what is an alternating current (ac)? what is an ac generator? what is an ac transformer? how to...
TRANSCRIPT
• What is an alternating current (AC)?
• What is an AC generator?
• What is an AC transformer?
• How to calculate a transformer’s expected step-up or step-down AC voltage?
ES Lesson 7: AC electricity
© 2012 C. Rightmyer, Licensed under The MIT OSI License, 20 July 2012
The magnetic field generated by a coil of wire that has a current flowing through it.
Electricity and Magnetism, Gareth Stevens Publishing, Steve Parker, 2007
A compressed coil of wire with a current passing through it acts just like a button magnet.
[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]
ES demo 7-1. A moving magnetic field inside a coil of wire induces current in that coil.
Make: Electronics, O’reilly [Publishing], Charles Platt, 2009
BE demo 1-2
How does an AC generator work?
Continuous slip rings required to connect current to the load.
[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]
Direction and amplitude of generated voltage
7IQT Corporation, Electric Pizza, An in house course, 2010
Electrical power delivery system
Electricity and Magnetism, Gareth Stevens Publishing, Steve Parker, 2007
Direction and amplitude of the generated current
[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]
How’d those electrons get into your outlet?
ES demo 7-2. Use a toy generator to produce AC and DC voltages. Display output using a multimeter and oscilloscope.
BE demo 7-1
ES demo 7-3. Transformer operation using two AC voltmeters and an oscilloscope.
~ 1000 turns
~ 142 turns
AC VOM
120 Volts AC
AC VOM
~ 17 Volts AC
Oscilloscope
AC Sine Wave
1 Megohmresistor
BE demo 1-4
Output on the secondary coil Output on the secondary coil depends on input voltage and turns ratio
(Vs) = Vp (Ns / Np)
where:
Vs = voltage in secondary
Vp = voltage in primary
Ns = number turns in secondary
Np = number turns in primary
Back up charts
Fields associated with different shaped magnets
[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]
[A.O.Smith:The AC's and DC's of Electric Motors]
Mutual coupling between electromagnetic fields
[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]
(a) strong coupling
(b) no coupling
(c) weak coupling
One way to measure input and output currents
LED
VOM
Amps
VOM
Amps
ACGenerator
(Volts)
Constructing a transformer with a circular magnet
Second method for measuring the currents
Light
VOM
V ac
VOM
V ac
ACGenerator
(Volts)