Low Tension Magneto Ignition

[DavidMc]

I have a question  about  2 cylinder Maxwell cars  From 1909 these cars use a 6V low tension magneto with coil and condenser for the ignition system.  A battery is used for starting on hand crank.

The ignition systems on these Maxwells has the coil in parallel with the points when running on magneto, which, according to my Dykes(16^th) is “the one in general use where a low tension magneto is used with a high tension coil”  (page 253).  With this arrangement the coil is bypassed when the points are closed and the high tension current to the spark plugs occurs when the points open and current from the magneto passes to coil.   This is contrary to my experience with later cars where the coil and points are in series and the spark occurs when the points open collapsing the magnetic field in the coil.

Can anyone explain why this arrangement with the coil and points in parallel was used on early cars with low tension magnetos?

[oldford]

There is not really much difference between the two. The secondary of the coil will be energized when the current in the primary is suddenly interrupted. The top circuit (series) will induce a current in the secondary when the points open and the bottom circuit (parallel) will induce the current when the points close...

 

Frank

[DavidMc]

Thanks Frank  but why?

 

I should have explained the question better.  The question only relates to when the car is running with the ignition circuit powered by the low voltage magneto with points and coil in parallel.  (The starting circuit, powered by the battery,  has the coil and points in series.)

 

On a car with the coil and points in series, as is normal practice with later cars, when the points are closed current through the primary windings creates a magnetic field around the core of the coil ,  when the points open, breaking the current through the primary windings, the magnetic field collapses and a high voltage occurs in the secondary windings connected to to the spark plugs.

 

With the Maxwell, and apparently other low tension ignition cars,  the coil and points are in parallel , with this arrangement when the points are closed all current bypasses the primary windings of the coil so no magnetic field is is created.  When the points open, the in rush of current through the primary windings creates the high voltage in the secondary windings connected to the spark plugs.

 

So my question is why wasn't  the same series circuit used for both battery and magneto?   Both circuits work.   It just seems odd and it complicates the switching from battery to magneto so there must have been an advantage.    What is that advantage?