Alt load imbalance

[CFIDave]

I have a similar problem on my DA62: when bringing the RPM back to idle on the ground, I get a temporary R ALT FAIL annunciation and hear a chime. This often happens when the automated run-up completes.

Swapping regulators didn't change the behavior -- and attempts to troubleshoot this when the plane was under warranty didn't work out.

I'm convinced the problem is with the right current sensor coil (that signals the G1000) that's located on a circuit board inside the right engine nacelle -- it probably needs replacement.

[Davestation]

My previous post seems to have been lost in the ether…

I called them earlier and we got the part coming to you overnight.

[Soareyes]

My previous post seems to have been lost in the ether…

I called them earlier and we got the part coming to you overnight.

Wow! I'm starting with you next time.

[ememic99]

The plane has been in the shop this time for five weeks so far

I'm really curious what they do to the aircraft on course of 5 weeks. My DA42 was in the shop for 5 weeks when the engines were exchanged to CD-155 and even that was a week longer than planned due to cowlings delivery delay rather than shop being slow. I accumulate 5 weeks in the shop usually in 5 years.

[Soareyes]

Not done with this one yet.

I picked up the plane today after it had the new left current sensor installed. The amp readings were nearly the same, it seemed like a fix.

During the 200 mile flight home there was a brief, one second L ALTN FAIL message, the amps momentarily went to zero but then right back to normal. On short final however the message returned and the left amps stayed zero.

Troubleshooting on the ground:

L ALT switch Off, R ALT switch On: L ALTN FAIL.
L ALT switch ON, R ALT switch Off: Normal amp readings both L & R.
L circuit breaker out, R breaker in: L ALTN FAIL.
L breaker in, R breaker out: current showing both L & R, but unequal.

I was surprised that turning off the right alternator did not only not trigger a fail message but it made both amps read normal. Pulling the circuit breaker for the right alternator similarly stopped the fail message for the left alternator. Is that how they are supposed to work?

A video of the above:
https://www.youtube.com/watch?v=ABoAhDhIZNk

[Davestation]

That is strange - the dashes make me think that there is a break in the circuit.

There are a few different things at play here.

1. G1000 voltage sense
2. G1000 amps sense
3. Paralleling regulator sense

IIRC there are four ammeters, two for the Garmin and two for the paralleling regulator (which does not display).

I also think that the fail caution is a voltage trigger, not amps. If it’s sensing above 25.5V, then it assumes the alternator is working because otherwise it would just be battery voltage. The system shouldn’t care how many amps you’re using or the state of battery charge.

In other words you could have them way out of sync where one takes the full load and the other next to zero without a fail indication, and vise versa (if the voltage sense is failed but the alternator is indeed charging). If either of the ammeters on the paralleling regulator is malfunctioning, you can get an amps split by itself. If either of the Garmin ammeters is malfunctioning, you can get the dashes like that (or otherwise unreliable readings), even if they are actually paralleled.

[Davestation]

I’m guessing since turning off the left doesn’t make the right go up, it is not merely a Garmin indication problem. And since the Garmin is dashing out, it is not merely a paralleling problem.

Not sure what the common denominator is, unless there are multiple issues simultaneously. Could be something in the control circuit, causing the left alternator to actually go offline.

—

Actually looking at the video again that seems to be the case. When you have the left on and the right off, it drops to battery voltage. The left alternator seems to be dead. I’d start with the switch, the relay, the connections on the alternator itself.

—-

Still can’t explain why pulling the right CB brings up the voltage though, very bizarre

[Soareyes]

Actually looking at the video again that seems to be the case. When you have the left on and the right off, it drops to battery voltage. The left alternator seems to be dead. I’d start with the switch, the relay, the connections on the alternator itself.

Still can’t explain why pulling the right CB brings up the voltage though, very bizarre

The voltages may be a red herring. I went back to the plane this morning, you know, hoping it healed itself, and repeated the test with a few variations. The amps didn't look any better but this time the voltages stayed steady at the 27.7 level in all configurations.

Remembering that the new current sensor worked well for an hour, then something broke. Maybe a short or something is killing the current sensor?

Bringing the power up above 20% causes 3 amps to show.

A video of this morning's test:

https://www.youtube.com/watch?v=_letuox8ZCY

[Davestation]

It’s true, they always act a little funny - even when you switch them off you get some residual output. I wouldn’t expect to maintain voltage though.

Which sensor did they replace?

[Soareyes]

Providing follow-up:

After the new current sensor failed they replaced the the current sensor again and installed a new voltage regulator at the same time. They also applied some sealant around the holes in the firewall (?) where the wires from the engine side penetrate to the compartment in the lower part of the nacelle where the current sensor and voltage regulator reside. The thinking was that water was getting in there somehow.

We just flew from Florida to Maine and back with no alternator load imbalance.