Is Hot-Swapping an EV Charging Solution? Sensata’s BMS Integrates Hot-swap Technology

December 11, 2021 by Nicholas St. John

EV battery charging is a constant stressor for EV adoption. Could idea of hot-swapping batteries provide a potential solution to ease EV integration and infrastructure strain?

As electric vehicles (EVs) continue to grow in popularity, engineers must meet rigorous specifications to achieve high performance, efficiency, and, most importantly, safety. 

These considerations affect two of an EVs most crucial elements: the power supply and distribution system. 

While in use, these systems must have excessive redundancy to continue operation amidst the failure of one part of it. Furthermore, mechanics must do maintenance work without taking apart or affecting the rest of the machine to get the EV back onto the road.

When performing these actions, an aspect to consider is the importance of power supplies to have a Battery Management System (BMS)


An example EV BMS block diagram.

An example EV BMS block diagram. Image used courtesy of STMicroelectronics


Hoping to improve BMS and make EV maintenance easier, Sensata Technologies recently announced its new i-BMS, the LiBAL i-BMS15, for electrified applications up to 60 V.

Using hot-swapping technology, designers can use this i-BMS solution within 2- and 3-wheeled EVs, automated guided vehicles (AGVs), and robotics. With Sensata's solution in mind, this article will dive into the concept of parallel pack technology and the i-BMS.


The Concept of Hot Swapping/Parallel Pack Functionality

In general, parallel pack functionality or "hot-swapping" allows the usage of multiple battery packs in parallel with one another, thus helping with the redundancy mentioned.


An example of hot-swap application diagram.

An example of hot-swap application diagram. Image used courtesy of Analog Devices


Hot-swapping allows users to quickly swap out dead batteries within a battery pack while the system continues running and replaces it. This ability can alleviate one of the most problematic hindrances during the switch from fossil-fuel-based vehicles to EVs, as one would no longer need to wait for a full charge but can stop at a station and swap the battery with a live one without shutting the vehicle off.

For Sensata's product, specifically, this ability to quickly and easily swap batteries could allow electric motorbikes to have this functionality, which could be a huge step forward in adopting and integrating more EVs into our lives.


Sensata's i-BMS Solution

Overall, besides the hot-swapping function of the LiBAL i-BMS15 solution, some specs include:

  • Area of only 65 mm x 200 mm
  • Ability to monitor up to 15 battery cells in series
  • High voltage (HV) measurement accuracy of +/- 100 mV
  • Cell balancing current of 200 mA
  • A +/- 0.5% current measurement accuracy of 120 A
  • A +/- 3% state of charge (SOC) accuracy (a SOC is the measurement of the potential energy within a battery)
  • A +/- 2% state of health (SOH) accuracy (a SOH measures the batteries ability to store and deliver power)

Additionally, the BMS' cell chemistry is agnostic, which means that the BMS can be used with different cell chemistries, fitting a wider array of applications.

The LiBAL i-BMS15 packs these specs into a device that requires no external components, as all components are pre-integrated to the BMS.


Sensata's BMS solution: the iBMS15.

Sensata's BMS solution: the iBMS15. Image used courtesy of Sensata


Some of the critical components that make up this BMS are:

  • A pre-charge circuit
    • Since EVs require the charging of high capacitive loads, a large inrush current spike with the ability to be thousands of amps can destroy the entire system on startup. A pre-charge circuit controls this inrush current, allowing for a more steady charging of the downstream capacitance.
  • An onboard current measurement
  • MOSFET power switches
    • Based on the current measured onboard, these switches will be either turned ON or OFF to either turn on the machine or protect it when issues such as short circuits occur.
  • A DC/DC power supply

All in all, Sensata claims that all of these components have met rigorous standards, obtaining the ASIL C Safety Rating as well as including self-testing for the user to ensure critical circuit functionality.

This BMS solution offers not only robust hardware but also capable software. The software allows the user to design their specific battery topology for the system. It will also notify the user of any events and system warnings while logging data to measure SOC and SOH. The system can also predict thermal runaway, regulate current dynamically, and set advanced parameter settings for CAN communication.

Despite the benefits that Sensata claims to pack into its BMS with hot-swapping in mind, could this type of technology really make waves when it comes to EV battery charging alternatives?


Could Hot-swapping Reach Mainstream?

Sensata is not the only player in this market, far from it. Analog Devices also has hot-swap capable controllers, and they highlight the design of these systems using its solution, the ADM1177.


Example block diagram of the ADM1177.

Example block diagram of the ADM1177. Image used courtesy of Analog Devices


Though hot-swapping technology is still a relatively newer technology that aims to get more companies on board, as it is currently, a potential solution for the long charging times of EVs. 

This technology is something to expect more of in the future; beyond the current applications of smaller EVs such as motorbikes and 3-wheelers, this technology could one day be more widely used in full-sized EV cars and more. 

As the concept of home charging and charging stations at work and other public facilities will help in the day-to-day, for EVs to truly take over, one of the biggest hurdles is the convenience of just filling up a gas tank rather than waiting for a full battery charge. 

While many think about making batteries last longer, making EVs more efficient and cost-effective is also important. One of the biggest bottlenecks will be the charging time and the impact that EV fast charging will have on our global infrastructure. 

Overall, this concept of hot-swapping could not only remove the time of charging but has the potential to be faster and even more convenient than pumping gas, with the possibility that one would not even need to get out of their car at a station that performed battery hot-swaps. 

Furthermore, on a larger scale, dependence on hot-swapping could remove the dependence on fast EV charging, which lessens the potential burden for the electrical grid when the time comes that EVs are universally adopted.

For EVs to become the norm, including hot-swapping technology into EV designs could ease the burden on the grid and lessen pit stop times. It will be interesting to see where this technology heads in the future and if other solutions come out to ease EV infrastructure and efficiency.