PCB Design for BLDC Ceiling Fan

flux

1:29

Analyzing BLDC motor question.

Gathering knowledge for BLDC requirements.

Providing criteria for BLDC fan operation.

Clarifying ceiling fan motor requirements.

Accessing knowledge base.

Analyzing BLDC voltage requirements and testing.

Short answer
  • A BLDC winding will only run from a 12 V DC bus if the motor is a low‑voltage winding. A conventional ceiling‑fan BLDC (mains winding) will not run properly from a 12 V (or even 24 V) bus.
  • Your 14.69 V open‑circuit reading between U and V is just a PWM artifact on an unloaded inverter output. It is not the DC bus and not the true phase voltage, so it does not tell you if 12 V is sufficient.
How to decide definitively (simple, safe)
  1. Back‑EMF spin test (best)
  • Spin the motor at a known RPM (drill + tach). Measure line‑to‑line RMS (any two phases) with the motor unpowered.
  • Compute Ke_LL = V_LL,rms / RPM.
  • Required DC bus for your target RPM: Vdc_min ≈ 1.2 × (Ke_LL × RPM_target) / 0.707 (the 1.2 is headroom; 0.707 is SVPWM utilization).
  • If Vdc_min is well above 12–24 V, your winding is not a low‑voltage type.
  1. Practical drive check (quick)
  • Power the inverter from a lab DC supply at 12 V, then 24 V, with the motor connected and your normal control loop active.
  • If it can start reliably and reach your target speed under load at 12 V, you can design around 12 V. If not, try 24 V. If 24 V still cannot meet speed/torque, you need a high‑voltage DC bus (rectified mains) or a different (low‑voltage) winding.
Why your U–V reading varies
  • The inverter outputs PWM pulses and commutates between states; with no load, a basic DMM averages unpredictable pulse trains, so readings drift. Measure the actual DC bus across the bulk capacitors to know what the inverter is switching.
Rules of thumb to set expectations
  • Maximum line‑to‑line RMS the inverter can synthesize is about 0.707 × Vdc (SVPWM) or 0.612 × Vdc (SPWM).
  • For a 12 V bus, that’s only enough for motors wound for very low voltage. Most mains‑rated ceiling‑fan BLDCs need much higher line‑to‑line RMS at operating speed.
What I need from you to lock this down
  • One spin‑test datapoint: RPM and the measured line‑to‑line RMS at that RPM (motor unpowered).
  • Or, tell me if your motor is explicitly a 12/24 V BLDC winding. If yes, we’ll proceed with a simple 12–24 V design; if it’s a mains winding, we’ll use a high‑voltage DC bus and keep the control simple while meeting your 30–45 W requirement.
Measure DC bus properly
Use back‑EMF to decide
Rule of thumb for 12 V
51 days
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