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Date: Sat, 5 Dec 2009 07:22:35 -0800 (PST)
From: Tom Walter <roundrocktom@yahoo.com>
Subject: Re:  Primer in AC/DC Electricity
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Before blinding following the wiring guide, do read over some of the comments in Bob Nuckolls web site.

Original Article:
http://www.eaa.org/experimenter/articles/0903_aircraft_wiring.pdf

Bob Nuckolls response starts here:
http://www.aeroelectric.com/articles/richter/richter.html

For an excellent book I still recommend a book titled "Basic Electricity" published by.... the US Navy. My sister gave me a copy for Christmas '70. It still stands out as a good basic primer.    http://www.amazon.com/Basic-Electricity-Bureau-Naval-Personnel/dp/0486209733  

The biggest reason for 24V vs. 12V... You can deliver the same power, but with less loss by the cabling.  Power = Current * Voltage.  So for that 100W landing light, with a 12V system we have 8 Amps (Hey, I'm rounding numbers to explain things).   Go to 24V, and I only need 4 Amps of current.   Power is also Current Squared * Resistance.   If my wire was tenth of an ohm, 0.010 Ohm..... with 8A I have a 0.64 Watts of power lost in that wire. Now if I go to 4A, it drops to 0.16 Watts.   As a result I can use wire with a smaller gauge to carry the same load, with the same power loss as I did with 12V.   So net results is by going to 24V I can use a lighter wiring harness!     That's it, I can save another six pounds of wiring.   Catch is now I need that $700 aircraft alternator, and so on. For experimental it is a headache to use 24V!   

For years I have been extremely "anti-solder" on any wiring harness.  Solder will wick down a wire, and that transistion from rigid to flexible wire is a stress point that will break after years of vibration.  Well  someone pointed out I was wrong as the GM electronics service manual shows solder repairs on the  harness being done. They also show the wire being fitted back into a harness, and the harness being  taped back together. That is the strain relief as one wire in a bundle will not see the vibrations forces leading to the breakage. 

I will be the first to admit that everyone has a different style.  If you listen to one expert they might tell you one thing, listen to another and it is different advice. Trick is to figure out what they agree on (i.e. using sub-d panel connectors.... beg, borrow, steal a set of DMC crimpers).    There is a "well known" Rotary Engine expert that says a rotary can not be mounted plugs up, yet despite "it will self destruct" plugs up engines have been running for over 10 years. :)

Tom
(digest mode.... catching up on email).