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Lead Acid Battery Systems

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Basic Chemistry of Lead Acid

Initial Charge:
Anode Reaction: 2H+(aq) + 2e− → H2(g)
Cathode Reaction: Pb(s) + 2H2O(l) → PbO2(s) + 2H+(aq) + 2e−

Discharge:
Anode Reaction: Pb(s) + HSO−4(aq) → PbSO4(s) + H+(aq) + 2e−
Cathode Reaction: PbO2(s) + HSO−4(aq) + 3H+(aq) + 2e− → PbSO4(s) + 2H2O(l)

Recharge:
Anode Reaction:PbSO4(s) + H+(aq) + 2e− → Pb(s) + HSO−4(aq)
Cathode Reaction: PbSO4(s) + 2H2O(l) → PbO2(s) + HSO−4(aq) + 3H+(aq) + 2e−

 

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Nickel Cadmium Battery Systems

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Basic Chemistry of Nickel Cadmium

Discharge: Anode Reaction: Cd + 20H > Cd(0H)2 +2c
Discharge Cathode Reaction: 2NiO(OH) + 2H2O +2e > 2Ni(OH)2 + 2OH
Net Discharge Reaction: 2NiO(OH) + Cd + 2H2O > 2Ni(OH)2 + Cd(OH)2
Note: During recharge the above reactions are reversed

Load Profile

Sizing the battery system for a specific location and application is based on a load profile identifying the applied loads vs. time as per the below example:

load_profile

This information will identify several factors essential to size both the type and capacity of the appropriate battery system.

In general secondary batteries are manufactured in three categories

High Discharge Rate – Normally high applied loads for short periods of time.
Medium Discharge Rate – Normally variable loads within a moderate range of applied loads, possibly with short spikes for moderate periods of time.
Long Discharge Rate – Normally moderate applied loads for long periods of time.