Battery
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Contents |
Types of Battery
Primary
Use once and discard. Some types will leak and explode if charged with a current of just a few mA.Secondary
Rechargable
Primary Cell Charactersitics
Rechargable Cell Characteristics
Always read the datasheets, particulary for lithium based batteries. The development is progressing so fast that information that is a year old may be completely outdated.
Lead acid
Cell voltage 2 V
Recharge (wet cells) constant current to gassing, then top up
Recharge (gel/sealed cells) at constant voltage of 2.3 V per cell, or at <C/100
Deep discharge reduces life
Recharge often, there is no memory effect
leaving discharged damages cell by sulphation
High rate discharge reduces the capacity for that discharge
NiCd
Cell voltage 1.2 V
Recharge at constant current until temperature rise or reduction in terminal voltage due to drop in internal resistance
Recharge continuously at C/100 for simplest possible charging circuit for stand by use.
Full discharge necessary to avoid memory effect
Discharge possible at 5C
NiMh
Cell voltage 1.2 V
Recharge at constant current until temperature rise or plateau of terminal voltage - do not charge NiMh in a NiCd charger
Limit charging to less than 100 hours
Much less memory effect than NiCd
Discharge possible at 5C
Lithium ion (Li-ion)
Cell voltage 3.6 V
Recharge at constant 4.1 V to 4.2 V per cell
Deep discharge reduces life
Storage with full charge reduces life and storage at high temperatures reduces life, a laptop is the worst possible environment for keeping a li-ion battery
Do not discharge above 1C to 2C
Lithium-ion polymer (Li-Poly)
Nominal Cell Voltage 3.7 V
Some versions can be discharged at 20C or higher and recharged to 85% in 15 minutes or less.
Lithium-ion polymer batteries are replacing the old lithium ion batteries because they are cheaper and more robust.
Real-world battery equivalent
- EMF - Electromotive force
- RS - Equivalent series resistance (ESR)
- RP - Parasitic leakage current
Maximum power output of a battery according to Ohm's law
