---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sun 01/03/21: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:18 PM - Re: Re: Clearance Delivery Diode Leakage (Robert L. Nuckolls, III) 2. 08:49 PM - Any ideas where to get electric motor brushes? (rparigoris) ________________________________ Message 1 _____________________________________ Time: 12:18:15 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Clearance Delivery Diode Leakage At 07:10 PM 12/31/2020, you wrote: > > >user9253 wrote: > > Check for electricity on the main bus using a test light. > > The light will not illuminate. That means there is no voltage on > the main bus. > > Leave the test light connected to the main bus, then measure the > voltage with > > the digital meter again. The main bus will now have zero > volts. The diode is OK. > > >I see....The test light (load) on the main buss drains the residual >voltage and kinda make the diode seal better like a check valve >with differential pressure would. No, leakage through the reverse biased diode is relatively constant irrespective of the load. Consider the attached drawing. The red boxes represent your ship's battery and the diode under study. I've depicted a reverse leakage resistor RL2 around the diode. To read 0.4v across a 10M resistor in series (your voltmeter) describes a ratio: RL2 + 10M 10M ---------- = ---------- 12V 0.4V Solving for RL2 RL2 + 10M = (10M x 12V)/0.4V RL2 = [(10M x 12V)/0.4V] - 10M RL2 = 290,000,000 ohms which represents a parasitic (leakage) load on the battery of 12/290M ~ 41 NANOAmps For this leakage to take say, an 18AH battery down to 1/2 capacity would require . . . 9,000,000,000 nAHr/41nA = 220 Million hours or roughly 25,000 years. The value for leakage current is generally always cited on data sheets for diodes but it's so tiny that only in very specialized, small signal applications is it significant to the design. We CAN measure it, as you have done, but in the airframe, its more of a curiosity than a concern. Also, reverse leakage varies widely with temperature, applied voltage and batch-to-batch variations. Going back to the drawing I show another 'leakage' resistor (RL1) that is internal to the battery. All batteries have one of these and depending on chemistry and temperature, it too will discharge the battery. Most secondary SLVA and Lithium products are good on the shelf for 1-2 years. I suggest that leakage inside the battery is of far greater concern than diode leakage(s) outside the battery. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" ________________________________ Message 2 _____________________________________ Time: 08:49:54 PM PST US Subject: AeroElectric-List: Any ideas where to get electric motor brushes? From: "rparigoris" Hi Group I need some brushes for the exciter on my Monarch EE lathe. Was making some aeroplane parts and it quit. Sizes needed: 3/8" x 3/8" and worn out length is 1.060", it has a shunt and terminal (need 4, will buy 8) 1/2" x 1/4" and worn out length is .495", it has a shunt and terminal (need 2, will buy 4) Any ideas where I can purchase from? Thanks Ron P. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=499971#499971 ------------------------------------------------------------------------------------- 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.