From 56c1d56626245bdf27abff1677037d37d33f68e1 Mon Sep 17 00:00:00 2001
From: mfuchs1984 <57141790+mfuchs1984@users.noreply.github.com>
Date: Sat, 7 Mar 2026 09:46:46 +0100
Subject: [PATCH] Loadpoint: fix fast charging phase scaling (#27972)

---
 core/loadpoint.go             | 10 +++--
 core/loadpoint_phases_test.go | 71 +++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 4 deletions(-)

diff --git a/core/loadpoint.go b/core/loadpoint.go
index 8d85af6fe..45401bb02 100644
--- a/core/loadpoint.go
+++ b/core/loadpoint.go
@@ -1282,12 +1282,14 @@ func (lp *Loadpoint) scalePhases(phases int) error {
 func (lp *Loadpoint) fastCharging() error {
 	if lp.hasPhaseSwitching() {
 		phases := 3
-		maxPower1p := Voltage * lp.effectiveMaxCurrent()
 
 		// load management limit active
-		if circuitMaxPower := circuitMaxPower(lp.circuit); circuitMaxPower > 0 && circuitMaxPower < 1.1*maxPower1p {
-			phases = 1
-			lp.log.DEBUG.Printf("fast charging: scaled to 1p to match %.0fW max circuit power", circuitMaxPower)
+		if lp.circuit != nil {
+			minPower3p := currentToPower(lp.effectiveMinCurrent(), 3)
+			if powerLimit := lp.circuit.ValidatePower(lp.chargePower, minPower3p); powerLimit < minPower3p {
+				phases = 1
+				lp.log.DEBUG.Printf("fast charging: scaled to 1p to match %.0fW available circuit power", powerLimit)
+			}
 		}
 
 		if err := lp.scalePhasesIfAvailable(phases); err != nil {
diff --git a/core/loadpoint_phases_test.go b/core/loadpoint_phases_test.go
index eefb6f6d4..d7e720cba 100644
--- a/core/loadpoint_phases_test.go
+++ b/core/loadpoint_phases_test.go
@@ -479,3 +479,74 @@ func TestScalePhasesIfAvailable(t *testing.T) {
 		ctrl.Finish()
 	}
 }
+
+func TestFastChargingCircuitBasedPhaseScaling(t *testing.T) {
+	Voltage = 230
+
+	tc := []struct {
+		desc                  string
+		phases                int
+		chargePower           float64
+		availableCircuitPower float64 // ValidatePower return for 3p request
+		expectedPhases        int
+		noCircuit             bool
+	}{
+		{desc: "no circuit", phases: 3, chargePower: 0, expectedPhases: 3, noCircuit: true},
+		{desc: "low limit, no surplus", phases: 3, chargePower: 0, availableCircuitPower: 3680, expectedPhases: 1},
+		{desc: "low limit, with surplus", phases: 1, chargePower: 0, availableCircuitPower: 11040, expectedPhases: 3},
+		{desc: "already charging, low limit", phases: 3, chargePower: 3680, availableCircuitPower: 3680, expectedPhases: 1},
+		{desc: "already charging, high limit", phases: 1, chargePower: 3680, availableCircuitPower: 11040, expectedPhases: 3},
+		{desc: "edge case: just below 3p minimum", phases: 3, chargePower: 0, availableCircuitPower: 4140 - 1, expectedPhases: 1},
+		{desc: "edge case: just at 3p minimum", phases: 1, chargePower: 0, availableCircuitPower: 4140, expectedPhases: 3},
+	}
+
+	for _, tc := range tc {
+		t.Run(tc.desc, func(t *testing.T) {
+			ctrl := gomock.NewController(t)
+
+			lp := NewLoadpoint(util.NewLogger("foo"), nil)
+			lp.minCurrent = 6
+			lp.maxCurrent = 16
+			lp.phases = tc.phases
+			lp.chargePower = tc.chargePower
+			lp.offeredCurrent = 0 // ensure MaxCurrent is called
+			lp.wakeUpTimer = NewTimer()
+
+			plainCharger := api.NewMockCharger(ctrl)
+			phaseCharger := api.NewMockPhaseSwitcher(ctrl)
+			lp.charger = struct {
+				*api.MockCharger
+				*api.MockPhaseSwitcher
+			}{plainCharger, phaseCharger}
+
+			if !tc.noCircuit {
+				circuit := api.NewMockCircuit(ctrl)
+				lp.circuit = circuit
+
+				minPower3p := Voltage * 6 * 3
+
+				// fastCharging call to ValidatePower
+				circuit.EXPECT().ValidatePower(tc.chargePower, minPower3p).Return(tc.availableCircuitPower)
+
+				// setLimit calls
+				circuit.EXPECT().ValidateCurrent(gomock.Any(), lp.maxCurrent).Return(lp.maxCurrent)
+				circuit.EXPECT().ValidatePower(tc.chargePower, float64(tc.expectedPhases)*Voltage*lp.maxCurrent).Return(float64(tc.expectedPhases) * Voltage * lp.maxCurrent)
+			}
+
+			plainCharger.EXPECT().Enabled().Return(true, nil).AnyTimes()
+			plainCharger.EXPECT().Enable(gomock.Any()).Return(nil).AnyTimes()
+
+			if tc.phases != tc.expectedPhases {
+				phaseCharger.EXPECT().Phases1p3p(tc.expectedPhases).Return(nil)
+			}
+
+			plainCharger.EXPECT().MaxCurrent(int64(lp.maxCurrent)).Return(nil)
+
+			err := lp.fastCharging()
+			require.NoError(t, err)
+			require.Equal(t, tc.expectedPhases, lp.phases, tc.desc)
+
+			ctrl.Finish()
+		})
+	}
+}