DC vs AC vs Brushless

same load, three motor types, three different ways to lose (or not lose) power

DC Motor (brushed)

Output power
Input power
Efficiency
Current drawn
friction/brush (fixed) copper I²R (variable)

AC Motor (induction)

Output power
Input power (real)
Efficiency
Power factor
Apparent power
Current drawn
core+windage (fixed) copper I²R (variable)

Brushless DC

Output power
Input power
Efficiency
Current drawn
core+ESC switching (fixed) copper I²R (variable)
Efficiency: η = Pout / Pin   where   Pin = Pout + Pfixed + Pvariable·(load)²
AC power factor: PF = Ireal / Iapparent   — the motor always draws magnetizing current, even at no load
Current drawn: DC: I = Pin / V    AC: I = Pin / (V × PF)
Same math, on a physical calculator
F5x² — square the load fraction first, since the variable-loss term scales with load squared, not load itself
A4+ — add output power, fixed losses, and variable losses together to get total input power
D4÷ — output divided by input is efficiency; input divided by voltage is current drawn
F4√ — AC power factor needs a square root: square the load and the magnetizing current, add them, then root the total
Why they lose power differently

DC (brushed)

  • Physical brushes riding on a commutator create constant friction, win or lose — that loss doesn't care how loaded the motor is.
  • Steady magnetic field means almost no core loss — no alternating flux, nothing to reverse-magnetize.
  • All electrical input is real power — no power factor to worry about, no reactive current.

AC (induction)

  • No brushes — that source of friction loss is gone entirely.
  • Alternating magnetic field means real core losses — hysteresis and eddy currents reversing 50/60 times a second.
  • Needs a magnetizing current just to sustain the rotating field, regardless of load — that's why power factor collapses at light load, drawing more current than the real power alone suggests.

Brushless DC

  • No brushes, same as AC — friction loss gone.
  • Permanent-magnet rotor means the field is just there — no induced rotor current, no "slip" loss like an induction motor has to pay.
  • No continuous magnetizing current needed either, so it stays efficient even lightly loaded — why cordless tools and fans (which rarely run at full rated load) switched to it.
  • Tradeoff: the electronic controller (ESC) that commutates it has its own small switching losses — real, just smaller than what it eliminates.