---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 04/03/17: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 03:38 PM - Lithium Webinar (Ken Ryan) 2. 10:35 PM - old B and C SD-8 Dynamo failure (Mark Todd) ________________________________ Message 1 _____________________________________ Time: 03:38:37 PM PST US From: Ken Ryan Subject: AeroElectric-List: Lithium Webinar Because there is interest on this list I thought it might be appropriate to post that there is an upcoming EAA Webinar on the subject of lithium batteries: http://pages.eaa.org/WBN2017-05-31LithiumBatteriesExplained_LP-Registration.html Ken ________________________________ Message 2 _____________________________________ Time: 10:35:38 PM PST US Subject: AeroElectric-List: old B and C SD-8 Dynamo failure From: Mark Todd Well, after 27 years and 2300+ hours, my good old SD-8 dynamo finally gave me a problem. It was installed in my day/VFR RV4 in 1989 as the only charging source. It could produce up to 8.6 amps at high RPM and met my modest electrical load requirements (<4 amps in cruise) for all these years. Of course, I could expect my low voltage light to come on (at 12.5V) at low rpms depending on the loads. I didn't mind. It made for a nice reminder to turn off my boost pump as I exited the runway on landing. On a recent flight, I noticed that the low voltage light came on a little earlier than I expected on landing. At high RPM, the voltage was only going to 13.9 instead of the usual 14.1V. A quick run through my switchable loads showed they were pulling their expected currents. I have a switchable volt/amp gauge on my panel so I can look at one or the other but not both simultaneously. The amp readings are taken off my B lead and it takes several seconds for the amp reading to stabilize on my gauge after it's selected. I never saw an unexpectedly high amp reading on the gauge. Back at the hangar, a brief look at my B lead connections didn't reveal any problems. On the next flight, the low voltage light came on even sooner and the voltage only got to 13.7V. A more detailed inspection was made of the wiring, including micro-ohming some connections (using Bob's 100mA current clamp micro-ohmmeter design I've enjoyed using for several years). I thought I detected a little bit of a burnt electrical smell near the dynamo housing where the armature leads pass through a clip screwed into the rim of the housing. Using a cheap digital multimeter, I checked the resistance across the disconnected dynamo leads and got 5.6 ohms. Not sure what it's suppose to be. I flew the plane again and this time, I got a low voltage light in cruise and zero B lead amps when checked. I checked the resistance across the dynamo leads again with the same meter.. and got a reading of zero. My micro-ohm meter said it was about 700 milliohms. I bought a new SD-8 and am back in the air trouble free. Since removing the problem unit, I removed the clip that held the leads at the rim of the dynamo housing and slid the protective sheathing back. The lead wires look fine, including the half-inch of wire I can see inside the housing. The resistance across the leads remains 'zero' when checked with another cheap digital mulitmeter. I concluded that I had probably experienced a progressive short within the dynamo, probably in the windings themselves. This dynamo was from the 1980's and the exterior design has changed a lot since then. This includes a protected routing of the leads out of the dynamo housing with a better clamping system. The insides have probably changed as well. Lord knows the new unit is easier to install with much better access to the mounting nuts. I have no complaints about this SD-8 failure. I certainly got a reasonable service life out of this unit. I just thought I'd share my story as just one more data point, although I appreciate it's kinda ancient history. I'm planning on taking the dynamo apart (curiosity) and maybe salvaging the magnets. Bob, if you wanted to look at this dynamo for some reason, I'll be happy to mail it to you. I suspect you've got much better things to do than 'paleo-forensics' on this dated item. 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.