Hi,
I have a SmartSolar MPPT with a 16S LiFePO₄ battery. The BMS turns charge MOSFET OFF below 0°C (discharge stays ON, so battery voltage remains present on the DC bus).
On the same DC system I have:
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a constant ~100W DC load
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resistive battery heating pads (silicone pads for warming the LiFePO₄ battery), switched ON/OFF via Cerbo GX relay logic
The intended behaviour is:
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PV should run the ~100W loads
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if battery charging is allowed: PV can charge the battery
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if charging is blocked (cold): PV should still run the loads, and any PV surplus (if available) should go to the battery heating pads to warm the battery
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even if heating pads are OFF and charge MOSFET is OFF, I still want PV to keep the system running (so PV output should be stable)
Problem: when charging is blocked (charge MOSFET OFF), MPPT power becomes unstable even in decent sun — it jumps rapidly (example 0W → 50W → 200W → 0W → 15W …). During the drops the battery supplies the loads, then PV returns, causing repeated battery “pulsing” charge/discharge.
Questions:
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Is this oscillation normal for SmartSolar when battery charge is blocked (charge MOSFET OFF but battery still connected)?
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Could the battery heating pads switching (simple resistive load ON/OFF) be contributing to the PV power jumping?
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What is the recommended Victron approach to keep PV stable for DC loads in this condition, and optionally divert PV surplus to a DC heater/dump load?