The electrical input of an automobile alternator.

zaveri

zaveri

@zaveri-5TD6Sk • Oct 24, 2024
The rotor of the alternator, does not contain a permanent magnet , but a coil with pole pieces arrangement, which then serves as an electromagnet.

but in order to make this into an electromagnet, some electrical input is required, and this is supplied to it through the "F" or "I" terminal of the alternator, from the ignition.

now my question is,

1) how much is this input, when compared to the overall output of the alternator ?

2) why aren't permanent magnets used ? is it due to the fact that magnets lose their magnetism at high temperatures ?
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  • zaveri

    zaveri

    @zaveri-5TD6Sk • Nov 15, 2012

    And another thing, are alternators using permanent magnets, available in the market ?


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  • ISHAN TOPRE

    ISHAN TOPRE

    @ishan-nohePN • Nov 15, 2012

    I guess the law is called faraday's law. The principle states that voltage generated is directly proportional to rate of change of magnetic field. The magnetic field is set up with the help of moving coil, pole arrangement. We use temporary magnets because what we are interested in is the rate of change and not magnetic field permanently set up. For this the magnetic flux should be cut by the coils at variable speeds.

    Yes, permanent magnets lose magnetism at high temperatures, but we can take care of that by providing fins (read cooling arrangements). High temperature is perhaps the secondary reason that we are not using permanent magnets.

    I am not aware of any permanent magnet alternator in market. May be some electrical engineer help us.
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  • Ramani Aswath

    Ramani Aswath

    @ramani-VR4O43 • Nov 15, 2012

    When I was a little boy (late 1940s) I had a large and heavy horse shoe permanent magnet that was part of a car's generator. In the early days of cars these were what were used. They were called magnetos.

    They were bulky and heavy. The commutator used to give trouble and breakdowns were common. When bridge rectifiers became common the much lighter and trouble free 'Alternators' became common. Only the much smaller excitation current is carried by the slip rings, so they run trouble free.

    Read the section on Automotive alternators here:
    <a href="https://en.wikipedia.org/wiki/Alternator" target="_blank" rel="nofollow noopener noreferrer">Alternator</a>
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