---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 11/12/24: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:28 PM - OVP relay in B+ lead bad idea (Finn Lassen) 2. 07:45 PM - Re: OVP relay in B+ lead bad idea (user9253) ________________________________ Message 1 _____________________________________ Time: 04:28:29 PM PST US From: Finn Lassen Subject: AeroElectric-List: OVP relay in B+ lead bad idea Putting a relay between the alternator B+ lead and the battery for over voltage protection is a bad idea! If the battery fails open and the alternator voltage momentarily drops below voltage to energize the relay, you no longer have system power: no battery and no voltage from alternator even if alternator works. This happened to me Saturday resulting in a hay field landing with a ground loop to avoid a fence. Buckled outer part of right wing and tore off right landing gear leg with damage to engine mount, firewall and forward part of fuselage. (In the RV-4 the landing gear leg sits in a socket in the engine mount.) In the process of trouble shooting noise and other issues in my electrical system I changed from a 160Amp schottky diode to a relay. My original thinking was that the diode would act as a fuseable link in case of an alternator over voltage run-away event, and leave the battery unaffected in case of an alternator short. I had experienced the breaker to the alternator field popping when reducing RPM. So I restored the alternator to its original integrated voltage regulator configuration and added the relay to ensure the alternator could be disconnected from the system in case of an alternator run-away event (over voltage crowbar shorting the power to the relay). Interestingly the alternator voltage regulator start-up input apparently also draws enough power to pop a 5A breaker when RPM is suddenly reduced, as I had this happen even after restoring the alternator to factory configuration. So this event could be the result of both a bad battery and alternator. Finn ________________________________ Message 2 _____________________________________ Time: 07:45:42 PM PST US Subject: AeroElectric-List: Re: OVP relay in B+ lead bad idea From: "user9253" Finn, I gather that your engine ignition system is electrically dependent. What type and brand is it? -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=514422#514422 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.