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

[Cactus Charlie]

At delivery (CubCrafters aircraft) you are not aware of an alternator failure until you are at -10A for alerts. I'm not sure when that occurs, maybe it's instant when the alternator goes offline, I'd have to pull the FLD (field) breaker to see what happens.

The battery discharge current will depend on system load and that will vary with aircraft configuration.

My aircraft with all avionics on, strobes on, and landing lights flashing, pulls less than 10 A. I would not expect to ever get battery AMPS Alerting in the "as delivered" alerting configuration.

If you test by pulling the Field CB you need to do it at typical cruise rpm as the ignition module current increases with rpm. Do it with and without the electric fuel pump on. (I would suggest not running the test in flight.)

The following plot is a typical flight for my FX-3. I derived system load by subtracting battery charge current from alternator output current. The variation of load for run-up, takeoff, and fuel pump on/off can be seen. Derived system load is the current that would have to be supplied by the battery if the alternator failed.

 

[Neal]

I got the new config installed but not yet tested, may be able to get the plane out of the temp hangar tomorrow. Was blocked tonight.

I changed the SHUNT 1 config so it will alert at -5 AMP instead of the factory set -10 AMP condition which is not a good config. My custom setup done by @Cactus Charlie will alert me at -3 AMPS with the engine running but everyone should consider the change below for your alert level of a failed alternator. Ignore the asterisked item, that's what @Cactus Charlie added.

FACTORY CONFIG:

NEW CONFIG:

 

[Cactus Charlie]

I cannot let this go without comment.

You need to know immediately if the alternator has stopped providing sufficient current to maintain all system loads. That point is reached when the battery current becomes negative.

Anyone who does not want their Carbon Cub wrecked because the alternator fails should configure a battery current alert that triggers at ZERO amps.

I did this over 4 years ago on my FX-3 and nothing in this thread has given me any reason to doubt or change that design decision.

(I created a red+alert configuration that tripped at -3 A for test because that is what I was requested to do, not because I thought it was a good design).

 

[Neal]

You certainly didn't give any feedback for discussion

It's dependent on the plane. My plane at max demand will go to zero amps which is landing lights on steady and taxi lights on. That's 4 x WAT G3's which can draw up to 3.8A each. Add in the avionics and I'm at zero amps at full load.

This is why I chose -3. Maybe I'll tweak it to -1. Maybe through discussion here people including self will learn that -5 for the alert is incorrect and it should be a lower threshold. In my case I'm expecting the custom config of -3 to alert me first. I expect at normal load for daytime flying on a glass panel, at least IFR config, -3 will trigger on alternator failure, if not even -5. This is assuming a fully charged EarthX which can draw over 20 amps when charging. But the calculation comes in as to what load am I pulling from the starter battery without an alternator and that's what people need to ensure that value that will go negative will trigger an alert.

It wouldn't hurt to set a low negative value such as -1 and see if you're getting false alerts. You probably won't. If you find you are getting alerts then adjust as needed. In the end, know how to make this change in your G3X configuration area.

The WAT Parmetheus Plus in your FX-3 and most other CubCrafters aircraft until recent are insufficient for lighting IMHO. I upgraded mine. Huge difference but needs more power. I digress.

 

[Cactus Charlie]

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

If the battery current is negative the alternator is not supporting the current system load and the battery is discharging. I want to know that immediately. No alerting threshold except ZERO gives me that information!

 

[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

 

[Neal]

Here is my latest revision which I flew last night. I did not mess with any breakers or test things, it's been a while since I flew and I was racing sunset. I made a revision prior to flight, didn't like it, revised after flight to come up with this. I welcome any and all feedback.

The * item is the conditional alert that only triggers with the RPM > 600, i.e. engine running alert.

I wish they allowed decimal amps.