Designing a safe EV battery pack for India

Even the most innovative and technologically strong electric vehicle manufacturers in India have no choice but to depend on imports for a few critical components like lithium cells and semiconductors that are not made in India. However, at the EV component and vehicle level, most components necessary for packaging production vehicles are possible to make in India. Autocar Professional spoke with Dr Amitabh Saran, co-founder of Bengaluru-based Altigreen Propulsion Labs to understand how it has dealt with limitations of material availability in the country.

On several occasions, you have talked about designing critical components like motors, controllers, DC-DC chargers and batteries.
Yes, and we continue to do it. We strongly believe that true EVs require very tight integration with components including a deep understanding of their behaviours in extreme cases. We have taken the approach of complete backward integration of all EV components including making our own motors, controllers, VCU, telematics, software stack, gearbox, BMS and the battery pack.

We understand a high-power EV ecosystem demands reliable and efficient DC-DC power conversion. What are the key safety considerations when designing one?
For smaller format vehicles, DC-DC converters are low powered and are needed only for the 12V circuit. That said, we have taken all precautions beyond the standard over voltage and over current protections for safety.

It can meet all Indian road conditions — IP67 rated and high shock and vibration withstanding capability proven in actual torture tracks.

It can withstand all Indian weather conditions, can work at 55° C ambient temperatures without forced cooling which is a result of proprietary PCB thermal design. It has an extremely rugged design to offer zero percent failure over the years.

We have factored in first-in-segment features like input disconnect switch assures safety of 12V devices in vehicle, inbuilt pre-charge and inrush control circuit. Practical features include PCB level and component level servicing possibilities. We are using component level EMI/EMC systems duly approved by ARAI.

For an energy efficient and safe electric vehicle like the ones you make, the overall performance depends on several factors like temperature, operating voltage, percentage of rated power and other environmental conditions. How much of these are done at your end and what is outsourced?
Since all EV components are built by us, the responsibility of the performance and safety also falls on the company. The factors you have mentioned are the starting points. Our systems gather a lot more intelligence from each component and make fine grained decisions with an effort to get the highest efficiency. FOC-based models in MCU and AI/ML engines making informed decisions in the VCU, help in this area.

The biggest concern with Lithium batteries that persists is the thermal management of electric vehicles and the risks associated with it. How are you addressing them?
We are happy that the Government of India proposed the new battery standards AIS156A (3) which takes safety to another level entirely. AGs batteries are compliant with the standard and are all certified. To us, that is not the end. We strongly believe that the software running in the BMS has to be developed keeping in mind all possible conditions that can emerge during road usage. At the end of the day, the temperature sensors do their job. Actions that follow are based on the sensitivity of the BMS. Here is where our years of experience in building and testing Li-packs comes handy.

When it comes to power electronic systems and the motor, why is thermal management so critical for these components? What are your main considerations and what technologies are being used to ensure peak performance and safety in the products?
It is important that small format vehicles need to be developed without the hassle of liquid cooling. That has been the design criteria for Altigreen components. Hence, thermal dissipation was introduced in the design itself versus an afterthought when systems start failing. We did thousands of kilometres of on-road testing with instrumented vehicles to understand the thermal management needs. Our choice of materials (Cu + insulation in motors, fins on motors, cooling of the controller without any forced airflow, material and thickness of heatsinks, PCB design to allow high temperature usage, and many more, were all an outcome of these design choices.

How do you design the battery pack with 100 percent assurance about its safety?
Testing, retesting, breaking, redesigning, retesting and working on multiple iterations. It takes time and hence Altigreen has invested years in it. There is significant work that has to be done on building the right BMS, with proper hardware and software failure thresholds. One starts where the other ends. Choice of cells is also very important and should be based on the use case.

In your opinion, what are the battery chemistry options that could offer safer solutions?
These are early days but solid-state, sodium and aluminium will be natural choices. Each has its own challenges in terms of maturity for commercialisation, so all bets are off on what we will pursue in future. For the near term, Li-variants are it.

What are the key risks from imports from the point of safety in general and batteries in particular?   
India’s needs are unique, for commercial vehicles, especially small format. Heterogeneous low speed traffic, 1.8x overloading, waterlogging, high ambient temperatures, potholes, vehicle costs — are some examples. EVs have to be designed keeping all these in mind. Imports meeting these criteria are either very expensive (pushing the vehicle price high) or will suffer in quality or perform poorly (efficiency) on road. For batteries, it is imperative to pick cells that operate at high temperatures (expensive), pack them such that vibrations are eliminated and finally, the BMS designed such that even the smallest nuances of cell misbehaving can be caught and action taken to arrest it.

This interview was first published in Autocar Professional's June 1, 2023 issue.