Question How to get a red CAS alert for an alternator failure on the Garmin G3X?

[Neal]

It’s fine. It’s how I iterate a problem to come up with a solution. If we didn’t have these discussions I would have never been aware of the current alert setting of -10 amps which obviously needs adjusting.

 

[Cactus Charlie]

You make something very simple seem complicated. It really isn't.

Well, having given everyone the chance to contest that statement, I'll tell you why it is actually a bit more complex.

In an FX-3 or EX-3 the ignition modules are powered directly from the battery and are powered regardless of the state of the Master contactor. They only draw a few micro amps when the ignition switch is Off.

When the alternator is working and charging the battery, the shunt current (AMPS display) is the sum of the battery charging current and the current drawn by the two ignition modules. Any system load (lights, strobes, avionics, etc) is powered directly from the alternator and this current does not pass through the shunt.

When the alternator fails, if MASTER remains On, the shunt current (AMPS display) is the system load (lights, strobes, avionics, etc) but does not include the ignition module current. The actual battery discharge current is now AMPS readout plus about 2.4 A for the ignition modules.

This does not change my position that zero amps is the correct threshold for AMPS alerting. However, it may provide some insight on how to interpret the AMPS reading, particularly when load shedding after alternator failure.

 

[Neal]

I don't see how alerting at zero amps can hurt for people to set as a starting point and learn from there. If you're getting alerts and you think you shouldn't then dig into why you're getting an alert. I may set my "engine running alert" to 0 and my default alert to -1 and see how that works. Knowing I'm exploring with alerting I'm not going to pull the BRS if I get an alert

In my case I need to test at full load as mentioned which is all 4 WAT lights on. I only tested this briefly to make sure I wouldn't go dark at night if I opted for all lights. I only anticipate using this configuration in a high traffic environment for anti-collision purposes.

 

[Cactus Charlie]

If all light on causes AMPS less than zero it is no reason to change the alert threshold from zero. It is correctly warning you that the battery is discharging, a condition that will eventually cause the engine to stop.

Don't want to discourage you from experimenting though and you need to decide what works for you.

 

[Neal]

Thanks. Good points. I'm just trying to learn and understand the ramifications so I don't get an alert unnecessary. This is the reason for this discussion and why I like this forum so I can learn and others watching this can learn too. Obviously the -10A alert should be a red flag to people to change, in fact CubCrafters should publish a bulletin to make owners aware after what I (we) have learned here.

Now I'm wondering if the advanced gauge setup is even needed if I'm going to set an alert at 0 amps? It may be moot now.

 

[Cactus Charlie]

Now I'm wondering if the advanced gauge setup is even needed if I'm going to set an alert at 0 amps? It may be moot now.

I have had yellow AMPS alerting at ZERO amps for over 4 years and it has never tripped in flight. I have not configured a conditional AMPS red alert but I do have Alternator current monitoring and alerting on my FX-3. Any red alert that I added would be on alternator current not shunt current.

I don't know what alerting convention was used in the A-10 but, for the transport aircraft I worked on, RED with master warning means immediate crew action required.

FX-3 alternator failure requires master warning but a brief battery discharge does not. You can't implement that with shunt current only, you also need alternator current monitoring.

 

[Neal]

Good point. Yeah, we had an entire panel of rows of lights that triggered the master caution. I think anything out of limits triggered, there was not warning stage. I think the yellow vs red concept is a good point. 0 for a yellow alert, use the conditional at -2 or -3 for a red alert so it is a progressive warning system.

 

[Cactus Charlie]

"If warning, caution, or advisory lights are installed in the cockpit, they must, unless otherwise approved by the Administrator, be--
(a) Red, for warning lights (lights indicating a hazard which may require immediate corrective action);
(b) Amber, for caution lights (lights indicating the possible need for future corrective action);
(c) Green for safe operation lights; and
(d) Any other color, including white, for lights not described in paragraphs (a) through (c) of this section, provided the color differs sufficiently from the colors prescribed in paragraphs (a) through(c) of this section to avoid possible confusion."

ref - https://www.faa.gov/regulations_pol...ttees/documents/media/TAEas-wcal-04232002.pdf