Cells & Batteries (1)

What is a cell?

A device that changes chemical energy to electrical energy.

How can a voltaic cell be constructed?

Using almost any two unlike metals and an acid, alkaline, or salt solution.

How is electrical energy stored in a cell?

In the chemical bonds in the electrodes and electrolyte.

What causes an EMF to develop between the two electrodes?

A difference in charge.

What does and does not determine the voltage of a cell?

The type of electrodes and the electrolyte used determine the voltage of a cell, while the size of the cell does not (Electromotive Series of Metals)

What increases the battery’s ability to produce high current for a shorter period?

The area of the electrodes

What increases the battery’s ability to produce current for a longer period of time?

The plate mass

What does the battery’s internal resistance depend upon?

The area of the plates, the distance between the plates, and the state of the electrolyte

How can we calculate the internal resistance of a battery?

VD (Internal) = V (No load) - V (With load)

What are some primary cells and their voltages?

Leclanche (1.5V), Alkaline (1.5V), Mercury (1.35V), Silver-Zinc (1.6V), Zinc-Air (1.4V), Edison-Lalande (0.8V)

What are some secondary cells and their voltages?

Lead-Acid (2.2V), Nickel-Iron (1.4V), Nickel-Cadmium (1.2V), Silver-Zinc (1.5V), Silver-Cadium (1.1V)

What does the Leclanche Cell contain?

Positive - Carbon Rod in Manganese Dioxide
Negative - Zinc Rod
Electrolyte - Ammonium Chloride (Liquid) / Zinc Chloride & Ammonium Chloride (Paste)

Compare the Leclanche Cell and the Alkaline Cell.

They produce the same EMF but the Leclanche cells have a better capacity.

What does the Alkaline Cell contain?

Positive - Zinc Powder
Negative - Graphite Carbon
Separator - Manganese Dioxide
Electrolyte - Potassium Hydroxide and Water

What are the types of Lead Acid battery?

Flooded Cell, Gelled Electrolyte Cell, Absorptive Glass Mat (AGM)

What does the Flooded Lead Acid Cell contain?

Positive - Spongy Lead
Negative - Lead Dioxide
Electrolyte - Sulphuric Acid and Water

What is the proportion of water to sulphuric acid in a lead acid battery?

64% Water, 36% Acid

What are the applications of the flooded lead acid battery?

Automotive, Solar & Wind storage, Emergency lighting

What is specific gravity?

A measure of a substance's density compared to water. AKA Relative Density. Measured with a hydrometer.

What range must the specific gravity of the lead acid cell be within?

1.275 and 1.3

What happens as the lead acid cell discharges?

The composition of the plates change and specific gravity of the electrolyte decreases. The acid nearly changes to water as cell becomes completely discharged.

How do we know when the lead acid battery should be recharged?

Specific gravity drops below 1.210, or the terminal voltage drops below 1.72V per cell

What are the hazards when recharging a flooded lead acid battery?

Leakage of Hydrogen and Oxygen gasses which are potentially explosive. Also sulphuric acid which is highly corrosive.

What are the advantages of the Gelled Lead Acid Battery?

Less maintenance. Does not leak or spill so can be installed in any position.

What is different about the Absorptive Glass Mat Lead Acid Battery?

It uses a porous AGM as a separator plate to immobilize the electrolyte.

Rank the current capacity of the flooded, gelled, and AGM lead acid batteries.

#1 - AGM
#2 - Gelled
#3 - Flooded

How is severe damage to Gelled & AGM lead acid batteries prevented?

Valve Regulated Lead Acid (VRLA) batteries have one way valves that release gas pressure due to incorrect or overcharging.

What is the accepted temperature limit for most lead-acid cells?

1108F / 438C

What is the general rule for charging current?

The current should not be greater than 1/10 the ampere hour capacity. Eg. 80Ah battery should not be charged with more than 8A.