Assessing a Pack Supplier

If you’re assessing a pack supplier what do you need to think about? What questions should you ask?

Ensure you have a clear set of requirements beforehand, at a high level these need to be:

  • usable energy
  • peak power
  • continuous power
  • voltage range
  • charge time
  • dimensions
  • maximum weight
structure of a battery pack

This list needs to have all of your requirements, be very clear on what you have to have and where you can change.

Break it then into functions and components:

  • Electrical
    • contactors, fuses – can they describe the layout and why it is like that
    • standard connectors? 
    • what creepage and clearance specification is it designed to?
    • what is the pack electrical resistance?
  • Thermal
    • what is the cell to cell maximum temperature delta?
    • fluid flow rates if applicable
    • how many temperature sensors can fail before pack shuts down?
    • materials and or components that set the temperature or thermal limits for the system.
  • Mechanical
    • what is the IP rating?
    • how are loads managed and how is the pack protected during abuse and impact events
  • Control
    • what data is shared by the pack?
    • limit and beyond behaviour – does it ask for power derate prior to opening contactors?
    • software updates – how are these handled?
    • what data is captured
    • SOC measurement accuracy? typically 1 to 3% but can they demonstrate how good it is?
  • Safety
    • iso26262 ? – do you need this and does it meet this
    • ask what the strategy is for preventing and managing thermal runaway events
  • Cells/Modules
    • Key here is that they have data or have tested the cell and module to establish the performance, safety and ageing characteristics
  • BMS
    • what is the BMS architecture?
    • what data is available over the communications?
    • who makes the hardware and software?
  • Cooling system
    • how is it designed and are the connections leak-proof?
    • is it possible to fill the cooling system without getting an air-lock?
    • what is the target cell temperature gradient?
    • what is the cell to cell maximum temperature gradient
  • HV distribution
    • are the busbars supported?
    • are the connection areas large enough?
    • are connections bolted and if so is there a specified torque?
  • Enclosure
    • how is it sealed and how is it tested to ensure it is sealed?
    • what type of seal is used and can it be replaced?
    • is there a breather and a burst disc?
    • what static and dynamic testing has been done to prove it meets requirements?

You will see that the questions are around the parts and the design, it is essential that you use these to establish the suppliers capability. This is both technical and commercial, it is no good if they have the best technical design and cannot source your volume requirements.

You also need to look at:

  • Sourcing
    • cells/modules – do they have  an agreement with the supplier?
  • Warranty
    • what do they offer? design errors, cell manufacturing errors?
    • what agreements are in place with the cell supplier?
  • Legislation
    • what standards and legislation is it designed to?
    • UN38.3 – can you transport the pack?
    • what legislation do the cells meet?
  • Manufacturing
    • what end of line tests on the pack do they do?
    • how many have they made?
    • do they match cells/modules?
    • how long does the first charge cycle typically take?
    • do they pressure test coolant system?
    • how do they manage cells/modules prior to pack assembly – are they held in temperature controlled storage (typically <15°C
  • Service
    • is the pack serviceable and who can service it?
    • are spare parts available?
  • Recycling
    • who does the recycling at end of life?
    • are there any materials / parts that have specific requirements?

You need to understand what you’re asking of the battery pack supplier. You are going to a supplier because you do not have experience or scale needed for costs, or this is low volume so a supplier will be able to do this better and cheaper than you can internally. Having this understood is the most important thing here and usually where issues arise. Different ones are good at different things and have different experience/capabilities.

Are they a full service supplier, contract manufacturing, or just a consultant with engineering know how? What capabilities and bandwidth do they have to support your project? You could get them to do full engineering, sourcing and manufacturing or just some of each. All suppliers will say they can do it all, need to ask a lot of good questions to determine their actual capabilities.

Not all battery pack suppliers work on the same type of battery packs. Need to ensure that they have experience in types of battery packs you need. What works in automotive/commercial is different from medical devices and military. Even just the supply chain know how and support for medical that is strictly controlled and US military require ITAR which can be difficult to manage. Some specialize in 48V 2-wheelers or e-bikes which does not carry into larger 400V – 800V packs for commercial, i.e. they don’t have know how in CAN or ISO 26262.

This post has been built based on the support and sponsorship from: Eatron TechnologiesAbout:EnergyAVANT Future MobilityQuarto Technical ServicesTAE Power Solutions and The Limiting Factor. 

This is only an initial list of things to think about. Please do send us any key things I have missed or got wrong.

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