In the first instance it is all about requirements. What are the hard points, the inviable parameters? My first thoughts are around these headings:
- Energy
- Power
- 10s pulse
- Continuous
- Maximum continuous current
- Charge
- Power
- Time
- Environment
- Cooling
- Heating
- Mass
- Volume
- Lifetime
- Control
- Legislation
- Design rules
- System voltage
This post has been built based on the support of and sponsorship from: Quarto Technical Services, Eatron Technologies and About:Energy
Initial sizing is around Electrical and Thermal.
- For a given cell can we get to a series and parallel configuration that meets the power demand?
- How fast do the cells heat up?
- What is the continuous coolant requirement?
The Battery Calculations Workbook has some great tools to help with this initial sizing.
We also need rapidly need to consider the Application as this has a significant impact on the battery pack.
- Land based transport
- Stationary storage
- Marine
- Aerospace
- Rail
- White goods
The System page has a more comprehensive list of applications and some of their specific requirements.
Then within that we need to look at the cycle. At a high level we can consider:
- System architecture:
- Pure electric
- Hybridised
- Range extended
- Environment
- Inside a dry and temperature controlled room
- IP rating
- Cooling options
- Installation and Service
- Recycling
This process adds boundary conditions and constraints. Often you will find that the customer will over-constrain the definition.
we need a 48V 2kWh pack that can deliver 45kW continuous, weighs less than 10kg, IP69 and passive cooling
OK, this might be solvable with lots of testing of cells, modelling and budget to match. Relax some of those requirements and the number of options increases considerably.
Symbolising the design as a circle and requirements as red dots we can see that it is easy to lay down too many points that the circle has to intersect. Some may end up having to be ignored, this trading of requirements will become part of the sizing.
In these cases it is useful to look at the complete space around those requirements. Thus allowing you to check that you haven’t missed an option or idea. Also, it can be useful to demonstrate the options to a customer as that will show that you understand the technology, what their requirements mean practically and how you could offer solutions with some movement in the targets.
See also: Pack Design, Battery Pack Sizing