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Dual Alternator "Failure" - SOLVED

 
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art(at)zemon.name
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PostPosted: Wed Aug 14, 2019 8:12 am    Post subject: Dual Alternator "Failure" - SOLVED Reply with quote

Charlie and Joe,
Thanks much for your quick replies. 
The problem was a blown fuse. Diagnosis was hindered because I had not bothered to update the wiring diagram.
I will write this up more verbosely on my blog because I think it will make a good article. Briefly for this list, I have a shared fuse for the overvoltage lamps on the primary and backup voltage regulators. That same circuit also feeds pin 3 on the B&C voltage regulators. That fuse blew. Both the LR3C voltage regulator and the SB1B backup regulator respond the same way to 0 volts on pin 3: they stay in "do nothing" mode.
Problems which contributed to the loss of both alternators in flight:
  • Shared fuse for pin 3 on both voltage regulators.
  • Inaccurate documentation. The wiring diagram shows independent fuses for each voltage regulator.
  • Lack of knowledge on my part, which allowed me to share the fuse.
  • Karma, which made this happen less than an hour after I had been proudly showing my friend how I had dual alternators.
Kudos to TJ at B&C Aero. When I called to get educated on what pin 3 does and how the voltage regulator acts in response to 0 volts, he had already read my earlier post here and knew the background of my situation.
Kudos to B&C Aero for providing an excellent troubleshooting guide within the LR3C Installation Manual. Step 2 pinpointed the problem.
    -- Art Z.

On Tue, Aug 13, 2019 at 10:30 PM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

Quote:
On 8/13/2019 7:48 PM, Art Zemon wrote:

Quote:
Folks,


I had a weird "failure" this afternoon: neither alternator was doing anything and neither alternator field circuit breaker had tripped. I put "failure" in quotes because I don't believe that the alternators actually failed; that is just too unlikely. Here are the details:


First, the wiring diagram:
 engine.pdf


I had taxied to the fuel pump, and back, and flown three legs. Five cycles of engine start, operation, and shut down. All with alternators operating correctly. As I started the takeoff roll for the fourth flight, the EFIS alerted that bus voltage was low. I continued the takeoff; it was only a 15 minute flight to home base.


I have two B&C alternators with B&C voltage regulators, one primary belt driven and one backup gear driven.


Once airborne, I cycled the alternator field switches. No joy from either alternator. I pulled and reset both field circuit breakers. No joy. I even power cycled the master, on the hope that the EFIS voltage regulator was at fault. No joy.


During the third flight, the primary alternator field breaker had popped. I reset it and the alternator returned to normal operation. It was stupidly hot in the cockpit and the sun was shining on my black glare shield and I know that I need ventilation behind the instrument panel. I chalked this up to heat and vibration. In 87 hours of operation, this is only the second time that that breaker has popped. After resetting the breaker, I checked both alternators independently (turning off each field switch in turn) and confirmed that each was operating normally.
I had 12.9 volts during the takeoff roll. It was down to 12.6 volts on landing. so definitely no output from the alternators. The voltage regulators are set for 14.5 volts and 13.0 volts. I typically see 14.8 or 14.9 volts from the primary and 13.1 from the backup alternator.


Do you have any ideas what could cause this? I did a tiny amount of debugging but I was hot and tired so I did not get into the weeds, yet. I confirmed that both current limiters between the alternators and the battery contactor are OK. I tugged on the cable between the current limiters and the battery contactor and it seems solid, no loose nuts. I removed the glare shield and checked the voltage regulators. Both were warm but not hot. All of the wires connected to them are tight.

Hi Art,

Looking at your pdf, the only thing in common is the 'fat' wire from starter to master contactor, then to your main bus. Any circuit protections anywhere along that path?

Regardless of where your current failure is located, that's something to think about; any issue along that path can take out both alternators.


--
https://CheerfulCurmudgeon.com/Love the stranger for you yourselves were strangers in Egypt. Deut. 10:19


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jluckey(at)pacbell.net
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PostPosted: Wed Aug 14, 2019 9:36 am    Post subject: Dual Alternator "Failure" - SOLVED Reply with quote

Ouch! The dreaded single point of failure! (all that redundancy compromised by a ten cent fuse;)

Glad to hear you found it and not (as our fearless leader says) "on a dark and stormy night"


-Jeff


On Wednesday, August 14, 2019, 9:24:50 AM PDT, Art Zemon <art(at)zemon.name> wrote:




Charlie and Joe,
Thanks much for your quick replies.
The problem was a blown fuse. Diagnosis was hindered because I had not bothered to update the wiring diagram.
I will write this up more verbosely on my blog because I think it will make a good article. Briefly for this list, I have a shared fuse for the overvoltage lamps on the primary and backup voltage regulators. That same circuit also feeds pin 3 on the B&C voltage regulators. That fuse blew. Both the LR3C voltage regulator and the SB1B backup regulator respond the same way to 0 volts on pin 3: they stay in "do nothing" mode.
Problems which contributed to the loss of both alternators in flight:
  • Shared fuse for pin 3 on both voltage regulators.
  • Inaccurate documentation. The wiring diagram shows independent fuses for each voltage regulator.
  • Lack of knowledge on my part, which allowed me to share the fuse.
  • Karma, which made this happen less than an hour after I had been proudly showing my friend how I had dual alternators.
Kudos to TJ at B&C Aero. When I called to get educated on what pin 3 does and how the voltage regulator acts in response to 0 volts, he had already read my earlier post here and knew the background of my situation.
Kudos to B&C Aero for providing an excellent troubleshooting guide within the LR3C Installation Manual. Step 2 pinpointed the problem.
-- Art Z.

On Tue, Aug 13, 2019 at 10:30 PM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

Quote:
On 8/13/2019 7:48 PM, Art Zemon wrote:

Quote:
Folks,


I had a weird "failure" this afternoon: neither alternator was doing anything and neither alternator field circuit breaker had tripped. I put "failure" in quotes because I don't believe that the alternators actually failed; that is just too unlikely. Here are the details:


First, the wiring diagram:
engine.pdf


I had taxied to the fuel pump, and back, and flown three legs. Five cycles of engine start, operation, and shut down. All with alternators operating correctly. As I started the takeoff roll for the fourth flight, the EFIS alerted that bus voltage was low. I continued the takeoff; it was only a 15 minute flight to home base.


I have two B&C alternators with B&C voltage regulators, one primary belt driven and one backup gear driven.


Once airborne, I cycled the alternator field switches. No joy from either alternator. I pulled and reset both field circuit breakers. No joy. I even power cycled the master, on the hope that the EFIS voltage regulator was at fault. No joy.


During the third flight, the primary alternator field breaker had popped. I reset it and the alternator returned to normal operation. It was stupidly hot in the cockpit and the sun was shining on my black glare shield and I know that I need ventilation behind the instrument panel. I chalked this up to heat and vibration. In 87 hours of operation, this is only the second time that that breaker has popped. After resetting the breaker, I checked both alternators independently (turning off each field switch in turn) and confirmed that each was operating normally.
I had 12.9 volts during the takeoff roll. It was down to 12.6 volts on landing. so definitely no output from the alternators. The voltage regulators are set for 14.5 volts and 13.0 volts. I typically see 14.8 or 14.9 volts from the primary and 13.1 from the backup alternator.


Do you have any ideas what could cause this? I did a tiny amount of debugging but I was hot and tired so I did not get into the weeds, yet. I confirmed that both current limiters between the alternators and the battery contactor are OK. I tugged on the cable between the current limiters and the battery contactor and it seems solid, no loose nuts. I removed the glare shield and checked the voltage regulators. Both were warm but not hot. All of the wires connected to them are tight.

Hi Art,

Looking at your pdf, the only thing in common is the 'fat' wire from starter to master contactor, then to your main bus. Any circuit protections anywhere along that path?

Regardless of where your current failure is located, that's something to think about; any issue along that path can take out both alternators.


--
https://CheerfulCurmudgeon.com/Love the stranger for you yourselves were strangers in Egypt. Deut. 10:19


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user9253



Joined: 28 Mar 2008
Posts: 1435
Location: Riley TWP Michigan

PostPosted: Wed Aug 14, 2019 4:51 pm    Post subject: Re: Dual Alternator Reply with quote

The above situation reinforces the recommendation to have a separate fuse for each and every load, no matter how small or insignificant. Fuse are inexpensive.

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art(at)zemon.name
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PostPosted: Sat Aug 17, 2019 5:45 pm    Post subject: Dual Alternator "Failure" - SOLVED Reply with quote

You're so right, Joe.
And for anyone interested, here is the full write-up on my blog: https://cheerfulcurmudgeon.com/2019/08/17/dual-alternator-failure/
Cheers,
    -- Art Z.
On Wed, Aug 14, 2019 at 8:07 PM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

The above situation reinforces the recommendation to have a separate fuse for each and every load, no matter how small or insignificant.  Fuse are inexpensive.
 

--
https://CheerfulCurmudgeon.com/Love the stranger for you yourselves were strangers in Egypt. Deut. 10:19


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Mauledriver(at)nc.rr.com
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PostPosted: Tue Aug 20, 2019 7:07 am    Post subject: Dual Alternator "Failure" - SOLVED Reply with quote

Late Post:

I've been down the troubleshooting road a few times with my Z-14 (dual bus/bat/alt).  I had to relearn this a few times but fully get it now - I treat LR3C and it's step-by-step Troubleshooting Guide as the very first step for any charging system problem.  And not skipping a step is step 0.  Glad you found and solved the problem.
Quote:
Kudos to TJ at B&C Aero. When I called to get educated on what pin 3 does and how the voltage regulator acts in response to 0 volts, he had already read my earlier post here and knew the background of my situation.


Kudos to B&C Aero for providing an excellent troubleshooting guide within the LR3C Installation Manual. Step 2 pinpointed the problem.


    -- Art Z.




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chaskuss(at)yahoo.com
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PostPosted: Wed Aug 21, 2019 7:11 am    Post subject: Dual Alternator "Failure" - SOLVED Reply with quote

is the troubleshooting guide available on their website?

Sent from Yahoo Mail on Android

Quote:
On Tue, Aug 20, 2019 at 12:17 PM, Bill Watson
<Mauledriver(at)nc.rr.com> wrote:


Late Post:

I've been down the troubleshooting road a few times with my Z-14 (dual bus/bat/alt). I had to relearn this a few times but fully get it now - I treat LR3C and it's step-by-step Troubleshooting Guide as the very first step for any charging system problem. And not skipping a step is step 0. Glad you found and solved the problem.
Quote:
Kudos to TJ at B&C Aero. When I called to get educated on what pin 3 does and how the voltage regulator acts in response to 0 volts, he had already read my earlier post here and knew the background of my situation.


Kudos to B&C Aero for providing an excellent troubleshooting guide within the LR3C Installation Manual. Step 2 pinpointed the problem.


-- Art Z.





Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]





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user9253



Joined: 28 Mar 2008
Posts: 1435
Location: Riley TWP Michigan

PostPosted: Wed Aug 21, 2019 7:44 am    Post subject: Re: Dual Alternator Reply with quote

The B&C LR3C Troubleshooting Guide is included in the Installation Manual.
http://www.bandc.biz/pdfs/LR3C_Installation_Manual.pdf


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