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How does a Magneto work

  1. Jan 27, 2011 #1
    how does a magneto work? does it have high amperage? if not how do i increase the amperage so it is high flowing current? is the spark coming from a magneto constant meaning does it continue to pulsate an electric spark NOT in terms is it constant AC or DC?
    My aim is to find something with high current and amperage not voltage that is small and compact that i can use for experimental purposes, if you need to know what exactly inbox me as i am having trouble writing this on here and people getting confused with what i am typing, especially the admin.. :)
  2. jcsd
  3. Jan 27, 2011 #2
    See theory of magneto in


    The primary current is not very high, it is generated by a rotating permanent magnet inside a magnetic circuit and breaker points interrupting the current.. See page 10 of pdf.

    Bob S
  4. Jan 27, 2011 #3
    with that rotating permanent magnet is that continuousy spinning causing continuous spark? how much amperage would come off one of these?
  5. Jan 27, 2011 #4
    Is it possible shoot a spark down the likes of a cable much like an ignition coil cable that can be attatched to a magneto? in other words the if you didnt have a lead on the end of the magneto is it possible to discharge electricity being made out the end of the magneto, if modification is needed, and also can it be modified to go along these lines?
  6. Jan 28, 2011 #5
    The basic concept of the magneto is shown in thumbnail and on page 10 of


    The rotating permanent magnet rotor in the magneto is essentially a dynamo, generating an alternating voltage in the primary coil. When the breaker points are closed, a current flows in the primary coil. When the points open, the current in the primary coil is suddenly interrupted, creating a very high dI/dt. The secondary coil on the magneto has a very high number of turns, and a high inductance L. The instantaneous voltage on this secondary coil is V = L dI/dt, probably 20,000 to 30,000 volts.

    This high voltage pulse occurs only when the points open, and is not continuous. The current is very small.

    Except for substituting the dynamo for a 12-volt battery, the operation is just like the traditional ignition systems in pre 1970 automobiles (excluding the Model T).

    Bob S

    Attached Files:

  7. Jan 28, 2011 #6


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    This seems to be asking whether there will be a voltage across the secondary of the magneto transformer even if the condenser and breaker switch were removed.

    I guess there would be a rough sinewave there (but at a much lower voltage than the spark voltage), due to normal transformer action, assuming the magneto was being rotated by a motor.

    Great web site, Bob S. Someone cared enough to go to a lot of trouble with that one.
  8. Jan 29, 2011 #7
    what would happen if i removed the condenser and the breaker switch exactly? then what on the circut board can i do to enable more current? is it possible to answer that one, like all i need is a circut board that will throw out high amounts of current that can be fed off a 12volt battery or a heavy duty 24volt battery, without killing myself.. :) what is an ideal amperage that can be used in conjunction with separating molecules on high demand?
  9. Jan 29, 2011 #8
    The high voltage magneto pulse is generated in the same way as the old automobile ignitions (pre-1970) that worked on a battery. The breaker switch interrupts the primary coil current creating a short high voltage pulse (V = L dI/dt) on the secondary coil. The condenser does two things: 1) It prevents a very high instantaneous dV/dt that will spark across the breaker switch and pit the electrodes, and 2) resonates with the inductance of the secondary winding to create a LC resonance, probably between 20,000 and 40,000 Hz*. The sinewave from the magneto rotor output might be only 3000 RPM (50 Hz). (It is just a dynamo)

    The magneto primary, without the condenser and breaker switch, might be able to generate 2 to 5 amps of AC current, depending on load. To electrolyze water, you may want a dc current (depends on whether you want to separate the hydrogen and oxygen).

    1 amp for 1 second should (100% efficiency) be able to create 3 x 1018 molecules of hydrogen (0.1 cubic cm)**.

    To electrolyze water and collect hydrogen, it is probably better to use the rectified 12-volt output of a car alternator.

    Bob S

    * This is a VERY low AC current. It is current, not voltage, that electrolyzes water.

    ** 1 gram-molecular-mass of hydrogen gas contains 6 x 1023 molecules and occupies 22.41 liters.
  10. Jan 29, 2011 #9
  11. Mar 4, 2012 #10
    Hi I have a problem with a magneto on hammer action engine for breaking concrete. I am getting a kick at the plug lead but it does not spark the plug The plug is new and the condencer.The points look good.Can you help
  12. Mar 7, 2012 #11
    I have a problem with an engine on a concrete breaker.The plug lead gives a kick but will not spark at the plug. The plug is new and also the condencer. I have cleaned the flywheel and coil pack.The points are ok. Can the coil be checked? Any help would be much appreciated.
  13. Mar 7, 2012 #12

    jim hardy

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    Lots of people have trouble with magnetos because we're used to seting points on a car, where gap isn't very critical.

    On a magneto the point gap is WAY more critical than it is on a battery system. That's because the points must open when the magnet is in exactly the correct spot over the poles.

    Check your point gap with a round wire not a flat gage. While you're in there make sure they're clean and not pitted.

    On outboards i do this :
    remove plug(s) so engine is easy to turn
    clean and set points
    hold plug wire between two fingers of left hand with wrist touching engine block
    with right hand slowly rotate flywheel through TDC
    if i can't feel spark, i redo point adjustment
    Your hand is a sensitive go-nogo on the point gap.

    After a few tries you will learn how fast to rotate flywheel so it's not overly painful.
    If you can't get a vigorous spark something is not right, usually point gap or condition of contacts.
    When you can get a good "bite", connect spark plug and rotate flywheel faster. You should be able to see a yellow spark if not in direct sunlight. Take apparatus into the shade of a tree.

    To check coil, read resistance to little ground wire that comes out of coil. A few thousand ohms on HV lead and just a very few on the one that goes to points.

    Most often, trouble is at the points, either gap is off a couple thousandths or contacts are dirty. Be careful cleaning them, a very fine sandpaper like "Wet or Dry" 600 is okay but wash them afterward with solvent and leave no oil.

    The little cam that operates the points is equally important obviously - make sure it's clean and smooth. It can rust and get uneven. There's a special extra sticky grease made for lubricating that part, use it sparingly so it doesn't sling off and land in between the points (again?).

    old jim
  14. Mar 7, 2012 #13
    Thanks Jim this is a great help
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