Cirrus Question.

SixPapaCharlie

SixPapaCharlie

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Look at the chart below (later, read first)

1. flying along and keep getting [ALT1] light on the panel.
It comes on and goes off. This SHOULD be an indicator that the #1 Alternator is not charging.

It is normal to get an ALT 2 light but never an ALT 1 light.
SO this ALT 1 is on and off and on for a loooooong stretch.

The Battery indicator however NEVER reports "LO" on the panel.

This is getting Cirrus specific pretty quick. Help me out @RudyP and @FastEddieB

So I am getting indications of an alternator failure but the battery is maintaining its charge none the less. 3 hours of flying and the battery is all "I'm good dude"

My assumption is I have a faulty sensor. Annual on the Cirrus was completed 2 weeks ago and this started on the following flight. Is it possible that some sort of sensor is failing?

If you look at the graph, the top is Alt 1 / Bus 1
The Buss is consistant as a mo.

The ALT reads dead mostly.

If the ALT was dead, I would expect the main bus to be degrading. No way I could maintain a static bus for an hour and a half flight with an ALT1 reading zero right?


EngineData.jpg


The bottom graph is bus2 and ALT 2 and is pretty consistent with all historical flights I have data on.

I am thinking of going on a flight tomorrow, and turning off ALT 1 with the expectation that I can download the same data and will see a major drop on MBUS.

If that is the case, it should be a faulty sensor / output of some sort.

I guess the question is, Is it true that it would be impossible for MBUS to maintain that level of throughput if ALT1 really was at zero for that period of time.

The 2nd question is if that is true, is this indicative of some sort of sensor failure?
 
Could be sensor, could just be that you don’t have enough load on the bus to discharge the battery and the other alternator is keeping up with the load.

Most twins are dual alternator systems and day VFR without every single thing turned on (pitot heat, whatever anti or de-ice they have, maybe an old radar or storm scope, all the exterior and interior lights on high, gas burning heater fan in the nose locker, gear in transit, etc etc etc...) the single alternator will keep up just fine.
 
Yup BUT bottom graph is ALT2 which is the one that sits on the sidelines going "Do ya need me coach???!?!??!"
So it is dead most flights. If needed, it powers only the EBUS (Essential bus)

The ALT1 light has never come on before and I looked at 2 years of flight data and never saw it at zero.
My first thought was that it is dying. After downloading the data I am thinking it is working fine but it is phoning in the reporting part.
 
Neither the thing labeled AMP1 nor AMP2 looks sane in either graph. Jumping from 0 to the top of the graph for short periods of time? Those look all wrong, unless “AMP” doesn’t mean “amperage”. WTF are those? Nothing on board goes from 0 current draw to 40 amps and back.

I’d check that the data the Saavy thing thinks it’s getting is actually the right channel of data and its handling it correctly, before anything. The data or the processing looks way wrong.

The other two lines, which I assume are current draw from both busses, look sane. Over 40 on top and less on the essential.

As far as how the alternators are wired in the Cirrus, you’d know better than I.

When your Alternator 1 light comes on is it momentary, or does it stay on? Could just be a loose connection if it’s momentary.
 
That's an odd one. Buss 2 is not supposed to feed buss 1, unless there is an issue (which you would have discovered when checking the flap switch in preflight to check the isolation)

Since buss 1 stayed healthy this would suggest to me it's some sensor acting up. The fact that the light was on and off is a hint it's a connection somewhere. Some of the wires and connections up there are surprisingly "consumer grade"

Curious what others have to say but that's my opinion based in in w you posted
 
denverpilot said:
how the alternators are wired in the Cirrus
Click to expand...
Basically you have a main buss and an essential buss. Alt 1 can feed both, but alt 2 feeds only the essential.

When you pre-flight you check the isolation by attempting flap extension with only essential buss on (which shouldn't be powered by buss 2). No flaps is good, things isolated. Flap extension means you have an issue.

That's why 6PC thing is weird. If buss 1 stayed good that means either buss 2 leaked in or that alt 1 was working just fine

...techn techni
 
Tantalum said:
Basically you have a main buss and an essential buss. Alt 1 can feed both, but alt 2 feeds only the essential.

When you pre-flight you check the isolation by attempting flap extension with only essential buss on (which shouldn't be powered by buss 2). No flaps is good, things isolated. Flap extension means you have an issue.

That's why 6PC thing is weird. If buss 1 stayed good that means either buss 2 leaked in or that alt 1 was working just fine

...techn techni
Click to expand...

Okay that makes sense, probably just a honking big diode isolating the two.

But it doesn’t explain what those spiky two graphs are. Maybe he’ll explain what those really are, because nothing on board draws that much current from alternating (no pun intended) busses like those show.

Something weird going on there, but I’d want the graph to show something sane first or I would be looking at the raw data and seeing if the Saavy thing is even graphing it correctly from the correct data channels.
 
Sorry, whatever expertise I may have had on such things is over a decade old and very stale.

These issues usually trace to either wiring or the MCU, or whatever they call it now.

Extensive knowledge of such things available over on COPA. If you’re not a member, you should be.
 
Sounds like a First World Problem.
 
Somewhere in the world a wiring schematic for the Cirrus must exist. Perhaps said schematic should be consulted to see exactly what might make the light of concern illuminate. Troubleshooting might proceed from that point...
 
The only way I can make the data make any sense is if the voltage levels were screwed with and the diode was reversed. This should not happen in an annual; but I have seen a Cirrus which came from the factory wired backwards. It was a good six years old before the mechanic found the problem.
How this makes sense is a constant draw on the essential bus, which is powering the plane; the ALT2 is not quite strong enough to run everything on main and essential with a reduced load. So every few minutes voltage drops just low enough for ALT1 to kick on; likely after transmitting on the radio. When it does, it spikes, battery buffers the load, and voltage steadies again.

Besides the flap check, verify the voltage levels.
On the ground at 1700 RPM (going on memory, in the standard checklist it should have the RPM required for both alternators to be kicked on).
The essential bus should be a half volt lower then the main bus.

The ALT light is more likely a loose connection, or the alternator is slipping.

Tim
 
The avidyne electrical system is a little rusty in my head too but I think you’ve covered most of the possibilities. It isn’t normal and should be looked at (unlike alt2 light on at low rpms). It could be an intermittent contact issue, legit alternator issue or MCU issue. Do you know which MCU you have (100, 120 or 130)?

I agree that the data isn’t all that helpful or definitive there. Do you have a copa account? Posting there will get you much more knowledgeable (than my half ass attempt anyway) comments.
 
Clark1961 said:
Somewhere in the world a wiring schematic for the Cirrus must exist. Perhaps said schematic should be consulted to see exactly what might make the light of concern illuminate. Troubleshooting might proceed from that point...
Click to expand...

A wiring diagram for an Intel Core processor must exist too. But try to follow it.
 
Sac Arrow said:
A wiring diagram for an Intel Core processor must exist too. But try to follow it.
Click to expand...
I am not so sure that the wiring complexity of a Cirrus approaches the complexity of an Intel Core processor. Perhaps it does. Perhaps it doesn't. Until such schemati are presented perhaps we'll never know.
 
Aw, come on....are we getting that useless here?.....the answer has ALWAYS been : PULL THE RED HANDLE!
 
Did you post this on the COPA board? Might get better answers there.
Our answers are entertaining though
 
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