Advantages of the series type voltage regulator on a motorcycle
The question is often asked, what is the advantage of the serial thyristor-diode rectifier compared to the classic parallel (factory) regulator? It is clear that the series regulator reduces the generator current because there is no short circuit current that the parallel regulator does.
In particular, we can show how the generator current and the heating of the stator winding depend on a given consumption in the amount of 50% of the maximum current for a single-phase full-wave regulator.
In the diagram above, the output mean current (blue) is given. The series regulator produces effective current in the generator (green). The rms current of the generator and the mean output current differ in amount. Since when the possible current from the charging generator (olive) exceeds the consumption current, it flows in periodic pulses, its effective value increases the stronger the current (although the pulse width is smaller). This also affects the heating of the stator winding. It is possible that using a measuring instrument that does not calculate the effective value will show data more similar to the average output current.
The diagram below shows the heating of the coil. Blue is the serial regulator. According to the diagram, it can be seen that when the series regulator starts to pulse rectify in order to maintain the required average output current, then there is a favorable effect for the coils and for the specific consumption current, it limits the heating to half.
Unlike the series regulator, the parallel regulator in this case (the output mean current is 50% of the maximum charge current) even boosts the generator current to higher than the one the generator gives when charging (how much the red curve is higher than the olive one). This is the result of a generator short circuit when the generator supplies more current than necessary. In a short circuit, the current from the generator increases because the closing voltage is lower than when charging. This is most visible when the voltage from the generator is lower and the influence of the low closing voltage has a greater impact. At high generator voltages, the current of the generator during charging and short circuit almost meet. The coil heating diagram below shows how the parallel regulator (with 50% default consumption) heats the coils twice as much.
It is expected that the consumption from the generator must be limited to about 50 to 60% of the maximum power of the generator so that the battery could be charged in the average number of revolutions. This makes these charts applicable for realistic comparison. Winding resistance, expected rectifier voltage, short circuit voltage were taken into account when generating the diagram. The vertical mark n0 represents the position of the idle throttle. It is possible that some generators cannot give 50% output current at idle, and some can.
Conclusion:
An additional conclusion that can be seen from the diagram is that a high number of revolutions of the motor enables high effective currents and that then the winding or regulator failure is most likely. Unlike a parallel regulator, the series regulator heats less (because a smaller effective current flows through it) and can completely stop working in case of overheating (if it has a thermal sensor - all serial SPER regulators have one), and the generator winding is loaded much less.
PDF text: Comparison_of_regulators.pdf