A sensor in the power path watches the current continuously and reports it to the charger’s control side. The charger needs that reading live, not just for the display: it enforces the limit it offered the car, runs its protective checks, and turns the same measurements into the session’s energy figure. Without measurement, a charger could offer a current but never know whether the car stayed inside it.
Key Takeaways
- A sensor in the power path reports the draw to the control side continuously — by shunt, transformer or Hall-effect sensing.
- The reading closes the loop: the charger can only enforce the ceiling it advertised because it measures the result.
- The same measurement protects the session and produces the display and energy figures.
- Session measurement is not billing metering.
Where the Measurement Happens
The sensor sits in series with the power the car draws, or around the conductor carrying it. Charger designs use a few standard sensing principles. Which one a given model uses is the maker’s design detail — not something you can see from outside the unit.
| Sensing principle | How it works, in one line | Where you meet it |
|---|---|---|
| Shunt | Current passes through a precision resistor; the tiny voltage drop across it is the reading | Compact electronics, moderate currents |
| Current transformer | A coil around the conductor reads the current without touching it, keeping the sensing side isolated | Higher-current paths wanting an isolated measurement |
| Hall-effect sensor | The sensor reads the magnetic field the current creates around the conductor | Isolated readings in a small space |
All three answer the same question — how much current is flowing right now — many times a second. The control side turns that stream into the decisions below. Leakage protection is a different measurement with a different job: it compares current going out with current coming back, as our guide to RCD protection for EV chargers explains.
The Closed Loop: Measure, Compare, Act
Measurement is what makes the charger’s promise enforceable. At the start of a session the charger advertises a ceiling through the pilot signal — its own rating, or a lower setting a user or installer selected. The car draws at or below that ceiling; the charger measures the draw and compares it, continuously, against the limit.
- Draw inside the limit: the session runs; the readings feed the display and the energy total.
- Draw at or beyond the limit: the charger can signal a lower ceiling, and if the draw stays wrong, end the session.
- A reading that makes no sense: a failed sensor shows up as an impossible figure — the safe response is a stop and a fault, not a guess.
On a three-phase charger the loop runs per phase: each of the three live paths is sensed separately, which is also how the unit can tell a car that charges on one phase from a fault on one phase.
Three Jobs for One Measurement
| Job | What the reading does |
|---|---|
| Enforce the offer | Keeps the car’s draw inside the advertised ceiling and the charger’s own setting |
| Protect | Feeds the over-current and abnormal-draw checks that can reduce or end a session |
| Report | Becomes the amps on the display, and — combined with voltage over time — the session’s kWh figure in the app or record |
That third job is why a charger’s energy figure exists at all. How far to trust it is a separate question — session measurement is not an approved billing meter, as our explainer of smart meters for EV chargers sets out.
EVDANCE Chargers and Their Readings
The EV-ACS4005T offers 16, 24, 32 and 40 A settings: a chosen setting is the ceiling the measurement loop enforces for that session. The EV-ACS3210E pairs with an app providing energy monitoring, and those figures come from the same internal measurement described here. EVDANCE does not publish which sensing principle either model uses, and none is claimed — the product facts are the settings, the monitoring and the ratings on their pages.
Frequently Asked Questions
Why do the charger and the car show slightly different amps?
They measure at different points with different instruments, and each rounds its figure its own way. Small differences are normal and both readings can be honest. A large or growing difference is a symptom to report, not a setting to adjust.
Does a three-phase charger measure all three phases?
Yes — sensing is per phase, because each live path carries its own current and the car may not load them evenly. That is also what lets the charger spot a problem confined to one phase.
Can the measurement itself fail?
A sensor or its wiring can fail, and the usual sign is a session that will not start, stops with a fault, or reports figures that contradict the car’s. The charger is a sealed unit: the route is the maker’s support and warranty, not an owner adjustment.
Related Reading
- Do You Need a Smart Meter for an EV Charger?
- RCD Protection for EV Chargers: Type A, Type B and 6 mA DC Detection Explained
- How Many kWh Does It Take to Charge an EV?
