PV Optimizer Design Guidance
Thought for 1 min 40 sec
Short answer: Yes—2 MOSFETs is OK if you use a synchronous buck and your panel voltage stays above the battery voltage during charging.
What that means
- Topology: A 2‑MOSFET synchronous buck (high‑side switch + low‑side synchronous rectifier) is appropriate for ~18 V panel -> 12 V lead‑acid charging. If you want to keep charging when panel voltage drops below the battery (e.g., dawn/dusk), you’d need a buck‑boost (4 MOSFETs).
- Duty example: With 14.4 V absorb target from an 18 V panel, duty ≈ 0.8.
- Power/current: A 500 W panel could deliver up to ≈ 41.7 A at 12 V; your 12 V 15 Ah lead‑acid typically can’t take that. Limit charge current (commonly 0.1C–0.3C ≈ 1.5–4.5 A unless your battery’s datasheet allows more).
Design tips (apply exactly as stated)
- Include a switching regulator IC, an inductor, and input/output capacitors to avoid unstable or non‑functional output.
- Inductor: ripple target 20–40% of full load; saturation current ≥ 1.2× peak load; low DCR and low core loss.
- Example inductor for 5 A bulk at 50 kHz, 30% ripple, 18 V -> 14.4 V: about 38 µH.
- MOSFETs: choose adequate VDS margin (for 18 V input, 40–60 V class is typical), low RDS(on), and thermal headroom for your limited charge current.
- Lead‑acid charging: implement bulk/absorption/float with temperature compensation; add polarity protection, battery protection, and simple charge status indicators.
If you confirm your intended max charge current (e.g., 3 A, 5 A), I can size the inductor and suggest MOSFET/diode ratings and initial capacitor values accordingly.
Specify charge current
Ask about MPPT
Battery-safe charging profile
Check panel voltage range
Thermal and copper sizing
