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« on: 03 September, 2018, 11:41:23 »
An explanation.
With the old points system, each 12V coil charges with energy every other cycle of the crank on its compression stroke. (left/right/left/right/etc) four stroke engine,
So each coil will have 12V across it before its point opens and the plug fires. Each 12V coil primary has a resistance of around 4 Ohms, giving a DC current of I=V/R, I = 12/4, i.e. current I = 3 Amps.
It is the 'rate of change of current' which governs the primary voltage. Although it appears to be instantaneous when the points open, it isn't because of the nature of the release of the magnetic energy is a discharge curve (hysteresis), and the internal resistance. But it is very quick.
The primary coil produces a back EMF (opposite polarity voltage spike/pulse) which opposes the applied 12V DC voltage of around 100V, which is transformed by the huge number of turns in the secondary into thousands of Volts at the plug gap. This voltage is high enough to ionise the compressed fuel/air mixture which significantly lowers the resistance, and an arc (spark) ignites the mixture at its timing point.
With an electronic ignition, the above still happens BUT, the coils are in series, both fire at the same time.
So here, we have 12V across two coils. *If they are 12V coils the available current is halved because the resistance is doubled, 8 Ohms, hence the available energy is also halved.
This is why 6V coils are recommended, because their primary resistance is around 2 Ohms, giving a total resistance similar to a single 12V coil.
The reg/rect unit prevents overvoltage to about 15V, this prevents the battery from overheating and the electrolyte boiling.
Although the 12V coils usually work, there is a snag if the battery is not in good condition, fully charged.
A bad battery may cause misfires, if the voltage is too low, a fully charged battery has a voltage of 12.6V. More when running (~14V).
Radiated and conducted voltages may affect the electronic components in the rect/reg, which is why loaded plugs or plug caps are recommended.
Especially from the spark plug, because it a mixture of various spikes at various frequencies, this load attenuates the spikes to a reasonable level.
The primary voltage is prevented from going back to the E.I. unit by blocking diodes/filters.
If you have charging problems, they are caused by 1) bad battery 2) alternator not coping with the load current 3) poor wiring/connectors.
Usually, the battery itself is the source. If any of the cells are damaged, it will hog current, which ought to power the normal electrics.
Simple test, ignition on, main beam on, motor not running.
From Sparx "a good battery should sustain 12 volts for 10 minutes". If the lights dim greatly within this time limit, get a new (tested) battery.