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Priority-Based Power Scheduling

When multiple SmartEVSEs share one mains connection (Power Share), there may not be enough power for all of them to charge simultaneously. Without priority scheduling, all EVSEs stop at the same time, restart, see insufficient power, and stop again — creating an oscillation loop where nobody charges.

Priority scheduling solves this by keeping some EVSEs charging while pausing others, then rotating who gets to charge so every car eventually gets its turn.

How it works

The problem

Imagine two EVSEs on a shared 25A connection. Each needs at least 6A (the IEC 61851 minimum). A dishwasher kicks in, leaving only 11A available. That is enough for one car (6A) but not two (12A). Without scheduling, the system sees "not enough for everyone" and cuts power to both — even though one car could have kept charging.

The solution

When available power drops below what all EVSEs need:

  1. Sort the EVSEs by priority (see strategies below).
  2. Allocate the minimum current (6A) to the highest-priority EVSE first, then the next, and so on until power runs out.
  3. Distribute surplus — any power left over after giving everyone their minimum is split equally among the active EVSEs (respecting each EVSE's maximum).
  4. Pause the remaining EVSEs that didn't get power. They are not in error — they are deliberately waiting for their turn.

When power increases again (the dishwasher stops), paused EVSEs are immediately reactivated in priority order.

Example

Three EVSEs (A, B, C) on a 25A connection, 1A baseload, MinCurrent = 6A:

Scenario Available A (prio 1) B (prio 2) C (prio 3)
Plenty of power 24A 8A 8A 8A
Some shortage 14A 7A 7A paused
More shortage 8A 8A paused paused
Total shortage 0A paused paused paused

When EVSE C is paused, it does not trigger an error or count towards a shutdown. Only when even the highest-priority EVSE cannot get its minimum (total shortage) does the system flag a real power problem.

Settings

These settings appear on the LCD menu and web interface when PWR SHARE = Master.

PRIORITY (LCD: PRIORITY)

Choose how EVSEs are ordered when power is scarce.

Value Name Description
0 Modbus Address Lower Modbus address = higher priority. Simple and predictable — Master always charges first, then Node 1, Node 2, etc.
1 First Connected The car that plugged in first gets priority. Fair for shared parking where arrival order matters.
2 Last Connected The most recently plugged-in car gets priority. Useful when the latest arrival is most urgent.

Default: Modbus Address (0)

ROTATION (LCD: ROTATION)

How often to rotate which EVSE is actively charging, in minutes.

Value Meaning
0 Disabled — no rotation. The highest-priority EVSE charges until done or disconnected.
30–1440 Rotate every N minutes. After this time, the currently charging EVSE is paused and the next one in priority order starts.

Default: 0 (disabled)

Tip: Set this to 60 (1 hour) if you want all cars to get some charge during a long parking session. Set it to 0 if you always want the highest-priority car to finish first.

IDLE TMO (LCD: IDLE TMO)

How many seconds to wait before deciding an EVSE is idle and skipping to the next one.

Value Meaning
30–300 Seconds. If an EVSE is allocated power but draws less than 1A for this long, it is considered idle and the next EVSE gets its turn.

Default: 60 seconds

This also acts as anti-flap protection: no EVSE can be paused or rotated away within the first IDLE TMO seconds after activation. This prevents rapid on/off cycling that could confuse cars or wear relays.

Timers and behavior

Each EVSE goes through this cycle when it gets activated:

         activate
            |
            v
    +-----------------+
    |   Idle Check    |  <-- IdleTimer counts up from 0
    |  (IDLE TMO sec) |
    +-----------------+
            |
     drawing power?
      /          \
    NO            YES
    |              |
    v              v
  pause       +------------------+
  next EVSE   |  Rotation Timer  |  <-- counts down from ROTATION * 60
              |  (if enabled)    |
              +------------------+
                       |
                  timer expires
                       |
                       v
                 pause this EVSE
                 activate next

Step by step

  1. EVSE is activated — it gets allocated current and its idle timer starts at 0.

  2. Idle timer counts up — every second, the timer increments. During this window, the EVSE cannot be rotated away (anti-flap protection).

  3. At IDLE TMO seconds:

    • If the EVSE is drawing less than 1A → it's idle (car finished charging, or not accepting current). Skip to the next EVSE in priority order.
    • If the EVSE is drawing 1A or more → it's actively charging. Start the rotation timer (if rotation is enabled).

  4. Rotation timer counts down from ROTATION * 60 seconds. When it reaches zero, this EVSE is paused and the next EVSE in priority order is activated. The cycle repeats from step 1 for the newly activated EVSE.

  5. Wrap-around — when the last EVSE in priority order finishes its turn, the first EVSE gets reactivated. Disconnected EVSEs (no car plugged in) are automatically skipped.

Power increase

If available power increases (e.g., the oven turns off), paused EVSEs are immediately reactivated in priority order — no need to wait for a timer. Their idle timers are reset so they get a fresh anti-flap window.

Solar mode

In Solar mode, paused EVSEs show "No Sun" instead of "Less 6A" since the shortage is caused by insufficient solar production, not a mains overload.

MQTT topics

When connected to an MQTT broker, the following topics are available:

Settings (read/write)

Topic Values Description
SmartEVSE-xxxxx/Set/PrioStrategy 0, 1, 2 Set priority strategy
SmartEVSE-xxxxx/Set/RotationInterval 0, 30–1440 Set rotation interval (minutes)
SmartEVSE-xxxxx/Set/IdleTimeout 30–300 Set idle timeout (seconds)

Status (read-only, published by the Master)

Topic Example Description
SmartEVSE-xxxxx/PrioStrategy ModbusAddr Current strategy name
SmartEVSE-xxxxx/RotationInterval 60 Current rotation interval
SmartEVSE-xxxxx/IdleTimeout 60 Current idle timeout
SmartEVSE-xxxxx/RotationTimer 1423 Seconds remaining until next rotation
SmartEVSE-xxxxx/ScheduleState Active,Paused,Inactive Per-EVSE schedule state (comma-separated)

Home Assistant

All settings and status values are automatically discovered by Home Assistant via MQTT discovery. You will find them under the SmartEVSE device on the MQTT integration page.

REST API

GET /settings

The response includes scheduling settings and status:

{
  "settings": {
    "prio_strategy": 0,
    "rotation_interval": 60,
    "idle_timeout": 60
  },
  "schedule": {
    "state": ["Active", "Paused", "Inactive"],
    "rotation_timer": 1423
  }
}

The schedule object is only present when PWR SHARE = Master.

POST /settings

Parameter Values Description
prio_strategy 0–2 Set priority strategy
rotation_interval 0, 30–1440 Set rotation interval (minutes)
idle_timeout 30–300 Set idle timeout (seconds)

Example:

curl -X POST 'http://ipaddress/settings?prio_strategy=1&rotation_interval=60' -d ''

These settings are only accepted when PWR SHARE = Disabled or Master. Nodes cannot change scheduling settings (they are controlled by the Master).

Web interface

When PWR SHARE = Master, the web interface shows a Scheduling section with:

  • Priority Strategy — dropdown to select Modbus Address, First Connected, or Last Connected
  • Rotation Interval — number input (0 = disabled, 30–1440 minutes)
  • Idle Timeout — number input (30–300 seconds)
  • Schedule State — read-only display showing each EVSE's current state
  • Rotation Timer — read-only countdown in seconds

Frequently asked questions

Q: What happens if I only have one EVSE? A: Nothing changes. Priority scheduling only activates when PWR SHARE = Master and there are multiple EVSEs. A single EVSE (PWR SHARE = Disabled) works exactly as before.

Q: Can I change priority strategy while cars are charging? A: Yes. The new strategy takes effect on the next scheduling cycle (within seconds). Active EVSEs are not immediately disrupted.

Q: What if rotation is disabled and one car finishes charging? A: The idle detection kicks in. After IDLE TMO seconds of the car drawing less than 1A, the next car in priority order is activated.

Q: Does priority scheduling work in Solar mode? A: Yes. When solar production drops, only lower-priority EVSEs are paused. The highest-priority EVSEs keep charging as long as there is enough solar power for them.

Q: What about the existing NoCurrent error? A: NoCurrent only triggers when even the highest-priority EVSE cannot get its minimum current (a true hard shortage). Deliberate pauses of lower-priority EVSEs do not trigger NoCurrent, preventing the oscillation bug.