110V DC SYSTEM

1.     DC system consist of:

a.     Battery

b.     Battery charger

c.      Loads

2.     Battery Introduction

If two electrodes of different metals are immersed into a proper solution or chemicals, a chemical reaction will occur such that there will be voltage (EMF) across the electrodes. Those arrangements are called cell. Batteries are combination of two or more cells.

3.     Types of Batteries

a.     Alkaline/Nickel cadmium battery

Positive electrodes – Nickel Oxides + Cadmium Oxides

b.     Negative electrodes – Nickel – Iron

c.      Electrolytes – Potassium Hydroxides in distilled water

4.     Charging & Discharging

When the cells are connected to loads, current will flow from negative electrodes to positive via the load connections. This is called discharging. This flow of current causes all the properties of the electrolyte and the electrodes to change and this reduces the capabilities of the cell to provide voltage.

To normalize the reduction and its properties an external DC current (charger) is introduced to the electrodes. This is called charging.

5.     Specific Gravity

5.1            is a method of measuring its contents or density of solution in water (S.G for water = 1).

5.2            Measurement of specific gravity is done using hydrometer

5.3            S.G for acid battery       = 1.25 to 1.28

S.G for alkaline battery> 1.120

Note; hydrometer used for acid not to be used for alkaline

6.     Terminal Voltage

6.1            The output voltage for individual cells

6.2            Values varies depending on manufacturer and setting but in sub-station normally:

Acid batteries       - 2.2 to 2.25 volt

Alkaline batteries- 1.4 to 1.5 volt

7.     Battery Ratings

7.1            Usually battery rating is rated at Ampere-Hours

8.     Battery charger

8.1            To inject DC current to battery to charge battery

8.2            Consists mainly of a rectifier that converts AC to DC

8.3            It can be single phase or three phase input rectifier. The three phase rectifier is superior and more stable (low ripple)

8.4            Battery charger is rated at the maximum current output it can produce

9.     Charging Facilities of A Battery Charger

9.1            Float charger

A system where the rectifier + battery + load connected together to maintain the DC voltage and at the same time charge the battery.

9.2            Boost charge

Charging batteries to higher voltage and current. This is usually done when:

a.     Commissioning

b.     AC failure

c.      Adding electrolytes

10.                        Meters on Battery Charger

Meters on battery charger varies depending on charger design but all chargers should have the following:

a.     AC input

b.     DC volt

c.      Battery ammeter

d.     Charger ammeter

e.      Load ammeter

f.       Electrolyte (warning/alarm)