Basic Characteristics of Battery Types
(For Guidance Only)
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Charging
The operating life of all rechargeable batteries is determined by four major
factors:
- Rate of discharge
- Depth of discharge
- Operating and ambient temperature
- Charging method
The first three are determined by the equipment designer but if the incorrect
charging technique is adopted the benefit of good design is minimised resulting
in battery service life and performance being significantly degraded.
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Characteristic
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SLA
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NiCd
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NiMH
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Energy Density (Wh/kg)
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30
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40
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60
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Volts/cell (nominal)
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2.0
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1.2
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1.2
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Operating cycles (typical)
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500
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1000
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800
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Self discharge (%/month)
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3%
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30%
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30%
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Equivalent series resistance
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low
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very low
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medium
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Operating temperature
(
o
C)
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5 to 35
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10 to 45
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10 to 40
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Maximum charge rate
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0.25C
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2C
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1C
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Charge method
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CV
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CC
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CC
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Memory effect
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No
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Yes
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Yes
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With all types of cells, it is only possible to realise optimum performance
when operating within the correct management of charge and discharge
characteristics., This is particularly important at the higher currents
normally associated with intelligent fast charging.
To prevent overcharging, accurate charge termination is achieved by using
proven techniques. In addition, intelligent chargers have to accommodate the
erratic characteristics of abused, unformed or old cells, as well as the
effects of protection circuitry and variations in operating temperature and
contact resistance.
Generally the problems are not so pronounced in the constant voltage charging
of sealed lead acid cells compared with constant current
charging of nickel cadmium and nickel metal hydride cells charged at higher C
rates.
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