Explain electric ignition to me...

Discussion in 'General Motorized Bicycle Questions' started by sparky, Sep 23, 2008.

  1. sparky

    sparky Active Member

    I think I have a magneto. Everybody told me when I wanted to wire in a toggle on-off switch (instead of the grounding out method), that I would need to splice the switch in between the magneto and CDI. I don't see a CDI... is that possible, or is it all built into one little box?

    The box has two wires that were originally for the momentary switch (to ground out), black & red... and there's also the spark plug wire. At the bottom is the magneto. All in one, right? The thing's glued up pretty nicely.

    Also... The plug connector is soo poor quality, so I was gonna try splicing a spare plug wire this guy gave me, and when I cut into it... I didn't find ANY wire. Just some rubber, fibers, & plastic. I really must be losing my marbles.
    I guess the best thing for me to do is try and find a Tanaka magneto/CDI, since this is supposedly a rip-off of the Tanaka 33cc.
     
  2. heathyoung

    heathyoung Member

    There really is nothing wrong with grounding (shorting) the magneto. It produces bugger-all current, and has a pretty high resistance. You would be dissipating the energy across a LOT of wire, it wouldn't even get warm.

    Spark plug wire used on these (as with most (all?)) engines is resistance wire to suppress EMF. It is carbon fibres + graphite IIRC. Apparently it unscrews from the CDI.

    A non-resistance wire will produce a hotter spark, but will basically swamp any am radio reciever (FM will be pretty bad) in a 15m radius. Not very sociable.
     
  3. sparky

    sparky Active Member

    Well, my bike came with stranded copper wire, and the plug wire from some guy's car had NO wire whatsoever! I couldn't understand that.

    Anyway, I'm guessing my magneto and CDI are both in this little black box, I couldn't just have a magneto, right?

    Hopefully just temporarily, I've put the magneto/CDI/plug wire from my old engine on, and it runs alright... BUTTT... it whistles now, like an alien ship floating right above/behind me. At least, I'm pretty sure that's what it is. I'll have to take the cover off again to take a closer looksy & listen.

    I shoulda just bought a Tanaka.
     
  4. heathyoung

    heathyoung Member

    Magneto is inside the engine - there is a magnet on the flywheel/crankshaft, and the coil is fixed to the body of the engine. The black box is the CDI.
     
  5. sparky

    sparky Active Member

    Yea, my magneto & CDI are an all-in-one unit, I guess.

    I guess I should look into seeing if a genuine Tanaka replacement will actually fit this Tanaka knock-off.

    EDIT: wait a minute, are the magnets on the flywheel considered the magneto... or is the "pickup" magnet with the coil the magneto?? And is there even a capacitor in this "CDI", or are there just one or two coils?

    I also looked at the Tanaka replacement "coil, ignition", and it seems that one of the bolt holes is in a different place, so I'm stuck with dealing with FiveFlags. =-(
     
    Last edited: Sep 25, 2008
  6. duivendyk

    duivendyk Guest

    There are magnetos that directly fire a plug,without any CDI unit in fact it is incorrect to talk about a magneto with CDI.The original magnetos were originally developed by Robert Bosch in Germany and directly generate a spark.They had big horseshoe magnets on them hence the name "magneto".These magneto based systems were standard for many years.Later with batteries becoming more common,battery ignition gained a foothold (cost).Until about 20 years ago all magneto ignitions had breaker points (contacts).The spark discharge would be initiated when the points opened and the energy stored in the magneto HV coil is released in a high voltage pulse (actually a series of pulses) to fire the plug.More recent magneto systems use a solid state switch instead of the "points",but the principle of operation is the same.
    Capacitor discharge systems use the stored energy in a capacitor to fire the plug (via a pulse transfomer).They can generate very high voltage, but shorter duration, high energy ignition pulses that can fire even leaky plugs,but may not be as effective in firing the micture due to the short pulse duration.Most car ignitions still use coil discharge systems, which are just as effective.Sophisticated CDI systems are widely used for racing applications, they generate a series of high energy pulses for fast burning of the micture charge
     
    Last edited by a moderator: Sep 25, 2008
  7. keatonx

    keatonx Member

    I'm confused too... I researched electronic ignition and it seems to require a battery, but these engines dont have a battery...
     
  8. BillMckraken

    BillMckraken New Member

    Hello,
    I might be able to help offer some assistance on how these systems work. I don't want to be real technical, but if you know a few things; these circuits are pretty simple.

    oh @Sparky, the squeak noise is a "leaking" HV cap in the CDI (black box) prolly should replace it.

    Okay onto the ignition system.

    -First you have the magneto (magnets on a rotor). With these systems it serves 2 purposes; Both timing and ignition energy. Timing is, of course, "where" they are placed in relation to the pistons' degree of cycle. Ignition energy comes from both the strength of the magnets (mainly) and the speed they are moving.

    -Second you have a coil (essentially a "pickup" like in car dizzy's) This receives the magnetic energy (Iron core) and transfers it to the CDI through the "primary" wires wrapped on the Iron core.

    -Third you have the CDI circuit. This "stores" the energy in capacitors (condensor in a car) and then transfers this energy BACK through your coil (in a different wire).

    -Fourth, the coil (secondary circuit) "steps up" or transforms the "stored" capacitor energy to High Voltage, this goes through the spark plug wire.


    That's basically the operation step by step. So, to directly answer the question "why no battery" the "juice" is coming from the magnets alone.

    A couple of other things that may be worthwhile to point out as well.

    Something key if your playing with timing in these systems. The HV spark "fires" just AFTER (ms) the magnet (s) pass the coil. I can explain more about this, but I don't imagine it's necessary. So the "trailing edge" of the magnets is closer to the firing point in time. Don't time off the front or middle.

    Ignition energy can be affected by Magnet strength and spacing to the "Iron" part of the Coil's core. With Magnet's too weak or spacing too far; not enough energy gets transferred and stored to create a HV spark.

    For Coils (in these low energy systems) they would probably fail slowly and you would get a weak spark. You could also test the wires if you can access them.

    For the CDI's they should be mostly a "go no go" situation as their parts usually fail catastrophically. You have the one exception with a leaky cap and a squeak. ;)

    I think that covers it, lol. Sorry to be windy. Hope this helps
    Thanks
     
  9. srdavo

    srdavo Active Member

    Nice explanation.

    thanks
     
  10. sparky

    sparky Active Member

    Wow... Didn't even know I had started such a thread YEARS ago.

    If I use a voltmeter to test the ignition coil, should I just take the spark plug out.... and put one wire on the ground (engine head) and one on the plug's inner electrode dealy??

    I shipped my two faulty ignition coils back to the dealer for him to test at the price of $6, not even thinking about harbor freight selling voltmeters for less than $10....
     
  11. BillMckraken

    BillMckraken New Member

    for testing these coils....

    there should be 3 total wires on it. Basically these are identical (in wiring) to all ignition related coils. Heh, even the Model T coils were 3 wire.

    Anyhoo, when you go to test them, it may seem hard to figure out the connections. The 3 wires are; Positive (+) low voltage, AC High voltage out and a common ground (both coils share ground).

    You can check resistance several ways, the easiest way to check HV integrity is as you mentioned; from the HV insulated lead (doesn't have to be on the plug, could be socket) to ground.

    If you have the whole coil off then you can check the individual leads. Because the 2 coils share a ground, you can actually get resistance to show on all leads. I believe the CDI has 2 wires to the coil (correct me if not). One of those is positive, the other is the common ground.
    The only trick when it's completely unknown, is to find the ground wire. Once you do that, the other two are simple to identify.

    I don't have one of these to check their proper resistance, but I could throw some assumptions out for testing examples.

    the low voltage coil- should have a low resistance probably a few milliohms.
    the high voltage coil- should have more resistance probably a few ohms to maybe 15 (doubt that high).

    ** if all wires are unknown and you check (accidentally) between Low voltage positive and AC HV output; you should show a resistance of BOTH coils added together.


    Finally, if you get "proper" resistance on the coils; then there is no short (break) in the coils. This means the coil is functional. If you know it is being driven correctly (e.g.- CDI working and magnets good); then a weak spark most likely means there has been an insulation breakdown between wires.

    If you have multiple fail from insulation breakdown, then that's probably in the coil design rather than a "bad one".

    Hope this helps
     
  12. darwin

    darwin Well-Known Member

    Turn key mofo starts!
     
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