" capteric36" wrote: > The field connection on a battery switch is > there to protect the alternator diodes in the > event that the battery switch gets turned to the > off' position while the alternator is spinning.
Close, but no cigar. > If > there is still field current but no load (battery) > the output voltage of an alternator will very > quickly rise high enough to destroy the diodes. True. > Thus the field connection in the battery switch is > designed to open before the battery connection, > shutting down the alternator. DO NOT rely on this, > as the time it takes the magnetic field in the > alternator to collapse may often be enough time to > destroy the diodes. True. Basic rule of the boat battery switch. If the alternator is rotating, DO NOT TOUCH THE BATTERY SWITCH. WHY? The generated alternator voltage that is developed without being connected to a load (Battery) will generate an inverse voltage that will destroy the silicon diode bridge. The above is totally independent of the alternator field circuit. Turn the battery switch "ON" or "OFF" only when the engine/alternator is at rest. The use of the oil pressure switch in the field circuit is used to reduce the starting torque requirement of the cranking motor. There is enough residual magnetism in the rotator of the alternator to generate a limited amount of power at the output terminals, thus the need to be connected to the battery. An old trick, if the AC output terminals are available, is to connect a half wave rectifier bridge to the coil of a relay whose contacts are in the field circuit. Thus the cranking motor did not hasve to overcome the alternator starting torque. As soon as the engine is cranked over and starts, enough voltage is generated to close the relay thus applying power to the field circuit which starts the alternator charging. No AC terminals available, the oil pressure switch works just fine. Lew _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to [EMAIL PROTECTED] To unsubscribe send an email to [EMAIL PROTECTED] The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
