28V Charging system issues on M20R

[FJC]

Hello,

For the past few weeks I have had charging system issues on my ’97 Ovation. The situation presented itself in the air as a bight flashing VOLT AMP indication on annunciator.  I am not stranger to this condition as I notice this light any time engine is slowly idling. I’ve never observed this light above ~1000 rpm ever till now.

I reduced electrical load and quickly landed and determined that that system was running completely off of the battery. When I plugged into battery minder batter was quit discharged. It appeared that the alternator was not keeping up with any load even low ones because there was not much when I turned off unnecessary items . I followed guidance from POH and nothing changed.

Upon recommendation by local shop, I sourced a 100amp alternator from Quality Aircraft Accessories which they installed. Upon startup, it appeared that the situation had been remedied or so off I went. On the next flight I checked the system for positive charging and all seemed well. It was a particularly hot day so I had air conditioner running and when I got up in the air, I noticed a “DIM” VOLT AMP indication on annunciator and once again, I shed load and landed.

After speaking with Consolidated Aircraft and detailing my experiences and actions, it was decided to send in the Voltage regulator for a check and if necessary, a rebuild. Turnaround time was 2 days not including shipping (some bad solder joints were corrected but no components were found defective). Regulator was reinstalled. The situation as before still persists…under heavy load (ac on low/high), a dim VOLT AMP indication is shown on annunciator. I'm not seeing the bright VOLT AMP indication.

This condition of dim VOLT AMP only takes place with the air conditioner on. It seems to me like the alternator cannot keep up with the demands of this heavy load. It displays positive current on AMP gauge however but value cannot be quantified.

The shop is stumped and so am I. The alternator came from a reputable rebuilder. They claim that everything is checked prior to shipment. Now the regulator has been gone through. I no longer see the bright VOLT AMP light (only the dim one). I've asked a few wise sages in MS. I've even consulted with MSC in Chandler. Does anyone have any ideas on what might be logical next steps? Aircraft seems flyable providing I do not use AC but I live in an area where I use it for every flight from around May to October. It is not an option to not use it and so I’d like help and thoughts on how to proceed. There seems to be thresholds for the circuit to annunciate and in the case, two: bright VOLT AMP for lower voltage, and dim VOLT AMP for voltage around 27.4 or so.

Thank you.

 

Freddy

 

[Marc_B]

Plane power has a troubleshooting guide. Always seems the best step is to see what the voltage is at each step of the way with a DMM. Corroded terminals, frayed ground wires, disconnected field wire, bad field switch, until you know the issue it’s hard to know what to replace. 
https://planepower.aero/wp-content/uploads/2018/02/Troubleshooting-Single-Engine-Externally-Regulated-Alternators.pdf

When low voltage is detected internally or when low current is detected the annunciator channel flashes , and when overvoltage tripped is detected the annunciator channel illuminates steady.  Even the annunciator could be an issue if all the voltages are checked and normal. 
 

How much load should the AC pull and did you check to see if this is within spec or not?

[LANCECASPER]

Have your batteries been tested?

This may not be related to this, but your Mooney (1997) falls under SB 20-275. When you look in the logs has this SB been done (the trickle charge circuits to each battery been modified to have an in-line slo-blo fuse)?

https://www.mooney.com/wp-content/uploads/2020/12/SBM20-275.pdf

[GeeBee]

When you replaced the alternator did you check the drive coupling with a torque test and/or did you replace the coupling?

[PT20J]

A few points to consider:

1. Since the ammeter shows a positive indication (no matter what the value) the charging system is working. What is the bus voltage?

2. The air conditioner compressor is engine driven not electrically driven according to the M20R manual.

3. The annunciator flashes to indicate a low voltage (charging system failure) or it is steady on to indicate that the overvoltage protection circuit has tripped (usually a voltage regulator failure). Dim is not a valid indication.

Since this only happens when the air conditioner is on, perhaps something is amiss with the annunciator or the air conditioner. The service and maintenance manual has procedures for checking out the electrical system and the air conditioner. You might call the manufacturer of the annunciator to inquire what would cause a dim indication. https://www.internationalavionics.com/

 

[FJC]

Thank you everyone for responding so quickly! Thanks for the guides.

Trying to capture and respond to comments and questions posed above:

Yes, there is a vbelt that drives the compressor...also, there are big condenser and blower fan(s) that require lots of power to operate. In the past, I've used this system as an operational check for the charging system as it draws a considerable load as viewed on AMP gauge (has consistently done this for years).

Drive couple was checked twice and passed torque test both time with consistent output measure. I initially thought it was slipping but spoke with alternator ship and they indicated that this clutch is pretty much a firm hold or a complete slip if the alternator has seized or bearings are causing issues (makes sense).

This is very much a quasi undervoltage condition. What I do not know is voltage versus current output from the alternator. As I understand this setup, a 100amp alt SHOULD be able to keep up with my setup. From what I've observed, when the voltage is < 27.4 or close, we get a dim flash. When it is much lower, we get a brighter flash of the ALT VOLT annunciator light. So, I've observed two flashing conditions: slightly low voltage, and low voltage. I do have a call into International hoping to discover detectable conditions by annunciator. Anyway, I do have a video but its not compatible with this site. Perhaps I'll post a link to it when I get more time.

It is possible the ac system is drawing excess current. Next steps seem to be to check load output of alt, and then functioning of ac, and then see if I have response from International.

 

Freddy

 

[Marc_B]

FYI if you need it:  I've dealt with International Avionics Inc with annunciator modification and with my IAI voltage regulators.  855-417-2820 based out of Addison but ground locked so they only have capability to do workshop/bench testing, not field testing.  The contact person for VR/Annunciator work is Kenneth Snowden.  I do believe there is a way to bench calibrate the annunciators and voltage regulators that you may not be able to do in the field.  But both are basic circuitry from the 70's that can be repaired and overhauled.

https://www.internationalavionics.com/

[FJC]

More info:

I spoke with Kenneth. He shared with me the fact that "way back when..." they set the voltage threshold too high (he mentioned 27.5) and they no longer do that. He also indicates there is a potentiometer behind the display which should be adjusted downward. Since we are able to maintain >27 volts, the system according to Kenneth is operating as expected. I am unable to explain why my voltage before with old alternator didnt trigger this annunciation. Next steps are to recalibrate/set annunciator voltage threshold.

[PT20J]

3 hours ago, FJC said:

More info:

I spoke with Kenneth. He shared with me the fact that "way back when..." they set the voltage threshold too high (he mentioned 27.5) and they no longer do that. He also indicates there is a potentiometer behind the display which should be adjusted downward. Since we are able to maintain >27 volts, the system according to Kenneth is operating as expected. I am unable to explain why my voltage before with old alternator didnt trigger this annunciation. Next steps are to recalibrate/set annunciator voltage threshold.

Now you're getting somewhere 

According to the Service Manual, the low voltage light should flash when the voltage drops to between 26.6 and 26.4 volts. The pot may need to be adjusted.

A properly operating voltage regulator will drive the alternator to maintain the voltage at its sense input (which connects to a breaker on the panel) to whatever the regulator is set for. The voltage at the sense input may or may not be the same as voltages measured elsewhere in the system, but bus voltages measured at various points should be within a few tenths of a volt of each other.

If the ammeter is showing positive charge, the alternator is working. If it's voltage output is low, it's likely an issue with a high resistance connection somewhere, worn out batteries drawing excessive charge current or a voltage regulator adjustment. 

 

[FJC]

Hi Everyone,

Just wanted to provide an update since this is still not resolved. I continued to fly given that we were still charging, but a Friday or so ago, I had a complete charging failure while up in the air for what seemed like an eternity but probably was only 10 mins. Charging eventually resumed after several field resets and I was able to get home. Still thinking that I had an alternator issue, it was pulled out and sent for a load test.

Here is what I received as a preliminary:

per shop:    Field failure; possible: bad rotor, brush seating issue, or unpolished slip ring.
Causing inconsistent field connection.

Stator diode issue; found one phase failure on oscilloscope. 
Requires Overhaul, possible new rotor

In other words, what wasnt wrong with this unit? In retrospect, I probably should have ordered a load test as soon as I discovered the annunciations from day 1. I just did not think an alternator would get out of the door w/o a proper QA check given what was spent on it. My thinking was that I'd bite the bullet and have shop "fix" the alternator but they recommended I get waranty replacement (it was that bad). I think/hope this is it with this issue but we shall see!

 

Freddy

[PeterB]

A&P here.  I just read this, so I realize you are far down the road.  But what I didn't see in any of the posts is a recommendation to take a hard look at the grounds in the circuit.  Make sure they are clean, tight, not corroded, etc. I always start with the simple stuff first before replacing components. Good Luck!

[LANCECASPER]

On 8/2/2024 at 7:38 PM, FJC said:

Hi Everyone,

Just wanted to provide an update since this is still not resolved. I continued to fly given that we were still charging, but a Friday or so ago, I had a complete charging failure while up in the air for what seemed like an eternity but probably was only 10 mins. Charging eventually resumed after several field resets and I was able to get home. Still thinking that I had an alternator issue, it was pulled out and sent for a load test.

Here is what I received as a preliminary:

per shop:    Field failure; possible: bad rotor, brush seating issue, or unpolished slip ring.
Causing inconsistent field connection.

Stator diode issue; found one phase failure on oscilloscope. 
Requires Overhaul, possible new rotor

In other words, what wasnt wrong with this unit? In retrospect, I probably should have ordered a load test as soon as I discovered the annunciations from day 1. I just did not think an alternator would get out of the door w/o a proper QA check given what was spent on it. My thinking was that I'd bite the bullet and have shop "fix" the alternator but they recommended I get waranty replacement (it was that bad). I think/hope this is it with this issue but we shall see!

 

Freddy

Circuit breakers are designed to protect the wiring. You might try to re-set a breaker once to see if that solves it, but personally I'd never try more than that, since by doing so I'm over-riding the protection for that circuit.

If there's one thing much worse than landing at an unfamiliar airport away from home due to an electrical failure, it's an electrical fire in flight.

[GeeBee]

On 8/3/2024 at 11:58 AM, PeterB said:

A&P here.  I just read this, so I realize you are far down the road.  But what I didn't see in any of the posts is a recommendation to take a hard look at the grounds in the circuit.  Make sure they are clean, tight, not corroded, etc. I always start with the simple stuff first before replacing components. Good Luck!

Excellent advice. I have been having charging issues with my 2005 M20R GX. Especially battery #2. I ultimately removed all the battery cables (the ground cable on #2 is a real PIA to get). The cables and terminals looked good, but I cleaned them anyway with contact cleaner and scotchbrite pad as well as the ground points. Put it all back together and NO MORE PROBLEMS! In fact it has never charged as good as it does now.

[kortopates]

On 8/3/2024 at 6:02 PM, LANCECASPER said:

Circuit breakers are designed to protect the wiring. You might try to re-set a breaker once to see if that solves it, but personally I'd never try more than that, since by doing so I'm over-riding the protection for that circuit.

If there's one thing much worse than landing at an unfamiliar airport away from home due to an electrical failure, it's an electrical fire in flight.

Absolutely! but Freddy doesn't say it perhaps, but no breaker ever popped. He is merely describing the procedure to reset the VR and Alternator which almost every time brought the alternator back on line; except one leg that it too a few tries spread out. Yeah, I was right seat. I'll add too that the shop that thoroughly checked out Freddy's new alternator and found out all the issues was Robert at Aero Accessories in Van Nuys - highly recommend them.

[FJC]

Hi Everyone,

Alternator was returned/exchanged under warranty. New one was installed. Ground run up was good (not lights) and so off I went. There is more to it than this but suffice it to say that upon first issue encountered, I should have ordered a load test which would have saved alot of time. Because I did not, I probably needlessly spent money on sending out/checking voltage regulator that didnt really have any problems.

regards

 

Freddy

[jetdriven]

I hope somebody checked the alternator  coupler per a bunch of service bulletins because if that fails, it trashes your entire engine. I’ve seen it happen.

[MikeOH]

15 hours ago, jetdriven said:

I hope somebody checked the alternator  coupler per a bunch of service bulletins because if that fails, it trashes your entire engine. I’ve seen it happen.

YIKES!

That seems kind of lame; isn't the whole idea of the coupling to PROTECT stuff if the alternator seizes...but if IT fails, the engine is trashed??

[jetdriven]

The gear walks all over the crank gear and trashes that and you have to remove the crank from the engine to change that ring gear plus it puts any pieces of metal into the engine as well, but yeah, it trashes the engine and people have taken to inspecting these things every 500 hours, but it needs to be good when it goes on as well. You can’t just slap it on there.