AeroElectric-List Digest Archive

Tue 04/08/14


Total Messages Posted: 2



Today's Message Index:
----------------------
 
     1. 08:08 AM - Re: Magneto Noise (Robert L. Nuckolls, III)
     2. 08:32 PM - When are diodes needed? (Thomas Blejwas)
 
 
 


Message 1


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    Time: 08:08:34 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Magneto Noise
    At 12:04 PM 4/6/2014, you wrote: I flew w/ a friend recently and when trying to get awos for our destination airport (which is a pretty weak signal) it was almost impossible to hear due to magneto noise. The radio is a Garmin 430W in a Cherokee and we were around 10 miles from the airport. When we got within 3 or 4 miles the signal was much clearer. All other transmissions with ATC & towers were acceptable but I noticed at high volume I could clearly hear magneto noise in the background. I'm wondering if that's just the way it is or if there is a problem with the magnetos or P lead wiring. Was this a new condition or has it been that way 'forever'. It's difficult for the neophyte observer to tell the difference between ignition noises getting into the system by way of plug wire radiation versus p-lead radiation. First, make sure that the perceived noise goes up and down with volume control settings on radio. This all but guarantees that it's coming in through the antenna. Then, disconnect both p-leads from the back of the magnetos and run the engine. See if the noise is still heard . . . turn to unused frequency . . . open squelch. If you can still hear it, then look for bad plug wire. If not, hook up one p-lead at a time and repeat experiment . . . see if noise is predicated on either or both of the p-leads being hooked up. Once you've identified the offending radiator, you need to figure out why. If this is a 'new' condition, then you're looking for something that has changed. Bad cap in mag (probably not both) broken ground lead on p-lead shield. If possible/ practical wire p-lead wires per Figure Z-27 http://tinyurl.com/n3oy37f Ground p-lead shields at magneto end only . . . use p-lead shields to ground mag switch. Remove and existing ground to the mag switch. If the noise is coming from both p-leads, there are 'approved' magneto noise filters http://tinyurl.com/l3s4mrj that most mechanics will install with a simple log-book entry. Bob . . . Bob . . .


    Message 2


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    Time: 08:32:09 PM PST US
    From: Thomas Blejwas <tomblejwas@yahoo.com>
    Subject: When are diodes needed?
    In adapting Z-07 and/or Z-19, I'm confused about the use and purpose of dio des.- As I understand them, diodes allow current to flow in one direction , with a small voltage drop, but not in the opposite direction, except for a small leakage.- The voltage drop times the forward current yields a pow er loss that results in heat, which may need to be dissipated to keep the h eat from damaging the diode or other nearby equipment.- The power lost ma y also be an issue in a battery-only situation after loss of an alternator, for example.- O.K. so far?=0A=0APairs of diodes are used in Z-19 for the two battery feeds for the main fuel pump, for example.- When both feeds are on, this would keep a "good" battery from feeding a "bad" one.- Is th at the primary purpose?- In Z-07, only one feed to the bus with the fuel pump has a diode because judicious switching can isolate either battery.- Correct?- Is there something more that I'm missing?- For example, if I 'm not concerned about one battery "feeding" another, do I still need diode s to "smooth" the feed to a bus from two different batteries?- Thanks.=0A =0ATom=0A=0ASent from my iPad




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