Hawker F20/4H1C-R Operating And Maintenance Manual page 7

1.2.2 THE CELLS
Figure two: The cell
12
13 11
14
15
16
17
9
18
1 negative electrode
2 positive electrode
3 separator
4 plate stack
5 negative pole terminal
6 positive pole terminal
7 electrolyte level indicator
8 spacer
9 seal
The cell comprises an assembly of positive (2) and
negative (1) sintered electrodes, alternately arranged and
meander-like separated with very thin hydrophilic layers of
polymer materials (3). The plate stack (4) with the two pole
terminals (5, 6) is placed in a prismatic plastic container
(18) which is leak-proof welded with a cell lid (10) that has
two bores for the poles and a centric threaded hole for the
vent (12). The vent closes the cell house filled with alkaline
electrolyte.
1.2.2.1. Positive and negative electrodes
The positive and negative electrodes are made of a
sintered metallic structure containing electrochemically
active masses in its pores. The metallic tabs welded to the
electrodes are acting as current collectors.
1.2.2.2 Separators
Three layers of oxidations-resistant separator made of
non-degradable synthetic materials separate the positive
and negative electrodes, arranged alternately. The outer
layers are of nonwoven fabric, whereas the inner layer is
a very thin hydrophilic polymer film. The film acts as
a gas barrier that is reducing the exothermic oxygen
recombination during charge and thus ensures excellent
charge stability of the cells.
1.2.2.3 Electrolyte
The electrolyte is a solution of potassium hydroxide in
deionised water with a typical density of 1.28 ± 0.02 kg/l
at 20°C.
The document reference is online, please check the correspondence between the online documentation and the printed version.
6
10
5
8
7
4
3
2
10 lid
11 seal (vent)
12 vent (plug)
13 upper terminal nut
14 springwasher
15 lower terminal nut
16 sealing cap
17 seal
18 cell case
1
1.2.2.4 Vent plugs
The cell vents release the gas generated during float
charge, whilst also preventing electrolyte leakage and
contamination of electrolyte.
1.2.2.5 Pole terminals, connectors and terminal nuts
Pole terminals, nuts and connectors used for the inter-cell
connection are made of highly conductive nickel-plated
copper material.
1.3 Basic electrochemical reactions in
cells
Positive Electrode = Nickel hydroxide – electrode
Negative Electrode = Cadmium/Cadmiumhydroxide –
electrode
POSITIVE NEGITIVE
ELECTRODE ELECTRODE
+
2Ni(OH) Cd(OH)
2
Due to the very small changes in density by charge and
discharge operation, the density of the electrolyte cannot
indicate cell's state of charge.
7
POSITIVE NEGITIVE
ELECTRODE ELECTRODE
CHARGE
+
2NiO(OH) Cd+2H
2
DISCHARGE
0
2