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Camillo

Well Known Member
Hallo.
I'm flying since 2011 without issues.
Three weeks ago I moved my battery aft for CG reasons. Airplane is now a joy to land. I locally grounded the battery with a strap connected to the center aluminium angle and a couple of other wires (see my www.rv9.it site, flight! page - all bottom - for photos).

I had a couple of flights with no issues with the new configuration.

Today the first flight was OK. During lunch, a storm passed.
After switching on engine, the alternator field breaker popped. I tried to put it again in but popped one more time. So I did not touch it any more. No problem, I thaught. I have a 25' flight to do. Will go with battery only.

After a while, radios got stuck. I couldn't hear my partner and he couldn't hear me. Our friends told us later that everything we were saying was broadcasted since we had trigger on. But we hadn't. I believe once I pulled the radio PTT something happened and it remained stuck. Also we could hear some noise in the headsets even with radios and audio panel off. That is strange.

I tried to switch off the GMA audio panel, the GNS430W and the SL40 radios and again on. Nothing to do. All stuck again. Actually, when I first switched on the audio panel, the COM1 button blinked (that means PTT is engaged, I believe) and then when I also switched on radios, we could hear a lot of noise in the radio. So we shut them off again.

Just before landing, I tried to push the alternator field in and it came alive. I also tried again with radios, but the same issue occured.

Once on ground, I removed the seat floors and the cowl. All in order. I switched on battery master and avionic master, and radios worked properly.

I can't imagine what happened and if this can happen again. Next friday I will depart for Greece and it would be a shame if I will have to abort my trip.

My only thaught is the storm made wet some part under the cowl OR the avionic ground return via the airplane frame is not enough (I monitored battery bus voltage and it was 12.5-12.7; maybe a ground bottle-neck effect can't be detected from voltage...). I can't imagine other solutions.

Do you have any idea?
Thanks.
Camillo
 
Camillo,

These are all things you probably thought of, but check your radio stack for water migration. Sounds like perhaps you had multiple problems, perhaps some water in your voltage regulator that caused your field CB to pop; perhaps some water in your radio connectors that caused your PTT pin to ground out. It doesn't sound like one single thing, just a lot of moisture, and once you dried everything out, all was well. If you investigate and find water between your radios or around your voltage regulator, you might consider building rain gutters over your radios to shed water that might find its way inside your airplane. I doubt you will have the problem while flying through rain, it's probably more likely to happen when you leave the airplane outside during a rain storm.

Hope this helps! By the way, I became extremely hungry after perusing your photos! Wow! Great looking dishes! I miss my flying in Italy, especially around Albenga and Genoa.
 
Thank-you, Pat.
It may be moisture. More probably on the regulator, which is on the engine side of the firewall. Difficult to understand how water could have travelled inside and reach ptt pin. However, it may happen.
I may use the ebus power wire (6 awg) to make a temporary dedicated ground from battery to avionic ground bar, just to be sure to not riun my travel to Greece. And then investigate further once in Italy again.
Regarding cooking, ehi, isn't that also building? Building made to last a few hours. What a waste... ;-)
 
I have seen low bus voltage cause avionics to act strange/unpredictably, if the proper voltage was restored and everything worked good that's what I would suspect.
 
Camillo said:
Thank-you, Pat.

I may use the ebus power wire (6 awg) to make a temporary dedicated ground from battery to avionic ground bar, just to be sure to not riun my travel to Greece. And then investigate further once in Italy again.
Click to expand...

Camillo, I agree, it's definitely a good idea to run a ground from your battery to a dedicated ground bus. You may want to make this permanent at some point, and if you do, it's probably a good idea to remove your local ground near the battery to avoid ground loops. Have a great trip and let us know how the electrical system behaves on the trip. :)
 
I placed a 8awg from the battery to the ground tab.
Hope it is enough.
Once in Flight, all worked well, even if I could head some creeks in the headsets and even if radios seemed sensitive on ground (light rough rx signal). Once at 2.000 all worked without problems. Maybe I will have to eliminate the second ground connection, the one locally attached to the longeron, as Pat suggested.
 
An 8awg wire is not really adequate for starter currents if that is your only ground.
 
Camillo, yes, if you are going to make your new ground wire permanent, you are going to need at least a 4 AWG, 2 AWG optimum, with a rear-mounted battery. The problem is the voltage drop during engine starting amps across a rather lengthy ground wire. This is one of the drawbacks of a rear-mounted battery. Not a major problem, though, and as in all things aviation, everything is a compromise. So before you disconnect your local ground permanently, find a way to run a 2 or 4 AWG wire to your ground bus up front. Consider that during a start you are drawing over 200 amps from the battery and because of the length of your new ground wire, you will get a significant voltage drop, which could cause problems on a cold winter's day start. On the other hand, do you really want 200 amps running all over your airframe? Probably not.

Your plan sounds good for now and should be fine for your trip. You could try a little experiment: with your airplane on the ramp, disconnect your local ground and see if your radio noise gets any better. Just don't try to start your engine without the local ground, of course.

So when you get some time, consider making a permanent modification, I think your radio noise will probably be eliminated, too.
 
That is a good advice.
My collegue borrowed me his portable radio.
Once back in Italy, I will try to disconnect the local ground.
Thanks both.
Camillo
 
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