Un commentaire que j'ai trouvé sur le SH 775 ( pas pour contredire maitre flap,
mais pour dire que tout choix technique a son revers ) :
The way I've understood it is tht a series Mosfet RR shuts off (opens) the stator circuit to prevent over voltage which isn't possible with a regular Mosfet RR. This emulates a true alternator shutting off the current to its electromagnet to prevent the electromagnet from continuing to induce voltage into the stator beyond what is needed by teh bike's electrical system. That is, over voltage.
Both true alternators and stator/rotor/RR alternators produce voltage by rotating a magnet around a coil of wires (stator). The basic difference between the two is that a stator/rotor/RR alternator uses a permanent magnet which unlike the electromagnet in a true alternator, a permanent magnet in the lesser brethren can't be switched OFF and ON to match the fluctuating electrical demands.
Instead, a series Mosfet achieves the same objective as a true alternator by shutting off (opening) the stator circuit in a stator/rotor/RR alternator. It's permanent magnet still rotates around the stator (coils of wires) continuing to induce over voltage, but at the same time, since the induced voltage can't go anywhere in a open stator circuit, there's no electrical flow, aka current, harmful or otherwise for the duration that the stator circuit is kept open (OFF). That is, analogous to an unconnected battery, an open-circuit stator has electrical potential in life, but no current to reach a destination in the outside world, R/R, so on.
Essentially all it boils down to is an either/or situation. Either disable the stator or the deactivate the magnet, one option or the other. Here, a series Mosfet endows a stator/rotor/RR alternator the capability to shut off the stator circuit while the voltage output is already sufficient for the bike's electrical system where surplus voltage only equates to over voltage. Again, in a stator/rotor/RR alternator, its magnet is a permanent magnet which can't be shut off thusly a series Mosfet's only option is shutting off the stator circuit to cease the over voltage production.
The olde and recurring debate about this scheme is that the inherent electrical spikes from the collapsing magnetic fields will eventually degrade the lacquer coating on the stator wires. Remember, a true alternator has both options at it's disposal. That is, a true alternator could just as well shut off either the stator circuit OR the electromagnet component, but the knowledgeable designers choose to shut off the magnet not the stator circuit. The difference may seem subtle but the switching takes place thousands of times per second.
In an ignition coil, the electrical spikes induced in the primary coil from its collapsing magnetic fields is absorbed by the secondary coil which sends and disperses the energy directly to the plugs. On the other hand, with the scheme employed by the SH775 series Mosfet, the energy from the collapsing magnetic fields wholly impacts the stator wires. I surmise the SH775 is internally wired with a condenser, etc, to serve as a spike suppressor. I'm also thinkin there's a secret ingredient especially with the low price of the SH775. Esperons donc que ce SH775 a bien une capa intégrée pour absorber les pics de tension
dus à la rupture de circulation de courant (phenomene utilisé dans le temps pour créer
une etincelle aux bougies
)
En repensant à nos tres anciennes mobylettes 'bleues', dont j'ai usé longtemps,
je ne me souviens pas d'avoir trouvé une seule fois une panne de bobinage
dans le volant magnetique. Donc ce phenomene de 'pic de tension' ne doit pas
etre aussi destructeur que l'actuelle solution triumph 'stock' où tout le courant en excedent
repasse dans les enroulements.
