total electrical failure

[mooneyflyfast]

Returning from Harlingen to Bulverde Airpark IFR today I was being vectored west of KSAT when everything went dead. I was in and out of the clouds and there was a good VFR ceiling fortunately. Also fortunately my KI 256 is vacuum powered and I had a Garmin 795 battery powered GPS. I stayed on my assigned heading until clear of Class C then headed to 1T8.  I lowered the gear manually but was not sure It was really down and locked. I was surprised there was no positive indication on the floor mounted gear indicator. Guess it was because there was no light.  Landing was no radio, no flaps of course and it was a sweet sound when the tires hit the pavement.. San Antonio Approach was very understanding and said no problem and no paperwork required.  It was a character building experience but makes you think what would have happened if the weather had been really crappy.

[1964-M20E]

Glad you were able to land safely.  Back to basics of training. 

I hope the electrical problem is not too serious.  Probably something with the master relay.

[Hank]

A flashlight will reveal the floor indicator . . .

My total electrical failure was during the day, after descending through the clouds on a VOR approach over the hills of the Ohio River. Flew the procedure turn, came over the station, dropped gear and lost everything. Hand cranked them the rest of the way down and flew home low and slow.Turned out to be the circuit board behind the panel-mounted dimmer knob. Something was fried too much to tell what it had been, and I was unable to locate a diagram. After 3 months, I found a replacement board.

Good luck troubleshooting! 

[carusoam]

Nicely done, and great Pirep!

Let us know what you find out...

Best regards,

-a–

[RLCarter]

WOW, Harlingen made MS

[Yetti]

Well done.   Is Bulverde hard to land at night?   It is closer to where I need to go but I chose Stinson and a bigger Uber bill since it was dark when I went last.

[LANCECASPER]

44 minutes ago, Yetti said:

Well done.   Is Bulverde hard to land at night?   It is closer to where I need to go but I chose Stinson and a bigger Uber bill since it was dark when I went last.

I based in Bulverde 20+ years ago and I remember a power line to go over on short final. Maybe that's changed.

[mooneyflyfast]

1 hour ago, Yetti said:

Well done.   Is Bulverde hard to land at night?   It is closer to where I need to go but I chose Stinson and a bigger Uber bill since it was dark when I went last.

Not the best at night-. deer, towers, terrain and not real clear approaches. I would recommend familiarization during daytime first.

[mooneyflyfast]

42 minutes ago, LANCECASPER said:

I based in Bulverde 20+ years ago and I remember a power line to go over on short final. Maybe that's changed.

There is a utility pole with a red light off to the side of the approach end of  rwy 16 but no actual wire across the end of the runway. There is a barbed wire fence and a road on the other side of that. 

[mooneyflyfast]

Battery shunt bus burned in half. p.n. MLA-70A-100mv

[Piloto]

5 hours ago, mooneyflyfast said:

Battery shunt bus burned in half. p.n. MLA-70A-100mv

Thanks for the input. The battery shunt is only used by the current meter. But a good digital voltmeter will do a better job in assessing the electrical system. I am going to bypass the shunt and replace the amp meter with a vacuum gauge. I already have two digital voltmeters with voice warning.

José

[mooneyflyfast]

32 minutes ago, Piloto said:

Thanks for the input. The battery shunt is only used by the current meter. But a good digital voltmeter will do a better job in assessing the electrical system. I am going to bypass the shunt and replace the amp meter with a vacuum gauge. I already have two digital voltmeters with voice warning.

José

Any ideas as to what could have caused this failure.. Something shorted downstream?

[Yetti]

Thanks for the PIREP...  I have been there once in a 172 several years ago.   Did not want to try it at night with the Mooney.  There are tricks to finding airports....

[carusoam]

Nice detailed Pirep, MFF.

I have not heard of a Shunt failure before.  They are an odd device that withstands all of the current flowing through the plane, usually. They have only enough resistance to generate a voltage drop to calculate current...

Wait, don't go too fast...  we may have discussed what happens when something accidently shorts the shunt.

Somebody had posted a short of something that fell against the shunt's terminals as they can be exposed.  They should probably get covered like battery posts do...

Consider looking (with your mechanic) for something else in the area with melted marks on it.

PP ideas. Not a mechanic...

Best regards,

-a-

Edited March 18, 2017 by carusoam

[Piloto]

13 hours ago, mooneyflyfast said:

Any ideas as to what could have caused this failure.. Something shorted downstream?

A possible cause was a loose or corroded connection nut that caused an overheat on the shunt element due to ohmic resistance. Resistance increase with heat and dissipated power increase with resistance(IxIxR). So once you have a small resistance increase it creates a progressive increase in heat that can destroy the resistor.

José  

[mooneyflyfast]

Here's the culprit. 60amp-supposed to be 70 but I wouldn't think that would account for what happened. No unusual electric load at time of failure and no evidence of arcing in the area of the buss.. 

[Marauder]

Here's the culprit. 60amp-supposed to be 70 but I wouldn't think that would account for what happened. No unusual electric load at time of failure and no evidence of arcing in the area of the buss.. 

Does it look like it melted? Wonder if it was just aged, corrosion and vibration did it in.


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[Yetti]

Recyle that thing.  Probably a couple dollars in copper

[mooneyflyfast]

13 minutes ago, Marauder said:

 

Does it look like it melted? Wonder if it was just aged, corrosion and vibration did it in.


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Age, corrosion and vibration might have started the process but I would say it melted.

[Piloto]

A loose screw or metal piece that fell into the bridge shorting it to ground.

José

[201er]

53 minutes ago, mooneyflyfast said:

Here's the culprit. 60amp-supposed to be 70 but I wouldn't think that would account for what happened. No unusual electric load at time of failure and no evidence of arcing in the area of the buss.. 

Pardon my ignorance... but if a 60amp breaker switch were installed in the place of a 70amp breaker switch, wouldn't the breaker have just shut off earlier because of the excessive load and NOT melted down? In other words you wouldn't be able to run everything on it without popping it, but you would still be safe running a less than full load?

[Shadrach]

1 minute ago, 201er said:

Pardon my ignorance... but if a 60amp breaker switch were installed in the place of a 70amp breaker switch, wouldn't the breaker have just shut off earlier because of the excessive load and NOT melted down? In other words you wouldn't be able to run everything on it without popping it, but you would still be safe running a less than full load?

That is indeed true, but I don't believe we're looking at a breaker switch.

[N201MKTurbo]

I hate to say it but I don't think that is your problem.

Just like when you blow a fuse. It wasn't a defective fuse but a short somewhere else. That shunt melted from over current. There is a serious short soewhere in your plane. The shunt just acted like a very expensive fuse.

Edited March 27, 2017 by N201MKTurbo

[201er]

Just now, N201MKTurbo said:

I hate to say it but I don't think that is your problem.

Just like when you blow a fuse. It wasn't a defective fuse but a short somewhere else. That shunt melted from over current. There is a serious short soewhere in your plane. The shunt just acted like a very expensive fuse.

Is it supposed to do that?

[KSMooniac]

Is it supposed to do that?

No, I think it is there just to measure current. Agree that there is a short somewhere in the system.

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