Three-Loop Cascaded Control: Three independent controllers run at different rates and stack on top of each other. The output current loop runs 10 times per second and drives the alternator field duty cycle to chase a current target. The voltage loop also runs 10 times per second during the voltage-hold phases (Absorption and Float) — it computes the current target that holds the battery at the configured voltage. In the current-limited phase (Bulk) the voltage loop stands aside and the system charges at the ceiling. The temperature loop runs once every 5 seconds, and outputs a single thermal penalty in amps that gets subtracted from the RPM Cap Table ceiling before the inner loops see it. The cascade is strict: temperature constrains what current the voltage loop is allowed to ask for; the voltage loop constrains what the output current loop is allowed to chase; the output current loop is the only thing that touches the field. Each layer never reaches past the one below it.

RPM Cap Table: For each engine RPM range, you configure a hard ceiling based on your installation's physical limits — belt load, shaft stress, alternator and battery bank ratings. This ceiling is enforced after the thermal penalty is applied and is never exceeded regardless of thermal state. The ceiling can be entered as either a current limit (Amps mode) or a power limit (kW mode) using the toggle above the table. In Amps mode the configured value is a fixed current ceiling. In kW mode the regulator divides your power limit by live battery voltage on every control tick to derive the amp ceiling — so the mechanical load on the belt and shaft stays constant regardless of voltage sag or rise during charging.

Forecasted Thermal Penalty: The temperature controller acts on the higher of two temperatures: the present filtered reading, and a projected temperature — present temperature plus the measured rate of rise multiplied by the Thermal Lookahead horizon. Projection is what lets the loop pull current down before the alternator actually reaches the limit, while taking the higher of the two means a hot alternator is never given current back just because the temperature trend has flattened. The setpoint is the real damage limit (Alternator Temp Limit) and the output is a penalty in amps: zero means no restriction, higher numbers mean more current pulled away from what the RPM Cap Table would otherwise allow. Because the penalty is relative rather than absolute, it transfers cleanly across RPM and stage changes. The penalty itself is slew-limited so brief temperature noise doesn't cause harsh current swings.

Voltage Loop: A proportional-integral controller (Voltage Loop Kp and Ki) holds battery voltage at target during the voltage-hold phases (Absorption and Float). Its output is an alternator-current target, capped at the RPM Cap Table ceiling (with thermal derating) and, when the Group 4 Battery Charge Current Limit is set, at that limit plus the measured house-load draw — so the battery's share of the output is bounded regardless of what the loads are doing. The current-limited phase (Bulk) commands alternator current the same way. The integrator uses asymmetric gain — it bleeds down fast when voltage runs above target and rises slowly when below, biasing toward safety. A deadbanded derivative term (Voltage Kd) trims current straight out of the command when voltage is climbing quickly, which checks overshoot during the approach to target. Anti-windup freezes upward integration whenever the current ceiling — not voltage — is the binding constraint, so the integrator does not load up while unable to act. The loop gains are set by the commissioning wizard's autotuning rather than tuned by hand (see below), and can be automatically re-scaled with board temperature to hold the loop's speed and damping constant as the battery's internal resistance changes with temperature.

Three-Stage Charging: The regulator implements a constant-current / constant-voltage / float charging cycle (CC/CV/Float), with an optional Idle mode after Absorption for lithium longevity.

In Bulk, the voltage loop is off and the system charges at the maximum thermally allowed current from the RPM Cap Table. This continues until battery voltage has been held at the Bulk Voltage target continuously for the Bulk Voltage Debounce Time — a debounce that prevents transient voltage spikes from triggering a premature transition.

In Absorption, the voltage loop engages and holds the battery at the Absorption Voltage. The battery itself now dictates how much current it accepts — current tapers naturally as the battery fills. The system exits Absorption when charge current has dropped to or below the Tail Current for the Absorption Completion Time, confirming the battery is genuinely full. If the system is thermally constrained — meaning the thermal penalty is meaningfully active AND current is already near the Tail Current — tail detection is suspended until thermal headroom recovers, preventing a false exit before the battery is truly full. A safety timeout (Absorption Timeout) forces a transition to Float (or Idle, if Use Float is Off) if Tail Current is never reached.

In Float, the voltage loop holds the battery at the lower Float Voltage. After the Minimum Float Time has elapsed, the system monitors for voltage sag or sustained discharge current. If either condition persists for the Rebulk Debounce Time, or if Float Duration expires, Bulk charging restarts — subject to SoC blocking if SoC data is available. If Use Float is Off, the system skips Float entirely and enters Idle after Absorption, charging again only when rebulk criteria are met.

Independent Protection Layers: Several fast-response protections sit outside the three-loop cascade and act on raw sensor readings without filter lag. Fast OV (Groups 1 and 2) caps current immediately when raw battery voltage runs above a margin below the charging target. Load Dump protection (Group 5) caps current when a sustained battery-current rise rate is detected, catching FET disconnect or load drop events. The over-current detector (iExcess, Group 3) caps the current ceiling when measured alternator current overshoots the commanded setpoint — with a strict regime near the voltage target and a looser one in bulk — and collapses the voltage-loop integrator at the same time so it can't immediately re-demand the excess. Its trip threshold is not a single fixed number: it is max(floor, percent·commanded current, ceiling), so the percentage term rides up with the commanded current — tight at low current (catches real over-current sooner) and looser under heavy output (tolerates the larger legitimate ripple that comes with load) — while the floor guards the low-command case and the ceiling caps it. You set those in Protections; the commissioning wizard measures the ripple and plots it against your thresholds so you can check them, but never sets them for you. None of these depend on the control loops being active — they are always armed.

Stability and Recovery: All mode transitions are bumpless — both the output current loop integrator and the voltage loop integrator are seeded to the operating point before the new mode takes over, so transitions never produce a setpoint step. If the temperature sensor goes stale, the temperature loop holds its last penalty value and re-enters smoothly when fresh data returns rather than snapping back. Anti-windup keeps the temperature integrator parked near any tighter non-thermal constraint when thermals are not the binding limit, so the penalty can climb the instant temperature demands it. A hardware-level shutdown path (GPIO4) provides two independent escape hatches: immediate cut for critical conditions (temperature critically over limit, hard fault) and a controlled ramp-then-cut for sustained warning-level conditions. GPIO4 protection remains active regardless of loop state. Any fault that interrupts charging restarts from Bulk when charging resumes, never mid-cycle.

Start with commissioning — it does nearly all of this for you. The Commissioning tab runs a guided wizard that measures your specific alternator and battery bank and sets almost every loop and protection parameter automatically. You creep the throttle when it asks and confirm each step; it does the math. On most installs this is the only tuning you ever do — the manual procedure below is for hand-verifying or fine-tuning after the wizard, or for the rare case where you want to override what it found.

The wizard walks nine steps, each writing real settings on Apply:

• Prep — snapshots your current settings and checks preconditions (engine running, headroom, a valid battery shunt) so a run can be reviewed or reverted.
• Field curve — ramps field duty open-loop and maps duty→output current, finding the saturation knee.
• Current Control Autotuning — a sine sweep on field duty measures the inner current loop's plant (time constant and gain) and proposes its PID gains and filter constants (also on the Plant Delay tab).
• Verify Current Control — a closed-loop sweep with the new inner-loop gains, confirming the loop is stable before anything downstream trusts it.
• Disturbances — you creep idle→cruise while it records the worst ripple per RPM range (belt resonance) on both the alternator and battery signals, building the Resonance & Ripple Map.
• Fault Threshold Autotuning — sets the over-current detector's trip line from the ripple just measured: the line runs a Safety Margin above the ripple and is drawn against the measured points so you can confirm it clears them. It writes straight to the Protections settings — adjust the margin or the individual values by hand if you like.
• Voltage Control Autotuning — commands one bounded current pulse through the tuned inner loop and measures how battery voltage responds to the current step (the finite-horizon gain K20), then computes the voltage-loop gains from your chosen response time.
• Min% Floor & Field Decay — at each of three held speeds (max working → mid → idle) it finds the field onset knee, filling the per-RPM Min% floor column, then cuts the field once and times the alternator-current drain at that speed; the three drain points fit the speed-dependent line the over-voltage response's field-drain timing reads.
• Stress Test — charges at idle until the battery voltage settles, parks the bus at a constant-voltage target it can actually reach, then you snap the throttle to about half max RPM so the over-voltage protection fires on a reachable setpoint; the protection response and recovery are graded, with corrective actions offered on a poor result. Writes nothing — a pure acceptance check.

Every step is advisory — it proposes, and nothing changes until you press Apply. You can re-run a single step, or clear and start over. Progress is stored on the regulator, so it survives a reload and looks the same from any device.

Manual tuning (optional). The output current loop and the voltage loop each also have their own live tuning mode you can drive by hand — Tuning Mode for the inner current loop (Current tab), and the Auto-or-Manual gain selector on the Voltage tab for the voltage loop. Tune them in that order — inner loop first, then voltage — because each layer depends on the one beneath it being stable. The rest of this section covers hand-tuning the inner current loop; the voltage loop has its own dedicated tab with a built-in step test, an Auto mode that reuses the commissioned fit, and live scoring. The temperature loop is tuned offline from logged data (no live step test) — its tab shows the live control plot and the controller parameters.

Three-Phase Process: The goal is to tune the core PID first, then verify it handles the rate limiters gracefully with anti-windup tracking. Tune in bulk stage — absorption and float share the same output current loop, so a well-tuned bulk response carries through automatically.

Phase 1 — Core Loop (Unrestricted):
Set both slew limiters to very high values to effectively disable them:
• Setpoint Rise Rate: 1000 A/s
• Setpoint Fall Rate: 1000 A/s
• Duty Ramp Rate: 1000 %/s
Enable Tuning Mode and watch the step response on the plots. Tune Kp, Ki, and Kd until you get well-damped step responses with minimal overshoot (10–20%) and fast settling time (2–4 seconds).

Phase 2 — Actuator Slew + Anti-Windup:
Re-enable the actuator slew limiter by setting Duty Ramp Rate to a realistic value (typically 10–30 %/s). Keep setpoint slew limiters high (1000 A/s). Run tuning mode again and watch for overshoot after transitions. If you see overshoot once the duty ramp catches up, increase PID Tracking Gain until the overshoot disappears. This is the back-calculation gain that bleeds the integrator down whenever the duty output is rate-limited.

Phase 3 — Production Verification:
Set Setpoint Rise Rate and Setpoint Fall Rate to your desired production values (typically 5–20 A/s rise, 20–50 A/s fall). Run tuning mode one final time to verify the loop remains stable and well-behaved with both rate limiters active.

Tuning Philosophy for Cruising:
Run tests at moderate RPM within your typical cruising range. A slower, well-damped loop (4–6 second settling time) is preferable to a fast loop that causes harsh load transitions. The independent protection layers (Fast OV, Load Dump, the Group 3 iExcess detectors, GPIO4 hard cut) handle the unsafe edges — you don't need the loop itself to react instantly. Smooth and stable beats fast and harsh.

Every installation is different — always verify with a step test in your own setup.