Lead-acid battery, Battery care, Charging, Hydrometer.

Lead-acid battery, Battery care, Charging, Hydrometer. School Science Lessons
(UNPh32.7)
2024-07-25

Lead-acid battery, lead cell accumulator
Contents
32.7.1 Lead-acid battery, lead cell accumulator
32.7.2 Lead accumulator cell
32.7.3 Battery care (Instructions)
32.7.4 Battery capacity, Ampere-hour (Ah)
32.7.5 Battery storage capacity
32.7.6 Cell connections of a lead cell battery
32.7.7 Charging the battery
32.7.8 Construct a lead cell accumulator
32.7.9 Deep-cycle battery
32.7.10 Discharging and charging a battery
32.7.11 Starting the engine with jump leads
32.7.12 Lead-acid battery secondary cell
32.7.13 Prepare lead-acid battery electrolyte
32.7.14 Starter battery, car battery
32.7.15 State of charge of a motor vehicle battery
32.7.16 VRLA sealed battery

32.4.6.5 Battery, source of emf
33.3.0 Cells and batteries, dry cells (Physics)
22.2.08 Starting battery
32.5.3.5 State of charge of a motor vehicle battery, Battery hydrometer
7.9.51.1 Sulfation
22.2.08 Starting battery, car battery
32.5.3.5 State of charge of a motor vehicle battery
22.2.07 VRLA sealed battery

32.7.3 Battery care
Instructions
Be careful! Never short-circuit an automotive battery.
Excessive current demand may cause battery acid to boil out.
1. Keep the battery case clean.
Use hot soapy water then make it perfectly dry.
Clean the battery terminals at vehicle service.
2. Remove filler caps and check the electrolyte level each month.
Fill the battery with deionized water or distilled water to just above the battery plates.
Do not overfill.
Mop and dry any spillage of water.
3. The battery must be secure in its cradle.
Vibrations of the battery can damage the battery plates.
Loose or corrodes battery terminals may cause breakdowns.
4. The battery will run down without regular use.
It runs down quicker if use is infrequent or used only for short runs.
To avoid problems make sure that the battery is regularly recharged and tested.
5. If battery is drained, because of leaving lights on revive it with a slow charge.
Under-charging and over-charging will shorten battery life.
6. Poor engine condition will shorten the life of a battery.
7. When working on a battery, do not smoke or have a naked flame nearby, because batteries produce hydrogen gas.
8. Before trying to jump start by pushing the car or using jump start cables, make sure that you understand the electrical design of that particular make of car.
Do not try to jump start a car fitted with electronic systems, but get expert assistance.
9. Battery patrol check list
9.1 No load battery voltage
9.2 Discharge test voltage
9.3 Discharge test gassing
9.4 Physical damage evident
9.5 Electrolyte level
9.6 Terminal security and cleanliness
9.7 Discharge to earth
9.8 Alternator drive tension
9.9 Alternator output
9.10 Age of battery

32.7.12 Lead-acid battery secondary cell
See diagram 32.5.3.2: Lead-acid battery secondary cell.
Lead acid battery
The lead acid battery is a group of two or more electric cells connected in series.
A 12 volt battery has six 2 volts cells.
A 6 volt battery has three 2 volt cells.
Secondary cells, which can be recharged many times, are also called storage cells or accumulators.
The chemical action can be reversed by passing a current through the cell in the direction opposite to the discharge current until the chemicals have been changed back to their original form, the cell is charged again.

6 volt battery
The 6 volt battery has three identical lead-acid cells connected in series, so their voltage is added.
The current is the same in all cells.
Charging or discharging current must pass through all the cells in the battery.
The positive and negative plates correspond to the positive and negative electrodes of a primary cell.

Battery plates
These thin plates expose a large surface to the action of the electrolyte.
The plates are constructed from a lead-antimony grid filled with lead (IV) oxide, PbO, in the positive plate and a spongy form of pure grey lead (Pb) in the negative plate.
Separators are insulators to prevent contact between the plates and allow circulation of the electrolyte, a dilute solution of sulfuric acid in water.
The order of plates within the cell is negative plate, separator, positive plate, separator with the final plate in the series a negative plate.

Voltage
The voltage (emf ) of a lead-acid cell varies from 2.3 volts when the cell is fully charged to 1.9 volts, when the cell is fully discharged.
A voltmeter connected to the battery terminals of a discarded battery containing some liquid will still show some reading.
When a lead cell accumulator is fully charged, the concentration of sulfuric acid is at maximum.

Electrolyte
When the accumulator is fully discharged, "flat battery", the concentration of sulfuric acid is at a minimum.
A battery hydrometer is used to read the relative density (specific gravity) of the sulfuric acid in the electrolyte and check the charge of the battery.
The density varies from about 1.28 in a fully charged battery to 1.15 in a discharged battery.
The density of sulfuric acid purchased for use in accumulators is about 1.25 at 20^oC.

32.7.10 Discharging and charging a battery
Discharging --->
PbO + 2H2SO4 + Pb ---> 2PbSO4 + 2H2O
<--- Charging
Lead (IV) oxide + sulfuric acid + lead ---> lead sulfate + water

Discharging
When the battery is discharging, lead (IV) oxide in the positive plate combines with sulfuric acid (sulfuric acid) in the electrolyte to form lead sulfate (lead sulfate) and water.
Lead in the negative plate combines with sulfuric acid to form lead sulfate and water.
How much lead sulfate is produced is directly proportional to how much current flows.
The electrolyte not only takes part in the conversion of the stored chemical energy to an electric current, but also provides a low resistance path for the current through the cell.
The battery is discharged when not enough sulfuric acid is left in the electrolyte for effective chemical action and most of the active materials, lead (IV) oxide and lead, in both sets of plates have been converted into lead sulfate.
During discharge the electrolyte becomes weaker as the acid combines with the plates.
The lead sulfate that has formed fills the pores of the plates so circulation of the electrolyte decreases and the voltage of the battery drops.
The battery is fully discharged when the electrolyte cannot reach the remaining active material of the plates and react with it fast enough to maintain the working voltage and produce an effective current.

Charging
When the battery is charging, current passes through the battery in the reverse direction to the flow on discharge to reverse the chemical reactions and reform the dark brown lead (IV) oxide on the positive plates and spongy lead on the negative plates.
When the battery is fully charged, the specific gravity of the electrolyte is restored to its original value.
If electricity is passed through the battery after it is fully charged then more electrical energy is being supplied to the battery than can be converted to chemical energy.
The excess electricity decomposes the water in the electrolyte to form hydrogen gas and oxygen, called "gassing".

32.7.6 Cell connections of a lead cell battery
See diagram 32.5.3.4 Cell connections of 6 volt batteries.
The lead-acid cell has a voltage of two volts when in average working condition.
Each cell has two terminals, the positive terminal and the negative terminal.
Inside the cell, the positive terminal is connected to the positive plates and the negative terminal to the negative plates.
The direction of conventional current flow is from the positive terminal to the negative terminal in the circuit outside the cell.
The movement of current carrying particles, i.e. electrons, is in the opposite direction.
In most of the electrical devices on motor vehicles it does not matter which way the current flows.
In most motor vehicles the negative terminal of the battery is connected to earth, so the current flows from the insulated live side of the circuit down through the appliance to earth.
However, in motor vehicles using alternators and rectifiers a wrong connection can cause damage.
A 6 volt battery has three 2 volt cells connected in series.
To simplify connection, the centre cell is placed in the container the opposite way round to the end cells.
Two complete 6 volt batteries form a 12 volt battery.
Two batteries may be connected in parallel for heavy duty operation.
Two identical batteries connected in parallel give the voltage of only one battery, but their capacity is double the capacity of each.
An extra battery may be connected in parallel with the battery in a vehicle to start the engine.
If a battery is put on charge with its negative terminal connected to the positive terminal of the charger, the battery may be badly damaged by reversal of the polarity of the plates.
If the name plate is facing the observer, the positive terminal will be at the front right hand corner.
Reverse assembly, the positive terminal will be at the front left hand corner.
The polarity of each individual cell can be found with a moving coil permanent magnet voltmeter with its terminals marked.
The positive post may be painted red, or becomes a dark chocolate colour after a very short period of use.
The negative terminal always looks cleaner and remains light grey in colour.
Each inter cell connector becomes discoloured in the same way, one end dark brown and the other end light grey.
The dark brown end is connected to the positive terminal of a cell, and the light grey end is connected to the negative terminal of the adjacent cell.
A lead-acid battery may self-discharge at the rate of 1% of its capacity per day.

32.7.15 State of charge of a motor vehicle battery
See diagram 32.5.3.5: Battery hydrometer.
There is no direct method to measure a battery's state of charge. Static voltage
Measure its static voltage and compare it to a standardized chart.
This is the least accurate method, but it only involves an inexpensive digital meter.

Amp-hour meter
Measure with an amp-hour meter which monitors all power moving in and out of the battery by time, and the state of charge is determined by comparing flow rates.

Electrolyte density
Measure the density, specific gravity, of the sulfuric acid electrolyte with a battery hydrometer.
This is the most accurate test, but yet it is only applicable to flooded lead-acid batteries.
Electrolyte density is lower when the battery is discharged and higher as the cells are charged.
The battery's chemical reactions affect the density of the electrolyte at a constant rate that is predictable enough to get a good indication of the cell's state of charge.

Maintenance free batteries
They are supplied to some modern motor vehicles under normal operation conditions will not need water addition within its average battery life.
The vent caps remain sealed and the electrolyte cannot be tested as explained below.
However, the vent caps are accessible for inspection of fluid level in the battery if required when using the battery under abnormal operating conditions.

Battery hydrometer
For battery testing, the hydrometer floats in a syringe.
The electrolyte is drawn into a glass tube so that level can be observed in relation to the scale marked on the narrow stem of the hydrometer.
Always take readings at eye level, i.e. your line of sight must be horizontal.
The battery hydrometer indicates the state of charge of each cell.
The electrolyte expands when heated and contracts when cooled so a reference temperature standard is needed.

State of charge
The specific gravity, SG, of the electrolyte in each cell of a battery shows the battery's state of charge:
Fully charged, SG = 1.280. Three quarter charged, SG = 1.240, Half charged, SG = 1.200, Quarter charged, SG = 1.160,
Discharged, SG = 1.120.
The state of charge of a battery is not a true indication of its internal condition if the battery has any bulging, cracking, leakage of electrolyte, or lifting of the cell covers at the positive post end.
Check that you have enough electrolyte above the plates to make a hydrometer test then read the specific gravity of the electrolyte in each cell.
If any reading is below 1.225, the battery has been recharged following the manufacturer's instructions.
A low reading in one or more cells after the battery has been recharged indicates internal trouble.
Test the ability of the battery to do the work required of it by drawing the normal starter motor current and measuring the voltage of the individual cells while they are discharging at a high rate with an accurate voltmeter.
No cell should read less than 1.5 volts.
As the cells of a battery are connected in series, each receives the same charging current and the same amount of current also flows through each on discharge.
If the cell voltages do not fall below 1.5 volts while the starter is being operated and the specific gravity readings are at least 1.250, the battery is in good condition.

32.7.13 Prepare lead-acid battery electrolyte, accumulator electrolyte
1. Prepare electrolyte for a lead cell accumulator
Be careful! Use safety glasses and nitrile chemical-resistant gloves!
Follow the recommendations of the manufacturers for filling and initial charging that is usually printed on the battery.
The relative densities of the sulfuric acid in the battery are as follows:
Fully-charged 1.28, Half-charged 1.21, Discharged 1.15. To make a solution of sulfuric acid, relative density 1.28, slowly add concentrated sulfuric acid to a strong beaker two-thirds full of demineralized water, until the solution is almost boiling.
Leave to cool and add more acid until the solution almost boils.
Leave to cool to room temperature.
Adjust the relative density by adding more acid or more water, according to the hydrometer reading.
When the cell is not in use, use a jar with a cover to prevent drying by evaporation.
Use safety glasses and nitrile chemical-resistant gloves!
Slowly add concentrated sulfuric acid, with stirring, to a beaker two thirds full of distilled water, until the solution is almost boils.
Leave to cool and add more acid until the solution almost boils.
After cooling to room temperature, adjust the relative density with more acid or more water, according to a hydrometer reading.
Sulfuric acid is highly corrosive and if spilt on the skin must be washed off immediately with plenty of water from a running tap.
Apply baking soda solution to the affected area then wash off with water.
Keep a labelled jar of baking soda solution near by in case of spills on the skin.
2. The electrolyte used in lead-acid batteries is a solution of chemically pure sulfuric acid in deionized water.
The efficiency and ultimate life of a battery depends on the purity of the electrolyte.
Always use deionized water or, demineralized water or rainwater to maintain the level of electrolyte in the cells, topping up.
Do not add tap water or water that has been in contact with metals, especially iron, because impurities cause secondary chemical reactions and the battery can self-discharge.
Do not fill above an electrolyte marker or the top of the splash guards, just fill to cover the separators that extend upwards above the top edges of the plates.
The electrolyte should be able to expand and rise when warmed without spilling out through the vent holes in the filler plugs.
BE CAREFUL! REMEMBER: ACID TO WATER, NEVER WATER TO ACID!
3. Charge the battery at the normal rate until the specific gravity stops rising and the cells are gassing.
If the SG is too high, draw off some electrolyte with the battery hydrometer syringe and replace it with deionized water or demineralized water or rain water.
If the SG is too low, draw off some electrolyte and replace it with 1.300 specific gravity acid.
Charge the battery for a further two hours after any replacement to mix the electrolyte thoroughly before taking another reading.
Use a clean glass container for mixing the electrolyte.
Put the water required into the container first then pour the acid slowly into the water while stirring.
Let the electrolyte cool to room temperature before taking the final specific gravity reading.
Keep the battery and its surrounding parts clean and dry to avoid corrosion of metal parts.
Overcharging may cause loosening and shedding of the active material from the plate grids.
The hot electrolyte may attack the separators and the life of the battery will be very short.
4. A battery is left for a long time in a partially discharged state is harder to recharge to its original capacity, because the fine crystalline lead sulfate may harden and become more dense, the battery becomes "sulfated".
To avoid sulfation, the generator must run long enough to restore the chemical energy used to start the engine and operate the lights and accessories while the engine is idle.
The internal resistance of the battery is higher when cold, and a short run may not raise the electrolyte temperature sufficiently to lower its resistance, so the voltage regulator operates earlier in the charging cycle, and at a lower specific gravity than it would do normally.
Do not allow the electrolyte level to become too low to expose the plates to the air, because oxygen in the air will combine with the spongy lead of the negative plate to form a layer of lead (IV) oxide.
5. Always take great care when handling concentrated acid.
Wear protective glasses and clothing.
To make a solution of sulfuric acid, relative density 1.28, slowly add concentrated sulfuric acid to a strong beaker two-thirds full of demineralized water, until the solution is almost boiling.
Allow the solution to cool, then add more acid until the solution is again almost boiling.
Leave to cool to room temperature.
Adjust the relative density by the adding more acid or more water, according to the hydrometer reading.
When the cell is not in use, use a jar with a cover to prevent drying by evaporation.
6. Fix two lead foil strips in a beaker and add 200 mL of 1 mol per litre sulfuric acid. Connect the lead electrodes to a power pack set at 2 V and switch it on for two minutes. The lead strip connected to the positive terminal becomes covered with brown lead dioxide. Disconnect the power pack and connect the lead strips to a torch battery. The battery glows, but the brown leads dioxide on the positive terminal does not disappear. Repeat the experiment with increasing charging times. The time the battery glows increases with charging time up to 30 seconds then hardly changes. Repeat the experiment with different charging voltages. Different charging voltage makes hardly any difference in the time the battery glows. However, at high charging voltages hydrogen is produced at the negative electrode and oxygen at the positive electrode. Charging
At the positive electrode: Pb(s) + 2H2O(l) --> PbO2(s) + 4H⁺(aq) + 4e^-
At the negative electrode: 2H⁺(aq) + 2e^- --> H2(g)
Also, lead reacts with the sulfuric acid to produce lead sulfate
At the positive electrode: PbSO4(s) + 2H2O(l) --> PbO2(s) + 4H⁺(aq) + SO4^2- + 2e^-
At the negative electrode: PbSO4(s) + 2e^- --> Pb(s) + SO4^2-(aq)
So sulfuric acid is produced during charging and is consumed during discharging. As sulfuric acid has about twice the density of water, the density of the electrolyte shows the state of charge of the battery. 7. When the battery is fully charged, the specific gravity = 1.280, electrode A is lead and electrode, B is lead dioxide.
When the battery is discharging, electrode A changes from lead to lead sulfate, electrode, B changes from lead dioxide to lead sulfate, and the concentration of sulfuric acid decreases.
When the battery is being charged, these processes are reversed.
The concentration of sulfuric acid suggests the state of charge of the battery so this concentration can be measured with a battery hydrometer.
Electrode A: Pb + SO4^2- --> PbSO4 + 2e^-
Electrode B: PbO2 + 4H3O⁺ + SO4^2- + 2e^- --> PbSO4 + 6H2O
In a motor car battery, the electrodes have a coat of lead (II) oxide (PbO) and lead powder (Pb).
In the electrolyte, electric current converts the PbO to Pb on the negative plate, and the PbO to lead (IV) oxide (lead peroxide) PbO2 on the positive plate.
Discharging -->
PbO2 + 2H2SO4 + Pb < = > 2PbSO4 + 2H2O
<-- Charging
If you pass electricity through the battery after it is fully charged, "gassing" occurs, i.e. water is decomposed into hydrogen and oxygen gas.
Never smoke or allow a naked flame near a charging battery.

32.7.4 Battery capacity, Ampere-hour (Ah)
1. Capacity of a battery refers to the quantity of electricity it can deliver.
The ampere-hour (Ah), is the quantity of electricity equivalent to a current of one ampere flowing for one hour.
The milliampere-hour is one-thousandth of an ampere-hour.
(1 Ah = 3 600 coulombs of charge, 1 amp = 1 coulomb per second.)
Capacity in ampere-hours = current in amperes × time in hours.
A battery with a capacity of 50 ampere-hours can deliver a current of 5 amperes for 10 hours, or 10 amperes for five hours, after being fully charged at the beginning and completely discharging at the end.
However, the capacity of a battery is not the same for different rates of discharge if the battery has already discharged within the rated time.
Amp-hour capacity for a battery, it is specified at either a given current, given time, or assumed to be rated for a time period, e.g. 8 hours or 10 hours.
Automobile batteries can be rated by measuring the ability to supply sufficient current to operate the starter, or operate the lighting system.

Amp-hour capacity
The approximate amp-hour capacities of some common batteries:
1. Typical automotive battery: 70 amp-hours at 3.5 A (secondary cell)
2. D-size carbon-zinc battery: 4.5 amp-hours at 100 mA (primary cell)
3. 9 volt carbon-zinc battery: 400 milliamp-hours at 8 mA (primary cell)

10-hour rating
For automobile batteries, a common standard rating is the 10-hour rating. It is the steady discharge current, in amperes, to reduce the cell voltage to 1.8 in 10 hours at 15^oC, with specific gravity of the electrolyte 1.120 when fully discharged.
The full theoretical capacity of a battery cannot be used, because the discharge current that must diffuse into the plates fast enough to replace the electrolyte used in the production of an electric current.
Lead sulfate clogs the pores of the plates and restricts the movement of the electrolyte so that chemical action is reduced, the voltage generated by the cell is lowered, and the useful current is reduced.
Also, the resistance of the materials on the plates increases as the cells are discharged and the resistance of the electrolyte increases as the battery discharges and the acid content of the electrolyte falls.
Both a 6 volt 50 ampere-hour battery and a 12 volt 50 ampere-hour battery will deliver a current of 5 amperes for 10 hours, so the stated capacity of 5 × 10 = 50 ampere-hours.
The advantage of the 12 volt automobile battery is that it has twice the watt-hour capacity of the 6 volt battery, i.e. it stores twice the amount of electrical energy.
The 6 volt battery delivers its 5 amperes at 6 volts, but the 12 volt battery delivers the same current for the same length of time at 12 volts.

Watt-hour capacity
Power from 6 volt battery, W = V × I = 6 × 5 = 30 watts.
Energy capacity of 6 volt battery = power × time = watts × hours = 30 × 10 = 300 watt hours.
Power from 12 volt battery, W = V × I = 12 × 5 = 60 watts.
Energy capacity of 12 volt battery = power × time = watts × hours = 60 × 10 = 600 watt hours.
Thus, watt hours = ampere-hours × voltage.
These calculations show that the watt hour capacity is equal to the ampere-hour capacity multiplied by the battery voltage.
Watt hour capacity = ampere-hour capacity × battery voltage.

32.7.5 Battery storage capacity
The storage capacity is the amount of energy a battery can store.
The storage capacity of a battery is the current that can be delivered × time, so the storage capacity of a battery in watt-hours = ampere-hour capacity × battery voltage.
The storage capacity of a battery will have a maximum value as "maximum deliverable current" or a minimum as "shelf life" in a supermarket.
Battery life / battery longevity may be expressed as Reserve Capacity, (RC), and ampere-hours, Amp Hours (Ah or AH).

Battery capacity
Amp hours is the most common unit for battery capacity.
Amp hours = current X time.
Batteries used in photovoltaic systems are rated in Ampere Hours, (AH).
So a 100 AH battery can supply 1 amp for 100 hours, or 100 amps for one hour.
Small cells have storage capacity up to 200 milliamperes, nAH.
Large lead-acid batteries have storage capacity more than 100 AH.
If a battery is rated 10 AH at 12 volts DC, Power, P in watts = VI, volts × amps, multiply both sides by t, Watt-hours, Pt = VIt = 12 × 10 = 120 watt-hours.
The Ampere hour rating, Ah, is the current available when discharged evenly over a 20-hour period, the standard time length for rating batteries.

Reserve capacity
Reserve capacity is the number of minutes that a battery can supply a useful voltage (10.5 volts or more), under a 25 amp discharge rate.
Reserve capacity is used for batteries that run heavy loads.
For example, a battery specification "RC@ 25A = 160 minutes" means that at 80^oF (about 27^oC), the battery can supply 25 amps of current at a usable voltage for 160 minutes.
Reserve capacity is often a truer test of battery life than amp hours, depending on how the battery is used.

Shelf life
The "shelf life" is the length of time a battery can remain in storage, (not connected to a load), without losing its energy capacity.
However, the metal plates eventually leak and react with each other, even though the battery is not in use.
Some people store their flashlight / torch batteries in a refrigerator, because they think this will extend the shelf life of the batteries.
Maximum deliverable current is the largest current a battery can push through a load without drop in its output voltage.

32.7.9 Deep-cycle battery
A deep-cycle battery should discharge at least 50% of its capacity, for the best life span versus cost.
It may be capable of withstanding repeated substantial discharges of up to 80% capacity.
The depth of discharge of the battery is related to the battery life, i.e. the number of charge and discharge cycles it can perform.
Deep-cycle batteries are used in sweepers, scrubbers, jacks, lifts, electric golf carts, boats, cathodic protection, uninterruptible power supplies for computers, and off-grid solar and wind power systems.
All deep-cycle batteries are classified and rated in amp-hours.
Amp-hours is the term used to describe a standardized rate of discharge measuring current relative to time.
It is calculated by multiplying amps and hours.
The generally accepted rating time period for most manufacturers is 20 hours.
Heavy duty deep-cycle batteries may rate up to 260 AH.
Deep-cycle batteries are generally rated in amp-hours at a C/20 discharge rate, which means 1/20 of the battery capacity for 20 hours until the battery reaches 1.75 volts per cell.
A battery rated at 100 amp-hours will maintain a 5 amp load continuously for 20 hours.
Actual capacity will vary with temperature, the size of the load and the rate of discharge.
Deep-cycle batteries used in UPS and telecommunication applications are rated in reserve capacity, which is the number of minutes the battery will maintain a constant 25A load at 80^oF until voltage drops to 1.75 volts per cell.
To provide an approximate conversion to amp-hours, multiply reserve capacity by 0.6.

32.7.16 VRLA sealed battery
A sealed VRLA battery (Valve Regulated Lead Acid), is maintenance free, produces negligible gas when charging, easier to transport, because, unlike wet "flooded"' batteries, they are not classified as "hazardous cargo".
The three sub-types are, wet, AGM, Gel.
The sealed wet type is primarily designed for the leisure and marine markets, some of which claim to be able to complete around 400 to 500 discharge cycles (to 80% depth of discharge).

32.7.14 Starter battery, car battery
A starting battery (starter battery), used in most motor cars provides short, high current bursts for cranking the engine.
So it frequently discharges only a small percentage of its capacity.
Engine starting batteries are rated in cold cranking amps, CCA.
Engine starting batteries are designed to provide a heavy surge current of as much as 200 amps for a period of 5-10 seconds.
There is no direct correlation between CCA and amp-hours, because starting batteries are not designed for slow periods of deep discharge.

32.7.11 Starting the engine with jump leads
Procedure before jump starting the engine
1. Ensure that the ignition switch is in the OFF position.
2. Turn off the lights and power draining functions to help ease the strain off the donor battery.
3. Ensure that the donor battery is the same voltage as the flat battery.
4. Ensure that the two vehicles are not touching in anyway.
5. Make sure that the vehicles are in either Neutral (Manual) or Park (Auto).
6. Remove the vent caps from non maintenance free batteries.
Be careful! Battery acid is corrosive!

Procedure for jump starting the engine
1. Connect the red coloured jumper lead to the (+) positive terminal of the booster battery and the other end of the red jumper lead to the (+) positive terminal of the flat battery.
2.
Connect the black jumper lead to the (-) negative terminal of the booster battery and the other end of the black jumper lead to a good earth point on the disabled vehicle.
The engine block is typically the best place for a good earth point.
3. Start the engine of the disabled vehicle.
4. With the engine speed at idle, disconnect the jumper leads in the reverse order of connection.
5. The car has now been started and after any caps and covers have been replaced it is ready to drive.
The cause of the flat battery should be identified and rectified as soon as possible.
6. Late model cars are generally more dependent on complex electronics to function and any voltage spike can damage the delicate electronic circuitry.
To avoid this problem, use jumper leads fitted with a "spike guards", (surge protectors).

32.7.2 Lead accumulator cell
The lead cell accumulator has emf about 2 volts and very low internal resistance.
It is a secondary cell.
The terminals are usually marked + (red) and - (black).
Since the internal resistance is very low, great care must be taken to avoid "short circuiting " the cell, i.e. there must always be a resistance of at least 1 ohm in the external circuit connecting the terminals.
(1.) Use a 250 mL beaker or jar with a cover to prevent drying by evaporation when the cell is not in use.
You need 2 sheets of 40 × 10 cm thin lead foil and 2 lead strips 2 × 14 cm as terminals.
These lead pieces require thorough cleaning by means of wire wool.
Fold the long sheets of lead tightly to the shorter strips so that they make good electrical contact.
The projecting ends will serve as terminals.
A blotting paper B lead c terminals A sandwich is made of alternating strips of lead foil and blotting paper.
When the sandwich is ready it is rolled up quite tightly, secured round the outside with one or two elastic bands, and placed with terminals at the top, in the cup or jar.
Mark one terminal positive, and the other negative.
The roll is covered with a solution of sodium sulfate made by dissolving 40 g of anhydrous sodium sulfate crystals in 200 mL water.
The cell is now ready to charge with electricity.
This can be done with a 6 volt battery charger, or with any low voltage direct current supply giving up to 10 amps.
Connect positive on the charger to positive on the cell.
After only a few minutes charging, the cell will light a 1.5 volt bulb.
Provided that the cell is always connected to the charger in the same way, as described above, the more times it is charged and discharged, the more efficient it becomes.
There will be enough current to make a small 1 volt electric motor spin round.
The cell will remain serviceable for several months if the cover is put on when not in use.
(2.) Charge a simple lead-acid battery with two electrodes, lead plates, in a sulfuric acid solution for a short time and then discharge through a doorbell.
Charge two lead plates in 30% sulfuric acid and discharge through a flashlight bulb.
(3.) Internal resistance of batteries, weak and good battery.
Measure similar no load voltage on identical looking batteries and then apply a load to each and show the difference in voltage between a good and weak battery.

32.7.1 Lead-acid battery, lead cell accumulator
See diagram 3.2.87: Lead cell accumulator.
(1.) Lead-acid batteries are one of the more common secondary cell battery types.
They are rugged and inexpensive per watt hour.
Flooded or wet batteries are the most cost efficient and the most widely used batteries in photovoltaic applications.
They require regular maintenance and need to be used in a vented location, and are extremely well suited for renewable energy applications.
(2.) 12 volt battery
The most common motor car battery, the 12 volt battery, contains six cells connected in series, each of which produces 2 volts.
Charged positive plate: lead (IV) oxide, Discharged positive plate: lead (II) sulfate
Charged negative plate: lead, discharged negative plate: lead (II) sulfate
Electrolyte: sulfuric acid
(3.) Construction of a lead-acid battery
Use a 250 mL jar or beaker with a cover to prevent evaporation when not in use.
Prepare two sheets of lead foil 40 cm X 10 cm and two lead strips 2 cm X 14 cm for terminals.
Clean the lead thoroughly with steel wool and degrease them by soaking in 0.5 M sodium hydroxide solution for 15 minutes, then wash in deionized water.
Fold the long sheets of lead tightly around the shorter strips to make good electrical contact.
The projecting ends serve as terminals.
Make a sandwich of alternating strips of lead foil and absorbent paper.
Roll up the sandwich tightly and put two elastic bands around it, and put it in the jar with the terminals at the top.
Mark one terminal positive and the other negative.
Cover the roll of lead with a sodium sulfate solution made by dissolving 40 g of anhydrous sodium sulfate crystals in 200 mL of water.
(4.) Charging a lead-acid battery
Use a 6 V battery charger or with any low voltage direct current supply giving up to 10 amps.
Connect the positive terminal on the charger to the positive terminal on the cell.
After charging for some minutes the cell lights a 1.5 V light bulb.
When charging at the negative terminal electrode, the concentration of sulfuric acid increases.
Pb(s) + SO4^2-(aq) --> PbSO4(aq) + 2e^-
The more times the accumulator is charged and discharged, the more efficient it becomes.
(5.) Discharging a lead-acid battery
When discharging at the negative terminal electrode, the electrons move through the circuit.
When discharging at the positive terminal electrode, the concentration of sulfuric acid decreases.
When charging at the positive terminal electrode, the electrons move through the circuit.
PbO2 (s) + 4H3O⁺ (aq) + SO4^2- (aq) + 2e^- --> PbSO4 (aq) + 6H2O (l)

Sulfuric acid
When a lead cell accumulator is fully charged, the concentration of sulfuric acid is at maximum.
When the accumulator is fully discharged, "flat battery", the concentration of sulfuric acid is at minimum.
Use a battery hydrometer to read the relative density (specific gravity) of sulfuric acid in the electrolyte and check how charged the battery is.
The density varies from about 1.28 in a fully charged battery to 1.15 in a discharged battery.
The density of sulfuric acid purchased for use in accumulators is about 1.25 at 20^oC.

Equations
Charging cell
Pb (s) + 2H2O (l) --> PbO2 (s) + 4H⁺(aq) + 4e^- (anode)
4H⁺(aq) + 4e^---> 2H2 (g) cathode
Discharging cell
PbO2 (s) + 4H⁺ (aq) + 2e^- --> Pb²⁺ (aq) + 2H2O (l) (anode)
Pb (s) --> Pb²⁺ (aq) + 2e^-(cathode)

32.7.8 Construct a lead cell accumulator
Fix two lead foil strips in a beaker and add 200 mL of 1 mol per litre sulfuric acid.
Connect the lead electrodes to a power pack set at 2 V and switch it on for two minutes.
The lead strip connected to the positive terminal becomes covered with brown lead dioxide.
Disconnect the power pack and connect the lead strips to a torch battery.
The battery glows, but the brown leads dioxide on the positive terminal does not disappear.
Repeat the experiment with increasing charging times.
The time the battery glows increases with charging time up to 30 seconds then hardly changes.
Repeat the experiment with different charging voltages.
Different charging voltage makes hardly any difference in the time the battery glows.
However, at high charging voltages hydrogen is produced at the negative electrode and oxygen at the positive electrode.
Charging
At the positive electrode: Pb (s) + 2H2O (l) --> PbO2 (s) + 4H⁺ (aq) + 4e^-
At the negative electrode: 2H⁺ (aq) + 2e^- --> H2 (g)
Also, lead reacts with the sulfuric acid to produce lead sulfate
At the positive electrode: PbSO4 (s) + 2H2O (l) --> PbO2 (s) + 4H⁺ (aq) + SO4^2- + 2e^-
At the negative electrode: PbSO4 (s) + 2e^- --> Pb (s) + SO4^2- (aq)
So sulfuric acid is produced during charging and is consumed during discharging.
As sulfuric acid has about twice the density of water, the density of the electrolyte shows the state of charge of the battery.

32.7.7 Charging the battery
When the battery is fully charged, the specific gravity (relative density) = 1.280, electrode A is lead and electrode, B is lead dioxide.
When the battery is discharging, electrode A changes from lead to lead sulfate, electrode, B changes from lead dioxide to lead sulfate, and the concentration of sulfuric acid decreases.
When the battery is being charged, these processes are reversed.
The concentration of sulfuric acid suggests the state of charge of the battery so this concentration can be measured with a battery hydrometer.
Electrode A: Pb + SO4^2- --> PbSO4 + 2e^-
Electrode B: PbO2 + 4H3O⁺ + SO4^2- + 2e^- --> PbSO4 + 6H2O
In a motor car battery, the electrodes have a coat of lead (II) oxide (PbO) and lead powder (Pb).
In the electrolyte, electric current converts the PbO to Pb on the negative plate, and the PbO to lead (IV) oxide (lead peroxide) PbO2 on the positive plate.
Discharging -->:
PbO2 + 2H2SO4 + Pb < = > 2PbSO4 + 2H2O
<-- Charging
If you pass electricity through the battery after it is fully charged, "gassing" occurs, i.e. water is decomposed into hydrogen and oxygen gas.
Never smoke or allow a naked flame near a charging battery, because it may produce the inflammable gas hydrogen.
Also, the lead-acid battery is dangerous, because it can produce very high currents and contains sulfuric acid that may be spilt.
It is the only common wet battery.

Charge and discharge a lead accumulator cell.
Prepare a simple lead accumulator cell consisting of two pieces of lead dipping into sulfuric acid.
To charge the cell connect three 1.5 volt batteries in series for two minutes.
To discharge the cell connect a torch cell lamp, light globe.
Note the time that the lamp remains lit.
The cell is now discharged.
Repeat the experiment by increasing the time of charge and noting the time until discharge.
Draw a graph of the results with time charged (x axis) against time discharged (y axis).