Lead Acid Batteries
Ampere Hours is?
(A/H) rating states the theoretical current the battery can supply in one hour
the electrolyte of a battery is what percentage of water and acid?
70% water and 30% acid
What is meant by "Cell Imbalance"?
A healthy battery should maintain approximately equal voltages across all its cells during discharge, and when fully recharged. Faulty batteries often develop problems in one or more cells that have a much lower terminal voltage than the rest.
what is the storage of a battery
Charge every 4 to 6 weeks. Charge and capacity check before returning to service. Capacity test new batteries every 6 months. Capacity test used batteries every 3 months. Insulation check every 12 months. Store batteries for no more than 18 months. Do not store in a discharged condition. Do not allow temperature to exceed 48°C. Record all maintenance.
How should exposed battery terminals be treated to prevent corrosion?
Coat exposed battery terminals with petroleum jelly or general purpose grease to exclude moisture, prevent corrosion and the formation of deposits on the terminals.
what four factors affect the capacity?
Plate area Amount of active material Quantity of electrolyte Temperature
leaving a battery permanently low discharged rate can what?
damage it
How should multiple batteries be charged using constant current charging?
multiple batteries are connected in series and the maximum supplied current is the capacity of the lowest battery
what is the charge of a cell when fully charge, but generally rated at
2.2V but usually rated at 2V
What is a typical constant voltage level used to charge a 24V battery?
28 volts
What SG readings indicate low charged lead acid battery state?
1.24 to 1.2
What SG readings indicate medium charged lead acid battery state?
1.275 to 1.24
What SG readings indicate high charged lead acid battery state?
1.3 to 1.275
what rate does the battery internal resistance increase?
Doubles
When should hydrometer readings be taken if water is to be added?
Hydrometer readings should be taken before adding water as it takes time for the additional water to mix thoroughly with the electrolyte allowing an accurate reading to be taken.
What capability does a battery require if used as an emergency power source?
Once airborne batteries often comprise the aircraft's emergency power supply and must be capable of operating emergency systems for thirty minutes. For these reasons aircraft batteries must be monitored for condition and replaced or serviced when required.
What can affect SG readings?
The two factors are temperature a impurities
what is the purpose of the vent cap?
allows gases to escape and you can check the electrolyte levels
what is a hydrometer?
an instrument that measures the relative density of a battery electrolyte compared to pure water. calibrated in SG
How does constant voltage charging current vary as the battery charges?
as the voltage of battery increase the current supplied drops off slowly
when charging several batteries together what can you do?
batteries of the same voltage can be charged together in parallel using the constant voltage method
how to calculate the internal resistance of a battery if? A battery containing 12 cells connected in series and charged to 2.1 V per cell delivers 6A of current into 4 Ohms resistance. Calculate the internal resistance of the battery.
calculate the terminal voltage 12 x 2.1V = 25.2V, use ohm's law to calculate the V = 6Ax4ohms = 24, voltage drop 25.2V - 24V = 1.2V, and internal resistance is 1.2V ÷ 6A = 0.2 Ohms
Why is moisture between the terminals undesirable?
can cause a current to flow and will discharge the battery of a period of time
what affect could be cause by moisture and / or dirt deposits between a lead acid Battery terminals?
could cause slow discharge of the battery
Why should lead acid batteries be kept in a high state of charge?
due to the heavy loading they are under, starting of engines requires a high charge state
how is the life of battery determined?
for example a 40 A/H battery should provide 20 Amps for 2 hours or 10 Amps for 4 hours.
When does a Lead Acid battery release the most gas?
gassing mostly occurs towards the end of the charging state
blue marks on a battery terminal hardware indicate?
high resistance is present due to loose hardware
How should multiple batteries be charged using constant voltage charging?
in parallel
What is excessive water consumption an indication of?
indication of overcharging, possibly a deflective cell or internal short
What causes slow loss of fluid from the electrolyte?
is caused by evaporation and decomposition during charging
terminal voltage is?
is determined by the number of cells in series
what is the standard rating used to specify the capacity of the battery?
is five hours
what does cold temperature to the battery current draw?
is reduces the chemical reactions
what is cold cranking amps?
is the maximum starting current a battery can provide
what main problem caused by sulphation in lead acid batteries is?
isolating the active material from the electrolyte
can multiple batteries be charged using the constant current method?
only if connected in series and limited to the lowest maximum charge current of any of the batteries being charged
what are the plates constructed of?
positive is lead peroxide and negative plate uses spongy lead
the main purpose of cell separators is to?
prevent the plates from touching
What type of water should be used when servicing batteries?
pure distilled water
Which temperatures require a correction of SG readings?
readings for temperature are not required between temperatures of 20 and 32°C(70 and 90° F). Outside of this range a correction chart must be referred to.
How high should the electrolyte level in the battery be?
should be same level just above the plates
what do you neutralize acid spills with?
sodium bicarbonate solution and rinse with water
what increases the internal resistance of a battery due to as it discharge?
sulphate forms on the outside of the plates. Not only is the amount of active material reduced, but the remaining surface area available for the electrolyte to react with is also reduced by the blocking effect of the sulphate.
what happens to the SG as the battery charges
the SG rises
What happens to the electrolyte during charging?
the acid content and density of the electrolyte increase
What advantage does a fully charged lead acid battery have in freezing conditions?
the electrolyte is less susceptible to freezing due to the increased density
How should acid and water be mixed when preparing fresh electrolyte?
the electrolyte should be mixed for cells that are dry, the acid should be added to the water and not the other way around, because will will float to the top and cause a violent reaction at the boundry
what determines the voltage of a battery?
the number of cells
What is the outer casing made of and why is there a space at the bottom?
the outer casing is made of hard rubber or high impact plastic. the sump in the bottom collects any sediment chamber that permits accumulation of lost plate material to prevent shorten of the plates
what is specific gravity?
the ratio of the weight of a substance to the weight of the same volume of pure water
what can determine the current delivery
the surface area of the plates as more chemical reactions can occur
what determines the capacity of a battery?
the thickness of the plates
how are the plates arranged?
they are arranged so that they are interleaved, with each positive plate sandwiched between two negative plates, the plates of each polarity are connected in parallel, and collectively connected to a terminal post plates of each polarity
What is the purpose of the separators?
they keep the plates apart while allowing electrolyte to contact the plates, channels are included to allow sediment to drop
what is the main reason why inter-cell hardware should be kept clean and properly torqued?
to prevent high resistance joints and heating
How should a battery's damaged painted surfaces be repaired?
touched up with acid resistance paint
when charging a battery typically you charge above the battery rated voltage true of false?
true
What effect does over-charging or heavy discharge have on a lead acid battery?
will result in excessive sulphation, heats the plates up and can cause shedding of the active material and also internal discharge
What test for cell imbalance can be performed on a battery installed in an aircraft?
• Crank the starter for three seconds • Turn on loads of about ten amps • Measure voltage of each cell good cells indicate 1.95 volts each and not more than .05volts difference
