Engineering Guide
How to choose an EV current sensor: BMS, traction drives and charging equipment
Where current is measured in an electric vehicle and its charging equipment, which sensor technology fits each point, and the seven parameters to send your supplier.
“EV current sensor” covers several very different jobs. The sensor that measures 600 A of pack current in a battery management system is not the one that measures phase current in a traction inverter, and neither is right for metering 32 A in an AC wallbox. This guide maps the measurement points in an electric vehicle and its charging equipment, explains which sensor technology fits each, and ends with a checklist you can send to a supplier.
Where current is measured in an EV system
| Measurement point | What is measured | What matters most | Typical technology |
|---|---|---|---|
| Battery pack (BMS) | DC charge and discharge current | Accuracy and low offset over temperature, for state of charge | Hall sensor with voltage output, or digital sensor with CAN output |
| Traction inverter / motor drive | AC phase current and DC link current | Fast response and bandwidth for the control loop | Closed-loop or open-loop Hall sensor |
| DC-DC converter, on-board charger | DC and switching-frequency current | Response time, compact size | Open-loop or programmable Hall sensor |
| DC fast charger output | High DC current | Range, isolation, accuracy for the charging protocol | Hall sensor (open- or closed-loop) |
| AC charging station | AC charging current per phase, residual current | Metering accuracy, leakage detection | Current transformer + Type A + DC 6mA RCD sensor |
| Energy storage system | DC battery current, often many strings | Accuracy, communication, multi-channel | Digital or multi-channel current sensor |
The rest of this guide explains how to make the choice for each point.
Step 1: AC only, or DC too?
This one question narrows the technology:
- AC only (for example the charging current of an AC wallbox): a current transformer (CT) is simple, accurate and needs no power supply. But a CT cannot see DC.
- DC, AC or pulsed (battery, DC link, DC charging, inverter phases): you need a Hall-effect sensor, which responds to the magnetic field of the conductor directly and therefore works down to DC.
Almost every measurement point inside the vehicle involves DC, which is why Hall sensors dominate EV current sensing.
Step 2: choose the Hall architecture
There are two basic Hall architectures. We compare them in detail in open-loop vs closed-loop Hall current sensors. In short:
- Open-loop: a Hall element in the air gap of a magnetic core measures the field directly. Compact, low power and cost-effective. Accuracy is typically around 1%.
- Closed-loop: a secondary winding cancels the core flux, and the compensation current becomes the output. Better accuracy, linearity and drift, with very fast response, at the cost of more power and size.
For the control loop of a traction inverter, where speed and linearity matter, closed-loop sensors are the conservative choice. For monitoring and protection functions, and where space and power are tight, open-loop sensors are usually enough.
Step 3: analog or digital output?
- Analog voltage output (for example 2.5 V ± 2 V around a midpoint) suits controllers that already sample current with their own ADC. It gives the fastest signal path.
- Current output (closed-loop sensors) is robust over long cables in noisy cabinets.
- Digital CAN or RS485 output delivers a calibrated current value. The sensor handles offset, gain and temperature compensation internally, and the BMS or energy management system simply reads the number. This is attractive in battery packs and storage systems where many sensors share one bus.
Step 4: size the measuring range correctly
Choose the nominal range from the continuous current, then check that the sensor can measure the peak current without saturating, for example the peak discharge current of a pack or the short-circuit current that your protection must still see.
Do not oversize too much: a 1000 A sensor measuring a 20 A standby current wastes most of its resolution, and the offset error becomes a large share of the reading. For battery packs that must track both high load current and small quiescent currents, a digital sensor with a wide dynamic range is often the best compromise.
Step 5: check isolation, aperture and environment
- Isolation / withstand voltage: the sensor separates the high-voltage conductor from your low-voltage electronics. Match the test voltage to the system voltage and the insulation coordination of your product. EVsense current sensor families cover withstand voltages from 1 kV up to 6 kV depending on the family.
- Aperture and mounting: busbar or round cable, PCB-mounted or panel-mounted. Measure the conductor, including insulation.
- Temperature: automotive and outdoor charging equipment typically needs −40 °C operation. Check offset and gain drift over the full temperature range, not only at 25 °C.
Matching EVsense families to EV applications
| Application | EVsense family | Range | Output | Accuracy |
|---|---|---|---|---|
| BMS pack current, energy storage | Digital signal current sensors | 0.01–800 A | CAN / RS485 | 0.15–1% |
| BMS, electric drive, electronic control | New energy current sensors | 50–1000 A | Voltage | 1% |
| Inverter and drive control loops, traction | Closed-loop Hall sensors | 10–5000 A | Current / voltage | 0.5% |
| Power supplies, converters, monitoring | Open-loop Hall sensors | 15–5000 A | Voltage | 1% |
| Multiple circuits in one module | Multi-channel current sensors | 5–900 A | Multi-channel voltage | 0.6–1% |
| AC charging station current + leakage | CT2728 / CT1719 | 32 A / 20 A rated | CT output + leakage trip via ILM2112TQC | Class 0.2 (CT2728) |
Ranges are family summaries; the combination of ratings for each model is in its datasheet. The full family overview is in our current sensor selection guide (PDF).
AC charging stations: measure current and leakage together
An AC charging station has two current-related jobs. It measures the charging current, for metering, load management and the pilot signal. And it must detect residual current, including smooth DC above 6 mA (see Type A vs Type B RCD for EV chargers).
The usual design uses two magnetic parts. The CT2728 and CT1719 combine an integrated current transformer with a Type A + DC 6mA leakage detection core. Used with the ILM2112TQC IC, one part covers both functions, which saves board space and assembly.
The seven parameters to send your supplier
To get a correct recommendation on the first reply, send:
- Current type: DC, AC (frequency) or pulsed
- Nominal and peak current
- Required accuracy and over which temperature range
- Response time / bandwidth needed by your control or protection
- Output interface: voltage, current, CAN or RS485
- Supply voltage available on your board
- Conductor and mounting: cable diameter or busbar size, PCB or panel mount, and system voltage for isolation
Summary
- Decide AC-only or DC first: CTs for AC, Hall sensors for anything involving DC.
- Closed-loop Hall sensors for fast, precise control loops; open-loop for compact monitoring and protection.
- Digital CAN/RS485 sensors simplify BMS and storage systems that need calibrated values.
- Size the range for the peak current, and check isolation, aperture and temperature drift.
- In AC charging stations, an integrated CT + leakage detection core such as the CT2728 measures current and leakage with one part.
Frequently asked questions
What is the difference between a current sensor and a current transducer?
In practice the terms are used for the same kind of product: a device that measures the current in a conductor and converts it into an isolated signal the controller can read, such as a voltage, a current or a CAN message. 'Transducer' is more common in traction and industrial catalogs, 'sensor' in automotive and BMS work.
Which current sensor is best for an EV battery management system?
For pack current, BMS designers usually choose a Hall sensor with a measuring range above the peak discharge current, or a digital sensor with a CAN output when the BMS needs calibrated current values directly. EVsense digital signal current sensors cover 0.01A to 800A with CAN or RS485 output and 0.15-1% accuracy; new energy current sensors cover 50A to 1000A with voltage output.
Can a Hall current sensor measure DC current?
Yes. Unlike a conventional current transformer, a Hall-effect sensor responds to the magnetic field of the conductor itself, so it measures DC, AC and pulsed current. That is why Hall sensors are used for battery, DC link and DC charging current, while current transformers are limited to AC.
What current sensor is used in an AC EV charging station?
An AC charger needs to measure the charging current on each phase, typically with a current transformer, and it also needs residual current detection. The EVsense CT2728 (32A, accuracy class 0.2) and CT1719 (20A) integrate a current transformer with a Type A + DC 6mA leakage detection core, so one part can serve both functions.
Need help choosing a sensor?
Send the nominal and peak current, AC or DC, supply voltage, output interface and aperture size. Our engineers reply with a model recommendation, datasheets and sample options.