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Battery Pack Structural Design
A well designed battery pack protects and replicates the individual cell performance
of multiple cells in the pack. It provides mechanical protection and integrity,
thermal stability, and electrical protection and performance. The electrical
interconnections, mechanical supports and thermodynamic systems are all essential
elements of the battery pack’s structural design. This section covers:
•
Electrical Connection and Protection
•
Mechanical Cell Support
•
Thermal Management
Electrical Connection and Protection
The electrical interconnections in a battery pack must be designed to carry the expected maximum current for
both the maximum time and ambient temperature in which the pack is expected to operate. In addition, the
electrical interconnections shall be designed to prevent accidental short circuits that may result from heavy
vibration (vehicle operation), or extreme shock (drop or impact), or loose hardware.
Cell Interconnections
Cell interconnections should be sized for the expected maximum current carrying capability. Improperly sized
interconnections could heat up excessively, resulting in damage to themselves, nearby components, structures or
even the cells. For reliable welded connections at the AMP20 cell terminals, A123 recommends either copper or
copper alloy straps welded to the copper tabs and aluminum straps welded to the aluminum tabs. For A123
cylindrical cells, cell interconnections (straps) should be neither soldered on the cells tabs nor attached using
extreme heat. A123 recommends nickel or copper alloy straps be resistance or laser-welded to the terminals of the
cells. See the Cell Welding section on page 58 for more details.
AMP20 Cell Insulation
The outside of the prismatic cell is electrically isolated from the electrode terminals but at a high enough voltage
(> 2500 Vrms Hi-Pot testing), a flashover can occur. Therefore in the battery pack design, it is important that there
is adequate and consistent insulation between the outer surfaces of the cell and any surrounding conductive
surfaces, such as heat sinks, conductors, and/or the chassis.
Cylindrical Cell Insulation
The outside case of the ANR26650 and AHR32113 is electrically connected to the positive end (cathode) of the cell.
The outside case of the APR18650 cell is electrically connected to the negative end (anode) of the cell. Take care
to keep this surface electrically-isolated from any electrical bus bar or mechanical support that may be of different
voltage potential. Insulation, such as tapes, shrink wraps, or sleeves, must have at least a 150 °C melting point. This
helps ensure that the cells do not short circuit to each other in a high temperature fault condition, which could
cause even more widespread damage.
Structure
Cell Configuration