Flickering Alternator Light

[slowflyin]

Gents,

Looking for some advice regarding my alternator idiot light. The light for my left alternator will occasionally flicker while in cruise.   I’ve turned off the right alternator with no drop in voltage with the system loaded up.  Lights, pito  heat, prop heat............ I have tested this way several times and it seems the flickering subsides with the right alt offline.  Is there a threshold setting?   

Thanks,

joe 

[carusoam]

What idiot light do you have?  Ship’s annunciator panel? 

What voltage readings do you get from your alternators..? (Above 26v(?) when charging)

The POH has a description of each alert in the message center, and what sets them off...  they are not all the same... especially the low fuel alert. Where pushing the reset actually enables the function to work on every flight. No reset, no lo fuel warning...

Expect that there is probably an adjustment for that, or a loose sensor wire...

PP thoughts only, not a mechanic...

Best regards,

-a-

[DVA]

Gents,

Looking for some advice regarding my alternator idiot light. The light for my left alternator will occasionally flicker while in cruise.  

 

Is there a threshold setting?   

Thanks,

joe 

 

Yes, there are threshold settings, it’s an relatively easy procedure and I can send you the maint manual pages for it if you have them.

 

However, the circuit that drives those alt lamps was poorly designed and used a series of steering diodes to make a high-low threshold system. When those diodes start to leak (from age) the circuit becomes unstable and you can get exactly what you’re seeing to a ton of other odd flickers. Very hard to find a shop to work on those.

 

Good luck.

 

 

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[slowflyin]

I’ll review the m manual.  Thanks for the advice.  Fingers crossed hoping the diodes   haven’t degraded.  

[slowflyin]

1 hour ago, carusoam said:

What idiot light do you have?  Ship’s messaging system? (There is a proper name for this alerting center)

What voltage readings do you get from your alternators..? (Above 14v when charging)

The POH has a description of each alert in the message center, and what sets them off...  they are not all the same... especially the low fuel alert. Where pushing the reset actually enables the function to work on every flight. No reset, no lo fuel warning...

Expect that there is probably an adjustment for that, or a loose sensor wire...

PP thoughts only, not a mechanic...

Best regards,

-a-

The lamp is located in the Bravo annunciator panel.  28 volt system indicating 28.5 under load.  Thanks 

[carusoam]

Great signs, SlowFlyin...

Sounds like the charging system is working as expected...

The annunciator panel (thanks for the reminder) is an electrical engineer’s magic box... the MM has the detailed drawings...

Your mechanic can probably ferret out the diodes, especially if you can find them in the manual drawings.

Mooneys have a few diodes in odd places related to the two battery and charging system... not sure if these are at all related. I think @LANCECASPER may have photographed the tail related diodes in his Bravo...

Diodes tend to fail miserably, easy to see the burnt and/or broken pieces... or measurable resistance in one direction, not the other...

Any idea if the warning light was battery dependent, L vs R?

PP thoughts only, not a mechanic...

Best regards,

-a-

[DVA]

Your mechanic can probably ferret out the diodes, especially if you can find them in the manual.

...

Diodes tend to fail miserably, easy to see the burnt and/or broken pieces...

Most mechanics (not all though) have little electronic theory or experience - won’t likely want to touch a thing except run the settings adjustment

The diodes in this circuit are very small and under very low current. They won’t fail like the big ass protection diodes in the battery charging circuit. They will look normal, and you can only tell which one(s) of the many are bad is to measure the reverse voltage drop across them -out of the circuit - and find the one(s) that exceed the 0.7v drop. It’s a pain.


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[carusoam]

Dave,

Any thoughts related to the protection diodes in the back?  

If any of them fail, could they cause the light in the annunciator panel?

The issue I was referring to, was a broken wire of the diode itself...

Wondering how that broken wire might show up elsewhere...

Best regards,

-a-

[DVA]

Dave,
Any thoughts related to the protection diodes in the back?  
If any of them fail, could they cause the light in the annunciator panel?
The issue I was referring to, was a broken wire of the diode itself...
Wondering how that broken wire might show up elsewhere...
Best regards,
-a-

This appears to be classic diode leakage in the annunciator panel. I’ve worked on a few of these and (provided that the alt / regulator / threshold adjustments are correct) this looks like a common mode failure. The big diodes in the back are for the charging and battery 1 2 circuits and would likely not affect the indicator intermittently. But you’re correct to point them out as Mooney trouble spots, especially when peeps have trouble with charging batt number 2.

Mooney also provided me with the original engineering drawings and ToO for those pesky multi-led flap, rudder trim and cowl flap indicators on the M’s. I build a test bench for them and have repaired a few. According to my friends at Mooney I’m one of the only ones doing that. Mooney won’t touch them anymore. I hesitate to, because they’re as much of a PIA as the annunciation panel.


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[LANCECASPER]

1 hour ago, DVA said:

Mooney also provided me with the original engineering drawings and ToO for those pesky multi-led flap, rudder trim and cowl flap indicators on the M’s. I build a test bench for them and have repaired a few. According to my friends at Mooney I’m one of the only ones doing that. Mooney won’t touch them anymore. I hesitate to, because they’re as much of a PIA as the annunciation panel.

 

Most of the time on these (multi LED indicators) it's the 1/4 amp pico fuse that's bad.

 

[PilotX]

Does anybody have the maintenance manual for the Bravo? I have a 1990 reached out to @DVAbut he hasn’t got back to me yet. My alt lights are flickering. 

[carusoam]

Got a video of what is going on?

Post to YouTube, copy link here...

Best regards,

-a-

[LANCECASPER]

9 hours ago, PilotX said:

Does anybody have the maintenance manual for the Bravo? I have a 1990 reached out to @DVAbut he hasn’t got back to me yet. My alt lights are flickering. 

At all RPMs or just low RPMs?

[N201MKTurbo]

On 11/24/2018 at 8:14 PM, DVA said:

 

Most mechanics (not all though) have little electronic theory or experience - won’t likely want to touch a thing except run the settings adjustment

The diodes in this circuit are very small and under very low current. They won’t fail like the big ass protection diodes in the battery charging circuit. They will look normal, and you can only tell which one(s) of the many are bad is to measure the reverse voltage drop across them -out of the circuit - and find the one(s) that exceed the 0.7v drop. It’s a pain.


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FWIW,

Vbe is measured forward biased...

https://www.asc.ohio-state.edu/gan.1/teaching/summer04/Lec5.pdf

Edited June 7, 2021 by N201MKTurbo

[Danb]

My master light has been blinking for a couple years they can’t find the problem everything is ok. I have. G1000 which shows all in green or within tolerance. Label it inop.

[PilotX]

7 hours ago, LANCECASPER said:

At all RPMs or just low RPMs?

Well the RPM gauge wasn’t working either so I probably only had it up to 1400. 
 

When I shut off the L Alt the R alt light went or (l alt light was solid), the reverse is also true. I found a maintenance manual and sent the sections to the avionics tech but usually there is somebody who has seen and fixed it already. 

Edited June 7, 2021 by PilotX
Amplification