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  #1  
Old 07-18-2016, 11:30 PM
FitzRX7 FitzRX7 is offline
 
Join Date: Jan 2013
Location: FL
Posts: 103
Default IFR RV-4 Schematic

Just finished wiring my RV-4 panel up, Garmin G3X everything. GPS-only IFR, redundant on almost all fronts, I think I have all my bases covered except dual engines.

Wanted to see what the masses thought about how we ended up designing it. I had a lot of help from some very smart people, many many thanks are in order. Especially Paige Hoffart and Jim Beyer, lots of their brain-bytes when into making this reality.

Some neat things on this are:
-$30 backup battery system instead of >$300 backup battery system.

-$5 bluetooth audio + $10 dual comm relay + built-in intercom instead of >$1000 audio panel, and also takes up way less space which was very important to me.

-$5 circuit designed by Paige to enable automatic remote on-off functionality of GDL39 with battery pack. Folks familiar with the battery pack know that it turns on when power is applied but doesn't turn off unless the power button is pressed, or the remote on/off wire is grounded and then ungrounded once power is applied. This automates that process.


I just can't figure out how to get it to post an uncompressed image, so here's the full Res on Google Photos

Questions/comments/thoughts?

Jon
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  #2  
Old 07-19-2016, 12:23 AM
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flightlogic flightlogic is offline
 
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Location: Prescott, AZ
Posts: 1,674
Default schematic

I have wondered about the GDL39 power down method. In my case, I took the battery off. The Garmin display will run on batteries as will the GRT EFIS. I might re-think this pwr down circuit you came up with.
Anyway, it looks good at first glance. Well designed, now practice some approaches to minimums. (personal mins !!!)
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  #3  
Old 07-19-2016, 12:25 AM
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flightlogic flightlogic is offline
 
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BTW... with that much work put in... you might add an LED that shows the starter is drawing current. The relay is 18th century after all....
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  #4  
Old 07-19-2016, 02:52 AM
FitzRX7 FitzRX7 is offline
 
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Location: FL
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Quote:
Originally Posted by flightlogic View Post
BTW... with that much work put in... you might add an LED that shows the starter is drawing current. The relay is 18th century after all....
I have thought about that, but what I'd really like to do is power the starter switch on the stick from the oil pressure switch, so it only works when there is no oil pressure. But I need to look up the current capability of the oil switch, probably would have to run another relay which I was trying to avoid.

Jon
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  #5  
Old 07-19-2016, 06:38 AM
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Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
Posts: 6,345
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A few observations:
If com 1 fails, com 2 won't work?
Com 1 power?
Aux battery won't charge very well with a 25 ohm resistor.
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Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 2000+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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  #6  
Old 07-19-2016, 08:33 AM
FitzRX7 FitzRX7 is offline
 
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Location: FL
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Quote:
Originally Posted by Walt View Post
A few observations:
If com 1 fails, com 2 won't work?
Com 1 power?
Aux battery won't charge very well with a 25 ohm resistor.
I hadn't thought of that, but yeah with Com1 failed I lose both coms, intercom, and alert tones! (But same thing happens if you have an audio panel fail I think) Guess that's what the 7600 squawk code is for!

Com1 (GTR 200) is powered by the emer bus through the aux battery. That way if the contactor or main bus or main battery fails it still has power.

Aux battery does have a reduced charge voltage with the diode voltage drop (and very little with the resistor at low current if my JV level electrical understanding is correct), but I adjusted the volt reg up to the PC680 desired charge of 14.7, so the voltage at the aux bat (PS-1250) should be close to 14v, which should work pretty good. I check the charge condition at startup with the emer bus voltage plus .5 for the diode drop.

Great comments! Keep em coming!

Jon
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  #7  
Old 07-19-2016, 10:10 AM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
Posts: 3,234
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The diodes drop between 0.5 and 1 volt, depending on the type. That might not be desirable when the alternator fails and the batteries are slowly being discharged. Bob Nuckolls electrical diagrams have the diode located so that it conducts alternator current pushed by 14+ volts. At that voltage, diode voltage drop is not important.
I suggest that only one diode be used and located where the avionics circuit breaker is. In fact, that circuit breaker is an unnecessary failure point.
Connect the aux battery to the avionics bus without an additional battery or resistor.
Engine-starter voltage-spike is an old wives tale. The only danger is voltage sag during starting. The aux battery will prevent that.
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  #8  
Old 07-19-2016, 07:49 PM
PaigeHoffart PaigeHoffart is offline
 
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Quote:
Originally Posted by Walt View Post
A few observations:
Aux battery won't charge very well with a 25 ohm resistor.
I believe it is a 2.5 ohm resistor

Paige
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  #9  
Old 07-19-2016, 07:56 PM
PaigeHoffart PaigeHoffart is offline
 
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Quote:
Originally Posted by Mich48041 View Post
The diodes drop between 0.5 and 1 volt, depending on the type. That might not be desirable when the alternator fails and the batteries are slowly being discharged. Bob Nuckolls electrical diagrams have the diode located so that it conducts alternator current pushed by 14+ volts. At that voltage, diode voltage drop is not important.
I suggest that only one diode be used and located where the avionics circuit breaker is. In fact, that circuit breaker is an unnecessary failure point.
Connect the aux battery to the avionics bus without an additional battery or resistor.
You can do that, but you will easily exceed the max charge current of the battery if you ever allow it to discharge (tried it once, the smell will get your attention). With a 2.5 ohm resistor, and basically no load, the standby battery will be held pretty close to bus voltage. We also used oversized Schottky diodes to minimize the drop.

Paige

Last edited by PaigeHoffart : 07-19-2016 at 07:59 PM.
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  #10  
Old 07-19-2016, 07:59 PM
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Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
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Quote:
Originally Posted by FitzRX7 View Post
I hadn't thought of that, but yeah with Com1 failed I lose both coms, intercom, and alert tones! (But same thing happens if you have an audio panel fail I think) Guess that's what the 7600 squawk code is for!

Com1 (GTR 200) is powered by the emer bus through the aux battery. That way if the contactor or main bus or main battery fails it still has power.

Aux battery does have a reduced charge voltage with the diode voltage drop (and very little with the resistor at low current if my JV level electrical understanding is correct), but I adjusted the volt reg up to the PC680 desired charge of 14.7, so the voltage at the aux bat (PS-1250) should be close to 14v, which should work pretty good. I check the charge condition at startup with the emer bus voltage plus .5 for the diode drop.

Great comments! Keep em coming!

Jon
If your audio panel fails the typical fail safe mode is direct connection to com 1 which will continue operate normally.

Your diode during transmit will be handling up to 10 amps.
__________________
Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 2000+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154

Last edited by Walt : 07-19-2016 at 08:02 PM.
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