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05-19-2017, 06:38 AM
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Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 1,055
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Gad27 Voltage Stabilizer
I'm thinking that the IBBS backup battery really isn't needed in my dual-alternator application. If the battery won't start the engine I can't fly anyway, and if it fails in flight I have two alternators.
So the question is about the GAD27. How well does the voltage stabilizer feature work? Can it handle two GDU27 and GEA 24 powered up while starting the engine? Would it be best to have one GDU and the 24 only, and leave the PFD for the avionics master? I'm hoping someone with some experience in it can give a report on it....
thanks!
__________________
Ser 104142, RV-14A flying - N1463 
Ser 83825, RV-8 building - N8638? 
USN Ret, Urologist, AME, Repeat Offender
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05-20-2017, 11:42 PM
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Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 1,055
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Does 122 reads and no replies mean that nobody uses this feature? That is an answer all in itself I suppose....
__________________
Ser 104142, RV-14A flying - N1463 
Ser 83825, RV-8 building - N8638? 
USN Ret, Urologist, AME, Repeat Offender
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05-21-2017, 06:09 AM
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Join Date: May 2005
Location: X35 - Ocala, FL
Posts: 3,679
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I am installing a GAD27 now. It will be powering the single GDU, the GEA, the ADAHRS and the GAD29 I think. Haven't tried it out yet, but should be this week.
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Jesse Saint
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05-21-2017, 06:27 AM
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Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
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Per page 23-4 (old rev AA) of the manual:
KEEP ALIVE POWER VOUT
OUTPUT POWER FOR “KEEP ALIVE” BUS (GREATER OF +12VDC OR INPUT POWER, 3.5 A OUTPUT MAX.)
I've ditched the backup battery because I'm adding a GAD 27 and my backup instruments have their own internal batteries (but I'm going to run 1 alternator). My electrical system is setup with a more modern solenoid that uses 1/7th the current draw, so I don't have to worry about parasitic draw of the master in the case of alternator loss (the standard ones draw 1amp) http://www.vansairforce.com/communit...ad.php?t=48693. My intended mission is predominantly VFR with some enroute IFR. If I push the IFR further in the future, I may add an 8 amp backup alternator when I make that choice. YMMV.
Tom.
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05-21-2017, 08:54 AM
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Join Date: Sep 2010
Location: Olathe, KS
Posts: 2,885
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Quote:
Originally Posted by JDA_BTR
So the question is about the GAD27. How well does the voltage stabilizer feature work? Can it handle two GDU27 and GEA 24 powered up while starting the engine? Would it be best to have one GDU and the 24 only, and leave the PFD for the avionics master? I'm hoping someone with some experience in it can give a report on it....
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Hello JDA_BTR,
The GAD 27 keep alive power output works great to keep PFD1, GSU 25 #1, and GEA 24 #1 going while you start the engine.
Just wire the Power 2 input on the PFD/GSU/GEA to terminal 2 on TB273 and you are all set.
Thanks,
Steve
__________________
Garmin G3X Support
g3xpert@garmin.com
1-866-854-8433 - 7 to 7 Central Time M to F
Please email us for support instead of using Private Messaging due to the limitations of the latter.
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06-10-2018, 03:39 PM
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Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
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Hi All,
Is this "keep alive" power always hot, or does the line only become live once the battery voltage falls below XX volts? I say this because I have the situation were the EI Commander I want to power only has one power input, and it's current draw is next to nothing, so I was hoping to run it directly and continuously off the Keep Alive power coming out of the GAD27.
Cheers,
Tom.
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06-10-2018, 04:40 PM
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Join Date: Sep 2010
Location: Olathe, KS
Posts: 2,885
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Quote:
Originally Posted by tgmillso
Hi All,
Is this "keep alive" power always hot, or does the line only become live once the battery voltage falls below XX volts? I say this because I have the situation were the EI Commander I want to power only has one power input, and it's current draw is next to nothing, so I was hoping to run it directly and continuously off the Keep Alive power coming out of the GAD27.
Cheers,
Tom.
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Hello Tom,
The keep alive power is always present anytime the keep alive input power is present.
As long as you stay within the 3.5A maximum current budget, no problem connecting other devices like this.
Thanks,
Steve
__________________
Garmin G3X Support
g3xpert@garmin.com
1-866-854-8433 - 7 to 7 Central Time M to F
Please email us for support instead of using Private Messaging due to the limitations of the latter.
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06-10-2018, 06:19 PM
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Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
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Excellent news Steve. Thanks for the quick response.
Tom.
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06-28-2018, 08:49 PM
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Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
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Hi All,
Another question on this keep alive power, specifically regarding the grounds. I've just finished my avionics harness and was completing my power and ground checks, when I noticed that I had not included a second ground on the GDU 460.

The interesting thing is that although the GSU 25 has two power inputs also, it does not have two grounds.

I guess my question is, will the Keep Alive power work if I do not have the second ground installed on the GDU 460. I'm no electrical engineer, however I would think that if the primary ground is still in place, then the device shouldn't be fussy so long as it is getting power from its main supply or the Keep Alive power. As you can probably guess, I really don't want to be having to tear this completed harness apart.
Cheers,
Tom.
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06-29-2018, 07:58 AM
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Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
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Hi All,
I just spoke with the Garmin tech support line, and they said to check the resistance between the two ground pins on the GDU460 (also the GEA24 as this as two ground pins also). If I have continuity, or near zero ohms resistance, which they suspect will be the case, then the two pins are joined internally and subsequently I would not need the second ground wire. If this is not the case, then there is some type of switching that goes on when the voltage drops, and thus I will need to connect the second ground wire for the keep alive function to work. Fingers crossed it's option one.
Tom.
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