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Electrical issue=> I have symptoms but can't find the disease

Bastien

Well Known Member
For the last two flights I am having electrical issues on the transponder and radio noise with the right landing light…

The first time I experienced the transponder failure was last week in flight. The VP-X indicates “SHORT” and so the transponder line was shot down to preserve it.
I did a “RESET” on the transponder breaker through the Dynon skyveiw EMS page. It worked a few seconds and then indicated “SHORT”.

Today I tried to troubleshoot the problem on ground.

*With the battery ON and tranponder ON, everything is working well.
*With the battery ON, transponder ON and engine turning, everything is working well
*With the battery ON, transponder ON engine at idle RPM and alternator ON everything is working well.
*With the battery ON, transponder ON, engine turning over 1400RPM, alternator ON it fails (“SHORT” before it shorts, I read over 15A through the transponder on the VP-X page).
*With battery ON, alternator ON, engine turning without the transponder DB connector plugged in, I have no short circuit…

According to the Dynon, the alternator is working properly.

I removed the cowl and looked for a broken wire or something like that… Nothing
I plugged the “+12V” of my car to the alternator wire and ground to the ground. Start up the car and accelerate…. Nothing, transponder is working properly…

I did not remove the panel yet as it was a bit late in France and the temperature was getting below freezing.

I also have a symptom that is surely linked to the transponder failure. When I switch on the landing light (the right one) with the same conditions as above, I get a RX on the radio with a very high noise in the headset.

Ground problem?
Lose wire crimp?
Other?

I am getting out of ideas..


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May be two different problems.
My guess is higher vibration at higher powers is causing an intermittent short to show up. I would look very carefully at the power wire from the VPX to the transponder. Look especially where it passes over or near any metal. You're looking for a tiny cut in the insulation which can cause a short; or, at either end, a stray strand of bare copper that can touch where it doesn't belong. You could try to simulate the engine running by powering the transponder on, engine off, and then shake and move the wire a reasonable amount by hand, see if you can induce the short to appear.
Unfortunately one of the most likely places for a stray bare wire to exist is at the transponder connector. It will be difficult to access there.
 
Hi Bob,
Thank you very much for your answer. I thought about it but when alternator is OFF whatever the RPM is , transponder is working properly. I tried to simulate the engine running by moving the power wire from the VP-X to the transponder but nothing..
I will try it again when I'll be back at the hangar.

I am really thinking about the alternator.
Is it possible to have a leak of current from the alternator itself ?
If my ground isn't a ground anymore but is +12V, it would explain the radio noise and why my transponder fails isn't it?
 
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I think I'm with Bob on this one.......

The fault should be isolated to the power wiring between the VP/X and the transponder.

Since the build is probably too new to have worn through the wire insulation, the next likely culprit is a bad crimp job in one of the connectors, most likely the one at the transponder. It's real easy to splinter off a couple strands of wire and not notice it when crimping. If one of these strands hits and adjacent pin or wire, you've got a short.

If the alternator was shorted, you would be seeing all kinds of other symptoms (i.e. smoke being released from the wires)

The Vertical Power guys are usually pretty quick to assist if you post to their support site. if the short error is only showing for the transponder pin on the VP/X, the problem has to be on that line.

bob
 
Bob,
Thank you for your answer. I visually checked the transponder side crimp yesterday and did not see anything. I will have a closer look at it in few days and inspect the VP-X side.
As recommended, I will write to vertical power support.
 
A few items to check........

Visual inspection looking for a stray wire stand is like looking for a needle in a haystack.

With the power off, using a ohm meter from the power pin on the transponder connector, see if there is any continuity to ground.

Another test would be to put the transponder out of the tray or disconnect the connector with the power and ground. What are the systems then? The VP/X should show it as open, not shorted.

I assume that you did visually check the pins in the connector and the tray to make sure that none are bent.

You may also want to consider asking a friend to check. Sometimes these types of issues are too difficult to find and will turn out to be something dumb and simple. People tend to do things consistantly, so you may be overlooking some key detail that a fresh pair of eyes may pick up.

Just suggestions......

bob
 
I'd recommend a fresh set of eyes on the problem as Bob suggests. This is an unusual set of circumstances which should not correlate with each other. So to me anyway the answer is not clear.

There is no correlation between the alternator and transponder circuits internal to the VP-X that would cause a short like you describe. Just to be safe, check that the secondary alternator is set to 'none' in the configurator. This won't cause a short if set incorrectly, but it is one more thing to confirm.

I suspect the problem is in the wiring or maybe the transponder. Put a 5A fuse in line with the male test pins (that came with your wiring harness) and connect that to the battery. Then plug in the male test pin into the transponder terminal in the wiring harness connector. See what happens (does transponder come on?), even wiggle some wires around to see if it causes the fuse to blow.


The noise issue is likely related to how the landing lights are wired. Recommend contacting the light manufacturer for guidance.
 
I agree, most likely two problems. You did not say what type of landing lights you have. HD and high power LED's usually have switching circuits which can generate RF noise. If traditional incandescent lights then that would be unusual.
 
Electrical Issue

Don't forget that the culprit could be internal to the transponder. Could be something loose inside the unit which is stimulated by vibration and causing a high current condition. If you had access to such, I would also put a dummy RF load on the transponder RF connection (antenna) to make certain that the RF output amp stage(s) aren't seeing a bad RF circuit to the antenna and thereby pulling a lot of current until the EMS trips the breaker.

Good luck!
 
Just a thought, but you may want to check output of alternator with a meter set to read ac. May have a diode going bad putting out to much ac and the transponder may be more sensitive to it.

Jay
 
Above two suggestions are easy to check. Just pull the transponder out and repeat the test with everything on and running. If the problem is still there then it is not the transponder.
 
check diodes across starter and master solonoid

Ask me how I know... :mad:we fried an alternator even though I didn't have a VP power distribution box.
 
Thank you very much to all for the support,
I will work on the airplane to do all the suggested tests this weekend.
When the problem will be identified, I will report it.

I plan to travel with the plane (or my "resume") on March 15 for an foreign engineering internship interview (weather permitting of course)... I hope the problem will be found until there.

PS: Landing lights are Aeroleds MicroSun.
 
noise / short

Is the noise only when the landing lights are on? If the noise goes away when the transponder is shut down by the vpx (landing lights are on) the short must be on the transponder power circuit assuming that only the transponder is fed by that power circuit.

An intermittent short that appears with vibration can cause noise, and an additional electrical load with the landing lights can decrease the filtering effect of the main battery.

Someone stated that the airplane is too new to have wires worn through, but if those wires pass accross a sharp surface, and the wire was pressed onto that sharp edge in the process of work on the airplane it could still have a problem. If the tansponder wire is traceable, look for any sharp edges it passes and concentrate on that area.

Wiggling wires can sometimes isolate a problem, sometimes it can reposition wires so the short is no longer in contact.

Sometimes it is more time efficient just to replace the power wire from source to destination.
 
Is the noise only when the landing lights are on? If the noise goes away when the transponder is shut down by the vpx (landing lights are on) the short must be on the transponder power circuit assuming that only the transponder is fed by that power circuit.

Hi Larry,
Thank you for your message.The noise I have in the headset is when the right landing light is ON, the noise seems to come from the radio as I have the RX indicated on it. My radio harness is also on the right side. Even if I payed attention during wiring keeping a safe distance between the landing light wire/radio wire it seems that this is the reason of the noise. I have approx 70hrs on the plane and the noise issue started a week ago (same time as the transponder "SHORT" .It seems that the two symptoms are independent).

I will inspect the transponder wire this weekend, the access is easy and the wire is pretty short so I will directly try an other wire to see if it really comes from it.
I will also do all the suggested tests to solve the problem.
 
Hi everybody,
I worked on the airplane today and did the tests suggested above :

Replace VP-X to transponder wire ==> Transponder still fails when battery/alternator ON and engine running

On the VP-X, the second alternator option was already set on "None".

I tried an other pin on the VP-X==> Transponder still fails when battery/alternator ON and engine running

The problem is there only when I switch On the alternator...

I noticed that when I move the transponder (which is mounted on the rear panel door that many RV8er build), whith 7000 GND (French VFR code and ground mode), I have an current fluctuation (from 0,1/0,2 to 2 Amps).

Alternator (Plane power internally regulated) output voltage is 14,9V (too high??)

Maybe it's the transponder :confused:

I wish you a RV filled Weekend.
 
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Yes 14.9 volts is too high. Check with a second voltmeter first.

Not to hijack the thread, but...what is the allowable range? I usually see 14.4-14.6, with a 6 or 7 amp draw after starting, decreasing to 1 amp in cruise...

Is that voltage too high? If so, how would one adjust it (Plane Power alternator)?

Just curious...
 
Problem seems to be solved

TRIG has sent me a replacement unit friday.
I flew 8.5 trouble-free hours with the plane this week-end.

TRIG avionics support was outstanding, sending me a replacement unit for free in less than two days.
Special thanks to VAF members for the answers you brought me.

Fly Safe
 
Xpndr Issue

So it was the transponder then. Correct?
Does that mean I win the prize? ;)

Glad you got it straightened out. Good for you sir.
 
I would be please to say you win the prize but problem came back once on a flight few days ago...:mad:
I have been contacted by a RV10 builder who had the same problem and it seems that the problem is related to an internal broken wire of the alternator that cause fluctuating amps coming out of it. He reported that the VP-X have some difficulties to deal with fluctuating amps.
I also find somebody who reported the same issue few days ago on VAF http://www.vansairforce.com/community/showthread.php?t=97723

I am contacting PlanePower to see directly with them what it would be possible to do.
 
it seems that the problem is related to an internal broken wire of the alternator that cause fluctuating amps coming out of it. He reported that the VP-X have some difficulties to deal with fluctuating amps.

Bastien, Glad you are making progress.

I can understand why it would seem that way, but the VP-X is not a line conditioner or boost regulator. It is accurately reporting the fluctuations in current caused by the broken alternator, as it should. It appears in both cases the VP-X is providing valuable information to help you diagnose the problem. Further, I understand the VP-X was working flawlessly in spite of the dirty electrical system.

My guess is you would have had a much harder time figuring this out with old-fashion wiring! Please let us know how this progresses.
 
Ditto

I agree with Marc. Without the reporting capability/information from the VP-X, I probably would have been troubleshooting my problem a lot longer. I'm the RV-10 guy Bastien references.

http://www.vansairforce.com/community/showthread.php?t=97723

One other lesson I learned from this difficult troubleshooting situation: it's tempting (and probably normal) to feel pretty sure that you "know" what the problem is early on, and a tendency to sort of jump on one idea to the exclusion of others. That might mean a component, software, wiring, whatever. It was much more productive to avoid the temptation to point the finger at one component or another but instead contact the excellent vendors we have and solicit their ideas and input. They are all really willing to help - and did - but I suspect if I was calling and ranting and irate I might have gotten different service. I was pretty sure my problem was the VP-X early on because I didn't understand my system (or the VP-X) as well as I should. I was dead wrong; in fact, the VP-X helped me figure it out sooner, and did what it was supposed to do in protecting my system. Looks like Bastien is doing the right things in right ways. I'm sure most of us would do this, but I know I definitely felt the temptation to jump on what I was pretty sure was the problem early on.
 
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