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  #21  
Old 11-28-2012, 06:49 PM
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Bill.Peyton Bill.Peyton is offline
 
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I'll throw in my two cents.... If you truly are designing an aircraft to be used in frequent IMC, then a power failure of the main buss in an all electric dependent aircraft while IMC, should not be treated mildly. It should be a non-event! By that I mean that your backup buss should cover all the required instruments to continue IMC to a successful approach without cleaning your shorts. If you are going to go through the trouble of installing a second battery, a charging system for that power source, and wiring to the panel, then why not back up everything you need to continue, less transponder. Yes, you should power the audio panel in a two place aircraft, after all, there may be a very capable pilot sitting next to you that you might want to communicate with, removing your headset to yell at him while trying to communicate with approach is not the safe way to handle this situation.
IMHO, anything placed between your equipment and the battery such as a the master relay and the VPX distribution system can become the source of a failure. If the alternator fails you should have plenty of time to get down with the main buss. And yes, I have seen 2 master relays fail!
All the garmin products have a secondary power input to make it easy to back them up. Run a switched bus forward, leave it on all the time and fuse it to all your instruments (except the transponder). In an emergency, shed the power as needed manually.
The advantage of a true secondary buss, is the ability to turn on your instruments prior to engine start and get your flight plan loaded, get your weather and clearance, then start your engine with all of that still up and running.
A good example of a truly redundant system is demonstrated in the Beech G36 or the Cessna G 1000 182.
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  #22  
Old 11-28-2012, 09:24 PM
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Quote:
Originally Posted by Bill.Peyton View Post
All the garmin products have a secondary power input to make it easy to back them up.
None of the Garmin GNS products (430W) nor any of the GTN products have backup power inputs, nor does an SL-30 or an SL-40, so don't assume all Garmin products do when planning your wiring.

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  #23  
Old 11-29-2012, 06:30 AM
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Ian,
You are not totally correct. You are correct, the SL30/40 do not have secondary power pins and require a back to back diode on the primary pwr in.
The GNS400 series does have secondary power inputs. P4001, pins 15 and 72.
I did not look at the GTN installation manual, so I can't comment on whether it contains secondary power inputs. I will look and report back.
Bill
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  #24  
Old 11-29-2012, 08:05 AM
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Quote:
Originally Posted by Bill.Peyton View Post
The GNS400 series does have secondary power inputs. P4001, pins 15 and 72.
In the GNS400 installation manual, Figure H-5, Power, Lightning, and Antenna Interconnect, Note 2 says "If the aircraft has multiple power buses, It is recommended that all GNS 430W power inputs be connected to the same power bus".
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  #25  
Old 11-29-2012, 09:27 AM
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Quote:
Originally Posted by larrynew View Post
In the GNS400 installation manual, Figure H-5, Power, Lightning, and Antenna Interconnect, Note 2 says "If the aircraft has multiple power buses, It is recommended that all GNS 430W power inputs be connected to the same power bus".
But Note 10 is applicable to the pins that Bill mentioned.

Yes, there are three separate power supplies here and yes they should all be on the same bus.

However, on 4001 there is diode isolated power inputs, which provides redundacy for the GNS portion of the unit only. You are still SOL on the comm side.

What Steve did for Option B on the VPX is a good way to deal with this for the GNS or GTN series units.
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  #26  
Old 11-29-2012, 05:15 PM
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I did check the Garmin pin outs, and Ian is correct, the GTN series do not have secondary power inputs. Garmin has informed me that the G3X and GNS dual power inputs are isolated only by back to back diodes. This is something that can easily be done externally. Bob is correct in that the secondary power inputs for the GNS 430 exclude the comm radio and only back up the GPS and Nav.
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  #27  
Old 11-29-2012, 05:43 PM
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We've found that the best way to back up the Garmin certified GPS/radios with the VP-X is to use backup method B (as described in the VP-X install manual). Typically in newer certified aircraft the have one radio on the avionics bus and the other on the essential bus.

The G3X components do have dual power inputs and you can run one to the VP-X and the other input to a backup battery use use backup method C.
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  #28  
Old 03-22-2018, 12:56 PM
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I'm resurrecting an old thread rather than restarting a new one.

I've been thinking long and hard about design of my electrical system and have read Ausman's book and the relevant sections of Knuckol's as well. Things are starting to gel.

My plane is going to have dual alternators and dual batteries. It will be fully IFR capable and will utilize the SDS system as well as the VPX PRO. The panel will be Garmin (G3X x 3, GTN 650, G5, + Garmin (audio panel,transponder,2nd Nav Comm).

Where I'm stumbling is configuring the backups of the essential buss in case of failure of the main power supply or VPX. I've studied Options B and C in the VPX install manual. It looks to me like both of these solutions are rather switch intensive in that they require an extra switch for each component that I want to back up. I would prefer to have a single switch that would provide power to all that is needed. Can this be done?
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  #29  
Old 03-22-2018, 03:33 PM
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Randy,

Shoot me a PM and I'll share with you my wiring schematic. I'm running the same setup. Would also like to talk to you about your engine.

Tim
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  #30  
Old 03-21-2019, 07:15 PM
gsmini gsmini is offline
 
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Quote:
Originally Posted by RandyAB View Post
I'm resurrecting an old thread rather than restarting a new one.

I've been thinking long and hard about design of my electrical system and have read Ausman's book and the relevant sections of Knuckol's as well. Things are starting to gel.

My plane is going to have dual alternators and dual batteries. It will be fully IFR capable and will utilize the SDS system as well as the VPX PRO. The panel will be Garmin (G3X x 3, GTN 650, G5, + Garmin (audio panel,transponder,2nd Nav Comm).

Where I'm stumbling is configuring the backups of the essential buss in case of failure of the main power supply or VPX. I've studied Options B and C in the VPX install manual. It looks to me like both of these solutions are rather switch intensive in that they require an extra switch for each component that I want to back up. I would prefer to have a single switch that would provide power to all that is needed. Can this be done?
Randy,

Can I ask what you came up with? I’m going through the same thing. Did you put one switch between the battery and fuse block?
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