When you plug in, nothing is live yet. For a few seconds the charger and the car hold a short, low-voltage conversation on a signal wire called the pilot. They confirm the connector is fully seated, agree on the most current the car may take, and run safety checks. Only then does a heavy switch inside the charger, the contactor, close with a click and power starts to flow. That pause is the handshake, and it happens before every session.
Key Takeaways
- The pilot-signal handshake confirms the connection and sets the current limit before power flows.
- The contactor click is the sound of the session actually starting.
- Unplugging breaks the signal first, so power stops before the pins separate.
- If the handshake fails, the charger stays off by design.
The Handshake, Step by Step
| Step | What happens | What you notice |
|---|---|---|
| 1. Plug in | The connector latches. The power pins are still dead; only the low-voltage pilot signal is present. | Nothing, or a status light waking up. |
| 2. Charger announces itself | Through the pilot signal, the charger tells the car the maximum current it is allowed to draw on this circuit. | A few seconds of waiting. |
| 3. Car answers | The car changes the signal to show it is connected and ready, and that its own checks have passed. | The car may show “connected” before “charging”. |
| 4. Final checks | The charger confirms the protective earth is present and tests its ground-fault protection. | Still no power at the pins. |
| 5. Power on | The contactor closes and AC power flows to the car’s on-board charger, which does the actual charging. | A single click, then the session starts. |
| 6. Unplugging | Pressing the latch button breaks the signal first. Power stops before the power pins separate, so there is no spark. | Charging stops the moment you press the button. |
The site guide to how home EV chargers work gives the short version of this sequence. The detail that matters day to day is step 2: the limit travels with the signal. The car may never take more than the lower of two numbers, the charger’s limit and the car’s own limit.
Why the Agreement Matters
The pilot signal is also how the deal can change mid-session. The car can ask for less as the battery fills or warms up. The charger can lower the limit it advertises, for example when a load-balancing system sees the house approaching its supply limit. The background explainer on what J1772 is shows where this signal pin sits in the North American connector.
- The connector in your hand carries no charging power until the handshake completes.
- Either side can end the session at any moment by breaking the signal.
- A failed handshake means no charging at all, by design, not a half-started session.
What Follows the Handshake
Once power flows, the charger mostly supervises: it watches temperature, leakage and the pilot signal, and opens the contactor if anything goes wrong. Chargers that follow this pattern, such as the EVDANCE EV-ACT5006T 48A Level 2 wall charger and the EVDANCE EV-ACS3210T 32A NACS portable charger, differ in power and features, but the plug-in conversation is the same idea.
Frequently Asked Questions
Why does charging take a few seconds to start?
Those seconds are the handshake and the safety checks. A short, consistent delay is normal. A car that never starts, or clicks repeatedly, has a handshake that keeps failing; check the connector is fully latched and follow the manual.
Is the connector live while I am holding it?
No. The power pins stay dead until the handshake completes with the connector latched into the car, and power stops before the pins separate when you unplug.
Why do I sometimes hear two clicks?
One click closes the contactor at the start and another opens it at the end. Some cars and chargers also run a brief second stage at start-up. A single click at each end is the healthy pattern.
Related Reading
- How Do Home EV Chargers Work?
- What Is J1772? The North American EV Plug Explained
- Mode 2 vs Mode 3 Charging: What IEC 61851 Means for Portable EV Chargers
- Are EV Chargers AC or DC?
