The purpose of the bulb is to allow sufficient current - a couple of hundred milliamps - to allow the regulator to control the stator field current on initial startup. Once the system is running, the current is supplied by the auxiliary rectifier diodes from the rotor commutator. At that time, the voltage at the main and auxiliary regulators are nominally the same, and are at the system charge voltage.
If the output from the stator differs from the battery voltage, then the bulb has a voltage across it and glows to indicate a problem. - if the stator coil is open circuit or the regulator dies, or the brushes fail completely, then there is no or very little output voltage and the bulb glows brightly. - if there is an intermittent brush contact (common with high-hours alternators) then the output usually drops a volt or two, on average, and the bulb glows dimly. - if the auxiliary diode pack dies, the voltage at the regulator input drops, the regulator attempts to increase the output voltage, and depending on how much load is being taken, the voltage at the output terminal can go up or down. The bulb will *usually* but not always glow dimly, since the regulator is trying to get its voltage back at the auxiliary diodes. (This is a rare failure mode; I've never seen it.) - if the main diode pack dies, the output voltage drops, often to below battery voltage, but the regulator is unaware of the issue. So now the bulb has a higher voltage on the alternator end than the battery end, and lights 'backwards' - this doesn't bother a bulb, but with an LED/resistor combination this common fault will not be indicated. As mentioned earlier, residual magnetism will often generate enough volts on the auxiliary diodes to wake up the regulator. In most instrument packs, a common bulb is used for lighting and indication; the charging light is usually a higher wattage type. Neil -- You received this message because you are subscribed to the Google Groups "Quantum Owners Group" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/quantumowners?hl=en IMPORTANT NOTE: All information presented herewith is provided on an "As Is" basis, without warranty or the implication thereof. Neither the Quantum Owners Club nor the individuals associated with the Quantum Owners Club or in the preparation of the above information shall have any liability to any person or entity with respect to liability, loss, or damage caused or alleged to be caused directly or indirectly by the instructions contained within this or related message(s).
