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Transient Short Indicator -- Dynon, EarthX, VP-X

spatsch

Well Known Member
Need some help from the brain trust.

First my setup.

I got a standard alternator (for IO360 M1B from Vans) an EarthX battery a VP-X pro and a Dynon (including there transponder) as well as a Garmin SL40 radio.

This setup has been working without any issues for close to 4 years now.

So about a week ago the Dynon gave me a warning that I had a short on my transponder which is mounted in the back of my RV-8 with the VP-X in the front.

Couldn't reproduce it on the ground no matter what I tried. As those things usually don't fix themselves I took the panels off and checked the connectors (took them apart) on both side as well as the wire. Couldn't find anything. (checked it twice ...).

So I put everything back together and did another testflight. Worked all fine on the ground but when I was up in the air the transponder indicated short on the VP-X again.

Now I couldn't even reset the short via a Dynon on the VP-X. Then I noticed one thing. If I switched the alternator off I could reset the transponder and it would not trip again.

When I switched the alternator back on not only the transponder showed a short, the radio which has a 100% diverse wiring path showed one too.

When I experimented a bit more I noticed that when the current from the alternator is low there are no issues but if it's high (like the first few minutes after you start the engine and it recharges the battery) there is an issue.

So at this point I am inclined to believe there is no real short and the problem is either with the alternator, the VP-X or the ErathX. Here the 3 theories:

1. VP-X is broken (I have a request in with VP-X support to see what they think).
2. The Alternator is somehow broken and causes the VP-X to be confused triggering there short protection.
3. The protection circuit on the EarthX is somehow broken causing the alternator to cause spikes which confuses the VP-X

Question is what to do next?

Thx

Oliver
 
Replacing the VP-X is not the solution.

I have a similar setup, except mine is a G3X. What CB value are you using for the transponder, what is the draw for the transponder, and is it the only device on the circuit? What gauge is the wiring to the transponder? How many power leads are there for the transponder? (Mine has two, but are fed from the same circuit atm.) Is there any correlation between the circuit tripping and the ack reply by the transponder? What is the ammeter telling you when the see the ack reply? Are you seeing any voltage spikes? What do the Dynon logs say? Have you checked the transponder antenna and cabling? I always check everything, even tangential stuff when I troubleshooting just to get a baseline.

Do you have a spare alternator you can swap in?


Good luck.
 
Last edited:
Replacing the VP-X is not the solution.

I have a similar setup, except mine is a G3X. What CB value are you using for the transponder, what is the draw for the transponder, and is it the only device on the circuit? What gauge is the wiring to the transponder? How many power leads are there for the transponder? (Mine has two, but are fed from the same circuit atm.) Is there any correlation between the circuit tripping and the ack reply by the transponder? What is the ammeter telling you when the see the ack reply? Are you seeing any voltage spikes? What do the Dynon logs say? Have you checked the transponder antenna and cabling? I always check everything, even tangential stuff when I troubleshooting just to get a baseline.

Do you have a spare alternator you can swap in?


Good luck.

Couple of answers. I am using:

a Dynon SV-XPNDR-261

http://www.dynonavionics.com/mode-s-transponders.php

with whatever setting Dynon configures it by default.

It's the only device on the circuit. Wire is 18G with a single lead. Breaker is set to 3A based on Dynon install guide it's on a 5A VP-X port.

I did check the trasnsponder cabling to the Dynon as well as the power leads (multiple times). Didn't check the antenna cable but it's about 1 foot long entirely visible and I didn't see any external damage. Will add that to my list.

Typical current << 0.5A . Don't recall what the spikes are during ACK replies and if that correlates. Something else to check.

Now one thing is that it worked flawless for 4 years. So something changed recently and I didn't change anything ... .

I don't have voltage spikes tripping the VP-X but that doesn't mean there aren't any... . They could be to short to trip the VP-X. I am wondering actually if that is what's going on but I don't have the correct instrument to measure those... .

Good tip with the Dynon logs. I didn't even think about those... . Wonder if the VP-X has any logs too.

I don't have a spare alternator will see if I can borrow one at the airport.

Thx

Oliver
p.s. and yes replacing the VP-X it is not an option... . There are so many benefits to this setup... . It's like saying to somebody who's fuel injector is acting up why don't you fly a glider ... . Never had engine problems while flying those ... .
 
Couple of answers. I am using:

a Dynon SV-XPNDR-261

http://www.dynonavionics.com/mode-s-transponders.php

with whatever setting Dynon configures it by default.

It's the only device on the circuit. Wire is 18G with a single lead. Breaker is set to 3A based on Dynon install guide it's on a 5A VP-X port.

I did check the trasnsponder cabling to the Dynon as well as the power leads (multiple times). Didn't check the antenna cable but it's about 1 foot long entirely visible and I didn't see any external damage. Will add that to my list.

Typical current << 0.5A . Don't recall what the spikes are during ACK replies and if that correlates. Something else to check.

Now one thing is that it worked flawless for 4 years. So something changed recently and I didn't change anything ... .

I don't have voltage spikes tripping the VP-X but that doesn't mean there aren't any... . They could be to short to trip the VP-X. I am wondering actually if that is what's going on but I don't have the correct instrument to measure those... .

Good tip with the Dynon logs. I didn't even think about those... . Wonder if the VP-X has any logs too.

I don't have a spare alternator will see if I can borrow one at the airport.

Thx

Oliver
p.s. and yes replacing the VP-X it is not an option... . There are so many benefits to this setup... . It's like saying to somebody who's fuel injector is acting up why don't you fly a glider ... . Never had engine problems while flying those ... .

You might want to check with Dynon to see if they have any history with their transponder and the VP-X. I know my EI vendor specifically said to "oversize" (over value) the VP-X ECB, even though the EI draws very little.
Apparently quick transients in the EI system could cause the VP-X to trip - not good for an ignition system, ahem. You *might* be able to uprate the circuit to 5A and test that out without damaging the 18AWG wiring.

I understand that this issue recently began after 4 years of trouble-free ops - that's why I suggested to swap the alt as an experiment since you noticed a difference with the alt on vs. off.

Good luck.
 
No 2 - Voltage regulator triggering OV protection in the VPX. Swap out the VR/Alt assembly and test
 
Yes the alternator is on the top of my list too. So will try that and see what happens.

Just to be clear though it doesn't trigger the over voltage on the VP-X it triggers the short on the transponder circuit.

Oliver
 
Transponders are 250 watt+ transmitters. 250W/14V=17.8 amps. Duration is very, very short, so you can get away with the recommended *circuit breaker*, which is typically very slow acting. The VPX's current detection time constant is unknown by anyone out here in the real world.

Just something to chew on....
 
Transponders are 250 watt+ transmitters. 250W/14V=17.8 amps. Duration is very, very short, so you can get away with the recommended *circuit breaker*, which is typically very slow acting. The VPX's current detection time constant is unknown by anyone out here in the real world.

Just something to chew on....

Interesting. Time is 3ms.

I would totally go for this explanation if they system hadn't worked just fine for 4 years... . So why now ... .

Thx

Oliver
 
If there is a high resistance connection, avionics with a switching power supply will draw more current to compensate.
 
Plus component tolerance drift in the vpx and/or the transponder. None of us have any way of knowing how close to the edge the vpx was operating for those years.
 
Plus component tolerance drift in the vpx and/or the transponder. None of us have any way of knowing how close to the edge the vpx was operating for those years.

OK you convinced me. So I figured I will perform the following tasks in that order when I head back out to the airport:

1. Reproduce the fault and fault behavior -- make sure I didn't overlook something I should have noticed or noticed something that was a coincidence leading me in the wrong direction.
2. Check the Alternator wires and belt tension and general condition. -- easy to do and most people which responded public or private were voting for the alternator.
2. Increase fuse limit from 3 to 5 A on the VP-X. This would be the easiest fix as nothing is really broken... . Components just drifted a bit which is normal.
3. Replace the EarthX with my old battery. I got some private communication that indicates that the EarthX protective circuit could cause issues and it's easy to do as I still have the old battery takes 5min to switch.
4. Replace alternator -- I don't have a spare one so unless I find one I have to spend some $$. That's why I ranked it last even though most people are rooting for that one ... .

Thx

Oliver
 
If your efis has data logging, look at the system voltage track over the period you've been having the overcurrent notices. If the alternator is going out of spec, you should see it in the history, even if the alarm set points are wide enough to hide it in real time.

If it were my system and everything is *functioning* correctly (voltage within limits, xponder works properly), I'd be betting on instrumentation error over any actual defects in the system.

Do you get to set the 'trip point' in that vpx circuit yourself? If so, how about bumping it up to 5 amps & see if you still get the alert.
 
If your efis has data logging, look at the system voltage track over the period you've been having the overcurrent notices. If the alternator is going out of spec, you should see it in the history, even if the alarm set points are wide enough to hide it in real time.

If it were my system and everything is *functioning* correctly (voltage within limits, xponder works properly), I'd be betting on instrumentation error over any actual defects in the system.

Do you get to set the 'trip point' in that vpx circuit yourself? If so, how about bumping it up to 5 amps & see if you still get the alert.

OK I owe you a beer or something.

Went to the airport after work. I could reproduce the issue now reliably:

1. Switch alternator off to let battery drain a bit.
2. Switch alternator on -- transponder triggers as short
3. Wait till alternator load < 10A reset transponder everything works

Then I followed you advice and bumped the fuse value to 5A. Tried to trigger the short again on the ground and couldn't. Went flying and tried different things to trigger it and couldn't.

So that does seem to have solved the issue. Still baffled by the fact that it worked flawless for 4 years at a 3A setting... . What's the odds..... .

Oliver
 
Glad you could solve it without injecting money. :)

If you have data history from the efis, I'd still check the system voltage history. If the regulator's set point is drifting upward slightly, that could account for the change in behavior. Again, if the vpx trip point was very close to actual current over the prior years, even a very slight uptick in system voltage (even if well within normal range) could drive current up slightly, causing the current detection to fire.
 
Very Timely!

This thread was very timely! After four years of flying (250+ hours) my SV-XPNDR-261 began tripping the VP-X Pro circuit when transitioning from GND to ALT mode.
Resetting the circuit resulted in the transponder operating properly throughout the rest of the flight. Until yesterday (Wednesday, 28 August) the circuit tripped twice. On the second tripping, I notices the transponder was pulling 4+ Amps during the transition from GND to ALT Mode. After resetting, it would only pull 2.5 Amps throughout the flight.
I sent an inquiry to Dynon late last evening before reading this thread. During the flight I thought that maybe "upping" the trip-point on the VP-X Pro might be in the plans, but I'd wait until I heard from Dynon.

Seems odd - interesting - transponders from the same manufacturer with VP-X Pro in different aircraft, each with about four years of operation are experiencing very similar issues...

And like the OP, - S.A. comments about swapping out the VP-X Pro to archaic circuit breakers is not in the works - no panel space and not going backwards in technology.
 
Perhaps a simple test. Bypass the VPX and power the transponder (or anything else you suspect) via an inline fuse. It all works then you verified the VPX is the issue.

Carl
 
When did you switch to the EarthX battery? They typically initially charge at a higher amp rate verses a standard battery. Asking because you mentioned the charging amps in your solution.
G
 
This could all make sense if it was just a marginal condition that is resulting in the transient condition. If the transponder has a switching power supply then at a constant power out and a lower voltage in it will draw more current. That means it could be just marginally triggering the fault condition in these events. Your ground test seems to align with this argument. Bad or deteriorating connections could cause the same result though so that would be worth checking as well.
 
The reason a problem is showing up after 4 years is because it took that long for
corrosion to form on a bad connection. Take all connections apart, both power and ground,
and clean and reassemble. Tug firmly on terminal wires to be sure that crimps are secure.
 
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