10 Frequently Asked BMS Engineer Interview Questions

BMS engineers are sought-after professionals in top OEMs, including Mercedes Benz, Tata Elxsi, Tata Technologies and many other key players. Their major responsibility is to design and develop efficient BMS by considering industry standards and system requirements.

Candidates who apply for such roles are required to answer questions based on some basic concepts related to battery technology. Our domain experts have compiled frequently asked BMS Engineer interview questions. Check out our students' answers that led them to bag high-paying jobs in top companies.

1. What is BMS, and Why is BMS required for EV?

A BMS or Battery Management System is essential to actively manage the SOC (State of Charge) and maintain SOH (State of Health). The main function of a BMS is to communicate between different control systems. For example, it monitors the battery pack's temperature using temperature sensors. If the temperature crosses the maximum limit for that instance, it sends a signal to the battery cooling system and regulates it.

2. What are the characteristics of an EV battery?

An electric vehicle battery should have high-specific energy, high battery capacity, high energy density, long shelf life, and a wide operating range. It must also be fast changing.

3. What do you mean by the capacity of the battery?

The battery capacity or otherwise is the charge of the battery that can be utilized to perform a specific task or function. It is the direct measure of the active material stored in a battery. The battery capacity is measured in terms of watt hours, kilowatt hours, or ampere hours.

4. What do you mean by the specific energy of a battery?

The specific energy of a battery is a measure of its capacity or charge compared to its weight. The lithium-ion battery has a high specific energy and is used in most electric vehicles.

5. What is the range of voltage levels of EV batteries?

The nominal voltage of a battery pack varies from vehicle to vehicle, depending upon the degree of hybridisation. The nominal voltage is higher for fully battery electric vehicles, ranging from 400V to 800V.

A plug-in hybrid vehicle or mild HEV doesn't require a battery with high nominal voltage. Hence its nominal voltage ranges from 100V to 200V.

6. Name the fault conditions that can occur in the Battery pack.

Many reasons can account for the reduction of SOC (State of Charge) and impact the desired performance. A few conditions that could be diagnosed using a fault detection algorithm include overcharge, short-circuiting, over-discharging and thermal runaway.

7. What is meant by Power factor correction? Why do we need it?

Power factor denotes the power used by the circuit or component against the power supplied. It is calculated as the ratio of working power to apparent power. A low power factor signifies poor performance.

Power factor correction is a method used to increase the power factor of power supplies. It aids in the distribution of power across the circuit and enhances efficiency.

8. What temperature sensors are used to sense thermal runaway in Batteries?

Temperature sensors are the key components in a battery in controlling thermal runaway. Thermal runaway is when the temperature generated in the battery exceeds the dissipated heat. Eventually, this leads to an explosion. The temperature sensors constantly monitor the battery's temperature while charging and discharging to help regulate it. The few sensors used in a battery pack are the thermocouple, thermistors, RTD (Resistance Temperature Detectors) and optical fiber sensors.

9. Explain the series-parallel architecture of an EV battery.

As a single cell cannot supply the charge demand in an EV, a battery pack contains hundreds of cells connected in series and parallel. When cells are connected in series, the current remains the same but the voltage increases. On the contrary, when these cells are connected in parallel, the voltage remains the same but the current increases. A perfect combination of series and parallel cells is needed to discharge the required power into the circuit.

The Model S electric vehicle of Tesla is composed of 18650 cells. It means six cells are arranged in series, and each cell includes 74 cells in parallel. Each module has 444 cells arranged in a 6S 74P configuration.

10. What are the differences between a battery and an ultracapacitor?

Both battery and ultracapacitors are charged storage devices. Batteries use a cathode and anode immersed in a chemical electrolyte. When ions move between the cathode and anode, charging and discharging occur. This leads to the degradation of the battery.

An ultracapacitor is a large-size capacitor that stores static potential energy. The dielectric or insulator is sandwiched between two plates at a specific distance. The primary advantage of using ultracapacitors is they can be used for longer periods than conventional batteries without degradation.

Though ultracapacitors are advantageous in many ways, they cannot replace conventional batteries. Batteries have a higher specific energy than ultracapacitors. Hence they are used in applications where high voltage is required for a shorter time.

Conclusion

With the advent of the EV revolution, the battery technology market is expected to grow at 12% CAGR between 2022 and 2030. It translates to increased job opportunities in this domain.

Check out the battery technology course to learn how to become a BMS Engineer. Students who opt for PG programs can get a chance to attend mock interviews conducted by Skill-Lync experts. This will help to boost your confidence and answer BMS engineer interview questions.

If you want to understand the basic workings of BMS in an electric vehicle, watch the full video list with free access.