ProfileNi-MH BatteryBattery Pack Designs
  BATTERY PACK DESIGNS
 Ni-MH BATTERY
Specification tables
GREENCELL Nickel-metal hydride cells are versatile performers easily adapted to most application demands. Existing design libraries for nickel-cadmium cells can usually be easily modified to incorporate nickel-metal hydride cells instead. Economical off-the-shelf designs can be tailored to the specific voltage, space, and termination requirements of an application.Figure 26 illustrates a typical battery installation within a representative application, while Figure 27 diagrams many of the components recommended for a nickel-metal battery.
Overview
Features
Comparison of Ni-MH
   and Ni-Cd Cells
Major applications
Structural designs
Electrochemical processes
Discharge characteristics
Charge characteristics
Charging methods
Cycle life characteristics
Storage characteristics
Safety characteristics
Designing for Ni-MH cells
Battey pack designs
Battery pack configurations
  designation system
Precautions for using
  Ni-MH batteries
Figure 26.Installation Within Typical Application
Battery selection  1. Packaging Considerations
 
Nickel-metal hydride batteries are generally packaged in two forms:Hard plastic cases are recommended for applications requiring the end-user to handle the battery. These cases offer greater protection against handling damage and shock and vibrations stresses. But depending on the design, thermal management may be more difficult within the hard case. Injection molding of hard.
 
 
 
 
 
 
 
 
 
 
 
 
 
 Figure 27.Elements of Battery Assembly
cases requires a substantial investment for mold construction and is thus best suited for high volumes.Lighter shrink-wrapped plastic packaging may be used when routine battery removal is not expected. These packs, as illustrated in Figure 27, usually consist of the cell assembly with insulators covering the exposed terminals. Plastic shrink tubing then covers the whole pack. Shrink-wrapped batteries have acceptable mechanical integrity for assembly, and when properly secured, withstand normal portable-product shock and vibration levels. Shrink packaging provides ample opportunity for hydrogen to diffuse and for internally generated heat to dissipate. Additional insulation from heat my be needed at the tangent points within the cell stacks (where they shrink material directly contacts the cell).Either type of packaging must maintain adequate ventilation to the individual cells while providing room for cell interconnections, battery terminations, and requisite charge control sensors.
 
 
 
 
 
 
 
 
 
 
 
 
  2. Shape
 
Battery shapes can be adjusted to fit application constraints. Among the most popular battery shapes are the following:
 
 
>Sticks-the terminal of one cells butts against the base of the next cell forming a long, slender battery.
 
  >Linear-the cells are placed side by side in a straight line.
  >Paired-cells are arranged in two¡¾or more¡¿symmetric rows.
 
>Nested-the cells of one row are nested within the indentations formed by the adjacent row.
 
  3. Materials
 
Materials used in the assembly of nickel-metal hydride batteries must withstand the high temperature environment that accompanies venting of the cell. Because of the exothermic nature of the charging process, should cells vent in overcharge, the vented gases will be largely high-temperature hydrogen(>200 Celsius). Although these gases will quickly disperse and cool, all materials used in cell construction must be capable of withstanding elevated temperatures while remaining inert in a hydrogen environment. Recommended materials for use in nickel-metal hydride battery construction include those below. Consult with GREENCELL regarding specific material specification details.
 
 
 
 
 
 
  Wires
 
To connect the batteries to the device, the vinyl-clad electrical wire for heat-resistant device wiring cinforming to UL-1007 is generally used. Red for the positiveside and black for the negative side are the standard colors. The ends of the lead wires may be bare cut ends or connected to connectors, etc.All wire insulation should be Teflon® , Kapton® , or other material with a minimum temperature rating of 200 Celsius.
 
 
 
 
 
  Standard Lead wire
 
Applicable Battery Size
Lesd Wire
Size
Length(mm)
Color
AAA Size
UL1007 AWG 24
Approx.200
+ Red
- Black
AA Size
UL1007 AWG 24
Approx.200
A Size
UL1007 AWG 22
Approx.200
SC Size
UL1007 AWG 18
UL1015 AWG 18
Approx.200
C Size
UL1007 AWG 20
UL1015 AWG 18
Approx.300
SC Size
UL1007 AWG 18
UL1015 AWG 18
Approx.300
  Sleeving
 
Shrink sleeving made of polyvinyl chloride are used on many packs as the external cover.Tube thickness ranges from 0.1mm to 0.2mm depending on battery type andconfiguration. All shrink sleeving should be able to withstand 200 celsius. PVC sleeving is not generally recommended. Kraft paper or fishpaper sleeving should be approximately 0.007 inches thick.
 
 
 
 
  Insulation
 
All cell insulation should be able to withstand 105 celsius for 24 hours. Vent shields must be constructed of Nomex® or other insulating material capable of withstanding 210 celsius.
 
 
  Case Material
 
Plastic cases must meet UL 9V40. Case materials without a rating of 210 celsius DTUL(Deflection Temperature Under Load)must be provided with vent shields over the positive ends of the cells.
 
 
  3. Interconnections and Terminations
 
Cell interconnections typically consist of nickel(Ni200)strip or nickel-plated steel ribbon spot-welded from one cell terminal to the adjacent cell's case. Nickel bus strips offer good solder ability, that can be securely spot-welded to the cells, and that is highly electro conduvtive, and alkaline-resistant. Minimum recommended nickel strip size is 0.187 inches wide by 0.005 inches thick. Wire interconnections are rarely used because of the difficulty in attachment since soldering directly to cells is forbidden.Battery terminations come in a variety of configurations ranging from simple flying leads(wires soldered to weld lugs which are then welded to the cells)in permanent installations to much more elaborate contact or connector systems on removable battery packs. Removable battery packs should be designed with a connection system that produces a minimum of 2 pounds of force while incorporating a wiping action on insertion to cut through oxide layers on the connection surfaces.
 
 
 
 
 
 
 
 
 
  Recommended Terminal Plate Dimensions (Material:Nickle)
 
Dimensions(mm)
Applicable Battery Size
Internal Impedance
Configuration
L*W*T
13*3*0.12
AAA Size
2.5m ohm
19*3*0.12
AA,A Size
4.0m ohm
25*5*0.15
SC Size
2.5m ohm
27*6*0.2
SC Size
2.0m ohm
30*6*0.2
D Size
2.0m ohm
13*5*0.2
SC,C,D Size
1.0m ohm
  4. Other Components
 
Nickel-metal hydride batteries typically require more components than nickel- cadmium batteries because of the emphasis on careful, redundant charge control including adequate fail-safe charge termination in case of excessive temperatures. These components include the follows:
 
 
 
  PTC Resistor
 
Positive temperature coefficient resistors such as Raychem's PolySwitch® circuit protector provide a latching, but resettable device for protection against short-circuit conditions.
 
 
  Thermostat
 
Thermostats or other resettable thermal control devices are typically used for backup to the primary charge control system to guard against extended overcharge and the resulting elevated temperatures.
 
 
  Thermal Fuse
 
Thermal fuses that open at a suitably elevated temperature(nominally 90 celsius)are often used as a third tier of thermal protection(after the normal charge control system and thermostat). They are a fail-safe measure since the battery charging system will become inoperative.
 
 
 
  Thermistor
 
Thermistors are normally used for the temperature-sensing necessary for recommended charge control schemes.
 
  5. Standard Configurations
 
A wide variety of standard battery configurations have been developed by cell manufacturers encompassing permutations of cell size/capacity, voltage, terminations, and charge control and termination sensors.As a minimum,We recommends that the following be included in any standard battery design: 
 
 
  Primary Charge Control System
 
The standard temperature or time-based charge control system to switch to maintenance charging
 
  Backup Resettable Thermal Protection
 
Terminates charging if the primary control system should fail to switch prior to extended overcharge. Normally set to 70 celsius.
 
  Fail-Safe Thermal Fuse
 
Permanently opens charge circuit if battery temperature exceeds acceptable limits. Normally set to 90 celsius.
 
  Short-Circuit Protection
  Provides protection in cases of excess discharge current.
  Vents and Vent Shielding
 
Gas management system to diffuse and cool a vented stream of hydrogen.
   6. Location
 
Ni-MH cells are most commonly used in battery packs. In using Ni-MH batteries, the type of battery, the number of cells, the shape of the battery pack, and the components of the battery pack will be determined by the rates (voltage and current )of the device, the charging specifications, the amount of space available inside the device, and the usage conditions.While battery location is generally influenced by product design constraints such asavailable space, influence on center of gravity, and ease of access, battery locations should also provide adequate ventilation, isolation from ignition sources and separation from major heat generators.After consultation concerning specifications, if so desired, we can also provide assembly services for battery packs.