---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 10/26/15: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:17 AM - Re: Re: Newbie with PM alternator feed question (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 07:17:51 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Newbie with PM alternator feed question > > >I have read that for planning purposes, one should reduce the >alternator rating by 20% - with that thought my 30A alternator would >nominally be used as a 24A power source for continuous duty. Yes/no? > > Sortof . . . There's a fundamental notion in aircraft electrical system design that you should have enough alternator capacity to recharge a largely depleted battery in 60 minutes of flight. So if you've managed to get an engine started after dragging the battery down to 20% of capacity -AND- it's a 17 a.h. battery, then there should be approx 9A of 'excess' alternator capacity available to recharge a battery. If you've only got 30A total, then your full up running load needs to be 21A or less. For decades, Cessna and contemporaries were content to bolt the same 60A alternator to all their single engine models . . . which generally provided LOTS of excess snort. Further, if the battery is maintained/managed well -AND- you never launch into IFR -AND- your engine always starts in a few blades then the rule of thumb for 20% reserve becomes somewhat useless. THIS is why airplanes with smaller alternators benefit from an accurate load analysis along with some judiciously crafted standard operating procedures. If you're going to launch IFR then KNOWING that your battery capacity is sufficient to your battery only endurance goals is pretty important you your wife and kids. > >...I will do more homework and hopefully present some better, more >complete info. Looking forward to feedback from you and the group! If you don't have a copy of the 'Connection, you can download a .pdf from the website . . . or purchase a paper copy there too . . . but given the limited capability of your alternator combined with the electrically dependent engine, I recommend you educate yourself in the finer details of energy management for CONFIDANT/COMFORTABLE flight. Then sift the pebbles and twigs out with folks here on the List . . . I looked at the engine website briefly but didn't see any mention of a 50A option alternator. Can you point me to the information you were offered? Bob . . . ------------------------------------------------------------------------------------- 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.