40
Rev.12/31/97
6. VENTED NICKEL CADMIUM BATTERY PRINCIPLES
6.1 GENERAL
6.1 GENERAL
The principles of operation, maintenance, and care of nickel-cadmium (ni-
cad) batteries are different than those for lead-acid batteries. If a conflict is
encountered, use manufacturer's instructions in precedence to this manual.
IEEE-1106--
cad) batteries are different than those for lead-acid batteries. If a conflict is
encountered, use manufacturer's instructions in precedence to this manual.
IEEE-1106--
Recommended Practice for Installation, Maintenance, Testing, and
Replacement of Vented Nickel-Cadmium Batteries for Stationary Service --may also be
referenced for further information. Nickel cadmium cells are resilient to
both overcharge and undercharge and may even be recovered if they go into
polarity reversal. They may be used in a wide temperature range, from -40
to +140 EF. High temperatures do reduce service life but not as severely as
both overcharge and undercharge and may even be recovered if they go into
polarity reversal. They may be used in a wide temperature range, from -40
to +140 EF. High temperatures do reduce service life but not as severely as
lead cells. With proper maintenance, service life may be expected to be as
long as 25 years.
long as 25 years.
6.2 DESCRIPTION
6.2 DESCRIPTION
In a ni-cad cell, both positive and negative plates are similar in construction,
consisting of very thin strips of perforated nickel-plated steel screen. Active
consisting of very thin strips of perforated nickel-plated steel screen. Active
materials are nickel compounds in positive plates and cadmium compounds
in negative. The electrolyte solution is potassium hydroxide within a steel or
plastic container. Positive and negative plates are separated by means of
hard rubber or plastic. Sheet hard-rubber separators are used to insulate
steel containers on the inside. Almost no active materials migrate from the
plates, so space between the container and plates is small. Cells are
mounted in insulated trays when furnished in steel containers. Containers
are separated from each other with insulated buttons to prevent shorting
and to provide ventilation between cases. Vent caps are spring-loaded so
they remain closed and are only open when electrolyte is being checked.
in negative. The electrolyte solution is potassium hydroxide within a steel or
plastic container. Positive and negative plates are separated by means of
hard rubber or plastic. Sheet hard-rubber separators are used to insulate
steel containers on the inside. Almost no active materials migrate from the
plates, so space between the container and plates is small. Cells are
mounted in insulated trays when furnished in steel containers. Containers
are separated from each other with insulated buttons to prevent shorting
and to provide ventilation between cases. Vent caps are spring-loaded so
they remain closed and are only open when electrolyte is being checked.
6.3 CHEMICAL REACTIONS
6.3 CHEMICAL REACTIONS
Charging and discharging nickel-cadmium cells is similar to other storage
cells. During discharge, nickel hydrate is removed from positive plates by
the reduction of nickel hydroxide (OH) and combines with the cadmium of
the negative plates, forming cadmium oxide. This process is the reversible
action of nickel and cadmium. On charging, the OH leaves the negative
plate and returns to the positive plate. The chemical reactions taking place
in a storage cell are:
cells. During discharge, nickel hydrate is removed from positive plates by
the reduction of nickel hydroxide (OH) and combines with the cadmium of
the negative plates, forming cadmium oxide. This process is the reversible
action of nickel and cadmium. On charging, the OH leaves the negative
plate and returns to the positive plate. The chemical reactions taking place
in a storage cell are:
Battery Discharged:
Battery Discharged:
Negative Plate:
Negative Plate:
2Ni(OH)2 - 6H
2
O + 2KOH + 2H
2
O + CdO
Battery Discharged:
Battery Discharged:
Positive Plate
Positive Plate
2Ni(OH)
3
- 5H
2
0 + 2KOH + 2H
2
0 + Cd
The net result is the transfer of oxygen from the active material of one plate
to that of the other without measurable change of the electrolyte. In the
to that of the other without measurable change of the electrolyte. In the