Hello All,

Greetings from IIT Bombay Racing Team.

I am Mukul Jangid, Chief Engineer of our team. Our team builds electric cars for competing at Formula Student UK. We are from Mumbai, India's Indian Institute of Technology, Bombay (IIT Bombay).

We use LiPo cells from E Propulsions system based in Hong Kong. Our battery pack is of 96s1p configuration and cells are of 22 000 mAh. Our powertrain is from Compact Dynamics with nominal working voltage of ~350 V and peak power output of 80 kW. Our cells are connected to each other through busbars and mechanical clamping using screws and nuts.
One major issue in our last cars has been the unreliability of our BMS. We make our own BMS system using LT6804 IC from Linear Technology. Because of unreliable BMS, many a time the cells get into unfavorable situations which render them useless for rest of the season. This leads to a lot of cells being wasted, an unreliable battery pack and a very small testing time. This year we
want to make sure that these things are not repeated and hence we need to be sure of all the failure modes so that we can take an informed decision regarding the number of cells that we purchase as the purchase cycle is very long and ideally we would like to buy all the cells at once apart from the fact that the cells form a big slice of our budget as well.

So we need to be sure that once we use the new set of cells, they will not be abused. For this, we referred to a lot of online sources, clubbing those details with our own experiences we have listed down the following points.
  • Overvoltage and Undervoltage protection through BMS (3.3 V to 4.1 V is regulated in our team)
  • Operating in safe temperature limits regulated through temperature monitoring (50 deg C according to cell datasheet)
  • Keeping charging and discharge current within safe limits as specified by manufacturer
  • Storage strategy: should not be left charged while unattempted (should be down to ~3.6 V if unused, should not be left fully discharged as well). Also, not storing them at very high or very low temperatures.

Since our cars have not seen a lot of testing there could be several other practical issues that other teams might have observed with experience. If you guys could share some of this valuable information as to what other practical issues are we missing in the above list. This would really help us in designing a solution for such issues.

This information would be useful to other teams starting with EVs as well, so we hope we are able to gather some good information on this thread.