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Gad27 Voltage Stabilizer

JDA_BTR

Well Known Member
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!
 
Does 122 reads and no replies mean that nobody uses this feature? That is an answer all in itself I suppose....
 
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.
 
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/community/showthread.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.
 
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....

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.

RxQeNYbLGMa7Z8aHb3fpF1w_tr3H2NoACnfVxxaQL7pePMWoczLEmnJg8NR3a3po88TQOl2rOHXjo0JNI6TGL_uyflzWFol1BS6xJcx1HSectlhNYJx3w5W15ynyCPHLJ8r3cxj_LKOPUG8aEtetsvYwrnZwjegVxnkgTFqiv1Hfqnw53STBdKdslTk_4xk8dQeFYYDqXWNw22uDqGuBNhlP95KQCTFyQ59wioHlcPo8B9rs_WX8-EfJvLa5NQgw_RSVUvY4VaDv_fjiW4kO33h6sbkW4_oYCv91YG3_Tw1gKTHp9Dc_8T0BFH3B5-0rnqf4asJQYmDZWrQvyeT50D10trabBvvaU3NfeKFDPc39Q6n2lSVNn51t9dTCbcmOnp2qcWFKT49Oodr8rPh8CHrA7RgcBbINHfOCdtYTs_w9AJoSW-yKhg-7BocCg8YHaCwbOSAnqrvR9DO7oFPTgTCd4uNSADYDjGoeZR6S-2sIg1_agzF_1FgmeejsgLkkRuihV-qq1N0doftfRCUa7S3E3R5CHWjmvfdo3jb1MkmWqmOPtr76_CIiIdByi9sL1OhNsiI6BLOHfL8u1iOwNDkXUquzvVqAYj6hTEcAfBZChALfPjPo=w1057-h179-no


Thanks,
Steve
 
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.
 
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.

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
 
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.
jsczu9.jpg

The interesting thing is that although the GSU 25 has two power inputs also, it does not have two grounds.
2aaj4ll.jpg

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.
 
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.
 
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.

Hello Tom,

Ground pins 15,16 on the GDU 460 (and pins 6,9 on the GEA 24) are connected together to the same ground inside the unit.

When you have dual power source inputs to the display, it is ideal to have dual ground wires so in the unlikely loss of one of the ground wires you don't lose both power sources, but the display will work just fine with a single ground wire as long as the power ground is common to both power sources.

Thanks,
Steve
 
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Keep Alive Setup

Does the GAD 27 keep alive need to be powered from a separate battery? I'm struggling to understand how it can maintain voltage if the entire battery system is being pulled down by the starter. Big capacitors?
 
Does the GAD 27 keep alive need to be powered from a separate battery? I'm struggling to understand how it can maintain voltage if the entire battery system is being pulled down by the starter. Big capacitors?

Hello Michael,

No, the GAD 27 does not need to be powered from a separate battery.

The GAD 27 is designed to be connected to the same primary battery bus that is being used to start the engine. Even though the act of starting the engine may temporarily draw the bus voltage down below where some devices can continue to operate, the GAD 27 will condition that power and provide 12Vdc at up to 3.5A to several devices which you want to keep in operation through engine start.

For example, a common installation would be to wire primary power to power input 1 on PFD1, GSU 25, GEA 24, and the GAD 27. Next, the keep alive power output from the GAD 27 may be wired to the power 2 inputs on the PFD1 primary display, GSU 25 ADAHRS, and GEA 24 engine monitor.

When you turn on your primary bus, the PFD, ADAHRS, and engine monitor can come up running, and then when you start your engine, these devices will continue to run (automatically switch to using power input 2) when the voltage dips on power input 1.

This allows your PFD to stay running with engine information, your ADAHRS to either continue aligning or stay aligned, and allows your engine gauges to all operate before, during, and after engine start.

Best of all, it does all of this without a battery, so you don't have the long term maintenance requirements associated with a battery.

Let us know if you have additional questions.

Thanks,
Steve
 
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Endurance Bus

I'm organizing my endurance and main busses, and a thought occurred to me. Given the following setup...

PFD1, GEA and GSU A/C Power 1 <--> Main Bus
GAD 27 A/C Power 1 <--> Endurance Bus
PFD1, GEA and GSU A/C Power 2 <--> GAD 27 Keep Alive

If I kill power to the Main and run only on the Endurance, will the GAD 27 continue powering the devices connected to the Keep Alive. If it works this way, it would basically be an extension of the endurance bus.

Let us know if you have additional questions

I really appreciate the continuing support of the g3xpert team!
 
I'm organizing my endurance and main busses, and a thought occurred to me. Given the following setup...

PFD1, GEA and GSU A/C Power 1 <--> Main Bus
GAD 27 A/C Power 1 <--> Endurance Bus
PFD1, GEA and GSU A/C Power 2 <--> GAD 27 Keep Alive

If I kill power to the Main and run only on the Endurance, will the GAD 27 continue powering the devices connected to the Keep Alive. If it works this way, it would basically be an extension of the endurance bus.

I really appreciate the continuing support of the g3xpert team!

Hello Michael,

You are very welcome.

Yes, anytime you apply power to the GAD 27 Keep Alive power input on pin 1 of terminal block TB273, the devices connected to pin 2 on TB273 will receive conditioned power (all the time, not just during engine start).

The computer side of the GAD 27 even receives diode isolated conditioned power internally from the Keep Alive output, so the GAD 27 also protects itself from reset during engine start by using the conditioned power it sources.

Thanks,
Steve
 
Hello Michael,

No, the GAD 27 does not need to be powered from a separate battery.

The GAD 27 is designed to be connected to the same primary battery bus that is being used to start the engine. Even though the act of starting the engine may temporarily draw the bus voltage down below where some devices can continue to operate, the GAD 27 will condition that power and provide 12Vdc at up to 3.5A to several devices which you want to keep in operation through engine start.
...
Let us know if you have additional questions.

Thanks,
Steve

Hi Steve,
You answered Michael's question by again stating what the GAD 27 does, but he asked HOW it works - how does it supply 3.5A of current if it doesn't use a 2nd battery? As pilots and builders we're supposed to understand how our electrical system works, but I can't find an explanation of how this mysterious power appears. Is it stored somewhere in the GAD 27? How long does it last (e.g. if the engine is flooded and requires a lot of cranking)?
 
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