Data Required to Size a Pack

When thinking about sizing a battery pack it is worth stopping and considering the data required to size a pack. These are the requirements. If you don’t have these then the design is likely to change considerably, these changes will cost time and can ultimately end in a poorly optimised design.

  • Usable Energy (kWh)
    • at a defined discharge rate
    • when in the lifetime: beginning or end of life
  • Power (kW)
    • peak discharge power and time
    • continuous discharge rate
    • charge power available
    • charge time required

The usable energy for a battery pack reduces over lifetime. Therefore, it is important to understand if the battery needs to deliver a minimum amount of energy as this will define the lifetime or the starting capacity.

This end of life requirement also applies to the power. The battery pack resistance will increase as the pack ages. Increasing heat output and meaning larger voltage drops for a given current demand.

  • Voltage Range (V)
    • maximum and minimum
  • Maximum Current
    • what is the maximum current demand and for how long
    • continuous current rating (charge or discharge)

The voltage range will be defined by the system. Therefore, it is necessary to understand everything connected to the system and under all scenarios (eg charging and discharging).

The continuos current rating is a key parameter to fix as it defines so much of the battery and the system. Busbars, fusing, contactors and connectors.

  • External Load
    • type of load (motor, grid, computer, household)
    • load specifications
    • isolation of load

Knowing the external system to the battery is important. This will define the connection and disconnection strategy. It will define measurements that are required for isolation and how the system needs to respond in a fault or failure scenario.

This post has been built based on the support and sponsorship from: Eatron TechnologiesAbout:EnergyAVANT Future MobilityQuarto Technical Services and TAE Power Solutions.

  • Environment
    • temperature range of operation
    • solar load
    • storage conditions
    • humidity
    • water / dust
  • Heating / Cooling
    • is there an external heater/chiller
      • power capability
      • control interface

Do you need to insulate the battery housing? How much heating and cooling capacity is required to enable the performance requirements and lifetime?

What determines the heating/cooling capacity?

  • Physical Dimensions
    • limitations on any dimension
    • clearances required in installation
    • maximum weight
  • Mechanics
    • structural requirements for shipping and installed
    • static loads
    • dynamic loads
    • shock loads
    • crush specifications

In some installations there are critical dimensions. Related to an opening size, a maximum height (often an automotive requirement for underfloor packaging) or a weight limit for the product.

Lexus RZ vehicle and powertrain image
  • Safety
    • control
    • electrical
    • mechanical
    • thermal runaway

A huge topic in it’s own right and hence you need to consider this right from the start.

  • Transport Requirements
    • type of transport (road, rail, sea, air)
  • Servicing
    • Expectations on servicing
  • End of Life
    • second life
    • recycling

How are you going to transport the battery pack? What certification will it need? How will this change at beginning of life to end of life, recycling and if it has failed.

What is the service process, where, who and what training is required?

Don’t leave the definition of how this is going to be reused or recycled until after it has been designed. Recycling should be considered for every component and every aspect of the assembly.

Who is defining the legislative requirements of the product? Is it clear where this will be made and where it will be sold?

What design guides already exist and are they applicable?

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