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  #81  
Old 02-22-2020, 06:23 PM
ArlingtonRV ArlingtonRV is offline
 
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This is the shelf mount on the firewall. The shelf I used is an RV-12 part (P/N F-01201R-1), or you can fabricate one.







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  #82  
Old 09-27-2020, 06:11 AM
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Saville Saville is offline
 
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Default Question regarding Circuit Breaker and the GDL 82

Question: Are you REQUIRED to use the same circuit breaker that your transponder is on?

I have 2 Garmin installation guides for the GDL 82:

GDL 82 for the Mooney M20 series which says:

"This GDL 82 is protected by the existing transponder circuit breaker."


And then I have the "GDL 82 TSO Installation Manual"
which says:

"The GDL 82 CAN BE protected by the existing transponder Circuit breaker"


So I'm assuming that the reason they use the same CB in the Mooney is so that you don't have to install a new CB in the certified airplane panel and doesn't have anything to do with electronic technique.

So I read all this as meaning you CAN use the same CB as the transponder but you don't have to.

Am I misinterpreting?

Thanks
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  #83  
Old 09-27-2020, 07:18 AM
jliltd jliltd is offline
 
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The GDL 82 STC installation instructions for certified aircraft state that they must both be connected to the same circuit breaker, with their own individual ring terminals. I think the FAA wants to make sure one is never on without the other. And I think the individual ring terminal mandate is for reliability of some sort. I am aware of some experimental installations who use the switched power output of the transponder to power the GDL 82. Seems to work fine.
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  #84  
Old 09-27-2020, 07:34 AM
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Saville Saville is offline
 
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Quote:
Originally Posted by jliltd View Post
The GDL 82 STC installation instructions for certified aircraft state that they must both be connected to the same circuit breaker, with their own individual ring terminals. I think the FAA wants to make sure one is never on without the other. And I think the individual ring terminal mandate is for reliability of some sort. I am aware of some experimental installations who use the switched power output of the transponder to power the GDL 82. Seems to work fine.
Ok so let's suppose I want to connect both to the same breaker.
I have a GTX 327 Transponder

I am an electronics neophyte so I need some assistance:

The circuit diagram for the GTX 327 shows a 3 amp breaker.

The documentation does not specify a current draw but says that the max power is 22 watts. So I calculated the max current this way:

GTX 327 amps = watts/volts = 22.0/14 = 1.57 amps

The documentation for the GDL 82 says it draws 0.45 amps at 14 volts.

To total current draw of the two devices is:

1.57 + 0.45 = 2.02 amps

So one would think I could use a 3 amp breaker for the combined units.

BUT........

AC43.13 Table 11.3 shows that for 22AWG wire I need a 5 amp breaker.


The GDL 82 circuit diagram says I need a 5 amp breaker
(power line is 22awg I believe)

The GTX 327 circuit diagram says I need only a 3 amp breaker.

So I'm thinking I need to use a 5 amp breaker for the combined units. It's way over the 120% max current draw requirements in the documentation. I'm concerned that a problem would draw much more current than necessary before the breaker trips

Is the 5 amp breaker the correct breaker size to use for the combined units?

Thanks
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Last edited by Saville : 09-27-2020 at 07:36 AM.
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  #85  
Old 09-27-2020, 08:09 AM
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plehrke plehrke is offline
 
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Circuit breaker protects the wire. Wire is selected to handle the draw. Using a lower circuit breaker then called for by the standard is ok. Since they should be connected in parallel (separate ring terminal for each off of the breaker) each wire is selected for each draw. Circuit breaker should be selected for protecting the smallest gage wire in the circuit. I would select a 3amp breaker as there is no need to have more higher then the total draw, which is what I have for my GDL 82 and SL70.

FYI. AC43.13 Table 11.3 does not show what you need, it shows the maximum for 22AWG wire should be 5 amp breaker. Always want breaker to trip before wire catches on fire.
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Last edited by plehrke : 09-27-2020 at 08:12 AM.
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  #86  
Old 09-27-2020, 09:53 AM
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Thanks for the info Phillip
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  #87  
Old 09-29-2020, 09:41 AM
jliltd jliltd is offline
 
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3 amp will probably work but I always yield to the manufacturer's recommendation. Can't go wrong there. In the GDL 82 manual it says to use a 5 Amp breaker and in my upgrade installs I always change the original GTX 327 breaker from a 3 amp to a 5 amp and use 22 AWG power/ground wires for the GDL and 20AWG power/ground wires for the GTX in accordance with Garmin's installation manuals. The 5 amp is still appropriate for 22AWG for the distances available for wire runs in an RV. Here again I assume you are putting this in an EAB aircraft so you can do whatever you like, such as the aforementioned switched power output circuit from the transponder's D-Sub connector.
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Last edited by jliltd : 09-29-2020 at 09:47 AM.
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  #88  
Old 10-11-2020, 07:27 AM
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Saville Saville is offline
 
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Quote:
Originally Posted by jliltd View Post
The GDL 82 STC installation instructions for certified aircraft state that they must both be connected to the same circuit breaker, with their own individual ring terminals. I think the FAA wants to make sure one is never on without the other. And I think the individual ring terminal mandate is for reliability of some sort. I am aware of some experimental installations who use the switched power output of the transponder to power the GDL 82. Seems to work fine.
So there is no electronic "damage" reason to have one on and one off...it's an FAA thing where they want to be sure both are on?

Thanks
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  #89  
Old 10-11-2020, 01:47 PM
jliltd jliltd is offline
 
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Quote:
Originally Posted by Saville View Post
So there is no electronic "damage" reason to have one on and one off...it's an FAA thing where they want to be sure both are on?

Thanks
I have no idea. But I don't know if a GTX can transmit through a GDL 82 if it is off.

Jim
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  #90  
Old 10-11-2020, 02:14 PM
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Saville Saville is offline
 
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Quote:
Originally Posted by jliltd View Post
I have no idea. But I don't know if a GTX can transmit through a GDL 82 if it is off.

Jim
I doubt it since the antenna is hooked up to the -82.

But stranger things have happened
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