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

[Neal]

A new thread to discuss a specific topic from this thread from an engine failure situation that occurred due to an alternator going offline due to a wire terminal failure. This thread is to determine how to configure the Garmin G3X using the advanced gauge display functionality and logic controls to show a red CAS alert when the alternator amps go below zero with the engine running.

Thank you to @Cactus Charlie for helping to figure this out.

 

[Cactus Charlie]

Ok, the first step in any new design is to define the requirements.

We want to be alerted immediately to alternator failure but we don't want nuisance alternator fail alerts.

Most FX or EX with a Garmin suite will have standard CubCrafters instrumentation which means battery current is available but alternator current is not. So we use battery discharge as a proxy for alternator failure.

We are assuming that the existing amber BATT AMPS is not sufficient warning of alternator failure - Is that a valid assumption?

Battery will show discharge as soon as master is on and until engine start provides alternator output. Is engine running the only condition required for alternator fail alerting? If so, what rpm should we use?

Do we want alternator fail alerting on ground or only in flight? Can we assume that a pilot scans all the instruments before takeoff and would see amber BATT AMPS?

Garmin does not allow user defined alert text so any alert based on BATT AMPS will be "BATT AMPS". We define the color and the current (and other conditions for advanced gauges) at which it is displayed.

The simplest implementation would seem to be:

If engine rpm greater than idle (say 600 rpm?) and BATT AMPS less than existing BATT AMPS amber threshold then display BATT AMPS RED with aural "Current" alert.

It's easy enough to make the alert only display in flight based on airspeed and time but that may be an unnecessary complication.

Comments or suggestions?

 

[Neal]

We want to be alerted immediately to alternator failure but we don't want nuisance alternator fail alerts.

Correct

We are assuming that the existing amber BATT AMPS is not sufficient warning of alternator failure - Is that a valid assumption?

Correct

Battery will show discharge as soon as master is on and until engine start provides alternator output. Is engine running the only condition required for alternator fail alerting? If so, what rpm should we use?

600 RPM should work as it indicates engine started. I was thinking if we wanted higher like 1000 which is when loads are probably going to be brought online such as AV, etc. This may need adjusting.

Do we want alternator fail alerting on ground or only in flight? Can we assume that a pilot scans all the instruments before takeoff and would see amber BATT AMPS?

I want to know as soon as amps go negative so ground for me. I had a field breaker pop and I saw the negative amps. I'd rather not takeoff with a failure I didn't recognize.

My only concern in the config is that any loads added don't trigger an alert. My plane has two higher powered landing lights I upgraded to which draw 3.8 amps each (max) so if not in wig-wag and both are on it can be a higher load. Combine that with my pair of the same lights but taxi light versions I can get near 0 amps with the alternator running normally with iPhone connected (USB loads) and all four lights on in a worst case condition. So consideration for < 0 vs < -1 amps should be considered as to when we alert for a higher load scenario without failures.

 

[Cactus Charlie]

So consideration for < 0 vs < -1 amps should be considered as to when we alert for a higher load scenario without failures

The current readouts have some error so have to account for the worse case loading condition and any tolerance in the measurement. Give me a number and you can change it later if needed.

If you have logs showing battery current going negative with engine running at low rpm please email me.

I think I have enough to establish the structure. Fine tuning thresholds should be easy enough.

The basic concept is to establish an "invisible range" on the rpm readout. We'll assume that range is 600 - 3000 rpm. When rpm is in that range a logic signal will be set. There is no change to the presentation of the rpm scale. The change is invisible.

The BATT AMPS scale will be revised to have an addition set of color bands that are active only when that logic signal is active. The color band changes will include a "red +alert" range from zero to -30(?).

Maybe you can do it quicker than I can.

 

[Neal]

Let's use a negative 3 amps as the alert point. The gist for now is more how to do it, each aircraft owner can modify it. This is just a learning exercise to get us started and understand the advanced gauge and logic functionality.

Thanks!