DYNON HELP -BOTH ADAHRS/ EMS FAIL

[kurtfly]

Dynon,

On a trip from Fort Worth, TX to Meridian, MS I had a alternator failure about 40 miles from Meridian.  When the alternator failed it tripped the field breaker.  It also failed off the -201 ADAHRS, the ARINC 429, GPS-250 and the EMS.  The -200 ADAHRS displays bad altitude and airspeed data.  The altitude is jumping up / down over 1000 ft and 8000 feet too high.  Looks like all SV powered from the screen have failed? I had to return to Meridian using my D100 backup.  I tried to power SV with internal backup Battery with same results. Can all these be bad???  How should I proceed.  Stuck in Meridian, MS.

Thanks,

Kurt

 

[rvator51]

Just all I can think of at the moment is to disconnect the main battery, disconnect the backup battery from the SV and wait a few minutes then reconnect and see if it dies the same thing.

If it does, then turn everything off again and disconnect the EMS and the ADAHRS, then connect one thing at a time and turn the SVBack on and see if you can find which ones are bad. Since it didn't pop the breakers for th SV hardware, I am hopeful you can get it going again.

If not, Can you just turn every thing off and fly home using the D-100?

 

[kurtfly]

I will try these and see if anything recovers. It looks like all things powered via the SV display is affected. Looking at the forecast it doesnt look good for the next few days to go back west VFR...

Thanks,

Kurt

 

[dynonsupport]

Kurt,
This sounds like maybe one device in the network is really broken? Generally the network is very robust with lots of redundancy, but it is possible for certain shorts to take out lots of things. I'd unplug everything except the AHRS-200 from the network and see if it's OK, then work device by device. Gut feel is the EMS just because it's hooked to AMPS and volts from the Alternator.

The fact that the GPS also went out points to the power supply for all the network devices being shorted out. So now that I think of it, unplug all the network cables from the back of the screen and see if the EMS comes back. If it does, something out there is shorting out the network power.

The other possibility is that the failure somehow played havoc with ground paths and sent power through cables that it shouldn't have. Is this a metal or composite airframe?

 

[kurtfly]

Thanks Dynon, It is a composite aircraft, Glasair. I will check each device as you suggested once I get the alternator fixed. Just trying to get it working good enough to get back home.

The Dynon failed all at once when I re-set the breaker. The EMS is on a dedicated SV buss connector so that will be easy to isolate from the display.

Thank you,
Kurt

 

[tedbain]

Kurt please post what you find to be wrong. I have a Glasair and thought there was enough redundancy to just go with a 2 screen/2 adhars setup without any backup. Looks like I have to rethink this.

 

[jakej]

Kurt,
Does your electrical system have crowbar overvoltage protection ?

JakeJ

Glasair IIS FT
Alt 1 & Alt 2
Dual SV & Dual ADAHRS

 

[kurtfly]

I disconnected the EMS from Skyview buss and all the other devices came back online. So I recovered all capability except engine monitoring.  As Dynon's "Gut feel is the EMS just because it's hooked to AMPS and volts from the Alternator" is accurate.  I will be getting with Dynon to return this for repair / analysis once I can fly my airplane home.  At least now I have a better PFD / Map and Transponder that is not putting out random altitude of >8000ft above actual.

My alternator system is a B&C 14V / 60 amp alternator, and yes, it does have an overvoltage "Crowbar" that trips the 5 amp field breaker at >16 V.  I am surprised that even if I had a OV condition it would damage the EMS as it is rated at 30V and most likely can handle greater without damage.  The replacement of the Alt and regulator appears to have fixed the problem.

I am very glad I decided to have the D100 as my backup - independent system!!! I dont know if a two screen SV would have protected me from this??

Kurt 

 

[sunfish]

Kurt, I think it is possible for an alternator to put out a 400V spike as it trips. I'm not sure the EMS voltage inputs could handle that, thank goodness the rest of the system is so strong.

 

[kurtfly]

I wanted to update this problem as it may be valuable to many other Skyview installations and expose a possible venerability in this type of current monitoring circuit. I have my EMS-220 configured as “Position B” in the Skyview installation manual. This connects the ammeter shunt at the output of the alternator, reads alternator output current. I have attached a schematic of my system.

The problem comes into play when, by fault, or by accident the 60 Amp alternator circuit breaker opens (blows). If the 5 Amp field circuit breaker is closed (engaged) the regulator senses the battery voltage. With the battery voltage at ~12.6 VDC it turns on the field current to try to get the voltage up to 14.4 VDC. Since the output of the alternator is disconnected from the master bus / battery, the field is turned full on. The voltage on the alternator output cable is very high, especially since there is no load. This high voltage is directly connected to the current sense inputs of the SV-EMS-220 module. In my case I believe this high voltage “smoked” my EMS module. In doing that, it loaded down power supplies on the SV bus which basically took the entire Skyview bus system down.

I have contacted B&C Aero, the maker of my charging system who confirmed my beliefs. They could not quantify how high a voltage could be expected in this configuration. However, they do recommend that 18 Volt “TransZorbs” be installed on the shunt (see my schematic). They also recommend the 60 Amp circuit breaker be removed and an inline 60 Amp fuse be installed that will prevent pilot from inadvertently pulling this circuit breaker. If the 60 Amp breaker opens, and the alternator output goes above 18V, the “TransZorbs” short out to ground and blow the 1 Amp fuses at the shunt. Disconnecting the EMS module from the alternator circuit. These are very fast acting, in the sub-microsecond range.

I do not know what the absolute highest input voltage that the SV-EMS module can withstand. Perhaps Dynon can elaborate?

Bottom line is: I had an alternator that was acting up, and in-flight I decided to cycle circuit breakers to try to correct. This made an inoperative alternator turn into an alternator and Skyview system complete failure. Even though I have dual ADAHRS, all SV bus powered devices were offline. I was lucky I had a D100 system as backup and it occurred in VMC conditions. I just flew out of 2 Hrs. of IMC weather.

 

[swatson999]

What if you just put the shunt on the other side of the 60A ANL or CB?  Wouldn't that solve the problem without all the extra doodads at the shunt?

I'm also curious why the 1A fuses didn't blow on the shunt lines...but that's kind of a secondary thing.

If you put the shunt on the other side of the ANL or CB, when it opens, well, problem solved, no?

 

[kurtfly]

Putting the shunt on the other side of the Circuit breaker is an option; however, this will also require significant wiring changes.  Most, if not all circuit breakers are connected to a common bus.  So, you will have to remove the breaker from the bus and install the shunt in between.

The 1 amp fuses did not blow because it was a voltage event.  The current did not exceed the 1 amp, at least long enough to blow the fuses. The inputs to the EMS differential amplifier are high impedance.

Even with the relocation of the CB or ANL fuse one must remember that this is a 60 AMP circuit.  It is not going to be a fast acting.  If some kinda failure in the regulator circuit exists the Dynon SV-EMS has to be able to handle it.  The TransZorbs should provide some level of additional protection.  I would like Dynon to explain what level of protection the EMS inputs have, if any.

Ultimately, I may move the shunt to "Position A", indicates battery charge / battery output current.  Being so close to the battery will provide significant protection against any voltage spikes.  Or, change my current sense to a hall effect device. But knowing what I know now, I will always have the TransZorbs installed now.  You must remember - This failure brought down the entire Skyview system.  Doesn't matter haw many displays or ADAHRS you have.

 

[swatson999]

Well, to each his own, I guess. Funny how nobody else has to put in little doodads on their shunts, and plenty of planes are built with the shunt on the protected side of the ANL without any issues.

 

[cmgolden]

What is the purpose for the 60A breaker on the alternator anyway? (Other than everyone seems to have one?) Is there a real risk that one's alternator will ever produce more current than advertised?

 

[kurtfly]

The purpose of any breaker is to protect the wiring. If a short circuit happens it should prevent damage and/or fire. The battery is on the other side of this wire. It can put out a lot more than 60A.

 

[Dynon]

Dynon designs all inputs that hook to aircraft systems to be DO-160 compliant for 28V aircraft. Basically, this requires 40V to be handled for a second, and 60V for 0.1 seconds. This is the same level of testing that would be required for certified devices and is the industry standard for voltage spikes on aircraft systems with an alternator and a battery.

The EMS shunt input goes beyond this. It is capable of 70V continuously, but not much above that. It does have multi- thousand volt tolerance for very short duration such as static and load dumps, but this is not what an alternator generates when unregulated.

The reason DO-160 doesn't assume or test for hundreds of volts is that it assumes a battery is present in the system that will limit high voltages, or a regulator is present to limit the output of a generator / alternator. Thus, the loss of both regulation and a battery is considered a dual failure which is generally not handled.

The system here does have a unique design challenge where a single breaker popping can cause hundreds of volts to come out of the alternator (because becomes unregulated in that state when the alternator is disconnected from the battery), and because of the placement of the breaker, the only device that sees that very high unregulated voltage that is the EMS module. This does cause a single point failure in the system, which we'd recommend be eliminated in the aircraft electrical system. The trans-orb solution is likely acceptable, although Dynon has not tested this and we'd recommend that you actually test it by reproducing this situation before relying on it. We would much prefer to see the shunt located on the same electrical node as the voltage regulator so that this situation is eliminated, and that is what we have generally seen done in most aircraft installations.

In our documentation, we try to strike the right balance between providing relevant best practices for things that connect to our products without being too prescriptive about other areas of the electrical system that are more general. In this case, we'll add this situation to our install manual and recommend that the shunt always be located behind the alternator breaker to prevent other aircraft from experiencing this failure.

Thanks for documenting this and following up.

 

[N941WR]

Last weekend I landed, shut the plane down, powered down my SkyView with dual ADHARS, and put it in the hangar.

About an hour later I turned on my master to get the hobbs reading and was greeted with both an AHDARS and EMS Fail messages and big X's over both.

Turning off the master had no impact and neither did pressing any of the buttons on the SkyView.

To get it to cycle off, I had to disconnect the backup battery and since doing that, it seems all is normal. Although I have yet to start the plane due to a week's worth of rain but I have powered up and down the SkyView a number of times without any issues.

Any suggestion as to what is going on and if I should worry about this?

 

[vlittle]

Dynon designs all inputs that hook to aircraft systems to be DO-160 compliant for 28V aircraft. Basically, this requires 40V to be handled for a second, and 60V for 0.1 seconds. This is the same level of testing that would be required for certified devices and is the industry standard for voltage spikes on aircraft systems with an alternator and a battery.

The EMS shunt input goes beyond this. It is capable of 70V continuously, but not much above that. It does have multi- thousand volt tolerance for very short duration such as static and load dumps, but this is not what an alternator generates when unregulated.

The reason DO-160 doesn't assume or test for hundreds of volts is that it assumes a battery is present in the system that will limit high voltages, or a regulator is present to limit the output of a generator / alternator. Thus, the loss of both regulation and a battery is considered a dual failure which is generally not handled.

The system here does have a unique design challenge where a single breaker popping can cause hundreds of volts to come out of the alternator (because becomes unregulated in that state when the alternator is disconnected from the battery), and because of the placement of the breaker, the only device that sees that very high unregulated voltage that is the EMS module. This does cause a single point failure in the system, which we'd recommend be eliminated in the aircraft electrical system. The trans-orb solution is likely acceptable, although Dynon has not tested this and we'd recommend that you actually test it by reproducing this situation before relying on it. We would much prefer to see the shunt located on the same electrical node as the voltage regulator so that this situation is eliminated, and that is what we have generally seen done in most aircraft installations.

In our documentation, we try to strike the right balance between providing relevant best practices for things that connect to our products without being too prescriptive about other areas of the electrical system that are more general. In this case, we'll add this situation to our install manual and recommend that the shunt always be located behind the alternator breaker to prevent other aircraft from experiencing this failure.

Thanks for documenting this and following up.

Would a pair of matched resistors, say 5K0 in series with the shunt sense points provide adequate protection? If so, they could replace the fuses or fusible links currently used.

I know that they would change the gain of the current sense diff amp, but this could be adjusted in software or calibration.

Vern

 

[dynonsupport]

It is acceptable to use resistors, except they need to be remarkably well matched, within 0.1% of one another. This means 0.05% resistors or better, which are in the neighborhood of $3 each. The bigger issue is that 5K resistors would reduce the gain by 6X, so you'd have a lot less sensitivity even if we adjusted the calibration in software.

There's no evidence that 5K would help with high voltage tolerance. It would work to prevent high currents on these wires in case of an internal short, but may not have done anything in this case. Thus, given the expense and calibration issues, it isn't something Dynon has looked into further when fuses work well.

We will look into what it might take to make this input more robust to very large voltages, but as we said before, this is generally avoided in almost all installations by having the shunt on the same side of the breakers as the battery.

 

[N941WR]

Dynon, do you have any comment on my post above?