Electrical System Questions!

Discussion in 'Motorized Bicycle General Discussion' started by speedster239, Dec 21, 2009.

  1. speedster239

    speedster239 New Member

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    Sorry guys, I've got so many questions I don't even know when to stop, but you guys are doing me a real great favor. I don't know what I'd do without this forum.

    So, here's a simple one, though. What direction is the current flowing in the entire bikes circuit? From everything I ever learned, electricity flows from negative to positive. Negative having the surplus of electrons and positive having the deficiency. SO, when the block is "grounded" to the frame, are the electrons flowing through the frame itself, into the load and back into the positive terminal, or is it the other way around? With that answer in mind, how does the CDI work, creating the "spark", if the current flows from the frame, where does the electricity build up for this?

    I'm a bit confused, but I'm sure you folks can set me straight :D.
     
    #1 speedster239, Dec 21, 2009
    Last edited: Dec 21, 2009
  2. BarelyAWake

    BarelyAWake New Member

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    erm... it's pretty simple and self-explanatory once you realize you've got it a lil backwards - the current is generated by the magneto, the coil builds it up and discharges it to the plug, all in the interest of attempting to get to ground (you'll notice the battery in a car has it's neg terminal attached to the frame/body).

    It's only the crazeh brits and Lucas (prince of darkness) that used a "positive earth" where the frame was positively charged and the current went the other way - causing all sorts of gremlins that delighted in assorted shenanigans like extreme corrosion buildup and very odd effects when the inevitable shorts happened.

    I believe they've learned their lesson by now lol ;)
     
  3. speedster239

    speedster239 New Member

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    Alrighty, thank you! SO, the current is in fact flowing too the frame, not from it. The only thing that still confuses me is that everything I ever learned said that current flows from negative to positive..(negative having the surplus of electrons and positive having the deficiency) If the negative terminal in a car is hooked to the frame and current flows from negative to positive, wouldn't that mean the electrons are flowing from the frame instead of to it?

    Right? Even a google search seems to yield conflicting answers..
     
    #3 speedster239, Dec 21, 2009
    Last edited: Dec 21, 2009
  4. BarelyAWake

    BarelyAWake New Member

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    Well, it's best fer the brain to not dig too deep into the complexities of electricity - it only gets stranger lol, I'm no expert by any means - I just roll with the common conceptions. Generally we think of electricity as "trying" to get to ground, be it the planet or the negative terminal of a battery or electrical system... in actuality I suppose this transfer of charge is so instantaneous as to make the word "flow" fairly meaningless, but as a concept it seems to work.

    Heck - I could be wrong about the "direction" of current, but I don't even wanna think about that heh, my general understanding seems to work well 'nuff ;)
     
  5. Finfan

    Finfan New Member

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    You apparently learned electron flow theory which is the opposite of "Conventional" current. I fact you are right, electrons do flow from negative to positive. It also doesn't matter which side of the load you are on in a circuit. Both sides are carrying current. If it wasn't then there wouldn't be anything happening at all. Which direction you draw your arrows in the circuit diagram are arbitrary.

    zpt
     
  6. Norman

    Norman LORD VADER Moderator
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    all I can say about it is thiszpt
    a very enlightening experience if you touch the spark plug.............!
    makes ya shake and vibrate..........!
    put you tongue on the white wire and feel what happens...! better than 6 cups of coffee..Ha!ha.....makes Rufus twitch funny tooo.!!!!!!!!!!!!!
     
    #6 Norman, Dec 21, 2009
    Last edited: Dec 21, 2009
  7. GearNut

    GearNut Active Member

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    Electrons do in fact flow from negative to positive. We can all thank Benjamin Franklin for labeling + and - on a battery; bass ackwards from the actual electron flow. Once he did that, "the die was cast". Everybody who is not knowledgeable in fundamental electronics operation assumes that they flow from + to -.
    As for the CDI, it is Capacitive Discharge Ignition. The electricity is stored in a capacitor (a temporary battery like device) inside the black box. When the electronics inside the black box sense a pre determined voltage level has been met, they let the stored electricity in the capacitor discharge into the ignition coil. The coil then multiplies the voltage given to it to the level required to jump the sparkplug's gap, and you have ignition inside the engine.
     
  8. BarelyAWake

    BarelyAWake New Member

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    I stand corrected lol - tis what I suspected 'bout that pesky 'lectricty, better to jus' nod and smile and follow the instructions :p

    Lucas was still wrong tho o.o
     
  9. TheE

    TheE New Member

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    To make your life easy, assume that electricity flows from + to -. It may be wrong, but that's the standard. The only people who use - to + are scientists and mathematicians, and their circuits usually don't work anyways ;)
     
  10. civlized

    civlized New Member

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    I am really no one to dispute this, but why are fuses always placed on the positive side if this is true?
    Wouldn't the most protection come from fusing the ground?
     
  11. speedster239

    speedster239 New Member

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    So, is the current flowing from positive to negative or negative to positive? Is what we label as positive on the bikes and most automobiles truly negative..is that what you guys are saying?

    This seems important because I know that if the current were flowing from the frame, instead of to it, the capacitor would not charge/discharge into the coil and no spark would take place...

    Can you see my confusion?
     
    #11 speedster239, Dec 21, 2009
    Last edited: Dec 21, 2009
  12. TheE

    TheE New Member

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    The electrons technically flow from the - terminal of the battery to the + terminal, so they're correctly labeled. It's a bit strange to have the current flowing from the frame, but you should be able to analyze the circuit with both methods and get the same results. It's just a question how we assign arbitrary labels to things, really.

    When lightening strikes, the bolt you see is coming from the ground and going back up to the cloud. Trippy 0.0
     
  13. Evan

    Evan New Member

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    Definately right about the Lucas electric thing...........I had a Jaguar once. OMG! What a mess!
    E
     
  14. wjliebhauser

    wjliebhauser New Member

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    Like the man said, it's a waste of time to fuss about which way electrons are flowing in a DC system like a car or bike. It is a closed system, i.e. confined to the bike (or car), and electrical gizmos only operate when the circuit is complete. Same with where the fuse goes; the convention is to put them in the + side, but if you put them in the circuit between the gizmo and the frame, instead of the gizmo and the + lead, the result is the same. People often use the 'water in a pipe analogy' to explain electricity flow, but it is only partially valid, and thinking of electric current like it's water in a pipe can lead to ideas that are all wet... Electricity is not water. The theory behind English cars with + ground to frame was that there would be less electrolysis and corrosion. Good idea, but in practice, it ended up as useful as the old theory that lug nuts on the left side should be left hand threads to stay tight...cool theory, but not worth the effort in real life. Also, DC and AC act differently, so even all current is not the same; on AC, switches and fuses MUST be on the 'hot' or supply side to prevent YOU from being the gizmo if you touch something that is grounded. Luckily, not much chance of dying messing with a Chinese bike motor!
     
  15. 2door

    2door Moderator
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    My first question would be why do you need to know the direction of current flow? The point is moot however in terms of the ignition system of a Chinese 2 stroke engine because we're dealing primarily with A/C, alternating current, which flows both ways. Hence the name, 'alternating' current. Forget the bicycle frame. It has nothing to do with the circuit that fires the spark plug. The ignition system of your engine would function even if your frame were made of wood, as long as it is wired correctly. The only time the bike frame would come into play would be if you were using it as a ground to kill the engine through the kill switch; and then you'd need a good connection, no paint or rubber between the engine case and the frame's metal or a ground wire from the switch to the engine. There is another misconception that you might need to know about. The kill switch does not open the ignition primary circuit when depressed. It in fact closes a circuit between the black wire, (the engine ground wire) and the blue. Or if you prefer the white and black wire of the engine case (or bike frame if there is a good electrical connection between it and the engine). Forget about what you've been taught about electron flow. It has no bearing on your ignition system. Now let me confuse things. I use a battery (D/C power source) to power my lights. I run a wire from the battery negative terminal to a place on the bike frame, then run a wire from the positive terminal to a switch then out to the head/tail lights. I either ground the lamps/socket to the light case which is attached to the frame or a seperate wire from the lamp socket to the frame. The frame then becomes the conductor. This allows me to run a single wire to my lights instead of two wires; saves wire and looks cleaner. Hope these replies helped you and answered some of your questions.
    Tom
     

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