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Tach pickup

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N777TY

Joined: 09 Apr 2006
Posts: 69
Location: Charlotte, NC

Posted: Sat Dec 02, 2006 1:18 pm Post subject: Tach pickup

I'm wiring tach pickup wires to a switch that selects which mags gives the tach signal.  This switch is right above the two mag toggle switches.  Since I'm using EIS 4000, they say to wire from the P-lead through a 27k resistor to the tach selector switch.



Any concerns with just using a small pigtail off of the P-lead wire at the mag switch (going into the tach selector switch)?  I'd prefer not to run another wire all the way to the mag itself just for tach signal.  My concerns here are noise and functionality (eg. to ensure it works as wired up).



Also, any concerns with running the P-lead shielded wire together with the rest of wires, or should I find a separate path and firewall penetration just for these two wires?



PS.  Why does 20AWG shielded wire's inner conductor appear to be thinner than regular 20AWG tefzel wire (measured diameter including insulation)?  It looks the same to me as 22AWG tefzel wrapped in shielding (and my stripper won't strip it at 20AWG setting).

Thanks!

Radomir

_________________
RV-7A
N777TY

nuckollsr(at)cox.net
Guest

Posted: Sat Dec 02, 2006 2:44 pm Post subject: Tach pickup

At 01:18 PM 12/2/2006 -0800, you wrote:



 	  Quote: 	
		  



I'm wiring tach pickup wires to a switch that selects which mags gives the 

tach signal.  This switch is right above the two mag toggle 

switches.  Since I'm using EIS 4000, they say to wire from the P-lead 

through a 27k resistor to the tach selector switch.



Any concerns with just using a small pigtail off of the P-lead wire at the 

mag switch (going into the tach selector switch)?  I'd prefer not to run 

another wire all the way to the mag itself just for tach signal.  My 

concerns here are noise and functionality (eg. to ensure it works as wired up).


	


   . . . suggest you wire as shown in



http://www.aeroelectric.com/PPS/Engine/Ignition/Mags_with_Electronic_Tach_A.pdf



 	  Quote: 	
		  Also, any concerns with running the P-lead shielded wire together with the 

rest of wires, or should I find a separate path and firewall penetration 

just for these two wires?


	


   No. Run them together with other stuff as long as shields

   are grounded as shown above.

 	  Quote: 	
		  PS.  Why does 20AWG shielded wire's inner conductor appear to be thinner 

than regular 20AWG tefzel wire (measured diameter including 

insulation)?  It looks the same to me as 22AWG tefzel wrapped in shielding 

(and my stripper won't strip it at 20AWG setting).


	


   Maybe because it's not 20AWG wire but 22AWG.

   How do you come to believe that it's actually

   20AWG wire. If there's a mil number on the wire

   it will looke somethign like 22759/16-20-9 where

   22759 is the base spec. Slash 16 is the sub spec.

   20 is the AWG and 9 is color. If there's a third

   dash number then it's the stripe color.



   Bob . . .



      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

N777TY

Joined: 09 Apr 2006
Posts: 69
Location: Charlotte, NC

Posted: Sat Dec 02, 2006 3:22 pm Post subject: Re: Tach pickup

Bob, many thanks for the suggestion.  I like the simplicity of it very much!   Wish I found this drawing before drilling a hole for the selector switch... but no biggie, the hole can be filled.



I do have a quick follow-up question -- the drawing I was using (toggle mag switches with start button) call out for 20 AWG shielded wire for P-leads... This drawing calls out for 18AWG shielded... Any concerns with using 20, which I have on hand?  Or should I be ordering 18?

As for size of the wire.. I got the 20AWG shielded from B&C... Found the numbers on it and they read:  M27500-20 TG1T14  So I guess it is 20AWG.. but again.. I gotta use 22 setting on the stripper to strip it.. 

Thanks again!

Radomir

_________________
RV-7A
N777TY

klehman(at)albedo.net
Guest

Posted: Sat Dec 02, 2006 3:29 pm Post subject: Tach pickup

Ummm

Is this a test   ?

Why wouldn't 20 awg shielded wire have a 20awg center wire??

Ken

snip



 	  Quote: 	
		  

> PS.  Why does 20AWG shielded wire's inner conductor appear to be 

> thinner than regular 20AWG tefzel wire (measured diameter including 

> insulation)?  It looks the same to me as 22AWG tefzel wrapped in 

> shielding (and my stripper won't strip it at 20AWG setting).

   Maybe because it's not 20AWG wire but 22AWG.

   How do you come to believe that it's actually

   20AWG wire. If there's a mil number on the wire

   it will looke somethign like 22759/16-20-9 where

   22759 is the base spec. Slash 16 is the sub spec.

   20 is the AWG and 9 is color. If there's a third

   dash number then it's the stripe color.



   Bob . . .

N777TY

Joined: 09 Apr 2006
Posts: 69
Location: Charlotte, NC

Posted: Sat Dec 02, 2006 3:39 pm Post subject: Re: Tach pickup

Hmm.. but this makes the start button "live" when both mags are off... Is this a big concern in "real life?"  I did like the other drawing a bit better when the button was live only when left was on and right off..   I guess can't have it all?

_________________
RV-7A
N777TY

bob(at)bob-white.com
Guest

Posted: Sat Dec 02, 2006 4:06 pm Post subject: Tach pickup

On Sat, 02 Dec 2006 16:44:14 -0600

"Robert L. Nuckolls, III" <nuckollsr(at)cox.net> wrote:



 

 	  Quote: 	
		   

 >PS.  Why does 20AWG shielded wire's inner conductor appear to be thinner 

 >than regular 20AWG tefzel wire (measured diameter including 

 >insulation)?  It looks the same to me as 22AWG tefzel wrapped in shielding 

 >(and my stripper won't strip it at 20AWG setting).

 

    Maybe because it's not 20AWG wire but 22AWG.

    How do you come to believe that it's actually

    20AWG wire. If there's a mil number on the wire

    it will looke somethign like 22759/16-20-9 where

    22759 is the base spec. Slash 16 is the sub spec.

    20 is the AWG and 9 is color. If there's a third

    dash number then it's the stripe color.

 

    Bob . . .

 




	


I use quite a bit of the 22 AWG shielded wire.  The MIL spec for the

shielded wire I've been using and which seems to be commonly available

is M27500. The insulation is thinner than 22750/16. I haven't seen

shielded wire with 22750/16 conductors.



Bob W.



-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com

First Flight:  11/23/2006 7:50AM - 0.4 Hours Total Time

Cables for your rotary installation - http://www.roblinphoto.com/shop/

nuckollsr(at)cox.net
Guest

Posted: Sun Dec 03, 2006 9:00 am Post subject: Tach pickup

At 03:22 PM 12/2/2006 -0800, you wrote:



 	  Quote: 	
		  



Bob, many thanks for the suggestion.  I like the simplicity of it very 

much!   Wish I found this drawing before drilling a hole for the 

selector switch... but no biggie, the hole can be filled.



I do have a quick follow-up question -- the drawing I was using (toggle 

mag switches with start button) call out for 20 AWG shielded wire for 

P-leads... This drawing calls out for 18AWG shielded... Any concerns with 

using 20, which I have on hand?  Or should I be ordering 18?


	


    No, the currents that flow in these wires

    would be easily handled by 22AWG wire. There's

    a kind of rule-of-thumb for wires under the cowl,

    especially those that control the mags to make

    them mechanically robust. This suggests the use

    of 20 or even 18AWG wire. I've seen some drawings

    call out 16AWG.



 	  Quote: 	
		  As for size of the wire.. I got the 20AWG shielded from B&C... Found the 

numbers on it and they read:  M27500-20 TG1T14  So I guess it is 20AWG.. 

but again.. I gotta use 22 setting on the stripper to strip it..


	


    Interesting. This probably speaks more to the

    accuracy of the dies in your tool as opposed to

    variabilities in the actual size of the wire.



    Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

nuckollsr(at)cox.net
Guest

Posted: Sun Dec 03, 2006 9:03 am Post subject: Tach pickup

At 06:30 PM 12/2/2006 -0500, you wrote:



 	  Quote: 	
		  



Ummm

Is this a test   ?

Why wouldn't 20 awg shielded wire have a 20awg center wire??

Ken




	


    Was just inquiring as to the pedigree of the wire.

    I have a spool of perfectly good wire where the

    wire itself is not marked but label on the spool is

    incorrect. Just asking about the data he had to

    KNOW that the wire was indeed 20AWG. The source

    and markings suggest the wire is the size he believes

    it to be . . . which leaves tool variabilities as the

    probable cause for his observations.



    Bob.  . .

 	  Quote: 	
		  snip



>

>>PS.  Why does 20AWG shielded wire's inner conductor appear to be thinner 

>>than regular 20AWG tefzel wire (measured diameter including 

>>insulation)?  It looks the same to me as 22AWG tefzel wrapped in 

>>shielding (and my stripper won't strip it at 20AWG setting).

>   Maybe because it's not 20AWG wire but 22AWG.

>   How do you come to believe that it's actually

>   20AWG wire. If there's a mil number on the wire

>   it will looke somethign like 22759/16-20-9 where

>   22759 is the base spec. Slash 16 is the sub spec.

>   20 is the AWG and 9 is color. If there's a third

>   dash number then it's the stripe color.

>

>   Bob . . .



--



-- incoming mail is certified Virus Free.

Checked by AVG Anti-Virus.


	




        Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

nuckollsr(at)cox.net
Guest

Posted: Sun Dec 03, 2006 9:07 am Post subject: Tach pickup

At 03:39 PM 12/2/2006 -0800, you wrote:



 	  Quote: 	
		  



Hmm.. but this makes the start button "live" when both mags are off... Is 

this a big concern in "real life?"  I did like the other drawing a bit 

better when the button was live only when left was on and right off..   I 

guess can't have it all? 


	


   Yeah, that was a problem but I ran out of poles on the

   left mag switch. You could get a 3-pole switch for the left

   mag and produce the functionality you're interested in.



   Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

bob(at)bob-white.com
Guest

Posted: Sun Dec 03, 2006 4:05 pm Post subject: Tach pickup

On Sun, 03 Dec 2006 11:02:39 -0600

"Robert L. Nuckolls, III" <nuckollsr(at)cox.net> wrote:

 	  Quote: 	
		   

     Was just inquiring as to the pedigree of the wire.

     I have a spool of perfectly good wire where the

     wire itself is not marked but label on the spool is

     incorrect. Just asking about the data he had to

     KNOW that the wire was indeed 20AWG. The source

     and markings suggest the wire is the size he believes

     it to be . . . which leaves tool variabilities as the

     probable cause for his observations.

 

     Bob.  . .

 

 

 >snip

 >


	


Nope.  I finally found a quick summary for the M27500 specification.

(Available at http://www.awcwire.com/pdf/CT-G4-M27500.pdf.)  



M27500 can be made with any M22759 wire.  M22759 with

different /no. have different insulation thicknesses.  I've been

buying M27500-22TG3T14 which turns out to have M22759/18 wire in it.

That's specified by the TG.



Here are some wire outer diameters per the M22759 spec.:



M22759/16 20 AWG    0.058 - 0.062

M22759/18 20 AWG    0.049 - 0.053

M22759/16 22 AWG    0.050 - 0.053



This data is from

http://www.jaguarind.com/products/teflon/teflonwire.html



So if you have the M27500-20TG wire, the OD of the wire is identical to

the OD of M22759/16 22 AWG. 



If you want M22759/16 wire in your M27500 shielded cable, it has to be

M27500-xxTExxxx.



My experience stripping the 22 AWG M22759/18 wire with the 22 AWG

setting on my stripper is that sometimes it works and sometimes it

slips.  Once it's slipped, the insulation has been thinned some more

and I have to complete the strip with my el cheepo stripper similar to

your picture http://www.aeroelectric.com/articles/strippers/mvc829.jpg



Bob W.



-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com

First Flight:  11/23/2006 7:50AM - 0.4 Hours Total Time

Cables for your rotary installation - http://www.roblinphoto.com/shop/

N777TY

Joined: 09 Apr 2006
Posts: 69
Location: Charlotte, NC

Posted: Sun Dec 03, 2006 4:28 pm Post subject: Re: Tach pickup

Bob W. -- that's it.  I mic'ed both tefzel 22 and this shielded 20 and they both came out at 0.050... My stripper doesn't wanna strip it at 20.. but works at 22 fine.. so I'm good to go.



I decided to keep the selector switch, as I didn't like having a live starter button... It does appear that using a 3 pole switch woudl be ideal.  Since my left mag switch is close to the rib, not sure if 3 pole switch would fit in there (not sure about its size).. so this will work good.

Thanks to everyone!

Radomir

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N777TY

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