Following AC voltage from the stator in this circuit

Discussion in 'The Projects Forum' started by Danickstr, Jul 1, 2016.

  1. Danickstr

    Thread Starter New Member

    Jul 1, 2016
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    image.png The circuit shown is a rectifier regulator circuit for a three-phase motor cycle stator AC conversion to 14 V DC. The part I don't understand is that the diode bridges seem to allow the voltage directly back to the positive and negative buses. Since stator AC voltage will vary with RPM, and go as high as 45 volts AC, I am confused because the rectifier doesn't appear to me prevent the raw AC power to be controlled before going back to the DC return bus. But people have built this "instructable" circuit with success, so I am sure it's simply something I haven't grasped.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Those three bridges are configured as a three-phase rectifier with two diodes in each bridge in parallel. This makes 6 rectifiers total, as shown below.
    [​IMG]

    The regulator works by shorting the alternator windings with the TRIACs when the voltage gets too high. That may seem like an odd way to regulate the voltage since it dissipates a fair amount of energy as heat, but that's how it's commonly done for permanent-magnet alternators on motorcycles.
    You can't use a series regulator to regulate the voltage because the alternator voltage can then become high enough to damage the windings.

    Here's a article I wrote on an improved paper design (but somewhat more complicated) regulator, after I had 3 separate regulator failures on my cycle.
     
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  3. Danickstr

    Thread Starter New Member

    Jul 1, 2016
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    Thanks for that explanation. I guess "odd" is why I had a bit of trouble grasping it but if that is the way then so be it! The Kohler 675 cc motor is on my trencher and is actually only 2 phase so I like many who used that particular instructable am just dropping one phase and making it with the same parts just with 2 of the duty side phases.

    My brain wanted the rectified outputs to go directly to a triac and just open and close to pulse control the voltage with the zener watching and opening and shutting the triacs. Guess that must not work in the real world.

    I am going the paper link now...

    Your circuit looks to add a level of sophistication to the process that is above my freshman electronics comprehension but the idea of less heat seems like a good idea. I have burned up three of the simple Kohler-supplied rectifiers on two motors so am tired of the headache of thier poor design.
     
    Last edited: Jul 1, 2016
  4. crutschow

    Expert

    Mar 14, 2008
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    As I said, if you try to restrict the voltage by placing any type of control in series with the alternator output, the voltage can rise to damaging levels.

    Whatever design you do, be sure the Triacs and rectifiers are on a good sized heatsink and as far away from engine heat as possible.

    I added a computer muffin fan to blow over the fins of my last motorcycle regulator to help keep it cool.
    You might consider that as an option.
     
  5. Danickstr

    Thread Starter New Member

    Jul 1, 2016
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    I am sure it's not as easy as my mind wants it to be so thanks again for explaining that voltage issue although I have learned to not use my own logic I these matters. I have already bought the parts from mouser so will at least solder it up and am using a cast Al plate as a base with 4 fins. I like the fan idea and may place it near the hydraulic pump since it has a small rotor fan like a tefc.

    I am wondering also if anyone ever took apart the money clip-sized rectifier that comes stock on my 1500 dollar motor and what items are under the epoxy. It's a Kohler CH620 19hp. Current one melted in 30 hours of motor time.
     
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