Explain the operating principles of a lead acid battery, including:

Voltage characteristics of cells and batteries

Station battery systems are designed to satisfy many

voltage ratings. Most DC equipment systems fall

within one of the following DC voltage groups.

1) 24 volts – radiation detection equipment, audible and visual alarm systems, and communication systems.

2) 125 volts – switchgear systems, uninterruptible AC power supply systems, emergency lighting, and supervisory control systems.

3) 250 volts – large motor loads, motor-operated valves.

Series Connected Batteries

1) Negative electrode of the first cell connected to the positive electrode of the second cell.

2) Negative electrode of the second cell connected to the positive electrode of the third, and so on.

3) Used to increase battery output voltage.

Parallel Connected Batteries

1) Positive electrodes are connected together, negative electrodes are connected together.

2) Cells in parallel increase current capacity or battery capacity.

Series-Parallel Batteries

1) Provides higher voltage output and more current capacity.

Fully charged battery cells develop an open circuit voltage.

Fully charged battery cells on a float charge develop a voltage.

Definition of a CCA: Amount of current a given battery can deliver for 30 seconds at 0°F without dropping below a specified cut-off voltage.

(Typically 7.2 volts for 12-volt battery.)

A battery is considered fully discharged when any cell voltage reaches 1.75 volts. This is the normal method to assess whether or NOT a battery has been fully discharged.

Battery  Voltage Checks

1. Trend the effectiveness of a float charge.

2. To monitor battery performance during discharges.

Cell voltage

Normally taken from the negative and positive posts of the same cell. Remember, cell voltage will be around 2.2 Vdc when on a float charge.

Overall Voltage

Typically taken from where the battery is connected to the DC bus. Overall voltage will be equal to the sum of the individual cell voltage (if connected in series).

Factors affecting Battery Capacity

a. Design of the battery

b. Age of the battery

c. Discharge rate

d. Temperature

Specific Gravity

a. Ratio of comparing density of a substance

(electrolyte) to the density of water.

b. Determines battery state of charge.

c. Indicated values are affected by electrolyte level and temperature.

Battery Hazards

a. Batteries contain enormous amounts of energy.

b. Electrolyte is considered a hazardous material and requires special cleanup and disposal requirements.

c. Showers and eyewash stations are normally located close by should a worker come in contact with electrolyte.

d. Batteries generate oxygen and hydrogen gas during operation.

Battery Chargers

a. Convert AC to DC.

b. Normally supply a float charge voltage to the battery and supply power to DC system loads.

c. Equalizing charge is used to restore a battery after a discharge.

Used to connect plates of "like polarity" to the cell's terminal post.