Amps going negative intermittently

[hawgdrvr]

During runup I noticed the amps went from +3 to -4 at around 1500 rpm on the way to 1900 for the runup. It went back to +3 again and stabilized there. Later in the flight I was checking the engine page and saw this happen again. Did not see it again later in the 2.5 hour flight but not sure why it's going negative like this.

Any ideas or is this normal?

[Andy]

During runup I noticed the amps went from +3 to -4 at around 1500 rpm on the way to 1900 for the runup. It went back to +3 again and stabilized there. Later in the flight I was checking the engine page and saw this happen again. Did not see it again later in the 2.5 hour flight but not sure why it's going negative like this.

Any ideas or is this normal?

Not normal. It probably indicates that either the alternator, or the circuit between the alternator and Main Bus, is intermittent.

Check the data log. Find the battery discharge events (AMPS 1 negative) and see what VOLTS 1 is doing. Check the connections at the alternator, alternator 50 amp breaker, and Main Bus for security.

CAUTION - There are live wires behind the instrument panel even with Master Off.

[hawgdrvr]

I'm seeing several strange things of late:

1) Last night's flight I got an AHARS loss of GPS signal message, but everything appeared to work fine
2) I'm seeing a yellow caution and high GPH readings on takeoff
3) The amp situation
4) I'm getting sporadic terrain alerts with no towers in the area, etc.

I'm due for an oil change, and condition inspection is in two weeks. I'll check for loose connections after the oil change I'll probably do tomorrow. I was wondering if the alternator was going bad but will check connections first.

[Andy]

I edited my earlier post. Connections at the shunt are not likely to be the problem since current goes negative rather than zero. The applicable schematic seems to be -109 CC11-160 Alternator System.

[hawgdrvr]

I brought the SD card home after last nights' flight and will see if I can make sense of the data.

I did an oil change two days ago. I did an engine run prior to the oil change after removing top cowl and gills to inspect everything which looked secure in the engine area. On runup the amps were 0 for probably a minute and then rose to positive numbers and remained. Runup and leak check post oil change did not do this, all looked normal. Last night flew an hour, recorded the runup (which I'll do everytime for a while) and did not see anything abnormal. I did have one noticeable hiccup in the engine running during flight which I "think" has happened once before. Got my attention, no clue what that was. Essentially running 21 squared just droning around and noticed a very brief sound and also felt it in the aircraft, no other indications of anything. I will be changing all plugs at condition inspection next week.

[hawgdrvr]

Linked below is the G3X data from the SD card for Saturday's flight where I saw the unusual amp readings.

1) You can see the runup passing around 1700 RPM's (around line 594) the amps went to 0 and I noticed the engine was a bit rough at this RPM
2) You can see the amps go negative around line 1978

Any opinions?

For some reason I can't attach a 600 KB zip file, the forum says it has a limit of around 97 KB - someone needs to fix that.

Download from dropbox (zip file)

[Andy]

Last night flew an hour, recorded the runup (which I'll do everytime for a while) and did not see anything abnormal.

What do you mean by "recorded the runup"? I always have an SD card in the GDU. I have two allocated and rotate them when I want to take one home for archive or analysis. SD cards are inexpensive and you never know when you may want to review the data.

[hawgdrvr]

I have a GoPro over my left shoulder to record the G3X for flight debrief. I certainly can use the SD card but when I see something that catches my attention such as the AMP reading dropping it's nice to have that on video to verify "did I see what I thought I saw?" and then review the SD card data.

[Andy]

2) You can see the amps go negative around line 1798

Any opinions?

Not at the line number you indicated but I found the negative current event in cruise flight. The VOLTS 1 shows a clear drop at the same time.

Either your alternator stopped charging or there was a huge increase in alternator load. It would be easier to diagnose if you had alternator current monitored and recorded as I do in my FX-3.

I noticed that your normal voltage is lower than on my FX-3. My VOLTS 1 typically runs about 14.1.

[hawgdrvr]

Thank you for taking a look at my data. I sent it to CubCrafters but haven't heard back on it yet. What do you suggest may be the cause? I'm going to a CubCrafters service center next week for a condition inspection, it would be a great time for a warranty replacement of whatever is suspect such as an intermittent alternator?

Did you also see the drop around 1500 RPM on runup?