Dynon ACM electrics issue

[Nev]

While inflight recently I had a battery voltage alert that the voltage was at 14.0V (EarthX). Normally is sits around 14.2 inflight. I pulled up the ACM screen, and noticed that the current out of the battery was fluctuating. By the time I grabbed a photo it looked like this:
1AD63A6A-905B-4B73-93D7-C2A551FF0D1E.jpg

My question is, shouldn't the current be flowing into the battery? And I expected to see that the Alternator output would match the demand of the ACM + Battery. Next time I started the engine it started fine, and also the next day at -2°c it also started fine.

Later, I took the following photos before and after engine start. These indications look normal and make sense to me, it's the above that I'm not understanding. The battery voltage seems to indicate that it's receiving a charge, yet the diagram shows a discharge. Next time I go flying I'll get some more pics inflight.


Prior to starting, ALT OFF, Avionics OFF:
A3D9D5B7-87BD-46B9-A4FC-1655CE8CB363.jpg

Engine running, ALT ON, Avionics OFF:

BA88B38F-6FD5-43CA-AC32-05C6BF2681C1.jpg

Engine running, ALT ON, Avionics now ON:

1C27E884-477D-4B31-99CB-B1D9258737A2.jpg

[jaredyates]

Why not pull your EMS data and upload it to Saavy, then we can get a better look at what was happening.

I don't know the symbology of the ACM, but I don't think you would see a true voltage of 14 with an Earthx that wasn't getting some charge. Lots of possible explanations that I can think of relate to a gap between actual volts/amps in the system, vs indicated/measured. How are you measuring current, Hall effect sensors, shunts? Are such low amps to be trusted based on the capabilities of the current sensors? Does a voltmeter on the battery terminals agree with the voltage on the panel?

[Nev]

Why not pull your EMS data and upload it to Saavy, then we can get a better look at what was happening.

Excellent idea (wish I'd thought of it ) - I'll do that next time I'm at the hangar.

I don't know the symbology of the ACM, but I don't think you would see a true voltage of 14 with an Earthx that wasn't getting some charge. Lots of possible explanations that I can think of relate to a gap between actual volts/amps in the system, vs indicated/measured. How are you measuring current, Hall effect sensors, shunts? Are such low amps to be trusted based on the capabilities of the current sensors? Does a voltmeter on the battery terminals agree with the voltage on the panel?

A few good ideas there already Jared. I'll check the battery terminals with a multimeter and compare readings.

My aircraft has a Vertical Power PPS (black box) to handle the alternator, starter, battery etc, and it contains a shunt for the alternator, and one for the battery charging.

One additional piece of information (posted previously) that may be related, is that when I transmit on the VHF the ACM display goes nuts and shows a very high current draw. If it's shortly after engine start, (when the alternator is charging the battery at a high rate), it can exceed the limit I've set and trigger an alert. However most of the time it doesn't trigger anything and unless you check the display you wouldn't know. After chatting with Dynon they advised that it's likely interference from the antenna.

[kestrel]

Maybe a failed ground somewhere? ...bad ground is always a good answer for electrical questions.

Further thought, double check the ground strap to the engine? ...not enough data here to solve the problem, but something to check.

[Nev]

Great I'll check that.

[Richard E]

One additional piece of information (posted previously) that may be related, is that when I transmit on the VHF the ACM display goes nuts and shows a very high current draw. If it's shortly after engine start, (when the alternator is charging the battery at a high rate), it can exceed the limit I've set and trigger an alert. However most of the time it doesn't trigger anything and unless you check the display you wouldn't know. After chatting with Dynon they advised that it's likely interference from the antenna.

I had exactly this problem. It turned out to be the voltage regulator which we wrapped in reflective aluminium tape as the cause was overheating. However, it still failed completely shortly after. As the cause was overheating we moved the new regulator onto the other side of the firewall. Never had a problem since.

[Richard E]

Hi Nev,

One additional piece of information (posted previously) that may be related, is that when I transmit on the VHF the ACM display goes nuts and shows a very high current draw. If it's shortly after engine start, (when the alternator is charging the battery at a high rate), it can exceed the limit I've set and trigger an alert. However most of the time it doesn't trigger anything and unless you check the display you wouldn't know. After chatting with Dynon they advised that it's likely interference from the antenna.

I had the same issue of suddenly having high current draw when transmitting. It turned out to be the voltage regulator overheating. Initially we wrapped it in foil to reflect heat from the engine. Later it failed altogether. When we replaced it we fitted it on the other side of the firewall. No problem since.

[Nev]

Hi Nev,



I had the same issue of suddenly having high current draw when transmitting. It turned out to be the voltage regulator overheating. Initially we wrapped it in foil to reflect heat from the engine. Later it failed altogether. When we replaced it we fitted it on the other side of the firewall. No problem since.

Great info thanks Richard. I'll have to keep an open mind to the possibility that the voltage regulator could be behind both issues. I'm planning to go through and check all connections later this week. Will also download the data and take a look at it. Hopefully I'll be able to narrow it down.

Can you recommend a voltage regulator (preferably one that's available at the local "Bearhawk" store ).

[Richard E]

We originally had a B&C unit from the RV firewall forward kit. (One LAME described this as a Mickey Mouse car regulator!)

Following its failure we fitted a standard one used in Robinson helicopters.

[N3UW]

Nev I noticed on the first image you showed of the issue in flight that the field current was 0.0. There must be current to the field to excite the alternator to produce voltage/current. From that image it looks like your alternator was offline or the field current was so low that the alternator was only regulated to output 2.9A . That could be the alternator itself, the regulator, the field wire or anywhere between the input to the field breaker and the field terminal on the alternator. That regulator adjusts the field current to maintain a constant voltage on the battery. The field wires, connectors is a good place to look for a loose connection as a starting point. The field current should be proportional to the alternator output current (but not necessarily linear relation) . Zeftronics has a pretty good troubleshooting guide. https://zeftronics.com/wp-content/up...4/06/Z14PS.pdf

[Nev]

John, many thanks (and very well explained), I didn't know this. I'll be doing some troubleshooting on Wednesday and will report back how it goes. It's good to have a general indication of what to look for.

[svyolo]

I would check:

Engine/airframe/battery/voltage regulator grounds in that order.
VR wiring next. The 0 on the alt field like N3UW said.

I once trouble shot VR wiring by replacing the VR first. That seems to be a faulty troubleshooting technique I still haven't "cured" myself of yet. Maybe next decade.

[kestrel]

svyolo has it. I suspect that the 0A reported on the field in the first image is a rounding/calibration error and there is actually some current there. ..just not enough. ...but I am guessing.

I am using this VR. Seems to enjoy a good reputation and has OV protection. I have no idea how it would fit in with the rest of your system.

https://bandc.com/product/alternator-controller-regulator-14v-homebuilt/

[kestrel]

I might add that my 4 place had an automotive alternator and regulator when I bought it. No OV protection that I could find. I replaced the alternator once when its bearings where shot.

Here's the part that may be similar to your case. I later needed to replace the VR. The alternator would go offline. If I cycled the master switch in flight, it would come back on for a while and then go offline again. I replaced the VR and alternator with B&C equipment and have been very happy with it.

[Nev]

Thanks for the contributions above to get me pointed in the right direction.
Today I removed the cowls and spend a couple of hours going over the engine and electrical system. I found the main alternator cable wasn't completely tight at the alternator. It is now. (I also went over many other nuts and bolts to check for security.) Interestingly, after doing a short flight, I noticed the battery still shows a discharge at times, but the battery voltage is showing around 14.8V and the field breaker shows a current on the screen. So I'll keep that screen up over the next few flights and get an idea of what's normal.

[Nev]

I've downloaded some data relating to the alternator. I have a graph below showing amps. Unfortunately I'm unable to display volts, which is probably a configuration omission that I'll try and resolve.

The charts show two flights. The first is a sample from last year. The second is the flight that triggered this thread.

Question :
Most of the flights show "spikes" in the amperage. Is this normal ? Even going back to early test flights, there are spikes.
Secondly, the second graph shows a lot of "noise" - lots of small spikes. Is that normal ? I'm guessing not because it appears to be a recent phenomenon and may perhaps be related to the loose cable. The large spike during descent on the right side of the lower graph coincided with the battery voltage dropping to 14.1V and triggering an alert.


Sample flight from a year ago. Most flight show this pattern of "spikes".
EAD96509-1CE0-499E-811B-C99BFD07407D.jpg

Below is the flight where I observed the battery discharging in-flight:
E8947980-F239-4703-805B-63959D8DC45A.jpg