---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sun 03/23/14: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:22 AM - Re: P-Leads for a Seawind (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 05:22:35 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Re: P-Leads for a Seawind Oh Great Guru: Thank you sir . . . I'll endeavor to live up to your expectations . . . I am installing a dual efis single ahrs GRT system with remote eis in a Seawind. I am installing dual alternator dual battery electrical system per your Z-14 schematic with parts from B & C. Okay, you've got more SYSTEM reliability than most twin-engine, TC aircraft . . . Having experienced multiple electrical failures in 20 yrs. of a '63 Cherokee and already one alternator failure in 5yrs of my current '78 C-182RG, I'm dead set on having a few backup "steam" gages. Perhaps "living confidence" as opposed to "dead disappointment" is the better term . . . Using the 10.4" EFIS displays, I don't have much panel space to play with. There's just enough room under the EFIS's on the PIC side for 2 1/4 airspeed and manifold pressure gages, a Tiny Tach and a MicroTim altimeter, which have internal batteries. Why the batteries? You got more sources of 'juice' in this airplane than Jonnie Appleseed has apples . . . Emacs! GRT connects to the P-leads on each mag with a 39 or 27 Kohm resistor, claiming the resistor will act as a fuse if there's a problem in the EIS. The resistor isolated signal tap is a time honored, well proven technique for sampling the p-lead signals. Tiny Tach people want me to drill a hole in the plug wire cap and wrap several turns of "antenna" around a plug wire insulation. This "antenna" wire insulation is about .06" diam. The plug insulation is a close fit inside the rubber plug that seals the mag. The mag is pressurized from my supercharger. A good seal is desirable. I discussed this problem with a TinyTach tech and he allowed a direct connection is not their recommendation, but the tiny resistor might be o.k., especially if one also included a tiny fuse (my suggestion.) I am suspicious of his design. Getting into a spark-plug wire to sample engine rpm borders on . . . well . . . I'll be nice. I 'sampled' the #1 plug wire on a Baron WWAAAYyyyy back when for the purpose of driving a propeller synchronizer system. For that task, I found that one could detect the CURRENT in the plug wire from OUTSIDE the shield with a toroidal current transformer. Got a nice signal consistent with firing of #1 cylinder. But getting 'under the shield' is unnecessary . . . particularly for the purpose of measuring RPM. See if this guy will email me a copy of his schematic . . . honorable non-disclosure agreements assumed . . . and I'll see if there's a way to do more sanitary job of integrating his product onto airplanes. Alternatively, send me your tach and I'll do some non-invasive investigations as to the nature of its needs for an input signal. My question: How do I select a fuse? If I connected at the mag where the EIS goes, I would have twenty five feet of coax to get to the TinyTach. If I connect at the panel, not more that one foot. If the tach cannot be satisfied with perfectly good data available at the magneto switch, I'd look for a better product. Another question: Is Bogert the only place in the world I can get P-Leads for my TCM mags? $90 ea. for the smallest 30" leads seems awfully high. and they are charging $3 or $4/ft. for each additional foot. (14AWG MIL-C-27500 retails for $1.47 in Spruce.) Their catalog only goes to 20 ft. & I need closer to 25. Since I'd have to cut in anyway, couldn't I just buy the minimum 30" and splice in more coax with soldersleeves? Don't use factory fabricated p-leads. They're priced for the captive, TC aircraft market. You don't need 14 AWG wire either. Here's a good source for 16 AWG at 50-cents/foot http://tinyurl.com/nczzsfa Poke around on eBay and you might come up with some 20 or 18AWG which is more appropriate. Build your own P-leads. I have some shielded 22AWG trio wire left. You could used this stuff and just parallel up the strands. It's NOT critical. You may wonder why two great big EFIS displays. GRT is the only one to easily allow live video input. Seawind drivers are installing cameras in their tip floats to watch the hull approach glassy water--makes for "greasers" on pavement a possibility too. (My dirty old men copilots want to plug in a dvd player and watch dirty movies on the way to Oshkosh.) What ever floats your seaplane my friend. That's a really impressive machine. Lets not make it any more difficult than necessary to meet requirements. 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.