Cells

Action of simple cells;

At cathode: The zinc plate dissolves in the sulphuric acid solution and liberates electrons into the external circuit. The metal discus had to be of different material Volta used copper and zinc discs sand witched by cloth soaked in salt water. zn - 2e - Zn 2+ The 2n 2+ ions go into solution.

At anode: Positively charged hydrogen lons (H+) are attracted towards the negatively charged copper plate2H + + 2e ----- H2.The chemical reaction in the cell creates a potential different between plates, causing electrons to flow when the two plates are joined with a wire.

Connecting in series

When connecting your batteries in Series you are doubling the voltage while maintaining the same capacity rating (amp hours). This might be used in a scooter, Power Wheels kids vehicle, or other applications. Just use a jumper wire between the negative of the first battery and the positive of the second battery.

Connecting in series (double voltage, same capacity.

Connecting in parallel

When connecting cells in parallel, you are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries. This would be used in applications such as laptop batteries, some scooters, some ups backups, etc. Use a jumper wire between the positives of both batteries and another jumper wire between the negatives of both batteries.

Connecting in parallel (double voltage, same capacity

Simple Have two main defects, which cause the current to diminish quickly when the cell is being used.

Two defects of simple cell are:

1. Polarization
2. Local Action

Polarization

Polarization is the defect occurs in simple cell caused by the formation of hydrogen bubbles around the copper plate. These bubbles insulate the copper plate and prevent other positive hydrogen ions from receiving electrons from the copper plate to become neutral.

Local action

Local action is the process by which a cell is used up when no external current is flowing. Commercial zinc normally contains atoms of Iron, lead, carbon, etc called impurities

The leclanche cell: Is the cell uses an aqueous solution of ammonium chloride (sal ammoniac) as the electrolyte, amalgamated zinc rod as cathode. The carbon rod as anode fixed in a porous pot, containing a powdered mixture of carbon and manganese (iv) oxide.

The carbon makes the mixture more conducting, and the manganese (IV) oxide (manganese dioxide,MnO2) acts as a depolarizer.

The Dry cell Is a modified leclanche cell in which the main electrolyte is a paste of starch and ammonium chloride. The action of the cell is similar to that of the wet leclanche cell.

The paste is prevented from drying by sealing the top of cell with some insulating materials. This type of cell gives a larger current and have a shorter recovery (demoralising time) than the 'wet' type;

Hence it is useful for a greater variety of applications. However, Local action cannot be eliminated completely in these cells, so that the cells have a storage (or shelf) life ranging from a few months to up to several years if stored in a cool place

This is the cell which can be recharged after it has run down (used). This is done by passing a d.c current from a dynamo or similar device through the cell in the opposite direction to that in which the cell usually supplies current in an external circuit.

Also called storage cells or accumulator some common accumulators are:

• Lead Acid accumulators
• Nickel – Cadmium accumulators
• Alkaline and chloride accumulators

The lead – acid accumulator cell consists of two plates of lead immersed in sulphuric acid. The acid is in a plastic container. Two or more cells may be connected to forms battery

The positive terminal is lead (iv) oxide and the negative terminal is lead.

Wood / rubber/ separator/Insulator Cathode electrode: Lead plate (–) Anode Electrode: lead (iv) oxide (+)

Before the accumulator is use it has to be charged

Charging is done by connecting across its plates as source of direct current. If the current of 2A may be allowed to flow across the terminal of the cell. The positive terminals of the cell and the source of current (dynamo) must be connected together similar the negative terminal must be connected together.

Discharging accumulator

Discharging an accumulator is the process of using the electrical charges stored in a lead–acid accumulator to power a circuit.

1. When an accumulator is discharged after long use, both plates become coated with lead sulphate (PbSO₄).
2. The relative density (R.D.) of the acid becomes lower, and the potential difference (p.d.) of the cell drops.
3. Recharging the accumulator restores the plates back to lead (Pb) and lead(IV) oxide (PbO₂), and raises the R.D. of the acid back to about 1.25.
4. An accumulator should not be discharged below the recommended p.d. or R.D.; otherwise, it may become irrecoverable even after recharging.

1. This is the amount of current (in amperes) that the accumulator can deliver.
2. It is measured in ampere-hours (Ah).

• The recommended charging current is about one-tenth (1/10) of the accumulator's capacity in ampere-hours.

1. They provide a high electromotive force (e.m.f) of about 2V per cell.
2. They have low internal resistance.

1. Regularly check the acid level in the cell.
2. Refill only with distilled water when the acid level is low due to evaporation.
3. Do not add more acid unless some has been spilled.
4. Recharge regularly using the correct current as per manufacturer's instructions.
5. Never leave the accumulator discharged for a long time.
6. If unused, recharge at least once a month.
7. Never short-circuit the accumulator. It may cause excess heat, plate swelling, and permanent damage (called sulphation).

Electric cells are sources of energy, especially useful where mains electricity is not available or is inconvenient to use.

Applications of Primary Cells (non-rechargeable):

1. Portable radios
2. Torches
3. Calculators
4. Wrist watches

Applications of Secondary Cells (rechargeable):

1. In cars, to start the engine and run electrical circuits
2. Rechargeable batteries for radios, toys, and cameras

• A car battery (a secondary cell) is recharged by the alternator while the car engine is running.