Ammeter giving almost random readings

[dynonsupport]

Yep.

 

[TundraJoe]

I have an EMS 120 and my experimental has a Superior ( Lycoming) o-360. Recently, my ammeter has been reading in the negative 5-11 amp range, still in the green but negative. The volt meter holds at 14 volts.
Is this normal, or should I have my avionics guy check shunts ( whatever they are) ?
Thanks

 

[jakej]

I'd be checking the 'B' lead from the alternator to through the shunt.

Jake J

 

[Garth]

I just read through this thread since I may have just experienced a similar problem. I have a Jabiru 3300 and a Dynon 180, both with about 150 hrs of operating time. On my last flight, for about a 10 minute period, I kept getting a high current alarm. I think I have the alarm set at 30 amps and up until now it very rarely if ever alarmed. But for this period the amps were jumping all over the place even exceeding readings of 50 amps. I would think this couldn't be real since the alternator is only supposed to put out 20 amps max, more or less, and I have 25 and 30 amp breakers that did not pop. After 10 minutes of this arratic behavior the readings went back to normal, typically < 10 amps. Everything else with the engine/electrical system was performing fine. Switching to battery only didn't change the erratic readings. No smoke or odor when I inspected the wiring and all connections around the shunt were secure.

I take it there is no immediate answer/fix available but in the meantime how concerned should I be??

Thx

Garth

 

[pbennett]

Is your shunt in the alternator lead, the bus line or the battery lead?
What do you expect the current reading to do when you switch to "battery only"?

The symptoms you describe indicate that the shunt measurement leads are seeing a higher than normal voltage across the shunt. This could indicate indicate a faulty shunt where the shunt conductor is cracked or not securely bonded to its terminal blocks.

Peter

 

[Garth]

Peter, thanks for your reply.

The shunt is on the battery line before the alternator power ties in. So it will normally (in flight) read positive indicting more power is being produced than used, ie the battery is charging. If negative, the battery is discharging to meet the current load, whcih occurs at idle rpm on the Jabiru. With the alternator isolated, it should have gone negative, which it didn't, which further supports that the rasdings must have been bogus. When the weather clears I'll see if this reoccurs and I'll try isolating the alternator when the ammeter readings are normal.

Thx

Garth

 

[pbennett]

The faulty shunt hypothesis doesn't hold under those conditions. If the shunt was at fault you'd have seen the amps reading go from high positive to high negative when you shut off the alternator or backed off the RPM to idle.
I'd be looking at one of the shunt sense wires going open circuit. If that happened, the reading would stay in one direction regardless of the current direction in the shunt. The amplitude of the reading would depend on the circuitry in the D180. Check that a pin or receptacle hasn't got pushed out of a connector or otherwise damaged. Inspect and apply the pull test to all soldered and crimped connections in the sense leads. If you have fuses in the sense leads (you should!) ensure the connection is not intermittent. In line fuse holders are notorious for intermittents.

Peter

 

[Garth]

It seems that some people were really digging into this issue (random/unreliale ammeter readings) several months ago. Did anyone ever find a answer/fix? I still have this problem with my D180 and a Jabiru engine. The last post I see was 3/11/10. Thx.

 

[TundraJoe]

I decided to live with my ammeter readings slightly negative ( -1 to -7), as long as my battery was showing 14 volts---but last week, my ammeter started flippping back and forth between negative and positive---this causes my volt readings to exceed 14 and flash in the orange. Still waiting for Dynon to respond to this chain.
Frank

 

[Garth]

I'm thinking of hooking up an inexpensive anolog ammeter until this [hopefully] gets resolved. I'd really like to know if the alternator has quite before the battery dies! I've just had an e-mail exchange with "Mike H" at Dynon. He wasn't aware of the issue initially but indicated he would do some digging on it in case there has been any progress in the last few months. It would be nice to know if they are working on it as well. Garth

 

[TundraJoe]

That's a good idea--
Thanks for doggin' Dynon

 

[G3WGV]

It seems that some people were really digging into this issue (random/unreliale ammeter readings) several months ago.

That was probably me around March this year.

I did some oscilloscope trace captures with the engine stopped and some analysis, to which there was no response whatsoever. I also tried the Hall Effect device and found that I have exactly the same problem - the ammeter is stable without the engine running but is all over the place when the engine is running. I did do some 'scope captures with the engine running but with the complete lack of any response to my earlier diagnostics I haven't taken the time to post them here.

I have concluded after a reasonable amount of experimentation that there is no fix outside of the Dynon box. I've tried various filters in the lines to the Dynon and all result in meaningless ammeter displays. I tentatively conclude that the Dynon is integrating too few samples in the ammeter logic and is therefore responding to noise.

For the time being I've given up but if Dynon can be convinced to take the issue seriously then I am willing to put more effort into the matter. Certainly, as it stands, the ammeter function is quite useless.

 

[Garth]

Thanks John, sound like you did some good work on this ... now back to Dynon??

Garth

 

[jakej]

John

Did you fit an Electrolytic capacitor (10,000uF @50V) to the alternator output ? - this has fixed any issues I've had with the permanent magnet alternators.

Jake J

 

[Garth]

Yes, I have a capacitor on the alternator output.

I installed an inexpensive analog in-line ammeter the other day since I concluded I can't rely on the Dynon output to know if the alternator has failed. With the engine stopped or at idle it reads negative (battery draining), at higher rpms/cruise it initially reads about +5 (batter charging) but then quickly drops down to zero (battery charged). No change when put on full load, indicating the alternator can supply the full demand. Turing the alternator off and the readings are -5 - -10 depending on load. All this I believe is as expected. At least this give me some peace of mind. The Dynon during this time was bouncing all over the place, mostly on the negative side. FYI.

Garth

 

[G3WGV]

Did you fit an Electrolytic capacitor (10,000uF @50V) to the alternator output ? - this has fixed any issues I've had with the permanent magnet alternators.

Yes, I have the capacitor. ISTR it is a 22,000µF in my case and it certainly works because there is a definite voltage hang for a short time after turning off the master switch as the capacitor discharges. It's interesting, however, what you say. Perhaps it might be worth providing a better filtered 12V supply to the Dynon.

 

[jakej]

John

Clarification - the capacitor should be on the volt reg output to main bus, close as possible to regulator. Other than that I make sure any grounding is good & add an extra engine to main ground bus wire, just to be sure.
Another issue is the push on connectors on the alternator output wires, I now replace them with AMP brand as the originals are way too 'weak' and don't give a good grip on the spade resulting in a high resistance joint.

Jake J

 

[G3WGV]

Hi Jake,

Yes, the cap is directly attached to the regulator +12V output and is also well grounded. I also have a 4AWG ground lead between battery -ve and starter motor ground (i.e. the engine). I'm reasonably certain that grounding isn't an issue but I plan to have a better go at this problem when the flying season is drawing to a close. Like you, I replaced the alternator output wire terminals, being less than impressed by the ones supplied.

 

[jakej]

Hi John

There's gotta be something we're not seeing here - hard to troubleshoot by 'remote' control and you are obviously well versed in electronics - maybe a case of 'can't see the wood for the trees' As probably mentioned before, I have done many installs with Jabby engines and don't see these problems so don't think this is a systemic problem.

I'd be interested to hear the solution when you fid it.

cheers, Jake J

 

[PhantomPholly]

For what it's worth, I installed a D180 with the Dynon shunt and the readings are rock-solid and accurate. I've tried turning on known loads (landing light; gps; etc.) and the reading is +/- a few percent of exactly what the device claims as current draw.

Every problem I've ever encountered with sensors always tracked back to poor grounds - fixing those made everything swell.