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need help with ac to dc conversion

Discussion in 'General Electronics Discussion' started by frankmark, Sep 2, 2009.

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  1. frankmark


    Sep 2, 2009
    I have an older yamaha 4hp outboard that had cdi ignition which I was unable to locate parts for. I removed the ignition control module and coil and replaced it with a late model GM coil. Still using the original pulser and suppling the coil with 12 volts it runs. Under the flywheel is a coil that is producing 50vac at idle. It is grounded by the mounting bolts and has 1 wire coming from it. I would like to convert the ac to run the 12vdc coil to avoid being dependent on a battery. The replacement coil draws 1amp. Can this be done with a rectifer, voltage regulator and condensor? If so, what should be their values and in what order are they wired? Thanks for any help.
  2. Resqueline


    Jul 31, 2009
    The problem with the flywheel coil is that it's pretty much a constant current generator, and these are not the easiest to tame. The single wire output doesn't help either. Would you be able to measure the ac short-circuit current? It would tell us if it's able to do the job at all and how much surplus current there'll be.
    I'd suggest using a battery as an intermediate storage/regulator. The single wire means you'll have to use a single diode rectifier, effectively halving the available current potential of the flywheel coil.
    So if the flywheel coil delivers at least 2A you're in business. Rectify it with an 1N5408 diode for instance, and feed it into a battery - and then into the replacement coil (via a switch). Any surplus current will overcharge and heat the battery. Lead acid batteries are usually able to handle quite a bit of this.
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