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TechnologyPhase switching

the fuse trips on one phase

Most sites that run out of charging capacity still have two-thirds of it unused, on phases 2 and 3. VOOL's patented phase switching (European patent EP 4 285 454) measures all three and moves each charger to the phase with the most headroom, again every time a car changes how many phases it uses.

See it step by stepGet your proposed solution
more chargers on the same connection
6×
more chargers on the same connection
more cars charged in the same time
3×
more cars charged in the same time
fuse trips from imbalance
0
fuse trips from imbalance

Step by step

From a tripped fuse to a fifth car

MAIN CONNECTION 3 × 63 ABuildingL158 A · 92%L220 A · 32%L318 A · 29%fuse limit 63 AEV A3-phaseEV B1-phaseEV C1 to 3 phasesEV D1-phaseEV E1-phase
1/5

Every car is different

Every car charges differently

Some cars charge on one phase, some on three. Many start on one, step up to two and three phases, then step back down as the battery fills.

  1. Every car is different: Every car charges differently. Some cars charge on one phase, some on three. Many start on one, step up to two and three phases, then step back down as the battery fills.
  2. Problem: Everything lands on phase 1. Single-phase cars and building devices default to L1. Phase 1 runs at 92% while phases 2 and 3 sit at about 30%.
  3. The real cause: One more car trips the fuse. L2 and L3 still have about two-thirds of their capacity free. The connection was big enough; the load was on the wrong phase. L1 overloads, the main fuse trips and every car stops charging.
  4. Solved: VOOL phase switching. The load controller measures L1, L2 and L3 and switches each charger to the phase with the most headroom, again every time a car changes phases. Same cars, same 3 × 63 A fuse, nothing trips.
  5. Value: Room for more cars. A fifth car charges on the same connection. This headroom is how up to six times more chargers fit on an existing connection.

The physics

Why imbalance happens

Single-phase cars

Many cars charge on one phase only, at 7.4 kW or less. Plugged into a three-phase charger, they all draw from L1 by default.

Cars that change phases

Many cars start on one phase, step up to two and three, then step back down as the battery fills. The load moves during the session.

Building devices

Lifts, pumps and lights load the phases unevenly too, and change through the day.

How it works

Measured, then switched

  1. 01

    Measure

    Current clamps on the incoming cable read L1, L2 and L3 every 100 ms: building and chargers together.

  2. 02

    Decide

    The load controller knows each charger's phase and each car's phase use, and the headroom on every phase.

  3. 03

    Switch

    Each charger is switched to the phase with the most headroom; when a car changes phases, the charger is switched again.

  4. 04

    Share

    What is left after the building is shared between cars by need, departure time, price and priority.

The patent

Granted by the European Patent Office

Patent
EP 4 285 454 B1, European patent application 21703989.0
Title
A multiphaser device and method for uninterrupted AC power switching between sources of same or different phases
Proprietor
MultiCharge OÜ (VOOL), Tallinn, Estonia
Filed
26 January 2021
Granted
Decision to grant of 2 October 2025; grant mentioned in European Patent Bulletin 25/44 of 29 October 2025
Designated states
38 European Patent Convention states, Luxembourg included
What it protects
Switching a charger between phases without interrupting the charge: each relay closes at a voltage zero crossing and opens at a current zero crossing, timed from the relay's own measured switching times
Read it
EP 4 285 454 on Google Patents

Source: EPO decision to grant (EPO Form 2006A, 2 October 2025) and the published application EP 4 285 454 A1.

Compared

Phase rotation, static limits, phase switching

ApproachWhat it doesAMP X VOLTLimit
Phase rotation at installationElectrician wires chargers to different phases (L1, L2, L3 in turn)Fixed: cannot follow which cars are plugged in or how many phases they use
Static per-charger limitEach charger capped so the total stays below the fuseWastes most of the connection most of the time
Dynamic phase switching (VOOL)Measures all phases at the connection and moves chargers in real timeUses the whole connection; the limit is never crossed

Other makers offer phase balancing too; see AC charging systems compared for a dated, sourced comparison.

Ask your AI assistant

Phase switching questions

“Why does the main fuse trip when the grid connection is big enough?”

Because the load is on the wrong phase: single-phase cars and building devices default to L1, which overloads while L2 and L3 still have about two-thirds of their capacity free. Phase switching moves chargers to the free phases.

“How many more chargers does phase switching allow?”

VOOL states up to six times more chargers on the same connection and up to three times more cars charged in the same time, combined with dynamic load management. The real figure depends on the building's load and the cars' phase use.

“Is phase switching the same as phase balancing?”

Phase balancing is the goal: equal load on L1, L2 and L3. Phase switching is how VOOL reaches it dynamically, by moving each charger to the phase with the most headroom while cars are charging, rather than fixing the phases at installation.

“Is VOOL's phase switching really patented?”

Yes. European patent EP 4 285 454 B1, held by MultiCharge OÜ (VOOL), was granted with effect from 29 October 2025 (European Patent Bulletin 25/44), designating 38 European states, Luxembourg included. It covers switching a load between phases without interrupting it, timing each relay to the voltage and current zero crossings.

How many more chargers fit on your connection?

Send us the connection size and the parking spaces; we model it.

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