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

July 05, 2012 // By Paul Buckley
LEM has introduced 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 maximize 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 ±400 A, 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 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 12 V power supply, and is rated for operation from -40 to +105ºC.  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.

Visit LEM at www.lem.com