ammeter fluctation

[glenn654]

I have a D-180 and the ammeter fluctuates in the range of +/- 8 amps, everything in the charging sys has been replaced, but the problem remains. Is this fluctuation normal for the -180 like that seen with MAP? If so, could it be dampened? When the amperage drops to the lowest range the GPS (GNC-250XL) cuts off but immediately comes back on. I don't know if it is related to the amperage fluctuation or a problem in the GPS. What do you think? Any help you can give me will be greatly appreciated.

P.S. the voltage is always steady at 14.5v

Glenn Wilkinson

 

[dynonsupport]

We've heard that some Rotax generators can be noisy with their power output, and this has produced fluctuations in the amps readings.

There's no easy way to damp it like you can with MAP, though in all likelihood, the fluctuations are real.

The fact that the GPS goes off in concert with the low amperage reading also points to a real power supply problem.

 

[PilotKris]

I've had the same problem with my D180 since day one.

The output of the Alt. on the 912ULS might be noisey (I doubt it as there is no noise in any of the avionics) but that still doesn't explain the impossible levels the ammeter reads (+-40 amps).

I've put a mV meter across the shunt and it's rock solid at believable levels (like 14mV).

Any sugestions?

PilotKris

 

[PilotKris]

No Really....

Any sugestions how to fix the problem?

 

[josok]

While i have seen some fluctuating amp readings (rotax914 with extra generator on the vac drive) on both generators, +-40 never.
It looks you have an open circuit on one of the connections to the D180. Could you connect your meter to the D connector? Could you measure the AC component also?

Regards,

Jos Okhuijsen

 

[N112B]

I'm having an ammeter fluctuation issue. My EMS D-10 regularly shows a momentary discharge of 2 or 3 amps. (Superior IO-360 engine). But the downloaded datalog data does not agree with the onscreen discharge info and never logs a discharge while the engine is running. I've had this problem since before firmware 3.0.

 

[dynonsupport]

N112B - how often is that momentary reading? How long does it last?

The engine logger takes a snapshot every X seconds (where X is user-settable). It's likely that the momentary dips are just out of sync with the moment that the EMS grabs the data.

 

[N112B]

The momentary discharge to negative 1, 2, 3 or even 4 amps, usually happens at least once a minute. It lasts for a second or 2. The fluctuation from postive to negative happens more frequently than other times.

The engine logger was set to record every second on a recent download of a flight with 1500 snapshots. It looks like the logged data is running a couple amps higher than the onscreen info. The datalog shows no negatives while the engine is running, unlike the onscreen info.

 

[dynonsupport]

We're going to look into the datalogging storage to see if very short duration events might be getting missed in certain circumstances.

As for the actual reading - it's quite possible that the fluctuations are actually there. There are lots of things in airplanes that can pull large amounts of currents for short periods, particularly radios when transmitting, strobes, wig-wags, other external loads, or an iffy battery. Also, some alternators and voltage regulators may exhibit some variability from time to time.

 

[glenn654]

updated info.

I also  have fluctuation of amperage while on battery power alone. Usually in the range of 5 amps while voltage shows steady. I am using a Honeywell CS Linear Current Sensor to measure the amperage....is this compatible to the D180?
This is my only problem and may not have anything to do with the -180, as for the rest..... I am very happy and would recommend it.
Any ideas?

Glenn Wilkinson

 

[Thomas_Schaad]

I had exactly the same, on the old 912UL as also on my brand new 912ULS. I had the problem fixed by hooking a capacitor in. Since then it's gone.

Kind regards

Thomas

 

[PilotKris]

Hi Thomas,

What kind of capacitor and where/how was it installed?

PilotKris

 

[Thomas_Schaad]

Hi Kris,

Let me talk to my avionics engineer tomorrow, as I got a number of them and resistors as well in. Before my EMS10 was a pretty "nervous story" that did not really indicate how I wanted that to see. But I never had those fluctuations on the battery only, this started when the generator was switched on. But then not only the ammeter was jumping, but all kind of pressures and temperatures as well. This is no more issue and I do have a real nice indicator.

The last problem was solved, by having the engine cowling bonded. I do have a kind of heat isolating foil under the hood. According to my avionics engineer, this can create in flight, together with the airstream going over my epoxy skinn, a kind of a battery effect. I had then the entire hood wired together and grounded over the engine. Since then, guess what the problems are gone. This kind of problems I actually didn't only see on the EMS10, but best there. For example, I always could look at a number of VOR's on ground, but reception was poor in flight. Since the hood is bonded, it's gone.

Kind regards

Thomas

 

[dynonsupport]

We can't speak to the suitability of the Honeywell sensor, but the only shunt explicitly supported is the one we sell.

Generically, if your amps sensor produces 1 millivolt per 1 amp, it should work fine though.

 

[PilotKris]

Thomas,

I'm having pretty much the same "issues" you mentioned. Let me know what your Avionics Guy says.

Thanks

PilotKris

 

[XDT]

I am also having the same problem only the ammeter is unstable, it seems to occilate up and down over about a 5-10 second cycle, have not looked into it yet as its a minor problem!
I am interested in looking at smoothing with a large capacitor!

 

[Hal]

I am having much the same problem with my Sonex/Aerovee. When the secondary electronic ignition fires, it produces a large current draw momentarily. It seems that the Dynon is just taking an instantaneous reading of the shunt voltage and displaying it. Sometimes when these current pulses coincide with the Dynon sampling interval, I show a constant -8 amps (although the battery voltage is increasing). Sometimes it just hits randomly and shows +10 or -7 amps between refreshes. It is my opinion Dynon needs to keep a windowed running average of samples (an integrator) with a time constant of several seconds. This will filter the short duration spikes. How about it Dynon ?
Hal

 

[dynonsupport]

We do not do a ton of filtering on instantaneously for current, so Hal's explanation may explain what some are seeing. The sample rate there isn't high enough to support the sort of filtering we'd like to do digitally, but we have an idea as to what might work in terms of building an analog filter that may smooth out the voltage on the lines we measure amps on.

If anyone out there has some time to experiment and isn't afraid of putting together a few resistors and capacitors, send an email to support@dynonavionics.com and we'll work through it with you. Include a link to this thread. If we can get good results, we'll publish them on the forum.

 

[Hal]

I will be happy to try the experiments. I assume we will be building a first-order low pass filter. It should be no problem to solder up the components. Just contact me privately with details.
Thank you,
Hal Schwab
hschwab@mindspring.com

 

[PilotKris]

PLEASE let us know the results. I've be battling this problem for over a year...