Amps going negative intermittently

[Andy]

Unrelated to the main topic but your data log seems to indicate you are not turning on IBBS and allowing G3X to power up before engine start. Is that true?

My normal practice is to turn on IBBS when I get into the aircraft. G3X is powered up before I have the belts secured. GPS normally has a good fix and AHRS is aligned before I attempt engine start. I don't know that starting immediately after IBBS is turned on causes any problem. I simply prefer to check as much as I can, including all the alerts, before start. It also allows a confidence check of the loaded IBBS voltage and that all systems that should operate on IBBS actually do.

My logs show my GPS acquisition sequence is 3D, 3DDiff, 3D(XPDR), 3DDiff (XPDR). Your log shows only 3D, 3DDiff which indicates the GDU internal GPS is in use all the time and the higher integrity transponder GPS is never used. Don't know if your aircraft GTX/GDU interface is configured differently from mine perhaps because your original build included the GNC. It's something I'd want to understand if it was my aircraft.

More closely related to the original topic - I also noted that your battery charge after engine start peaked at 12 A but a recent log of mine showed peak of 28 A. It could simply mean you battery is in better condition than mine. Was this log with the new battery?

Cruise battery charge current is very similar to mine except for the brief discharge anomaly.

Still think you have an intermittent alternator or an intermittent wiring fault. A problem with the shunt sense wires would not cause the simultaneous drop in main bus voltage.

[hawgdrvr]

No, not the case. IBBS is definitely on (as well as Master) at engine start, which obviously is required TO start. Lately I've been turning IBBS on and then push the plane out of the hangar. Per a tip from TSquared I have the engine page as my default startup so I'm ready to monitor everything on power up.

This is a new battery which may also be why the 13.7V possibly as it's fully charged. I do know TSquared keeps his on a charger where I have not been lately as I'm flying every 3-4 days and want to see how things go without the charger.

As I replaced my ignition backup battery yesterday it is on a charger before my next flight which is slated to be Monday so I'll see how things look coming off the charger whereas my APR 30th flight was not on a charger prior to flight.

[Andy]

No, not the case. IBBS is definitely on (as well as Master) at engine start

The linked data log shows IBBS was turned on 2 seconds before cranking. Not long enough to evaluate system operation on IBBS. This is about the only time the IBBS is ever tested unless you perform the long duration loaded test suggested by the IBBS manufacturer.

[hawgdrvr]

The linked data log shows IBBS was turned on 2 seconds before cranking. Not long enough to evaluate system operation on IBBS. This is about the only time the IBBS is ever tested unless you perform the long duration loaded test suggested by the IBBS manufacturer.

Even if this was the case where I turn IBBS on while I'm running the checklist it would still be at least 30 seconds as I run the checklist, prime, then crank. I'm in a habit now of getting the IBBS on sooner so it is ready to monitor engine params (and voltages) at startup. When you have the engine as your startup page there is a strange layout issue where not everything appears (or is not online yet) so I have to press back then tap into the engine page again to view all params. To try and avoid this I get the IBBS on either at push out or before I get into the plane.

[Andy]

I have seen several cases where my log start was delayed from when I expected recording to start. This caused me to not have data for some tests I ran in the hangar.

I have asked Garmin what conditions must exist for log recording to start but they never answered. I suspect the GPS must have acquired a fix and be producing good GPS time for logging to be enabled.

That assumption is supported by the fact that the first line of my logs shows GPS Fix Status of 3D. It never logs what happens before GPS has acquired a fix.

Before anyone says the log would be useless without a time stamp - I disagree. Data is logged once per second. It would be easy to post process data with no time stamp and assign the correct time by working back from the time GPS time became valid.

[Andy]

I have asked Garmin what conditions must exist for log recording to start but they never answered. I suspect the GPS must have acquired a fix and be producing good GPS time for logging to be enabled.

Today I submitted a request for data logging to start as soon after boot complete as possible. I was told that request has been passed on for consideration. I was also advised that, in the current design, one of the following conditions must be true for logging to start:

Have a valid GPS fix
Engine running
System is in the air
Autopilot is engaged

[hawgdrvr]

Good to know. Thanks for sharing.

[dkelley]

When I finished my EX3 build, when testing/taxiing prior to first flight, my Volts were only 13.2-13.7 and was also showing negative 3-4AMPS. My previous CC build was always in the 14+V and +AMPS, so I knew something wasn't right. Turned out that I didn't have a good enough ground on the alternator. There is small Bracket that mounts the ALT to the block. CC started powder coating these brackets a couple years back and if the powder coat is not removed adequately, it results in Poor-NO Ground and your VOLTS and AMPS will do Exactly what you have been describing. I would check that the ALT is well grounded! Im sure you resolved by now, seeing this post is 7mos old.

Cheers!

D. Kelley

[Daveembry]

yep that’s right. The mounting fixture on the engine also needs to have powder coating removed. I covered this in this post since the manuals didn’t. https://forum.cubcrafters.com/showth...ll=1#post22606

3F43B8CF-764B-4096-938D-0051CBD2A0E0.jpg

When I finished my EX3 build, when testing/taxiing prior to first flight, my Volts were only 13.2-13.7 and was also showing negative 3-4AMPS. My previous CC build was always in the 14+V and +AMPS, so I knew something wasn't right. Turned out that I didn't have a good enough ground on the alternator. There is small Bracket that mounts the ALT to the block. CC started powder coating these brackets a couple years back and if the powder coat is not removed adequately, it results in Poor-NO Ground and your VOLTS and AMPS will do Exactly what you have been describing. I would check that the ALT is well grounded! Im sure you resolved by now, seeing this post is 7mos old.

Cheers!

D. Kelley

[stautz]

I have experienced the same problem in flight. Amps went to to as much as minus four on my last flight. I just got it back from annual and the shop said they loosened the alternator belt because it was too tight. I am going to check the alternator mount tomorrow and will let you know.