FAQ
TL;DR: To measure cos φ, sample voltage and current, time their zero crossings, then compute the phase angle. Statistic: 20 A × 120 V = 2400 W. Expert tip: “Take the breaker size and multiply it by the rated voltage.” [Elektroda, Anonymous, post #21682119]
Quick Facts
- Safety first: 230 V mains can kill. Use isolation and proper meters when probing live circuits. [Elektroda, Anonymous, post #21682116]
- Zero‑cross timing of V and I reveals phase shift in reactive loads for cos φ estimation. [Elektroda, Anonymous, post #21682118]
- Use a voltage transformer (VT) and current transformer (CT) to measure safely at mains. [Elektroda, Anonymous, post #21682120]
- Typical grid noted: 220 V, 50 Hz single‑phase supply as project context. [Elektroda, Anonymous, post #21682115]
What is power factor (cos φ) and why do I care?
Power factor indicates how in‑phase your load current is with the voltage. Reactive loads shift current in time versus voltage. Measuring that shift lets you correct the power factor and reduce wasted capacity. “In a reactive load they will be out of phase.” [Elektroda, Anonymous, post #21682118]
How do I measure the phase angle with zero crossings?
Sense voltage and current waveforms. Detect each signal’s zero crossing. Compute the time difference and convert to degrees at 50 Hz. This gives the phase angle to derive cos φ. This timing approach was suggested for reactive loads. [Elektroda, Anonymous, post #21682118]
Which sensors should I use to measure mains voltage and current safely?
Use a small voltage transformer for the line voltage and a current transformer for the load current. They provide isolation and scaled signals for your ADC or comparator circuits. The approach was confirmed by the thread author. [Elektroda, Anonymous, post #21682120]
Can I calculate load impedance and angle from V, I, and real power (W)?
Yes. If you know RMS voltage, RMS current, and true power in watts, you can infer VA and the phase angle. From the angle and V/I you can compute load impedance. This method was proposed in the thread. [Elektroda, Anonymous, post #21682116]
How do I improve power factor for inductive loads like motors or fluorescent lamps?
Once you know the phase angle and current, add capacitance to offset inductive reactance. Switch in capacitor steps until the angle approaches zero. The thread suggests compensating inductive loads by switching capacitors. [Elektroda, Anonymous, post #21682118]
Is working on 230 V circuits dangerous?
Yes. Treat live measurements with strict safety practice. Use isolation, insulated probes, and noncontact sensing whenever possible. As one responder warned, if you are working with 230 V, be very careful. [Elektroda, Anonymous, post #21682116]
How can I estimate maximum load from a breaker rating?
Multiply the breaker current by the circuit voltage for a simple upper bound in watts. Example: 20 A × 120 V = 2400 W. This is a quick check, not a design method for reactive loads. [Elektroda, Anonymous, post #21682119]
What’s a simple 3‑step way to find cos φ for my project?
- Use a VT and CT to acquire scaled AC voltage and current.
- Detect zero crossings and measure the time delta.
- Convert time to degrees (at 50 Hz) and compute cos φ.
This follows the forum guidance. [Elektroda, Anonymous, post #21682118]
Does this method work on a 220 V, 50 Hz supply?
Yes. The original question targets a 220 V, 50 Hz system, and the timing method applies at that frequency. Just use the 20 ms period for conversions. [Elektroda, Anonymous, post #21682115]
Will this help with motors and fluorescent lamp ballasts?
Yes. Those loads are typically inductive, so current lags voltage. Measure the angle, then compensate using capacitors to bring the phase closer to zero. [Elektroda, Anonymous, post #21682118]
