Electrical Technology

1. Chapter # 9
ELECTROCHEMICAL
POWER
SOURCES

2. Parts of a Lead-acid battery
The parts are as follows:
Negative & Positive Plates
Separators
Electrolyte
Container
 Bottom Grooved Support Blocks
 Connecting Bar
 Terminal Posts or Pillar
 Vent Plugs or Filler Caps
 External Connecting Straps

3. Plates
• The plates consists of lattice type of grid of cast lead alloy which is
covered with active materials
• The grid not only acts support for fragile materials but also conducts
electric current
• Grid for positive and negative types are often of the same design
although negative plates grid are somewhat of lighter weight

4. Separators
• They are thin sheet of porous material placed between positive and negative
plates for preventing contact between them and thus providing internal short
circuiting of the battery
• A separator must be sufficiently porous to allow the diffusion or circulation of
electrolyte between the plates
• These are made of especially treated cedar wood, glass wool mat, micro
porous rubber (mipor), microporous plastic (plastipore, miplast) and
perforated pvc
• A separator must posses high resistance and mechanical strenght

5. Electrolyte
• It is the di sulphuric acid which fills the cell compartentto immerse
the plates completely
• It is made of vulcanized rubber or moulded hard rubber (ebonite),
moulded plastic, ceramics, glass or celluloid.
• Vulcanised rubber -> car service
• White glass containers -> lightning plants and wireless sets
• A single mono block container with 6 compartments generally used
for starting batteries is shown in the figure below
Container

6. Parts of Container
Bottom grooved support block: These are raised ribs, either fitted in the bottom of the
container or made with the container itself. Their function is to support the plates and hold
them in position and at the same time protect them from short-circuits that would otherwise
occur as a result of fall of the active material from the plates onto the bottom of the container
Connecting Bar: It is the lead alloy link which joins the cell together in series connecting the
positive pillar of one cell to the negative pillar of the next one
Terminal post or pillars: It is the upward extension from each connecting bar which passes
through the cell cover for cable connections to the outside circuits. For easy identification, the
negative terminal post is smaller in diameter than the positive terminal post
Vent plugs or filler: These are made of polystyrene or rubber and are usually screwed in the
cover. Their function is to prevent escape of electrolyte but allow the free exit of the gas. These
can be easily removed for topping up or talking hydrometer readings
External connecting straps: These are lead alloys flat bars which connect the positive
terminal post of one cell to the negative of the next across the top of the cover. These are of
very solid construction especially in starting batteries because they have to carry very heavy
current