Smart EV Charging + KNX Load Management
Prevent main fuse trips with dynamic current allocation — Easee Equalizer, Modbus TCP current limiting, peak demand capping and KNX scene control for apartment blocks and office car parks.
The load management problem
A standard apartment block with a 100A main fuse and 20 EV chargers at 11kW (16A × 3-phase) each would theoretically draw 320A — three times the available capacity. Without load management, the only safe option is to limit each charger to 2–3A, making charging effectively useless. Dynamic load management solves this by distributing available current between active chargers in real time.
| Approach | Max chargers on 63A supply | Charging speed | Risk |
|---|---|---|---|
| No management (fixed 16A) | 3 chargers | Full 11kW each | Fuse trips if >3 cars charge |
| Fixed reduced current (6A) | 10 chargers | 4.1kW — slow | Always slow, even off-peak |
| Static scheduling (time slots) | 10–20 chargers | Variable by slot | No priority, bad UX |
| Dynamic load management | 10–20 chargers | Max available, shared | Best: full current when few cars |
Easee Equalizer: the standard solution
The Easee Equalizer is a current monitoring CT clamp device that mounts on the main distribution board and measures all three phases in real time. It communicates with Easee chargers over Wi-Fi/cloud and automatically allocates available current between active charging sessions.
Easee Equalizer specs
- • 3-phase CT clamp measurement (up to 630A)
- • Communicates with Easee chargers over Wi-Fi
- • Supports up to 400 chargers per installation
- • Updates charger current every 3 seconds
- • Configured via Easee Portal (cloud)
- • Works with Easee Home, Charge, Cable
Current allocation algorithm
- • Reads main supply current every 3s
- • Total EV budget = main limit − building load
- • Budget shared equally between active sessions
- • Minimum 6A per charger (IEC 61851 minimum)
- • Priority groups configurable (fleet vs residents)
- • Ramp-up: 2A/min to avoid inrush spikes
⚠️ Easee Equalizer requires cloud connectivity for dynamic allocation. For fully local operation, use Modbus TCP current limiting (see below) or a local OCPP server (e.g. EVCC on a Raspberry Pi).
Modbus TCP current limiting (local control)
Most smart EV chargers expose a Modbus TCP interface for local current control — no cloud dependency. Combined with a Modbus energy meter on the main supply, this enables fully local dynamic load management:
Local dynamic load management (Home Assistant / Node-RED)
Every 10 seconds:
main_current_L1 = read Modbus meter reg 0x0000 (A × 100)
main_current_L2 = read Modbus meter reg 0x0002 (A × 100)
main_current_L3 = read Modbus meter reg 0x0004 (A × 100)
max_phase = max(L1, L2, L3)
building_load = max_phase ← worst-case phase
supply_limit = 63A ← from main fuse rating
ev_budget = supply_limit - building_load - 5A ← 5A safety margin
active_chargers = count(charger_state == "charging")
if active_chargers > 0:
current_per_charger = clamp(ev_budget / active_chargers, 6, 32)
for each active charger:
write Modbus reg 0x0100, current_per_charger × 10
← Easee Modbus: reg 261 (max current × 10 = Amps × 10)
if ev_budget < 6A:
→ pause all EV charging (write 0 to Modbus reg)
→ restore when budget > 8A (hysteresis)Easee Modbus TCP registers (local access):
Charger state
1=requesting, 3=charging, 5=paused
Max charger current
Write in 0.1A steps. Min 6A, max 32A. Set to 0 to pause.
Session energy
Energy in current session (Wh)
Total energy
Lifetime energy delivered (kWh × 100)
Cable lock state
0=unlocked, 1=locked to car, 2=admin locked
KNX integration: relay control + visualization
KNX integrates with EV charging in two complementary ways:
1. KNX relay — simple enable/disable
- • KNX 230V relay output controls charger power
- • Charger power cut = charging stops (car resumes on reconnect)
- • Use case: night-time cutoff, holiday mode, overload protection
- • Solar self-consumption: relay on when PV surplus > 2.5kW
- • Simple and reliable — no API integration needed
- • Cannot modulate current — on/off only
2. HA bridge — full current control
- • Home Assistant Easee integration (local Modbus)
- • KNX scene telegram → HA automation → Easee API
- • KNX analog output → HA → Modbus current setpoint
- • Use case: solar surplus dispatch with modulated current
- • Bidirectional: charging state → KNX group address → room display
- • Session energy → KNX → billing/monitoring visualisation
KNX group address → Easee current (Home Assistant YAML)
# configuration.yaml / automations.yaml
automation:
- alias: "KNX EV charger current setpoint"
trigger:
- platform: event
event_type: knx_event
event_data:
destination: "7/0/1" ← KNX DPT 9.001 (2-byte float)
action:
- service: easee.set_charger_circuit_max_current
data:
charger_id: "EHXXXXXX"
current_p1: "{{ trigger.event.data.value | int }}"
current_p2: "{{ trigger.event.data.value | int }}"
current_p3: "{{ trigger.event.data.value | int }}"
- alias: "EV charging state → KNX"
trigger:
- platform: state
entity_id: sensor.easee_status
action:
- service: knx.send
data:
address: "7/0/10"
payload: >
{% if states('sensor.easee_status') == 'charging' %}1{% else %}0{% endif %}OCPP: the standard for multi-charger sites
For apartment blocks with 10+ chargers, commercial car parks, or installations requiring billing, OCPP 1.6/2.0.1 (Open Charge Point Protocol) is the industry standard. An OCPP server (Central System) manages all chargers centrally.
| OCPP function | What it enables | KNX relevance |
|---|---|---|
| Smart Charging | Central system sends current profile to each charger | Solar surplus → OCPP current profile |
| RFID authorisation | Only authorised RFID cards can start charging | KNX card reader → OCPP remote start |
| Meter values | Energy per session logged by OCPP server | Session data → KNX group address display |
| Remote start/stop | App, KNX trigger, or RFID starts session | KNX binary input → OCPP RemoteStartTransaction |
| Load balancing | OCPP 2.0.1 Smart Charging with power schedules | Replaces Easee Equalizer for mixed-brand installs |
Open source OCPP server: EVCC (ev.energy) runs on a Raspberry Pi on-site — local OCPP server with solar integration, Home Assistant plugin, and Modbus support. Free for residential use. Used for truly local, cloud-free EV management in KNX projects.
EV charger comparison for KNX projects
| Charger | Modbus TCP | OCPP | Load mgmt | KNX native | Best for |
|---|---|---|---|---|---|
| Easee Charge | ✅ Yes | ✅ 1.6 | Equalizer | ❌ via HA | Residential, apartments |
| ABB Terra AC | ✅ Yes | ✅ 1.6/2.0 | DLM built-in | ❌ via HA | Commercial, multi-unit |
| Keba KeContact | ✅ UDP/TCP | ✅ 1.6 | Backend | ❌ via HA | Residential, fleet |
| Wallbox Pulsar | ❌ No | ✅ 1.6 | Power Boost | ❌ via HA | Residential (simple) |
| Webasto Unite | ✅ Yes | ✅ 1.6/2.0 | Backend | ❌ via HA | Fleet, commercial |
| Phoenix Contact | ✅ Yes | ✅ 1.6/2.0 | EMS built-in | ✅ KNX module | Premium KNX projects |
Solar + EV: the ideal combination
Solar + EV combined dispatch logic
Priorities (descending):
1. House load (always served)
2. Main fuse limit (never exceeded — Equalizer/Modbus CT)
3. EV fast charge mode (user-requested: charges at max available)
4. EV solar mode (charges ONLY from solar surplus)
5. EV eco mode (charges from surplus + cheap grid tariff)
Solar EV mode example (30-second polling):
surplus_kw = pv_power - house_load ← from Fronius Modbus
if surplus_kw > 1.4: ← minimum 6A × 230V = 1.38kW
ev_current = min(32, surplus_kw × 1000 / 230)
set Easee current = ev_current
else:
set Easee current = 0 (pause charging)
Mode selection via KNX:
Group addr 7/0/20 = 0 → EV OFF
Group addr 7/0/20 = 1 → EV Fast (max available)
Group addr 7/0/20 = 2 → EV Solar (surplus only)
Group addr 7/0/20 = 3 → EV Eco (surplus + night tariff)The KNX room controller or touchscreen lets the user select the charging mode with one button press. Home Assistant then executes the appropriate dispatch strategy in the background — no manual current adjustments needed.
EV charging panel integration
We design panels with CT clamp measurement, Easee Equalizer pre-wiring, and KNX relay control for EV charger infrastructure — from single-family homes to 20-space car parks.
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