Alpha Technologies Lomain Ni-Cd Pocket Plate Battery - Manual (Page 21)

21 745-680-B10-001 Rev. A
4.9 Topping up interval
At the final stage of the charging procedure of a Ni-Cd battery the provided electrical energy
cannot be fully absorbed but is absolutely necessary to reach the fully charged state of
the cells. The difference between absorbed and provided energy leads to a break down of
the electrolyte’s water content into oxygen and hydrogen (electrolysis). This loss has to be
compensated by topping up the cells with pure distilled water.
The water loss depends on the current used for overcharging. A battery on standby operation
will consume less water than a battery that is cycled constantly, (e.g., a battery which is
discharged and recharged on a regular basis).
In theory, the quantity of water used can be found by Faraday’s equation that each ampere
hour of overcharge breaks down 0.336 cm 3 of water. Depending upon the operating
temperature of the battery and the charging conditions, the Alpha Lomain battery has a
recombination rate of 90%.
Calculation of topping up interval for KGL 1390:
A cell (KGL 1390P) is floated at 1.41 V/cell
The electrolyte reserve for this cell is approx. 8730 cm³
A standard cell at 1.41 V/cell will use approx. 0.025 cm³/month for 1Ah of capacity
When the KGL 1390P reaches a 90% recombination rate which means the use will only be
0.025 cm³/month for 1 Ah of capacity
Therefore, a KGL 1390P battery will use 0.025 x 1390 = 34.75 cm³ per month and the
electrolyte reserve will be used in 8730/34.75 (approx. 251 months)
Or, approximately 21 years at 20°C
4.0 Operating Features, continued