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Auto star-delta PMA alternator switchover

Discussion in 'Power Electronics' started by flippineck, Mar 3, 2018.

  1. flippineck

    flippineck

    268
    8
    Sep 8, 2013
    Trying to convert a car alternator into something suitable for a wind turbine project here.

    You can buy pre-made PMA alternators for wind turbines on ebay however decent ones are very expensive and virtually all only seem to be available from US-based sellers, which adds a huge postage and tax cost to UK orders :-(

    I'd previously investigated using a Ford car alternator as-is, however in general car alternators turn out to be unsuitable in unmodified form for a few reasons.

    So the plan is, to replace the powered rotor with a permanent magnet type and do away with the existing regulator.

    There are some pre-made rotor options on ebay for specific Delco alternator conversions, and also there are plans available for outfitting most any claw-pole rotor with a high strength ring magnet rather than a field coil. Both options would require some toolshop operations to work with the alternator I have but luckily I live local to a very good and reasonably priced one-off engineering shop.

    The existing regulator in my Ford alternator is heavily dependent on computer control from the vehicle ECU so the plan is to work purely with the existing 3 stator coils and an external rectifier and regulator. Maybe, butcher the Ford regulator and use it just for it's nicely mounted RPM sensor alone.

    Thus far I have removed the back end of the alternator along with the field coil brushes and computerised regulator, and the spinning armature complete with slip rings and field coil.

    By removing the regulator / rectifier plate I have exposed the stator coil connections of the 3 phase coils that generate the alternator's power output. These are arranged as 3 insulating plastic spout tubes each with a pair of stripped winding ends poking through.

    It appears each spout is presenting the 2 ends of 2 adjacent phases, and when assembled normally, the 3 alternator generator coils (stator coils) are connected in a fixed delta configuration onto the regulator with the 2 wires in each spout crimped together onto a regulator / rectifier post.

    If I wanted to try reassembling the alternator in a star configuration, I figure I could just short 3 of the coil ends all together to form the star point, then take each phase output from the 3 remaining coil ends?

    Thing is, it isn't easy to tell just by looking, which of the two wires in each 'spout' is the end of which phase. I'm trying to figure out how I could ensure I connected things together correctly (i.e. the correct end of each phase to the star point) by maybe spinning the shaft slowly and probing the coil ends with a multimeter.. can anyone explain how best to go about this?

    Or maybe I could examine & probe the regulator plate to try and work out a diode pack schematic?

    From what I've read, star connection is required for easy spin up in light winds, and then a switch over to delta is then required for lower voltage / higher current output once the blades are up to speed, and to help prevent the voltage rising too much too easily in high winds.

    Maybe the Ford regulator might have a use here as it does seem to include some kind of (hall effect?) RPM sensor (although as-is, I don't think the regulators computer outputs a direct RPM signal.. just some kind of PWM 'load' indication). I was wondering about using the regulator plate purely for it's conveniently mounted RPM sensor, that I could maybe wire to directly with some kind of homebrew circuit to control the star - delta switchover based on RPM?
     
  2. kellys_eye

    kellys_eye

    4,281
    1,144
    Jun 25, 2010
    Yes you can but you will need to determine the polarity of the outputs as you surmise and the method you propose is perfectly ok.

    Might be easier to source a different generator (DC Motor perhaps) than to 'faff around' with the modifications as you plan. The KISS principle is important here.......
     
  3. flippineck

    flippineck

    268
    8
    Sep 8, 2013
    Thanks. I've actually come a-cropper at the stage of trying to remove one of the claw poles from the alternator shaft. Typical me - couldn't wait for the machine shop to open so I impatiently tried pressing ahead & squeezing it off in the vice using various bits of shim, judicious and careful use of an air impact chisel and lumphammer, and liberal use of fire from a full can of map gas. despite best efforts and plenty of prior experience with this sort of mechanical stuff.. you can guess what's coming.. yeah I just bent the carefully factory-balanced claws right out of kilter without shifting it a millimetre.

    So hate to say, I've had to throw the entire box of assorted ford alternator parts in the skip. On the bright side, I did find an ebay seller listing a decent medium duty PMA wind turbine generator on ebay, America based but willing to ship to UK for a reasonable price.

    This one doesn't seem to involve multiple phases, it just has a 2-wire DC output. The current v voltage v RPM profile looks ideal though.

    Output voltage varies fairly wildly with RPM so I guess there's a challenge coming, interfacing it to my existing 4 12V SLA batteries which are fed from a solar PV controller. Maybe I'll be digging into a microcontroller of some sort for this.
     
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