Formulas for electrical work: voltage drop, Ohm’s law and power, resistors, power factor, transformers, energy cost, batteries.
Electrical calculations that rest on physics rather than on a code book: voltage drop from conductor resistance, Ohm’s law and the power triangle, resistor networks, power factor, transformer and battery sizing, and what a load costs to run. The formulas and the physical constants are shown with their sources, and the pages say what they do not decide — conductor ampacity, protection, and installation rules come from the code that applies to you, not from here.
Any two of volts, amps, ohms and watts give the other two; amps from watts or kVA for DC, single- and three-phase with power factor; kW to hp and BTU/h.
You get: The missing values of the circuit — voltage, current, resistance, power — or the full power triangle of an AC load, with the power also in hp and BTU/h.
Open Ohm’s Law & PowerEquivalent resistance of resistors in series or parallel, the voltage, current and power in each one at your supply, and the resistor to add to hit a target.
You get: One equivalent value for the network, a per-resistor table of volts, amps and watts when a voltage is applied, and the extra resistor that reaches a target value.
Open Series & Parallel ResistorsOutput voltage of a two-resistor divider, or the resistor that gives the output you want — with the load across the output taken into account, not ignored.
You get: The output voltage open-circuit and under load, the resistor value to design for, the current and power in each part, and the divider’s output resistance.
Open Voltage DividerVoltage drop in volts and percent for DC, single-phase, or three-phase runs from conductor size, material, length, current and temperature, or a datasheet Ω/km.
You get: The volts lost in the run and the percent of source voltage, the voltage at the load, the longest run for your target, and the smallest listed size that meets it.
Open Voltage Drop