Electrical Guides
Electrical Guides and Tutorials
Twenty-one worked guides on the theory behind our calculators — from the ohms law wheel and resistor colour codes to cable sizing, LED design and 555 timer circuits.
Showing 21 of 21 guides
FundamentalsThe Ohms Law Wheel Chart, Explained Quadrant by Quadrant
Twelve equations, four quadrants, one circle. Here is how to read the wheel and pick the formula that matches the two values you already know.
FundamentalsOhms Law Formulas and How to Rearrange Them
The full formula set with units, rearrangements and worked numbers — plus the unit-conversion slips that produce most wrong answers.
FundamentalsVoltage, Current, Resistance and Power Explained
What each of the four quantities really is, the analogy that makes them click, and how changing one changes the others.
FundamentalsKirchhoffs Circuit Laws Explained With Examples
Ohms law handles one resistor. Kirchhoffs two laws handle everything else — here they are, with sign conventions that actually make sense.
FundamentalsAC vs DC Circuits: What Changes and What Stays the Same
Where alternating current behaves just like direct current, where it does not, and why RMS is the number that matters.
Practice & ToolsOhms Law Practice Problems and Worked Solutions
Ten problems that build from a single resistor to power and cable loss, each with the formula choice explained rather than just the answer.
Practice & ToolsHow to Measure Resistance With a Multimeter
Isolate, discharge, compensate, measure. The four-step routine that turns a rough reading into a trustworthy one.
ResistorsResistor Color Code Chart and How to Read It
The full band chart, which end to start from, and the three examples that cover almost everything you will meet on a bench.
ResistorsSeries vs Parallel Resistors Explained
Series adds, parallel divides. The formulas, the sanity checks, and a mixed network reduced in four steps.
ResistorsResistor Power Rating and How to Size It Correctly
Calculate the dissipation, double it, then pick the next standard size up. Here is why that rule works and when it is not enough.
ResistorsE12 and E24 Resistor Values Explained
Preferred values are a logarithmic ladder sized to tolerance. Here is the logic, the tables, and what to do when you need a value that is not on them.
ResistorsThe Voltage Divider Rule Explained
Two resistors, one ratio, one very common mistake. How to design a divider that still reads correctly once something is connected to it.
LED & LightingHow to Calculate an LED Series Resistor
Subtract the forward voltage, divide by the current, round up. Plus the forward voltage table and why parallel LEDs need their own resistors.
LED & Lightingmcd to Lumens Conversion Explained
Candela measures intensity in one direction; lumens measure total output. The bridge between them is beam angle.
Wiring & CableHow to Calculate Voltage Drop
The cable is a resistor you did not plan for. The formulas for DC, single and three-phase, plus the percentage limits to design against.
Wiring & CableWire Gauge Amp Rating: Choosing a Conductor Size
Ampacity keeps the cable from overheating; voltage drop keeps the load working. On long runs the second one usually decides.
Wiring & CableThe Resistivity of Copper and How Temperature Changes It
One material constant, one formula, and a temperature correction that explains why a warm motor winding never reads what the datasheet says.
Power & EnergyWatts to Amps Conversion Explained
Divide watts by volts. Then handle the two complications: power factor on AC, and the root-three factor on three-phase.
Power & EnergyHow to Calculate Electricity Cost for Any Appliance
Watts times hours divided by a thousand gives kWh. Multiply by your rate and the mystery of a standby load disappears.
555 Timers555 Timer Astable Frequency and Duty Cycle
Two resistors and a capacitor set the frequency. Why the duty cycle can never quite reach 50%, and the three standard ways round it.
555 Timers555 Timer Monostable Pulse Width Explained
One resistor, one capacitor, one pulse. The formula, the trigger rules that catch people out, and how to stop it retriggering.
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