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07-19-2016, 07:04 PM
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Join Date: Jun 2005
Posts: 375
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Quote:
Originally Posted by Walt
A few observations:
If com 1 fails, com 2 won't work?.
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Well, you won't be able to hear comm 2 
On my plane, I used an audio mixer with a DPDT toggle to bypass. Other options are a relay, or second set of comm jacks.
Paige
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07-19-2016, 07:58 PM
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Join Date: Jan 2013
Location: FL
Posts: 100
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Quote:
Originally Posted by Walt
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.
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I didn't know that about audio panels. So to lose coms with one of those Com1 and then audio panel have to fail. I'm fine with just using 7600 if my #1 radio fails, same thing that single com aircraft would have to do.
Yes, the big diode can handle that. Neat thing about the GTR 200 is in one of the setup screens it'll show you how manny amps it's drawing, 3.5A is the most I've seen from it. Now with the GDU/GAD/GEA on the Emer bus and without the avionics bus on, yes It could be close to 10A. In normal operation though, the avionics bus voltage will be slightly higher (due to the schotty diode on the Emer bus) and with the internal diodes on the G3X components they should use the higher voltage input, leaving the Emer bus to just power the GTR 200.
Jon
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07-20-2016, 04:41 AM
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Join Date: Mar 2008
Location: houston, texas
Posts: 900
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Quote:
Originally Posted by FitzRX7
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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I would be concerned with getting a good connection to energize the starter if you had a situation were you needed to make a midair restart. It does happen, sometimes when you least want it to. Hope this helps. R.E.A. III #80888
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07-20-2016, 05:05 AM
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Join Date: Jan 2013
Location: FL
Posts: 100
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Quote:
Originally Posted by Robert Anglin
I would be concerned with getting a good connection to energize the starter if you had a situation were you needed to make a midair restart. It does happen, sometimes when you least want it to. Hope this helps. R.E.A. III #80888
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Since it's all together and flying, I'm inclined to just leave it be. Don't touch the green button after start is easy enough, and there's just one other person that flies the plane except me. The Infinity grip buttons take quite a bit of pressure to activate, that helps too.
I personally don't like the systems where you have to turn one mag off to get the starter to work, I don't think I'd remeber to do that under duress.
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07-20-2016, 06:17 AM
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Join Date: Jan 2016
Location: Granville, Ohio
Posts: 13
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25 ohm resistor
Don't understand the purpose of the 25 ohm resistor? Even if it is a 2.5 ohm resistor, it doesn't make sense. Under high current draw, it will get hot (if it is 2.5) and if it is 25, then it will limit the battery charging as mentioned before.
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07-20-2016, 06:53 AM
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Join Date: Jan 2013
Location: FL
Posts: 100
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Quote:
Originally Posted by acehiggy
Don't understand the purpose of the 25 ohm resistor? Even if it is a 2.5 ohm resistor, it doesn't make sense. Under high current draw, it will get hot (if it is 2.5) and if it is 25, then it will limit the battery charging as mentioned before.
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It's a 2.5 Ohm, misprint on my part that will be corrected shortly.
Quote:
Originally Posted by PaigeHoffart
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.
Paige
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Paige is the big brains on this one, but it's my understanding that the resistor limits the current into the Emer battery if it's significantly discharged, preventing it from popping. It is a big resistor, 50W rated with heat sinks on the case mounted to aluminum.
Also, the only current going through the resistor is for charging the aux battery. The bus current only "sees" one diode and goes straight to the emer bus.
Jon
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07-20-2016, 08:39 AM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,070
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The aux battery charging current depends on the battery voltage. If the battery voltage is say 10 volts, then 14.5V minus 10V = 4.5 volts dropped across the resistor. 4.5V x 4.5V divided by 2.5 ohms = 8 watts that the resistor needs to dissipate. The battery voltage would have to be less than 3.3 volts before the wattage rating of the 50 watt resistor would be exceeded. No worry about the resistor getting hot.
__________________
Joe Gores
RV-12 Flying
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07-20-2016, 06:11 PM
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Join Date: Jan 2016
Location: Granville, Ohio
Posts: 13
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Don't understand why the emergency battery would be much different voltage than the main battery since it would be charging all the time (when engine running) like the main battery. The main battery doesn't use a current limiting resistor so why should the backup? I would take out the one diode and resistor on the emergency battery ... don't think it is needed. With that said, it won't hurt anything to leave it in either.
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07-20-2016, 08:08 PM
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Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,435
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What are the pyro devices?
Dave
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07-20-2016, 08:42 PM
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Join Date: Jun 2005
Posts: 375
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Quote:
Originally Posted by acehiggy
Don't understand why the emergency battery would be much different voltage than the main battery since it would be charging all the time (when engine running) like the main battery. The main battery doesn't use a current limiting resistor so why should the backup? I would take out the one diode and resistor on the emergency battery ... don't think it is needed. With that said, it won't hurt anything to leave it in either.
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Well, if you ever lose your alternator, the battery will discharge. When you fix your alternator, you will be applying about 14V to the batteries. The internal resistance of the backup battery will not limit the current sufficiently (max charge current is only an amp or two for a 5AH battery) A full size battery has no problem absorbing 20 or 30 amps of charging current, a 5AH will vent and destroy itself. As I said earlier, I've seen it happen.
Using a current limiting resistor on small backup batteries isn't new. You can search the archives. I believe Brantel, Walt, and perhaps Ironflight have used similar systems.
Paige
Last edited by PaigeHoffart : 07-20-2016 at 08:59 PM.
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