---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 07/18/13: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:54 PM - Battery capacity tester- Why isn't there a flyback diode? (Mark Todd) ________________________________ Message 1 _____________________________________ Time: 08:54:16 PM PST US From: Mark Todd Subject: AeroElectric-List: Battery capacity tester- Why isn't there a flyback diode? I finally got around to building Bob's battery capacity tester and, as a long-time lurker on the Aeroelectric list, I'm primed to slap a 'flyback' diode on every switched inductive load I find. But, the schematic for the battery capacity tester ( http://www.aeroelectric.com/articles/battest.pdf ) doesn't appear to have one. My understanding of semiconductors is pretty weak but the datasheet for the NPN transistor I happen to be using (2N5961) says the max collector-base voltage allowed is 60V. Although the inductive load in this case doesn't appear to be huge (my relay coil draws about 36mA at 12.4 V), it seems to me like I might be able to do some damage to my transistor. Is there something about the behavior of the Zener or the transistor that moderates the flyback voltage effect? I don't see any harm in adding a diode, but I'm just trying to learn. Do I need to a diode across my coil before I actually use this thing? Mark ------------------------------------------------------------------------------------- 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.