed when the vehicle is actually being
  driven
• Charging voltage and
• Starting temperature

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1.1 Electrical loads

• the starter, the ignition, and the lighting
  system which were the major loads.
• electronically controlled ignition and
  fuel-injection systems, comfort and convenience
  systems using a variety of different drive
  motors, and safety and security systems.

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1.1.1 Starting systems

• The starter must crank the internal combustion
  (IC) engine at a given minimum speed and, after
  the first ignitions, bring the engine up to the
  minimum self-sustaining speed.
• Even though the starter is only switched on for a
  brief period, it has the highest current
  consumption of all the loads

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1.1.2 Further electrical loads

• Permanent loads (e.g. ignition, fuel injection
  and/or engine management)
• Long-time loads (e.g. lighting, heated rear
  window) and
• Short-time loads (e.g. turn signals, stop lamps)

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1.2 Operating conditions

• test vehicles are operated under extreme
  conditions
• battery characteristics
• freedom from maintenance, vibration-resistance,
  and resistance to deep cycling

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1.2.1 Starting temperature

• If the engine is to be started for instance at
  temperatures as low as -20 C, it is imperative
  that the battery has a minimum charge state.
• In Europe, for instance, the following minimum
  start temperatures are stipulated
• Passenger cars -18...-25 C,
• Trucks and buses -15...-20C,
• Tractors -12...-15C.

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1.2.2 External loading

• On commercial and industrial vehicles (passenger
  cars and trucks), and for special off-road
  applications such as ski-slope preparation, etc.,
  the short distances involved, together with the
  effects of vibration and shock, often result in
  very high external loading

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1.2.3 Climatic loading

• batteries are exposed to the effects of damp,
  dirt, oil, temperature, etc. and must also be
  able to cope with the specific climatic demands
  of the application in question.

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1.2.4 Installation point

• Regarding the installation point, the following
  critera are important
• Easy access for battery installation
• Protection against excessive battery heat-up
• Protection against excessive battery cooling
• Protection against damp
• Protection against mechanical damage (e.g. due to
  excessive vibration). The battery must be
  securely fastened and not be subjected to
  vibration
• Protection against oil and fuels, etc.

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• in the engine compartment, short lines can be
  used between battery, alternator, and starter so
  that voltage losses are kept to a minimum.
• The battery should not be exposed permanently to
  temperatures above 50 C, or its service life
  will be reduced (high levels of self-discharge).
• adequate ventilation must be provided around the
  battery for acid fog
• completely maintenance-free battery

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1.2.4.1 Impact of engine speed

• The battery charge largely depends on how the
  vehicle is driven (e.g. in traffic jams,
  stop-and-go, or without stopping).
• Driving mode acts on the engine rotational speed
  which the engine transfers to the alternator.
• Power generation in the alternator increases, the
  higher the engine speed.
• Long waiting times in traffic jams and at traffic
  lights, when the engine is only running at idle,
  result in low alternator rotational speeds and a
  low charge current.
• In addition, an automobile that is not driven on
  long over-land trips will have a poor battery
  charge balance.

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1.3Power demand1.3.1Standard version

• Winter commuter traffic with day and night
  driving for 2 weeks, of which 1 week is at 0 C
  and the other at -20 C
• The battery's residual capacity is to be at
  least 50 after completing these driving
  schedules
• The following must still function
• - Starting at-20 C
• - The parking lamps for 12 hours
• - The hazard-warning and turn-signal system must
  operate for 3 hours
• - All loads which operate with the key removed
  must run for 2 hours. It must then be possible to
  start the engine.

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1.3.2 Auxiliary equipment

• comfort and convenience systems with additional
  servomotors for roof and power-window drives,
  seat and steering-wheel adjustment as well as
  seat heating, air-conditioner, cooler unit or
  similar

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1.4 Retrofit equipment1.4.1 Auxiliary loads

• Sophisticated, high-performance car radio and
  audio systems with high power demands
• Auxiliary lamps and high-mounted stop lamps,
  fanfare horns, floodlamps and spot lamps, alarm
  system
• Auxiliary heating system
• Connection of equipment powered by the vehicle's
  battery through the cigarette lighter, for
  instance. These include small-power compressors,
  small lamps, and floodlamps
• Trailers and caravans connected to the vehicle's
  electrical system

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1.4.2 Increased power demand

• in order to power the above-mentioned auxiliary
  loads the original starter battery cannot simply
  be lifted out and replaced by a battery with a
  higher Ah capacity

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1.5 Extreme operating conditions

• It is impossible to completely cover the wide
  range of different operating conditions which can
  be encountered in the field with one single
  standard battery.
• Such a battery would be far too large for normal
  operation and far too expensive.

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1.5.1 Outside temperatures

• Batteries with higher starting power are needed
  for cold countries with very low temperatures,
  where starting must often take place at below -20
  C.

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1.5.2 Mechanical and cyclical loading of the
battery

• bus, taxi, ambulance, delivery van, etc. are
  repeatedly driven only short distances
• This leads to severe cyclical loading of the
  battery which is supplemented by further cyclical
  loading due to high power demands with the
  vehicle stationary
• off-road vehicles, commercial vehicles,
  construction machines, and tractor vehicles, and
  those in agriculture and forestry applications,
  must withstand high vibration and impact stresses
  during off-road operation and on building and
  construction sites.

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2.Method of operation

• This energy of starter battery must be made
  available to start the engine again after it has
  been switched off.
• the battery must be able to deliver a high
  current for a brief period in order to start the
  engine
• supply some or all of the electrical energy to
  other important components in the vehicle's
  electrical system
• absorbs voltage peaks in the vehicle's electrical
  system
• lead-acid storage battery suffices for meeting
  these demand
• 12 V for passenger cars, and 24 V for commerical
  vehicles

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2.1 Electrochemical processes in the lead storage
cell2.1.1 Generation of the cell voltage

• If a lead electrode is immersed in dilute
  sulfuric acid (the electrolyte), it has a
  negative potential referred to the electrolyte.
• If lead Pb and lead dioxide Pb02 are immersed
  in a common electrolyte, The difference in
  potential between the electrodes themselves is
  the cell voltage.
• If an external voltage is applied across the
  electrodes, it recharge the lead-acid storage
  battery

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2.1.2 Charging

• To charge the lead storage cell, its positive
  electrode is connected to the positive pole of a
  DC source, and its negative electrode to the
  negative pole.
• In a charged cell, this is normally ? 1.28 kg
  /l corresponding to an electrolyte comprising
  about 37 sulfuric acid and about 63 water.
• This means that the state of charge can be
  determined by measuring the electrolyte's
  specific gravity.

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• Charging is complete when
• - the lead sulfate at the positive electrode has
  converted to lead peroxide (Pb02), and
• - the lead sulfate at the negative electrode has
  converted to metallic lead (Pb), and when
• - the charge voltage and the electrolyte's
  specific gravity remain constant even though
  charging continues.
• If charging is continued at finished
• - electrolytic decomposition of the water. Oxygen
  is formed at the positive plate and hydrogen at
  the negative plate. The battery is said to be
  "gassing".

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2.1.3 Discharge (current drain from the battery)

• If a load (e.g. a lamp bulb) is connected between
  the poles of a lead cell, due to the potential
  difference between the poles (cell voltage)
  electrons flow from the negative pole through the
  load to the positive pole.

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2.2 Parameters2.2.1 Overview

• The European standards EN 60095-1 and national
  standards define the specifications and test
  methods for starter batteries.
• the battery can deliver within 20 hours at
  constant discharge current down to a defined
  cutoff voltage per cell (nominal capacity K20).

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2.2.2 Cell voltage

• The cell voltage Uz is the difference between the
  potentials which are generated between the
  positive and negative plates in the electrolyte.
• These potentials depend on the plate materials
  and on the electrolyte and its concentration.
• The cell voltage is not a non-variable figure but
  depends on the state of charge (electrolyte
  specific gravity) and the electrolyte temperature.

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2.2.3 Nominal voltage

• For lead storage batteries, standards (DIN 40
  729) define the nominal (theoretical) voltage UN
  of a single cell as 2 V.
• The nominal voltage of the complete battery
  results from multiplying the individual cell
  voltages by the number of cells connected in
  series.
• According to the Standard EN 60095-1, the nominal
  voltage for starter batteries is 12 V.
• The 24 V required for truck electrical systems is
  provided by connecting two 12 V batteries in
  series.

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2.2.4 Off-load and steady-state voltage

• The off-load voltage is the voltage across the
  unloaded battery.
• a final value which is referred to as the
  steady-state voltage U0
• the steady-state voltage is also dependent upon
  the state of charge and the electrolyte
  temperature.

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2.2.5 Internal resistance

• The internal resistance Ri of a cell is composed
  of a number of individual resistances together.
• Ri1, the contact resistance between the
  electrodes and the electrolyte (polarization
  resistance)
• Ri2, presented by the electrodes to the flow of
  electrons
• Ri3, the electrolyte's resistance to the flow of
  ions.
• Ri4, the resistances of the individual cell
  connectors
• Ri Ril Ri2 Ri3 Ri4.
• For a fully charged 50 Ah battery for instance,
  at 20 C Ri is 5... 10 mO whereas at 50 charge
  and at -25 C it increases to about 25 mO.
• Ri together with the remaining resistances in the
  starter circuit determines the cranking speed
  when starting,

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2.2.6 Terminal voltage

• The terminal voltage UK is the voltage measured
  between the two terminal posts of a battery.
• It is a function of the off-load voltage and the
  voltage drop across the battery's internal
  resistance Ri
• UK IE Ri
• Since an unloaded, uncharged battery has a cell
  voltage of about 2 V and a steady-state voltage
  of about 12 V between the terminal posts, this
  means that for practical purposes measuring the
  terminal voltage of an unloaded battery provides
  an unreliable indication of its actual state of
  charge.

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2.2.7 Voltage at commencement of gassing

• The voltage at commencement of gassing (DIN 40
  729) is defined as the charge voltage above which
  the battery clearly starts to gas.
• According to VDE 0510, a voltage of 2.4...2.45 V
  per cell, for 12 V batteries, is 14.4...14.7V.
• 12 V standard battery limited 14.4 V (2.4V/cell)
• maintenance-free 12 V battery limit is 13.8 V
  (2.3 V/cell).
• gel batteries????? 14.1 V (2.35 V/cell) charge
  voltage, charging time of max. 48 h.

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2.2.8 Capacity2.2.8.1 Available capacity

• Capacity K is the product of current and time
  (ampere-hours Ah).
• the battery's Ah capacity is not a fixed
  parameter, but depends on the following factors
• The level of the discharge current
• Specific gravity and temperature of the
  electrolyte
• Discharging process as a function of time (higher
  when a pause than continuous)
• Battery age
• Is the battery moved around during use, or does
  it remain stationary (electrolyte stratification)

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• a discharge current of 2.2 A means that the
  available 44 Ah capacity can be used for up to 20
  h.
• At a temperature of 20 C, and with a mean
  starter current of 150 A, this leads within 8
  mins to the available capacity dropping to
  approx. 20 Ah.
• high discharge currents cause these processes to
  take place mostly on the surface of the plates

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2.2.8.2 Influence of temperature

• The reduction in Ah capacity and discharge
  voltage the lower the temperature, the less
  efficient are the electrochemical processes in
  the battery.
• with a wrongly dimensioned battery, there is the
  danger that at very low temperatures the engine
  is not cranked fast enough and long enough to
  start it
• At low temperatures the starting power needed by
  the engine is correspondingly higher due to the
  increase in frictional resistance in the engine

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2.2.9 Nominal capacity

• The nominal capacity K20 is the battery's rated
  Ah capacity.
• EN 60095-1, at a fixed discharge current of I20,
  within 20 hrs until final discharge voltage of
  10.5 V at 252C is reached.
• I20 K20/20 hrs.
• 44 Ah discharged 2.2 Am, at least 20 hours (44
  Ah/20 h 2.2 A), final 10.5 V

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2.2.10 Cold-discharge test current Icc (formerly
Ikp)

• EN 60 095-1, the battery-terminal voltage when
  discharging at Icc and -18 C measured 10 s after
  commencement of discharge must be at least 7.5 V
  (1.25 V per cell).
• at -18 C and fully charged 12-volt battery, it
  is given by Ri 4,000/Icc (mO),
• For an automotive battery which must provide the
  electrical energy for the starter, starting
  capabilities at low temperatures are usually more
  important than the Ah capacity.
• the cold-discharge test current is therefore a
  measure for starting capability.

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END