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05-02-2006 #1
Any electrical engineers or the like?
somethings been bugging me the last few days. We know that change in magnetic polarity induces an electical current, but where do those electrons come from if they are not attached to the ground/earth? Do you have to have a battery? Old cars and didn't have batteries right? they just had a hand crank to start and a magneto to fire the spark plugs right?
-Tas
'04 Mustang Saleen sc281 speedster
'67 Mustang notchback: The fabled $500 non running project car: 308, auto, 2 barrel (now 4), AC(now removed), 5 lug, disk front, drum rear, power brakes and steering... that I got started and home for $65 :D
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05-02-2006 #2I'm an EE. I will give the quick and easy to digest answer.
Energy cannot be created or destroyed, but it can be converted. When you rotate a magnet, you are using kinetic energy to move it(cranking the engine by hand). This kinetic energy can be converted to electrical energy by taking advantage of the properties of electromagnetism(thats where the electons come from).Alcino Manuel Azevedo
76 Mustang II Cobra II
Featured in April 2006 Popular Hot Rodding
05-02-2006 #3
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Kind of on the same note I had a discussion with an EE today about the electron theory, conventional vs. the automotive world... negative to positive or positive to negative. While in this discussion we talked about alternators and how the current flow of AC current changes to DC using the rectifier (diodes) and how the current flow in the stator changes as the rotor moves past it. While discussing this I drew up a diagram of the alternator and rectifier and we got into a whole hoopwah about negative to positive theory and in the auto world positive to negative and how it should and shouldnt work. If you have any clear ways of describing alternator operations using postive to negative theory could you please share.
05-02-2006 #4I'm looking for more than quick and easy answer. I'm a manufacturing engineer so I know the theory and have done all the electicity and magnatism physics labs like 10 years ago, but where do the electrons come from when not connected to the ground? from all my thinking I have to imagine there would have to be some battery or sacrificial element somewhere.
Originally Posted by alcino
-Tas
'04 Mustang Saleen sc281 speedster
'67 Mustang notchback: The fabled $500 non running project car: 308, auto, 2 barrel (now 4), AC(now removed), 5 lug, disk front, drum rear, power brakes and steering... that I got started and home for $65 :D
05-02-2006 #5The electrons were always there. Everything is made up of atoms and atoms have electrons. So using Faraday's Law. An electric current(moving electrons) can be produced by a changing magnetic field. So the kinetic energy(something spinning) in the magnetic field is exciting the electrons and moving them in a direction to create current. The current squared times resistance of the sparkplugs is what is firing them up.
You don't need a ground per say, but you do need to "complete the circuit" for current to flow. A battery is not needed for producing current.
If my words don't help here is a good picture.
Alcino Manuel Azevedo
76 Mustang II Cobra II
Featured in April 2006 Popular Hot Rodding
05-02-2006 #6



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