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WE Boosts Voltage Rating for Isolated Signal Transformers

May 05, 2024 by Mike Falter

Würth Elektronik’s WE-BMS signal transformer series variants are now rated to 1500 VDC, making them ideal for large energy storage systems and electric vehicle charging.

Würth Elektronik is expanding its WE-BMS series of signal isolation transformers for battery management systems (BMS) with models rated to 1500 VDC.

With enhanced isolation capabilities, the new variants are compliant with IEC 62368-1 standards. The transformers use triple insulated wire for the primary and secondary windings, galvanic isolation, and a test voltage of up to 6400 VDC. Prior variants of the WE-BMS series were rated to only 1000 VDC.


WE-BMS series transformer construction

WE-BMS series transformer construction. Image used courtesy of Würth Elektronik


The higher operating voltage and isolation capabilities make the transformers ideal for BMS signal isolation in the growing number of energy storage systems needed for load balancing renewable power systems and electric vehicle (EV) charging applications.   


Need for Energy Storage

The use of renewable energy sources has been growing rapidly as energy suppliers and consumers look to improve the resilience and sustainability of their energy supplies. However, wind, solar, and other renewable sources are intermittent and must be paired with long-duration energy storage to meet users’ dispatchable power requirements.

EV charging stations rely on energy storage to supplement localized (microgrid) renewable power and implement utility pricing arbitrage strategies by purchasing and storing lower-cost, off-peak energy from the grid.


Solar EV charging system with storage.

Solar EV charging system with storage. Image used courtesy of the Department of Energy


In both instances, battery energy storage systems (BESS) are critical in meeting long-duration energy storage needs.  


Role of the Battery Management System Transformer

Within a BESS, the battery management system monitors the battery modules and cells, safely coordinates charge/discharge cycles, and facilitates communication with adjacent systems.    

The BMS transformer isolates the BMS controller from the high-voltage battery bus while facilitating the communication of key data from the battery cells to the system controller. 

In relaying signal data across the high-voltage boundary, Würth’s BMS transformers provide EMI suppression via an integrated choke, ensuring data integrity in the presence of external interferers.


BMS transformers relay data from high-voltage cells

BMS transformers relay data from high-voltage cells. Image used courtesy of EEPower


High-Voltage Design

According to Würth, the WE-BMS transformers have a creepage distance much larger than competitive offerings to help achieve the 1500 VDC of isolation and use a novel design to avoid increasing the package size. Fully insulated wires for the primary and secondary windings further assist with meeting isolation and safety standards.    


WE-BMS design provides more creepage distance.

WE-BMS design provides more creepage distance. Image used courtesy of Würth Elektronik


With the integrated choke, the WE-BMS transformer has a CMRR (common mode rejection ratio) of -50 dB up to 100 MHz to help suppress radiated or conducted common mode interferers. 

The insertion loss, or signal power lost between the input and output, is -0.25 dB at a typical signal frequency of 4 MHz. 


WE-BMS transformer relays data to the controller IC.

WE-BMS transformer relays data to the controller IC. Image used courtesy of Würth Elektronik


The single port 74942402 (order code) model transformer is available in a compact 12.5 mm x 28 mm x 7.3 mm surface mount package with 15 mm of creepage distance.