Categorized | Industry News, LEM


Posted on 05 July 2019

LEM brings high-accuracy current measurement to electric vehicle battery packs

LEM high accuracy current measurements








Key points:

  • Fluxgate sensor measures EV battery currents with <0.1% error
  • Isolated measurement technology ensures safety, cuts energy losses
  • Electric car makers maximise operating range, reduce battery over-provision
  • Sensor delivers CAN digital data stream to vehicle electronics


Transducer specialist LEM announces the CAB high-accuracy current transducer that enables makers of battery packs for Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs) to achieve a new level of precision when measuring current flow into and out of the battery. Car makers need this data to maximise the range of the vehicle, to keep the battery in good condition, and to enable use of the optimum size of battery pack.**

LEM's CAB transducer offers current measurement capability of up to ±400A, with unlimited overload capacity, and with excellent accuracy: Coulomb-counting error over the driving cycle is reduced to under 0.1%. It is galvanically-isolated and non-intrusive; no electrical connection to the power circuit is needed. This ensures safe operation and, in contrast to techniques that use a sensing resistor in the power feed, generates no waste heat or losses.

The CAB takes the form of a small panel-mounted module measuring just 71 x 52 x 21 mm, excluding mountings, that has an aperture through which the primary (battery feed to the vehicle motors) conductor passes. It operates from the vehicle's 12V power supply, and is rated for operation from -40 to +105 ºC.  The CAB transducer transmits its data to the EV/HEV's control circuitry using the automotive-industry standard CAN bus; LEM can supply variants that deliver data via other bus and interface standards, on request.

In the CAB transducer, LEM chose to use its proven implementation of the fluxgate principle. Fluxgate transducers use an advanced magnetic current-measurement principle that inherently cancels or nulls many of the offset and drift errors that appear in simpler current-sensing techniques.

**State-Of-Charge (SOC) is a critical measurement function in EVs and HEVs. During the driving cycle the battery is either driving the vehicle, or current flow is reversed in regenerative braking or charging, returning energy to the battery. In these transient conditions battery voltage does not give a good indication of SOC – each unit of charge (Coulombs) delivered by, and returned to, the battery has to be accurately tracked, which demands precise current measurement.

To ensure long battery life, EV and HEV batteries are typically never fully discharged, nor charged to the maximum, and are therefore over-sized compared to their nominal rating. Car makers must further increase this safety margin if they need to make allowance for inaccuracies in energy measurements.  With the advent of the CAB transducer, vehicle designers can have complete confidence in SOC estimation, and can reduce the size and weight of the battery pack accordingly.

LEM – At the heart of power electronics
LEM is the market leader in providing innovative and high quality solutions for measuring electrical parameters. Its core products - current and voltage transducers - are used in a broad range of applications in drives & welding, renewable energies & power supplies, traction, high precision, conventional and green cars businesses. LEM’s strategy is to exploit the intrinsic strengths of its core business, and to develop opportunities in existing and new markets with new applications. LEM is a mid-size, global company. It has production plants in Beijing (China), Geneva (Switzerland), Machida (Japan) and Copenhagen (Denmark). With its regional sales offices close to its clients’ locations, the company offers a seamless service around the globe. LEM is listed on the SIX Swiss Exchange since 1986; the company’s ticker symbol is LEHN.



For further information please contact:

Gauthier Plagne
Automotive Project Manager
Tel: +41 22 706 14 35

Stéphane Rollier
Product & MarComs Manager
Tel: +41 22 706 1449


Laura West
Napier Partnership Limited
Tel: +44 (0) 1243 531123 



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