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Load balancing behaviour

How Edge site controllers share the main connection between charge points. Per-second limits, the 6 A minimum and 8 A start threshold, failsafe on lost communication, site limit, solar modes and 1P/3P switching, with the configuration keys.

View as MarkdownUpdated 2026-09-22

This describes what the EVSE-SC-01 (clamps) and EVSE-SC-02 (P1) do, and what a third-party controller should do to behave the same way.

Inputs

Input SC-01 SC-02
Site current per phase 3 CT clamps, magnitude only P1 telegram, import and export per phase, 1 s
Site limit maxsitecurrent (A per phase), default 255 = uncapped same
Per-socket max maxcurrent, for example 3x25 same
Per-socket phases settings@<socket> bit 0 (0 = 1-phase, 1 = 3-phase) same
Minimum start current minstartc, default 8 A same
Minimum charge current minc, default 6 A same
Solar mode not reliable (no direction) solar, charge_solar

The loop

  1. Every second, read the site current per phase.
  2. Headroom per phase = site limit − site current + current already going to charge points.
  3. Distribute headroom over the sockets that are in state B (waiting) or C (charging), per phase, honouring each socket’s own maximum and its cable rating.
  4. A socket only starts when at least minstartc (8 A) is available. A charging socket is never given less than minc (6 A). If the headroom cannot serve all sockets at 6 A, the most recently connected sockets wait at 0 A.
  5. Write RemoteMaxCurrent (register 0x0201) to every socket. Budget: 50 ms per socket, so 4 sockets take 200 ms of a 1 s cycle; 10 sockets is the ceiling for the SC-02.

Failsafe

  • A charge controller that does not receive a write for 2 s reverts to its static limit (16 A or 32 A by jumper). Site controllers therefore write every second even when nothing changes.
  • The site controller reports mb_quality, the percentage of Modbus transactions that succeeded, on every status message. Below about 90 % something is wrong with the bus.
  • A site controller that loses WiFi keeps balancing locally. The platform only configures; it is not in the control loop.

Solar modes (SC-02)

solar charge_solar Behaviour
0 — Off. Charge at the site limit.
1 0 Solar assist. Use export first, top up from the grid so the car always gets ≥ 6 A.
1 1 Solar only. Charge only from export; below 6 A (1-phase) or 3×6 A (3-phase) of surplus the session pauses.

A socket configured for 3-phase can be switched to 1-phase to widen the solar-only window. The session is stopped, the phase setting changed, and after a 10 s pause restarted. Switching phases mid-session without the pause confuses most vehicles.

Whole-site 1-phase

Sites with a small connection can force every socket to 1-phase with the p1charge setting, and back with p3charge. The charge controller’s PHASES bit is written accordingly.

Behaviour a third-party controller must copy

If you drive Edge charge controllers from your own controller:

  • write register 0x0201 at least once per second;
  • never advertise between 1 and 5 A: use 0 or ≥ 6 A;
  • respect the cable rating in register 0x0102 low byte;
  • stop, wait 10 s, then restart when changing the number of phases;
  • treat error bits 1, 2 and 4 as “limit 0 and alert”.