Batteries for HTM D. J. McMahon 141004 rev cewood 2017-10-09
Key Points Batteries: - chemistry; know the characteristic cell voltages of common chemistries: NiCd/ NiMH 1.2V Hg 1.35V Zn Alkaline 1.5V Ag Oxide 1.55V Pb 2.0V Li 3.0V LiIon/ LiPo 3.6V - know which ones are primary, which ones are secondary - be very comfortable with volts times amps equals watts - understand capacity, measured in Ah - understand C-rate for battery discharge - know how to recycle depleted batteries - understand that specific battery chemistries require matching chargers
Basic Battery Parameters: Chemistry: The most common battery chemistries are based on Zinc, Lead, Nickel and Lithium. (Silver & Mercury are also used.) Each chemistry has a characteristic Cell Voltage and a characteristic Energy Density. Cell Voltage: Individual cells have a nominal voltage; however, the open circuit voltage (OCV) on a fully charged cell is 5-7% higher. Battery Voltage (V): Battery voltage is the cell voltage multiplied by the number of cells in series. C-rate: The C-rate specifies the speed a battery is charged or discharged. At 1C, the battery charges and discharges at a current that is on par with the marked Ah rating. For example, a 5 Ah battery discharged at 1C is discharged at 5 Amps. At 0.5C, the current is half and the time is doubled, and at 0.1C the current is one-tenth and the time is 10-fold. That 5 Ah battery at.1c would be discharged at 500 ma and would last for 10 hours.
Capacity (Ah): Capacity represents specific energy in ampere-hours (Ah). Ah is the discharge current a battery can deliver over time. You can install a battery with a higher Ah than specified and get a longer runtime; you can also use a smaller battery and expect a shorter runtime. Specific power: loading capability. Batteries for power tools, for example, are made for high specific power. They support a high C-rate. Load current: battery output current under a load. (Real) Power (W): (On a purely resistive load) Watts = Volts x Amps (also called VA) Physical size and dimensions: will it fit? Energy Density: watt-hours per kilogram. Thanks to, and further information from: http://batteryuniversity.com/learn/article/battery_definitions
from this excellent reference - https://en.wikipedia.org/wiki/list_of_battery_sizes
Primary Cell primary Batteries > irreversible chemistry > discarded after use
Zinc-Carbon cell (1.5v) primary Zn + Zn 2+ + 2e - e - + NH 4+ + MnO2 MnO(OH) + NH 3 > called Dry Cell > uses MnO 2 to absorb the NH 3 > usage consumes the Zinc case > obsolete
primary Alkaline Cell (1.5v) > Uses ZnO 2 and Zn > alkali used as an electrolyte > commercially most common
primary Mercury Cell (1.35v) > Zn + HgO + H 2 O Zn(OH) + Hg > higher current capacity > flatter voltage curve > expensive
Silver Oxide Cell (1.55v) primary > Zn + AgO 2 ZnO + 2Ag > very stable output, low current > common watch battery
Lithium Cell (3v) primary > Multiple chemistries > Lithium has the highest negative potential > Li cells have the highest energy densities (Do not confuse with Lithium Ion or Lithium Polymer cells!)
does not belong! CRxxxx identification: (Lithium coin cells) First two digits = diameter in mm Second two digits = height in mm x 10 eg: CR2016 is 20mm in diameter, 1.6mm thick
Secondary Cells: Rechargeable Batteries secondary i.e. chemistry is reversible
Lead - Acid (2.0v cell) Pb + (HSO4) - Pb(SO 4 ) + H + + 2e - 2e - + PbO 2 + 3H + + HSO4 - Pb(SO 4 ) + 2H 2 O > standard car battery (3 or 6 cells = 6 or 12v) > can be Sealed Lead-Acid (SLA) > can be activated glass mat (AGM) > can be Valved Sealed Lead-Acid > High current output, durable > Heavy, some hazards > FR in size code: Flame Retardant secondary > fully (freshly) charged: 13.8 volts (2.3v per cell) > fully discharged: 10.5 volts (1.75v per cell, < 76% of full)
Valve-Regulated Lead-Acid Batteries or Sealed Lead- Acid (SLA) batteries secondary Same chemistry as a classic lead-acid, but uses less acid, and recombines gas products to form water. Includes a pressure relief valve to vent gases if overcharged or overheated. Has a higher energy density than standard lead-acid batteries. Commonly used in medical electronics. fully (freshly) charged: 13.8 volts (2.3v per cell) fully discharged: 10.5 volts (1.75v per cell, < 76%)
Nickel-Cadmium (1.2v cell) NiCad batteries secondary 2NiOOH + Cd + 2H 2 O 2Ni(OH) 2 + Cd(OH) 2 > High efficiency, high current > Develop a discharge memory > Cadmium is highly toxic > Virtually extinct now
Nickel Metal Hydride Cell NiMH cell H 2 O + M + e (1.2v cell) secondary OH + MH > Replaced Ni-Cad > Higher energy density than NiCd > No memory issues > M is an alloy of Ni and another metal, formulated for best current delivery.
Lithium-Ion Cell (3.6v cell) (Do not confuse with Lithium cell!) secondary Li + + e - + LiCoO 2 D Li 2 O + CoO > Large proportion of consumer products > Highest energy density > No memory effect > Low self-discharge per month > Capacity fails with high current draw or heat > lithium-ion polymer battery LiPo has the same chemistry in a soft pouch format
Lithium-Ion
Boeing 787 grounded: Jan-May 2013 NTSB: scorched battery cells, likely cascading cell failure
Smart Battery > Rechargeable battery that includes a microchip that communicates information to the charger and the user. > Usually use the System Management Bus (SMBus): a 2-wire interface that signals the battery voltage, temperature, clock data, and the battery s type, birthdate, serial number, and cycle count as binary data. > More expensive, but more efficient. Regular batteries paired with Smart Chargers are becoming much more common.
Typical NiMH and LiON Battery Packs Fusible link: Thermal fuse:
When good batteries go bad: Watch for: > corrosion on terminals > corrosion damage to device
> leaking batteries
> bulging cases! > cell voltage reversal!
Charging Lead-Acid Batteries > Charger needs to be constant voltage only > Lead-acid takes longer to fully recharge (~12 hours), and current should be reduced gradually > Assume 2.4 volts per cell, and charge initially at 20% to 30% of current capacity Do NOT mix or swap battery types in chargers!
Charging Ni-MH Batteries: > Charge rate should not exceed 1/10 th of the battery s amp-hour rating. > Chargers need to be constant voltage and constant current. > Modern chargers drop down to a trickle charge when the battery is at 90% of capacity.
Battery Maintenance > Protect terminal connectors from shorts with insulators > Don t leave in a charger more than 24 hrs > Keep at room temp after charging (NiCd needed periodic full discharge, but memory is no longer a concern)
Expired batteries should be sent to recycling
Pull one or both terminals from a dead battery when discarding or wrap terminals with tape
Major vendors of batteries for medical devices:
Suggested reference: www.batteryuniversity.com Isador Buchman Part of Cadex company (www.cadex.com)