#### Hedges

##### Photon Sorcerer

Motors draw a startup surge of considerably more amps than they draw while running. With grid power you may see the lights dim briefly, but if you have a long skinny extension cord the motor could fail to start due to excessive voltage droop. With inverter power, there is the added problem of how much current the inverter can supply.

Power factor: For AC loads, a resistive load draws current proportional to voltage and in phase. The current is a sine wave exactly aligned with voltage sine wave. Vrms x Irms = "apparent power" in watts, same as actual power. That was the "dot product" of voltage and current. Actual power is determined by "cross product", which can be computed with an oscilloscope capture of voltage and current, then multiplying the voltage by current at each sample point (including sign as well as magnitude.) Then, take the mean average over time.

For an inductive, capacitive, or motor load, the current waveform isn't in phase with the voltage. Part of the time, power is shoved back into the supply; sign of the current measurement is opposite from sign of the voltage measurement. Driving an inductor, current lags voltage by 90 degrees. Capacitor, current leads by 90 degrees. Resistive load, current is at 0 degrees. Grid-tie inverter, current is at 180 degrees (all power delivered, never consumed.) Motors will be something off zero degrees.

Power Factor is ratio of "Actual" power (which can be computed from math on the waveform) to "Apparent" power (which can be computed as product of Vrms and Irms). Apparent power can be expressed in units of "VA" to distinguish from "Watts". A resistive load has power factor = 1.0, Inductor and Capacitor have power factor 0.0 (they don't consume any power), a motor might have power factor = 0.9

I have set up an oscilloscope with voltage probe and AC current probe connected to an electrical outlet. For now a typical 115V, 15A outlet but I plan to connect a 230V outlet to test larger motors. Pictures and results to follow.