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Thread: alternators, generators and motors

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    Default alternators, generators and motors

    G'day, I'm wondering a bit about some different types of motors and generators, most DC motors I've seen have had a permanent magnet for the armature, and an electromagnet for the stator, is this the case in ALL? What about generators? can they have a permanent magnet used in the stator also? I know if I spin a DC motor, it will generate a current, but I suspect it's not an efficient generator. What's the actual difference between a motor and a generator? Why is a generator efficient as a generator, but not a motor? Also can an ALTERNATOR be turned into an electric motor? Some videos would be good.

    Cheers, Gab



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    Back in the early days of motoring a lot of manufacturers used a combined starter/generator up until at least the mid 1920's, i know my Dad's old 1924 Dodge had one but then they moved to separate devices by 1925/26.

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    Quote Originally Posted by Gab250 View Post
    G'day, I'm wondering a bit about some different types of motors and generators, most DC motors I've seen have had a permanent magnet for the armature, and an electromagnet for the stator, is this the case in ALL? What about generators? can they have a permanent magnet used in the stator also? I know if I spin a DC motor, it will generate a current, but I suspect it's not an efficient generator. What's the actual difference between a motor and a generator? Why is a generator efficient as a generator, but not a motor? Also can an ALTERNATOR be turned into an electric motor? Some videos would be good.

    Cheers, Gab


    Every BRUSHED motor I have seen has an electromagnet for the armature and either permanent or electro magnets for the stator.
    Many motors would work reasonably well as DC generators when they get up to speed.
    Washing machine motors were often used for DIY wind generator projects, Silicon Chip had published such a project many years ago.

    Today we have highly efficient BRUSHLESS DC motors originally for RC models but have only fairly recently found their way into power tools and some appliances. Those are the type that have the armature stator arrangement you mention(the permanent magnets rotate). They are NOT DC motors but 3 phase AC motors that have a complex driver circuit(ESC) so they can be powered by DC .
    I am sure they would make great generators, you would just need 6 diodes to make DC from them. They would fall under the term Alternator.
    So an Alternator would need such an ESC specifically designed to run them as a motor from DC but this is as said complicated to get things right, not worth the effort.
    Car alternators also do not have dc magnets but need brushes to excite the rotor (become an electromagnet).

    It is all about matching the revs of the source to the voltage and power you need. Many motors would need to spin too fast.
    But those motors used in E-bikes would make excellent Alternators for windmills because the have a high pol count so they can generate a lot of power at relatively low revs to match the speed of the propeller.
    Gears to increase the revs generally have a lot of loss and the start torque of a propeller(the size you might be using in a back yard) would be to low to overcome this load.

    Of course the generator/alternator in my Plug in Electric Hybrid is used as a motor to start the ICE, which can happen 'hundreds' of times if I am driving in mountainous areas in series hybrid mode and less often in parallel hybrid, depending how I use the paddles for power REGENERATION, yes the drive motors become generators downhill and under braking before a curve, like F1 cars.
    To do that the ESC has to STEP UP the voltage so it is higher than the battery.
    Last edited by Uncle Fester; 01-07-22 at 03:03 PM.
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    Given the OP has not participated in this (and other threads) he started... saying he only started them as he 'was bored'.

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