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

[spatsch]

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

[JosephineJ79]

Replace VP-X with fuses. They are light weight, inexpensive, and easy to replace without sending unit back to manufacturer.

[maus92]

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.

[spatsch]

Originally Posted by maus92

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 ... .

[maus92]

Originally Posted by spatsch

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.

[VNS]

No 2 - Voltage regulator triggering OV protection in the VPX. Swap out the VR/Alt assembly and test

[spatsch]

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

[rv7charlie]

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....

[spatsch]

Originally Posted by rv7charlie

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

[Mich48041]

If there is a high resistance connection, avionics with a switching power supply will draw more current to compensate.