We’ve been looking at truck battery packs and a common thread is the parallel battery packs approach. As there is no need for a propshaft the packs are being arranged down the centre and either side of the ladder frame. The Iveco S-eWay shows this approach very clearly.
and this approach gives them flexibility in the total energy capacity.
Being able to build a unit in larger volume that then can be used across different size vehicles for different applications gives a real advantage in development cost, but does result in a higher part count.
Parallel then Series or Series then Parallel
How should you connect battery cells together: Parallel then Series or Series then Parallel? What are the benefits and what are the issues with each approach?
The difficulty with this is the BMS operation with packs in parallel. Each of the large 70kWh sub-packs needs to have it’s own BMS and full set of sensors and HV protection. These need to then communicate and allocate a master or a master control unit needs to go over the top to control how the sub-packs work together.
This post has been built based on the support and sponsorship from: Thermo Fisher Scientific, Eatron Technologies, About:Energy and Quarto Technical Services.
Shutting the contactors requires the system to ensure that the pack voltages are within a given limit of each other (around 10V to 15V maximum delta is often quoted).
The current flows between the series strings will flow when the strings are brough together in parallel. Hence it is important to measure the voltage of each string and set limits on the differences.
This requirement is there throughout the life of the battery packs and hence as they age differently this could become more of a problem. Also, if the packs on one side are being warmed by the sun and the other side is cooler does the difference in temperature and hence internal resistance result in a differential sub-pack discharge?
All interesting problems to find solutions for with packs in parallel.
See also: Cross-String Current Sharing, Busbar Layout for Parallel Strings
If possible kindly provide details of battery cooling and traction cooling system
We have a core page on thermal that covers some of the cooling systems: https://www.batterydesign.net/thermal/ we are also adding to this.
For packs in parallel you would need to supply cooling / heating to the packs in parallel to ensure that all of the packs are as close as possible in temperature. A good technique is to circulate the fluid even when not actively heating or cooling as this helps to maintain consistent temperatures.
a good analysis of parallel strings complexity and possible solutions https://www.orionbms.com/manuals/pdf/parallel_strings.pdf