Lem has introduced a pair of mains residual current monitors for electric vehicle charging that have both digital and analogue outputs.

LEM CDSR 1phase current sensor
One monitors single-phase live and neutral (CDSR 0.07-TP, photo right), while the other monitors three phases and neutral (CDSR 0.07-NP, photo below).

“Because electric vehicles use a high voltage battery, they are also a high-power energy source. This needs to be carefully monitored to avoid any electrical shock to users or damage to household switchboard protection,” according to the company. Meeting these requirements demands a method of monitoring AC and DC current leakages, with the ability to measure leakage as low as 5mA.”

LEM CDSR 3phase residual current sensorIn each of the monitors, the digital output is SPI bus while the analogue output is actually a 48MHz differential ΣΔ bit stream which requires a pair of external RCRC filters, followed by a high-impedance load, to create a 0 – 3V signal.

Suitable for PCB mounting, the sensed current conductors are built into the devices and terminate in pegs designed for 3.3mm diameter vias.

Up to 32A can be handled (3.3kA peak), allowing the devices to cover ac charging systems up to 300Vrms from 3.3 to 22kW.

Both IC-CPD (‘mode 2’, in-cable control and protection device) and wall boxes (mode 3) use is envisaged – the three phase version has a 56 x 51mm footprint and stands 26mm above the PCB.

A trip output is set at 70mArms of residual current – compliant to IEC 62752/62955/UL 2231 tripping standards according to Lem – and the measuring range is ±150mA.

Primary-to-secondary creepage and clearance are 10.15mm in the three-phase (‘NP’) version and 13.2mm in the single-phase (‘TP’) version. Primary to primary creapage and clearance is 5.64mm (NP) and 8.9mm (TP).

Inside, fluxgate sensing is used, requiring a separate 3.3V (50mA max) supply.

Errors add up to a maximum of 0.5mA up to 6mA residual primary current, then 1mA error up to 10mA residual and 10% above 10mA.

 

This is for both analogue and digital output, and is dependent on power supply accuracy. The digital output also has a higher bandwidth (2kHz against 10Hz) mode that looses some accuracy.

A test pin connected to an internal 10 turn coil on the internal core allows a test current to be injected.

Operation is over -40 to +85°C, and there is a five-year guarantee.