Motors Lecture 11.4

Hans Christian Oersted (1777 – 1851) Ref: In 1820 he showed that a current produces a magnetic field. X

André-Marie Ampère (1775 – 1836) French mathematics professor who only a week after learning of Oersted’s discoveries in Sept demonstrated that parallel wires carrying currents attract and repel each other. attract repel A moving charge of 1 coulomb per second is a current of 1 ampere (amp).

What do Maxwell’s Eqs. Predict? B = magnetic flux density (magnetic induction)  magnetic permeability B Magnetic field lines must be closed loops Force on moving charge q Lorentz force

Vector Multiplication Scalar (Dot) Product  A B Vector (Cross) Product  A B Direction of C given by "Right- hand rule" (into the screen)

Force on current in a magnetic field Force on moving charge q -- Lorentz force Current density, j, is the amount of charge passing per unit area per unit time. N = number of charges, q, per unit volume moving with mean velocity, v. j Force per unit length on a wire is

Rotating Machine B i i X Force in Force out + -

Rotating Machine B i i X Force in Force out + -

Rotating Machine B i i X Force in Force out + - brushes commutator

What do Maxwell’s Eqs. Predict? Corresponds to Faraday’s law of electromagnetic induction A changing magnetic flux B density induces a curl of E

B i i X Force in Force out + -  X r B l a b Back emf

B i i X Force in Force out + - a b Back emf

B i i X Force in Force out + - brushes commutator

Armature with four coil loops X X X X N S

Motor Circuit Power and Torque

Armature Current, Speed, Power and Torque

FF-130 Series Motors

Maximum Power

Generator Circuit