Add CP mode sanity check: validate current limit vs power at min voltage

CP=500W at V=50V needs 10A on the load side — if the supply I_limit
is only 20A and the MPPT has conversion losses, this can cause the
supply to current-limit and timeout. The check now catches this upfront:

  CP check: 500W / 50V = 10.0A (limit 20.0A) OK

Also raises ValueError if the worst-case current exceeds the limit.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

testbench/bench.py

@@ -564,11 +564,19 @@ class MPPTTestbench:
         self,
         max_voltage: float,
         current_limit: float,
+        *,
+        min_voltage: float | None = None,
+        load_mode: str = "CC",
+        max_load_setpoint: float = 0.0,
     ) -> None:
         """Check that the supply can deliver the requested V and I.
 
         Queries the supply's voltage range (max V) and verifies the
-        requested parameters are within bounds.  Raises ValueError if not.
+        requested parameters are within bounds.  For CP mode, also
+        checks that the supply current limit can deliver the requested
+        power at the minimum voltage.
+
+        Raises ValueError if the configuration is invalid.
         """
         supply_max_v = self.supply.get_voltage_range()
         if max_voltage > supply_max_v:
@@ -585,6 +593,21 @@ class MPPTTestbench:
             f"(range {supply_max_v:.0f}V)"
         )
 
+        # CP mode: at min voltage the load draws max current
+        if load_mode == "CP" and max_load_setpoint > 0 and min_voltage:
+            worst_case_i = max_load_setpoint / min_voltage
+            if worst_case_i > current_limit:
+                raise ValueError(
+                    f"CP mode: {max_load_setpoint:.0f}W at "
+                    f"{min_voltage:.0f}V needs {worst_case_i:.1f}A "
+                    f"but supply I_limit is {current_limit:.1f}A"
+                )
+            print(
+                f"  CP check: {max_load_setpoint:.0f}W / "
+                f"{min_voltage:.0f}V = {worst_case_i:.1f}A "
+                f"(limit {current_limit:.1f}A) OK"
+            )
+
     # ── 2D Voltage × Current Sweep ─────────────────────────────────────
 
     def sweep_vi(
@@ -630,7 +653,14 @@ class MPPTTestbench:
 
         # Sanity check
         max_v = max(abs(v_start), abs(v_stop))
-        self.check_supply_capability(max_v, current_limit)
+        min_v = min(abs(v_start), abs(v_stop))
+        max_l = max(abs(l_start), abs(l_stop))
+        self.check_supply_capability(
+            max_v, current_limit,
+            min_voltage=min_v,
+            load_mode=load_mode,
+            max_load_setpoint=max_l,
+        )
 
         # Auto-correct step directions
         if v_start < v_stop and v_step < 0:

testbench/gui.py

@@ -1192,7 +1192,14 @@ class TestbenchGUI(tk.Tk):
 
         # Sanity check
         max_v = max(abs(v_start), abs(v_stop))
-        bench.check_supply_capability(max_v, current_limit)
+        min_v = min(abs(v_start), abs(v_stop))
+        max_l = max(abs(l_start), abs(l_stop))
+        bench.check_supply_capability(
+            max_v, current_limit,
+            min_voltage=min_v,
+            load_mode=load_mode,
+            max_load_setpoint=max_l,
+        )
 
         bench.supply.set_current(current_limit)
         bench.supply.output_on()