Lead acid batteries Level 2

Batteries

LV03

​Level 2 Diploma in Maintenance and repair for light vehicles.

Intent

Describe the function and operation of light vehicle batteries

Identify components in the construction of a Lead acid battery

Describe how to remove and replace batteries

Know how to work with and dispose of lead acid batteries safely

​Describe the discharge and charging process inside the battery.

Poll

What is a battery?

• A device that powers the car

• A storage device

• A device that produces electricity

• A device that charges up the car

A battery stores electricity for future use.

It develops voltage from the chemical reaction produced when two unlike materials, such as the positive and negative plates, are immersed in an electrolyte (dilute sulphuric acid) H²SO⁴

In a typical lead-acid battery, the voltage, when fully charged, is approximately 2.1-2.2 volts per cell, for a total of 12.6-12.8 volts.


Electricity flows from the battery when a circuit is made between the positive
and negative terminals. This happens when any load that needs electricity, such as the radio or lights, are switched on.

Multiple Choice

What type of battery do we use in a 12v vehicle system?

• Lithium-ion

• Nickel-metal hydride

• Lead Acid

• Alkaline

Multiple Choice

What is the maximum voltage of a fully charged battery?

• 12v

• 12.8v

• 13.6v

• 14.2v

​

A lead-acid battery consists of two types of plates: positive, and negative plates. These plates are made of lead dioxide, and lead alloy respectively.

​

Positive plates are made of lead dioxide (PbO²) material. The grid framework is coated with a paste that contains lead dioxide, conductive additives, and a binder. The positive plates play a crucial role during the charging and discharging process where they undergo a chemical reaction to form lead sulphate and release electrons.

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The negative plates are made of spongy lead (Pb) . They are also coated with a paste consisting of lead and other additives. The negative plates react with the sulfuric acid in the electrolyte and generate lead sulfate as part of the electrochemical process.

Multiple Choice

What is the negative plate made from?

• Lead Dioxide

• Electron Lead

• Spongy Lead

• Springy Lead

The positive and negative plates are alternately arranged within the battery, with a separator placed between them to prevent direct contact and short circuits.

The lead-acid battery's construction includes multiple cells, each containing positive and negative plates.

These cells are connected in series to achieve the desired voltage, such as the commonly used 12-volt lead-acid battery consisting of six cells.

Open Ended

What would the voltage of the battery be if we connected the cells in parallel instead of series?

​What is the voltage of this battery? Explain your answer.

Labelling

Label the diagram

Drag labels to their correct position on the image

Positive plate

Dilute H²SO⁴

Protective casing

Negative terminal

Negative plate

Cell Separator

Positive terminal

When a lead-acid battery discharges, it undergoes a chemical reaction that converts the stored chemical energy into
electrical energy.

This electrochemical process results in the conversion of chemical energy into electrical energy.
The released electrons flow through an external circuit, producing an electric current that can power devices or recharge
other batteries.

During the charging process, the reactions are reversed. The application of an external electrical current forces the lead
sulfate to convert back into lead and lead dioxide, restoring the battery's stored chemical energy.

When a battery discharges, three reactions take place.

At the negative plate, the sulphate ions in the electrolyte react with the lead, to
produce lead sulphate. This reaction releases electrons.

At the positive plate, the sulphate ions react with the lead dioxide, also producing
lead sulphate.

Meanwhile, the hydrogen in the sulphuric acid reacts with the oxygen from the
lead dioxide to produce water. The positive plate requires electrons, and of
course it gets them from the negative plate.

These reactions remove sulphuric
acid from the electrolyte and
eventually they cease when there
is no more acid or lead (dioxide)
left to react.
The by-product of these reactions -
lead sulphate - coats the plates,
damaging them, reducing their
capacity, and increasing resistance
if it left to form hard crystals.
Immediate recharging is advised to
prevent it from solidifying.

Recharging a battery reverses the discharge process. It reconverts the lead
sulphate back to its original form, lead and sulphuric acid, in the process removing
the potentially damaging sulphate crystals from the plates.

As electricity passes through the mainly water electrolyte, a process called gassing
occurs. Electricity separates the water (H20) into Hydrogen and Oxygen, both
flammable and dangerous gases. In un-sealed batteries, this causes water loss,
meaning water levels have to be topped up regularly with distilled water.

In sealed batteries, the gases are contained within the battery to prevent water
loss, however, overcharging may cause excess pressure, causing emergency
vents to open and release the gases, in turn reducing the battery life.

Multiple Select

Which of the following will reduce the charging capacity of a lead acid battery?

• Acid level low

• Sulfation on the plates

• Battery temperature

• Leaving the battery disconnected

Battery capacity

Ah - Ampere Hours

The amount of time it will take
for the battery to discharge with a
Current draw.

74 Amps for 1 hour

1 Amp for 74 hours

Reserve Capacity

The reserve capacity is the amount of time in minutes that a battery at 25℃ can
deliver 25 Amps until the voltage drops to 10.5 Volts

25 Amps represents a typical electrical load on a car under normal running
conditions, so the Reserve Capacity gives an indication of the time that a vehicle
with a normal electrical load will run with a broken alternator or fan-belt. This is a
good, practical test.

30 - 50% concentration

​What is in a battery?

What are the dangers?

How could this end up on your skin or clothes?

What should you do if you spill it?

​Discussion

Battery Hydrometer

Refractometer

Internal battery resistance

Resistance is lowest when the
battery is half to fully charged.

Changing the acid concentration
dramatically increases internal
resistance.

The lower the temperature, the
higher the Internal resistance.

Internal battery resistance changes

Battery capacity is directly dependant on the number of and the surface area of
the plates.

The loss of electrolyte means that the plates are not submerged. This reduces the
surface area and reduces capacity.

When discharged, it is more difficult for the lead sulphate to be converted.

If left discharged the lead sulphate sets into hard crystals and becomes
chemically inactive. Sulphate crystals are not good conductors and will resist the
flow of current through the cell

Battery testing

The High-rate discharge test is a battery
load test designed to ensure that all of the
cells are supplying the necessary current
for starting.

It discharges the battery at a similar rate
to a starter motor.

This method of testing is very hazardous
and has been replaced by digital battery
testers.

Using a digital battery tester is the now the recognised way to test a battery
safely.

Vehicle details can be input and a printout is produced for reports and
warranty claims.

Some High
maintenance batteries
are delivered dry and
need to be filled.

These need to be fully
charged before
connecting to the
vehicle.

Maintenance free battery

Topping up a high maintenance battery

Exercise

Research then describe a general procedure for
recharging a High-maintenance battery.

1. Check the electrolyte level and top up if necessary. Do not overfill.
2. Remove the vent plugs.
3. Check that the charger is switched off.
4. Connect the charger to the battery by connecting the positive lead to the

positive terminal first and the negative lead to the negative terminal last.

5. Switch on the charger.
6. Stop charging if the battery starts to gas freely of if the battery heats up.
7. Switch off the charger.
8. It is safe practice to wait about 20 minutes for the gases to clear before

removing the leads from the battery as this can cause a spark which may ignite
the electrolyte gases.

9. Check the electrolyte levels in all cells and top up if necessary.
10.Refit the vent plugs
11.Wash the battery and dry it.

Stretch task

Research the following battery types and describe their construction and
which types of vehicles they would be used on.

Absorbent Glass Mat (AGM)
Nickel-cadmium (NiCad)
Lithium ion
Nickel metal hydride
Silver oxide and Mercury oxide.

Alternators

How does an electromagnet work?

What are the blue dots representing?

What happens when the iron core passes the magnets in one direction?

What happens when the iron core comes back to the start position?

​

​What is happening in the video?

Open Ended

What is the difference between the stator and the rotor?

Stator windings

The stator consists of 3 evenly spaced, insulated copper wire windings.
They are held in a frame of soft iron laminations.

The windings are connected in either star or delta configurations.

Light vehicles use mainly star configurations as they produce a lower amp
output.

Full wave bridge rectification

Slip rings

Voltage regulator

The regulator has two inputs and one output.

The inputs are the field current supply and the control voltage input, and the
output is the field current to the rotor.

Field current supply

Field current supply is provided from two different sources - from the alternator
itself, via the diode trio, and from the battery, via the alternator warning lamp.

The trio circuit is illustrated above. The trio gets it's name from three
additional diodes, located inside the alternator. These diodes simply provide
a parallel positive circuit, which is used only to energize the field coil and
voltage regulator.

Warning lamp

Fault finding