disassemble a cdi, magneto, coil

Discussion in 'Electrical' started by machiasmort, Aug 11, 2010.

  1. machiasmort

    machiasmort Active Member

    Anybody ever done it?

    I'm working on a Toro Lawn Mower that has a 2strk Sushi motor and the magneto's are very pricey.

    I'm looking at the mag and back at my dremel and my dremel to my propane torch!

    It's got the same sort of seal that our CDI's have on HT's, that sort of glue, wax or epoxy that's melted in there to keep guy's like us from monkey'in w/stuff!

    Sort of like grease on the bird feeder pole, only not as fun!


  2. machiasmort

    machiasmort Active Member

    Come on now guy's, 7 views and no thoughts on which way to go?

    Do I heat or cut???

    It can't get no more broke than it already is!
  3. GearNut

    GearNut Active Member

    Cut it. Melting it could render a proper autopsy impossible.
  4. blckwlfny1

    blckwlfny1 Member

    ok ill bite...
    I would cut....carefully That stuf could turn to goo when ou heat it and it would be like trying to get sauce off of spaghetti if this goes wrong
  5. machiasmort

    machiasmort Active Member

    appreciate the input! Thats 2 for the dremel!
  6. AussieSteve

    AussieSteve Active Member

    2 for the Dremel, 1 for nothing.

    My 2c worth - neither, don't waste your time.
  7. Pablo

    Pablo Motored Bikes Sponsor

    Norm did it a few years ago on the other site. Mostly he melted the potting away.
  8. GearNut

    GearNut Active Member

    Any word on how the autopsy is coming along?
  9. machiasmort

    machiasmort Active Member

    Thanks Pablo!

    Havn't had a chance yet, been looking for ways to bench test it first. The ignition is $150 new and you can't find a used one!

    Shouldn't I get continuity between one of the coil pick-ups and spark plug wire? I have none from either side of the coil! But have continuity between both pick-ups, its very odd because I don't know whats in there?
    Last edited: Aug 15, 2010
  10. GearNut

    GearNut Active Member

    It depends on how the high tension (voltage) part of the coil is grounded.
    Most, but not all will have a separate ground, independent of the pick up inputs.
    How many input connections does it have?
  11. machiasmort

    machiasmort Active Member

    There's 2 amatures that prtrude from the plastic casing that pick-up the magnets on the flywheel and make electricity. There is also a wire that acts as a safety switch to ground the spark in the event the handle is released.

    Right now, I'm not getting a meter reading from either side of the U (contacts) to the plug wire, I think I should be???

    Oddly, both sides of this U (pick-ups) are giving me a reading to the kill switch wire. I've got it out of the mower! Both of the pick-up (sides of the U) are grounded to the motor block. There must be a snubber inside the unit itself to prevent the current from reversing and going to ground on the block.
  12. AussieSteve

    AussieSteve Active Member

    Yep, as Gearnut says, often there'll be a step-up transformer with two separate isolated windings, or, alternately, it will be an auto-transformer with a common ground.

    External bench-testing will be useless unless you know precisely what's inside.

    Also, most common potting mixes are thermo-setting 2-part plastics and will not melt with heat. They will soften slightly at about 60 degrees Celsius, but that's about it, they won't do much else until they begin to burn. I've tried 'de-potting' circuits in the past, without much success.

    I've attached a block diagram as drawn by another member some time ago. (Sorry, can't remember who for credit where it's due.) In this circuit, an auto-transformer is shown.

    machiasmort, just saw your latest post. By 'armatures', do you mean wires?
    Next question, what 'U' contacts?
    Don't expect continuity between wires. There can be a lot going on that you can't see, as I mentioned earlier. Chances are there's a series capacitor or a semiconductor here and there that prevents continuity testing. There's no way you can determine what's inside by external measurements. Modern electronics is more complex than that. You really are wasting your time.
    (Prove me wrong, I don't mind.)

    Attached Files:

    Last edited: Aug 16, 2010
  13. machiasmort

    machiasmort Active Member

    What I'm calling armatures are the pick-up arms that pick up the magnet spinning on the flywheel and excite the coils thereby producing spark at the plug.

    My question? Shouldn't there be continuity between those arms and the plug wire?

    I never realized that only one side of the coil on our HT's was grounded!

    I appreciate all of the help and ideas, because I am clueless on this one! If I get it to work, will be attributed to act of God unless somebody really knows their stuff out there well enough to help a blind man thru this!

    Will post some pics in the days to follow. Thanks again!
  14. AussieSteve

    AussieSteve Active Member

    Now I'm with you. Those 'arms' are the coil core. There definitely won't be continuity between them and the plug wire. The core is at ground potential.
    (See the diagram that I posted above.)
  15. Turtle Tedd

    Turtle Tedd Member

    Mach..stop looking at the dremal and the propane tourch..Start looking at the sledge hammer..you will feel beter after and you will win..
  16. machiasmort

    machiasmort Active Member

    TT, I've thought about it!

    Steve, I appreciate your help greatly. I think I'm starting to understand a little more.

    Using the refferenced names on the schematic, Magnets pass the coil core, charging the exciter. Exciter then passes the charge to the diode (keeping it flowing one direction) and then to the capacitor where it is stored till there is enough juice. When the Cap hits it's limit it sends the juice to the "zero crossing switch" (point right?) which ok's it to go to the larger coil to be amplified and sent to the plug.

    I've got a feeling this thread might help somebody else out latter?

    So the reason I might not be getting continuity between coil core and plug wire is due to the fact there is a Capacitor in line with the flow of electricity.

    With all of the garbage in landfills, you'd think our Government would make them(manufacturer's) produce these things to be recycleable. Like put the assembly in a water tight box which could be opened.

    They stick their nose in everything else!
  17. AussieSteve

    AussieSteve Active Member

    Yep, pretty much. I'm not sure just how accurate that schematic is, but it's the best I've seen so far. Probably not 100% accurate though.
    In effect, as the magnet turns, it causes the two poles of the core to alternate between N-S to S-N, (hope you follow me), causing an alternating current to flow in the windings that are wound on the core.
    The core itself has no electrical connection to the circuit, except to ground. It only conducts magnetic flux and not electricity as such.
    As you say, then the alternating current is recified to pulsing DC by the rectifier diode, charging the capacitor. In the circuit would be a comparator, to sense when the cap is charged fully then trigger a transistor or MOSFET to dump the capacitor's charge into the primary of the transformer. The 'step-up' transformer ensures that several kV, (probably about 5kV-20kV), is applied to the spark plug.

    No. As mentioned above, the core is hard-wired to ground.

    Potting prevents copying, though. Also, it helps conduct heat away without needing metal heatsinks.
    All the same, I hate the unservicable nature of this stuff. In a way, give me points etc. any day.