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BATTERY TERMINOLOGY
PLATES/SEPARATORS/ELECTROLYTE
The basic principle of a battery is 'two dissimilar metals
immersed in an acid will produce an electric current'. The
metals used are lead dioxide for the positive plate and
'spongy' lead for the negative plate. To prevent a short
circuit between the two different plates, they are held apart
by a separator which must be highly porous to allow a
reaction between the plates. Electrolyte is the term used for
Dilute Sulphuric Acid used in automotive batteries. The
plates should be totally immersed, as any part of the plates
exposed above the electrolyte, will cause oxidation and
corrosion and will result in premature failure.
CCA (COLD CRANKING AMPS)
This is the best indication of how a battery will perform when
used to start a vehicle. It is the amount of Amps that the
battery can deliver - over a period of time - at a given
temperature - to a specific voltage. There are different
ratings at which this is done, so it is important to check which
has been used. The main U.K. specification is S.A.E (Society
of Automobile Engineers).
A battery rated at 500 SAE, means that the battery will
deliver 500 amps for 30 seconds at -18°C and the end
voltage must be 1.2 volts per cell or above (7.2v for a 12 volt
battery).
If a battery has been rated using a different CCA
specification i.e. DIN / IEC, then it will give a different result. If
you are comparing battery performances, you must ensure
you are measuring like for like.
The level of CCA is linked to the total surface area of all the
internal plates in contact with the acid and the quality and
type of separators used.
Ah (AMPERE HOUR CAPACITY)
Ampere Hours (the commonly used 20 Hour rating for
automotive batteries), is a measure of the 'low rate' capacity
of the battery and it's ability to give long low discharges.
Using the 20 Hour rating, a battery rated at 60 A/H will be
able to be discharged at 3 amps for 20 hours before
reaching a voltage of 10.5v, at a temperature of 25°C (20
hours x 3 amps = 60 A/H). A battery rated 60 A/H when
discharged at a current different to the 20 hour rating
current will not give 60 ampere hours. If the current is higher,
the ampere hours will be lower and vice versa. Ampere hour
capacity is generally related to the amount of active
material (lead) in the battery.
SULPHATION
A battery operated with insufficient charge over a long
period of time or left in a discharged condition, will develop
a type of sulphate on the plates which is dense and hard.
This cannot be readily converted back to active material. In
this condition the battery is unable to deliver it's full power.
OVERCYCLING (OVERWORKING OF IT'S CAPACITY)
Constant discharge and recharge over a period of time
greater than normally expected in a battery's life.
Under normal circumstances, overcycling will only occur due
to old age, but as with everything, if the battery is used
incorrectly, then it will fail prematurely.
The main causes are:- Incorrect application fitment (under specification)
- Non starter application (leisure, slave, separate power supply)
- Vehicle's electrical fault
Every time the battery is discharged, it's plates expand and
contract resulting in active material falling away from the
plates and sinking to the bottom of the casing - this
mechanically weakens the plates and will eventually cause
a short circuit.
On batteries specially designed for this type of use, the
separators are re-inforced with glass wool fibre which holds
the active material in place and when the battery is
echarged it is absorbed back into the plates. This also
prevents a build up of 'sludge' at the base of the battery, as
this will lead to a short circuit of the plates creating
premature failure.
OVERCHARGING
On an automotive application, when the vehicle is running, it
is the alternator that supplies the power for the electrical
system and maintains the charge in the battery.
If the alternator's voltage regulation fails and excess voltage
is applied, overcharging will occur which will corrode the
plates and destroy the composition of the active material
leading to premature failure. If the battery is charged off the
vehicle excessively in a similar manner, then the same
problem will occur.
UNDERCHARGING
If the voltage regulation of the alternator is too low or the
vehicle is only used for relatively short journeys, the battery
will not be charged sufficiently, ultimately resulting in a failure
to start.
Fitting a replacement battery will not correct the problem only mask it. Batteries that are chronically undercharged are
unlikely to be recoverable as the plates develop sulphate
chrystals, which become dense and hard. This is generally
known as irreversible sulphation.
UNDERWORKING
A problem will arise if the vehicle does very little mileage. In
these instances, the current is taken out of the battery to
start the vehicle is not replenished by the alternator.
There is no simple way to correct this, apart from the vehicle
doing more miles. A larger battery will last longer but will still
fail prematurely.
Head Office: Shield Batteries Ltd, 277 Stansted Road, Bishops Stortford, Herts CM23 2BT
Tel: 01279 652067 | Fax: 01279 758041 | Email: [email protected] | www.shieldbatteries.co.uk