ELECTRICAL / 15 TOOLS
Electrical Calculations
Common calculations for basic circuits, motors and cables.
Ohm's Law
Find voltage, current or resistance from the other two values.
U = I × RDC Power
Calculate DC power, or solve for voltage or current.
P = U × ISingle-Phase Current
Calculate single-phase operating current from power, voltage, power factor and efficiency.
I = P / (U × cosφ × η)Three-Phase Current
Estimate balanced three-phase operating current from line voltage and power.
I = P / (√3 × U × cosφ × η)Motor Rated Current
Estimate three-phase motor rated current from shaft power, line voltage, power factor and efficiency.
I = P / (√3 × U × cosφ × η)Motor Torque
Calculate steady-state shaft torque from output power and speed.
T = P / ω ≈ 9550 × P(kW) / n(rpm)Cable Voltage Drop
Estimate steady-state single-phase or three-phase cable voltage drop and percentage.
ΔU ≈ k × I × L × (R′ × cosφ + X′ × sinφ)Power Factor
Convert active power, apparent power and power factor, and calculate reactive-power magnitude.
cosφ = P / S · |Q| = √(S² − P²)AC / RLC Impedance
Calculate series RLC impedance, phase angle, power factor and resonant frequency.
Z = R + j(2πfL − 1/(2πfC))Power Factor Correction
Estimate compensation for an inductive load and single-phase, star or delta capacitor values.
Qc = P × (tanφ₁ − tanφ₂)Transformer
Convert ideal winding voltage and turns, and single-phase or balanced three-phase apparent power and current.
V₁/V₂ = N₁/N₂ · S = k × V × IRC Time Constant
Convert resistance and capacitance units and review capacitor charging and discharging times.
τ = R × CRL Time Constant
Calculate the current-response time constant from inductance and equivalent circuit resistance.
τ = L / RCapacitor Energy
Calculate energy stored in an ideal capacitor from capacitance and terminal voltage.
E = ½ × C × U²4–20 mA / PLC Scaling
Scale engineering values bidirectionally with 4–20 mA, 0–10 V or PLC raw counts.
y = yₘᵢₙ + (x − xₘᵢₙ) / (xₘₐₓ − xₘᵢₙ) × (yₘₐₓ − yₘᵢₙ)