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basic Ford alternator wiring questions

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CardinalNSB(at)aol.com
Guest

Posted: Tue Nov 28, 2006 10:20 pm Post subject: basic Ford alternator wiring questions

I'm finally free to experiment with my new "Coyote" project with a Lyc.  320.  I will be using the regular "Cessna" alternator/VR at least to begin  with (day vfr with electric starter/minimal avionics), basically a copy of my  Cardinal to start.  My confusion starts when I examine the Cessna  alternator wiring:

  

 My certified Cardinal has the same style alternator, wired as follows (all  wires are shielded):

  

 #8 from alt. A+ lug to Alt breaker, shield grounded  to alt. case only

  

 #8 from alt ground lug to firewall bolt, shield at each  end tied to end terminal 

  

 #18 from alt Field lug to VR  F lug, shield grounded to  alt case and firewall bolt

  

 #18 from alt A+ lug to VR A+ lug, shield grounded to alt case and  firewall bolt

  

 #18 from VR S lug to square metal filter lug to power buss, shield  grounded to firewall bolt and again next to filter, shield end at power buss  floats

  

 The above is per the factory manual, except for the shielded #8 ground  wire, the Cessna manual shows an unshielded #18.

  

 I assume the factory used shielded wire for abrasion protection and/or  noise protection, and that the #8 shielded ground wire was an undocumented later  field change?

  

 Questions:

  

 1.  I understand the Connection to say that shielding alternator/VR  wiring is not necessary for noise protection, did I miss something?

  

 2.  Does a shielded ground wire create any noise problem  potential?  If the engine ground straps are in good shape, is there any  reason for the #8 ground from alternator to firewall?  Or for any separate  ground wire from the alternator, inasumch as the alternator is bolted to the  engine with all metal bolts (no insulated washers)?

  

 3.  Is there any reason to run the A+ wire from the  alternator to the VR A+, I would prefer to run a shorter wire  from the VR  A+ to the  alternator side of the A+ alternator fuse on the  firewall (1 foot of wire on the firewall instead of 4 feet of wire  running beside the hot engine)?

  

 4.  Is there a need for wire protection, by shielding or  otherwise, since it runs next to the hot engine from the alternator?

  

 5.  Skycrafters sells a high temp "Varglass" sleeving advertised as  being rated to 200 degrees C.  Is this an appropriate protection for the  wires?  I can't find any information on the internet.

  

 6.  What temp rating should I use for the wires running next to the  engine?

  

 7.  Simply, is the following good practice for a Ford style  alt/vr:   all unshielded:

  

 #8 "A+" (alt to big fuse);  #18 "F" (alt to VR); #18 VR "S"  (VR to power buss); #18 VR "A+" (VR to alt side of big fuse)?

  

 This seems less complicated than my Cardinal.  Thank you.   Skip Simpson

  

  

  

  

  

  

  

  

  [quote][b]

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nuckollsr(at)cox.net
Guest

Posted: Wed Nov 29, 2006 6:12 am Post subject: Basic Ford alternator wiring questions

I'm finally free to experiment with my new "Coyote" project with a Lyc. 

320.  I will be using the regular "Cessna" alternator/VR at least to begin 

with (day vfr with electric starter/minimal avionics), basically a copy of 

my Cardinal to start.  My confusion starts when I examine the Cessna 

alternator wiring:



My certified Cardinal has the same style alternator, wired as follows (all 

wires are shielded):



#8 from alt. A+ lug to Alt breaker, shield grounded to alt. case only



#8 from alt ground lug to firewall bolt, shield at each end tied to end 

terminal



#18 from alt Field lug to VR  F lug, shield grounded to alt case and 

firewall bolt



#18 from alt A+ lug to VR A+ lug, shield grounded to alt case and firewall bolt



#18 from VR S lug to square metal filter lug to power buss, shield grounded 

to firewall bolt and again next to filter, shield end at power buss floats



The above is per the factory manual, except for the shielded #8 ground 

wire, the Cessna manual shows an unshielded #18.



I assume the factory used shielded wire for abrasion protection and/or 

noise protection, and that the #8 shielded ground wire was an undocumented 

later field change?



Questions:



1.  I understand the Connection to say that shielding alternator/VR wiring 

is not necessary for noise protection, did I miss something?



    No, you didn't. I was a tech writer at Cessna when the

    shielding protocols were first adopted on the single engine

    alternator installations. A prophylactic combination of

    "good things" were sprinkled onto some noisy airplanes where

    alternator noise was heard in the new ADF installations. The

    noise was reduced or eliminated and the practice adopted.



    There were NO formal studies as to the operating characteristics

    or effectiveness of any particular "good thing". The guy doing

    the work was a PhD physicist but he had no test equipment and

    zero experience with EMC issues. Nobody in the local industry

    did. Beech went on to acquire extensive testing facilities

    and experience but the roots of curiosity never took hold

    at Cessna's single-engine plant.



2.  Does a shielded ground wire create any noise problem potential?  If the 

engine ground straps are in good shape, is there any reason for the #8 

ground from alternator to firewall?  Or for any separate ground wire from 

the alternator, inasumch as the alternator is bolted to the engine with all 

metal bolts (no insulated washers)?



    Multiple ground wires give rise to dreaded DC GROUND LOOP

    and while they don't obviously "hurt" in most cases, they

    never help either. Bolting the alternator to the engine

    and strapping the engine to a single-point ground on

    the firewall is sufficient.



3.  Is there any reason to run the A+ wire from the alternator to the VR 

A+, I would prefer to run a shorter wire  from the VR A+ to the  alternator 

side of the A+ alternator fuse on the firewall (1 foot of wire on the 

firewall instead of 4 feet of wire running beside the hot engine)?



     I presume you're talking about a remote sense wire from

     the regulator. Cessna adopted remote sensing protocols

     in their regulator specs in the 80's and attached (+)

     and (-) sense wires directly to terminals on the alternator.

     The notion was that should an alternator experience

     an electrical disconnect downstream, that remote sensing

     at the alternator would prevent an unstable or runaway

     condition. Risks for wiring as you've described are

     not high . . . and you concerns for "wires next to hot

     engines" are not operable. Tefzel wire is quite content

     in the engine compartment compared to the nylon/PVC or

     nylon/dacron/PVC wire we were using before Tefzel.



4.  Is there a need for wire protection, by shielding or otherwise, since 

it runs next to the hot engine from the alternator?



     No.



5.  Skycrafters sells a high temp "Varglass" sleeving advertised as being 

rated to 200 degrees C.  Is this an appropriate protection for the 

wires?  I can't find any information on the internet.



     There are a variety of sleeving materials offered

     to satisfy a variety of protection concerns but for

     Tefzel wire under the cowl there are few if any

     concerns. Radiant heating from exhaust stacks are

     the high-stress heat sources. Keep your wires and

     accessories away from those antagonists and good

     order will exist under the cowl.



6.  What temp rating should I use for the wires running next to the engine?



     Tefzel is rated for continuous operation at 150C

     and is quite sufficient for the appplication we're

     discussing.



7.  Simply, is the following good practice for a Ford style alt/vr:   all 

unshielded:



#8 "A+" (alt to big fuse);  #18 "F" (alt to VR); #18 VR "S" (VR to power 

buss); #18 VR "A+" (VR to alt side of big fuse)?



This seems less complicated than my Cardinal.  Thank you.  Skip Simpson



     Keep in mind that what appears to be "more complicated"

     may have roots in rational design decisions (like the

     remote sensing at the alternator terminals) while

     others are wild ass guesses (like the shielding). Just

     because it has been done on tens of thousands of "certified"

     airplanes does not validate the science behind the

     practice. Operational risks for "rewiring" as you've

     suggested are very low. Shielding any of these wires

     is a waste of $time$ and empty weight budgets.



     Bob . . .

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