Spia carica batterie

[ste.fano]

uno Zener limitatore all'uscita dei diodi di campo non dura molto (se prima non bruciano i diodi).

Credo che lo zener sia di valore elevato solo come protezione (una specie di fusibile?), casulamente ho trovato il sito e spiega:
The Surge Quench Diode
When an alternator has its output disconnected whilst the engine is running, the sudden stopping of current flow through the stator causes the magnetic field that was being produced by the generated current to collapse. This causes a high, momentary, voltage surge that will damage the electronics in the regulator and the diodes.
If this happens one hopes that the surge quench diode (if one has been fitted) "opens" to let the voltage surge "run away to earth" so it is safely quenched.
It is probably safest to assume that any particular alternator is not fitted with one, so never disconnect the alternator, battery, or switch a master switch whilst the engine is running – you have been warned.
Occasionally the surge quench diode (when fitted) works, but destroys itself in so doing. If it fails open circuit you will not know because everything works – until the next time someone does something silly! If it fails short circuit the alternator will not charge. In an emergency, locating it and disconnecting it (if fitted) will restore charging – until the next time someone does something silly!
da qui: http://www.tb-training.co.uk/marinee08.html