DC Machine EMF Calculator
A 4-pole lap-wound machine with 20 mWb per pole and 500 conductors generates 200 V at 1200 rpm; wave-wound, the same machine gives 400 V.
200 V
- Parallel paths A
- 4
- Machine constant PZ/(2πA)
- 79.57747155
- EMF per conductor
- 1.6 V
Step-by-step solution
- E = PΦZN ÷ (60A) = 4 × 0.02 × 500 × 1200 ÷ (60 × 4)
- E = 200 V
DC Machine EMF Formula
E = PΦZN / (60A)
A = P for lap, 2 for wave windings; motor: E_b = V − IₐRₐ, T = E_b Iₐ/ω
Worked Example
A 4-pole lap-wound machine with 20 mWb per pole and 500 conductors at 1200 rpm:
- E = PΦZN ÷ (60A) = 4 × 0.02 × 500 × 1200 ÷ (60 × 4)
- E = 200 V
Machine constant PZ/(2πA): 79.57747155 · EMF per conductor: 1.6 V
GATE tip
Speed ratio questions: N₂/N₁ = (E_b2/E_b1) × (Φ₁/Φ₂). In a series motor Φ ∝ Iₐ (below saturation), so also scale the flux with the current.
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Frequently asked questions
Why does wave winding give a higher voltage?
A wave winding has only two parallel paths, so more conductors are in series per path. Lap windings have P paths and suit high currents.
How does speed relate to back EMF?
E_b = kΦω, so at constant flux speed is proportional to E_b = V − IₐRₐ. Weakening the field raises the speed.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
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APA
Scientific Converters. (2026, October 15). DC Machine EMF Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/dc-machine-emf-calculator/
IEEE
Scientific Converters, "DC Machine EMF Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/dc-machine-emf-calculator/