Electrical Single Point of Failure?

[RobertGary1]

13 minutes ago, EricJ said:

If you don't want to maintain it, as in keep buying pumps and AI overhauls,  or if you want the pad space back on the accessory case, or if you want the weight back, or if you want the panel space back, or if you want to declutter the associated hoses, etc., etc.

Never had to replace one more than every 10 years.  The weight is negligible. Just skip lunch. 

[chriscalandro]

8 hours ago, EricJ said:

I do think it's a little odd that the JPI primary displays don't have battery backup.   

They don't?  I find that odd as well.

 

[M20F]

4 hours ago, ArtVandelay said:

Because vacuum pumps fail with regularity (I average a failure every 700 hours). And attitude indicators almost as often. So if you have a battery as backup the failure rate should be lower.

I have 2 G5’s and a vacuum gauge.  I don’t disagree with your statement but when or if the electrical burns itself up as they do on occasion odds are the vacuum is fine.  
 
My point was is that I have 1100lbs of useful load in a plane that generally never carries more than 2 people.  No point in pulling the vacuum out, it is a nice back up.  

[PT20J]

One thing to keep in mind about instruments with backup batteries is that batteries degrade over time. The ICA for each instrument usually has a requirement for periodic test and also replacement intervals. Also the main battery should be capacity tested annually. As lead-acid batteries degrade, they lose capacity. Just because it starts the airplane fine doesn't mean it will run your panel for any length of time. 

Skip

[PT20J]

23 hours ago, smwash02 said:

As a data point, I tried this on my 252/Encore today and it did NOT behave this way. Hard to say if it was like this from the start or years of avionics changes have altered its behavior.

Despite the redundancies elsewhere (dual alt, dual vacuum), the master, avionics master, and each respective solenoid are single points of failures in a series line. Somewhat chilling to think about.

I was at the hangar today and pulled the Aux breaker with only the master on and the radios didn't come on. Weird, because I know that they did last time I tried it. But then I also noticed that I could turn the landing light on which is powered through the aux bus and should be disabled with the Aux breaker pulled. So I pressed the Aux breaker in and held it fully depressed and the radios came on and and the landing lights went out. When I released the breaker, it popped out a fraction and the radios went off and the landing light went on indicating power to the aux bus. Looks like the aux breaker is going flakey. This is only the second time I've tested it in 2-1/2 years. I'm going to add testing all the breakers to my annual checklist.

Skip

[ArtVandelay]

Never had to replace one more than every 10 years.  The weight is negligible. Just skip lunch. 

I had to replace AI, vacuum pump and my electrical vacuum pump failed, in first 4 years of ownership (~600 hours).
I got 20 lbs of useful load back, a bit more than a lunch.

[jamesm]

The other problem is with all these different portable backup's devices is trying to remember how to run each one and of course most of them have different connectors and keeping them charged when you really need them is another challenge . I am finding as I get older I am finding the user interfaces between the difference between brands garmin vs king or avidyne really  gets to be annoying to me. The IOS platforms such as apple vs android especially knowing that Apple and Andriod are derivatives of the  Linux kernel. It make me laugh when people argue which one is better.   If you have bug in the Apple IOS update it is highly likely to effect Android (Avare) and vice versa.  Of course Both IOS (Apple/Android) platforms beats the windows OS (Bill OS) any day.

[RobertGary1]

1 hour ago, ArtVandelay said:

I had to replace AI, vacuum pump and my electrical vacuum pump failed, in first 4 years of ownership (~600 hours).
I got 20 lbs of useful load back, a bit more than a lunch.

If the components have failed it’s a different story. But if they’re still working there is no way you’ll ever detect that 4 lbs of pump and indicator and you’ll never cry over too many attitude indicators. 

[Ragsf15e]

1 hour ago, PT20J said:

I was at the hangar today and pulled the Aux breaker with only the master on and the radios didn't come on. Weird, because I know that they did last time I tried it. But then I also noticed that I could turn the landing light on which is powered through the aux bus and should be disabled with the Aux breaker pulled. So I pressed the Aux breaker in and held it fully depressed and the radios came on and and the landing lights went out. When I released the breaker, it popped out a fraction and the radios went off and the landing light went on indicating power to the aux bus. Looks like the aux breaker is going flakey. This is only the second time I've tested it in 2-1/2 years. I'm going to add testing all the breakers to my annual checklist.

Skip

I’ve had 2xCBs fail in the last 3 years.  Resistance increased on the field CB until it became noticeable.  
 

Your test and results got me thinking about the electrical system again and I have a stupid question... if I turn off the battery master with the engine (and alternator) running, why does that turn everything off?  Wouldn’t the alternator keep powering it all?  The VR gets power through the alternator... anyway, probably dumb question, but I can’t get my mind around it.  

[PT20J]

2 minutes ago, Ragsf15e said:

I’ve had 2xCBs fail in the last 3 years.  Resistance increased on the field CB until it became noticeable.  
 

Your test and results got me thinking about the electrical system again and I have a stupid question... if I turn off the battery master with the engine (and alternator) running, why does that turn everything off?  Wouldn’t the alternator keep powering it all?  The VR gets power through the alternator... anyway, probably dumb question, but I can’t get my mind around it.  

There are no dumb questions  The alternator field switch gets power from the bus that the master feeds, so turning off the master kills the alternator.

[M20F]

2 hours ago, ArtVandelay said:

I had to replace AI, vacuum pump and my electrical vacuum pump failed, in first 4 years of ownership (~600 hours).
I got 20 lbs of useful load back, a bit more than a lunch.

Sell some more latex 

[carusoam]

kind of a summary...

Review the latest hardware needed to have an “essential bus”...

I believe the most modern Mooneys have the essential bus to support the minimum amount of equipment needed to get down safely...

So...

Yes, three buses... more parts, more expense... more is better...

Then the Euro solution where another power line can be switched on in case the standard power lines fail to operate...

 

You can’t possibly go wrong with three busses and two power lines...

And a portable radio/gps/ILS....

Fortune favors the prepared... - Louis Pasteur

PP summary only,

-a-

[Ragsf15e]

1 hour ago, PT20J said:

There are no dumb questions  The alternator field switch gets power from the bus that the master feeds, so turning off the master kills the alternator.

Ok, that jarred it loose!  Thanks.  I even replaced my master switch last year and already forgot it’s a “Single Throw, Dual Pole” switch. So not only does it cut power at the battery relay, it also cuts the field wire which shuts off the alternator.  Newer folks may have the battery/alternator split switches.  My brain was somewhere else.

[carusoam]

94 O has two different switches.... master and alternator...

You can imagine what type of failure you get with a split switch that is good at killing two systems at once...  

-a-

[jamesm]

The 67C that I own has single throw double pole master switch (one circuit provides gnd master power relay and the other circuit interrupts current flow to field of the Alternator to the Voltage regulator) ... If I feel that the the Alternator  is in over volt condition or  voltage regulator is in a running away  condition. I would pull the the 5 AMP Field breaker my understanding it is same having a "Dual switch" like the Cessna's have. The Alternator Field CB cuts the voltage (the way mine is wired) to the voltage regulator stopping voltage output from the alternator (the big fat cable 70 amp output). As I understand it, only battery Voltage would be present on the bus at that point. Since I have never experience an over voltage  condition ... I am a bit of chicken to try  this in flight. It would take two people (one flying and one experimenting ) to proof / verify my understanding on how the circuit is "suppose" to work..

just my thoughts,

James '67C

 

[carusoam]

James, I think you have that right...

My generator on the 65C I think went over voltage... and melted the solder out of the generator...

No warning lights... just stopped working...

The warning lights were low voltage bulbs flashing on everything...   

Beautiful VFR day... the Amp gauge was probably screaming at me...

PP thoughts only,

-a-

[jamesm]

If I recall correctly.... at least when my 67C had a generator. The only way to  kill the generator Field Was to kill the master Switch. However in the case where  " all the solder  melted out of the generator"  there isn't much you could do, except land.  When you loose control of accessory that is located on the opposite side Of the firewall from where you are it makes it a bit challenging.

Edited March 2, 2021 by jamesm

[JimB]

10 hours ago, RobertGary1 said:

If the components have failed it’s a different story. But if they’re still working there is no way you’ll ever detect that 4 lbs of pump and indicator and you’ll never cry over too many attitude indicators. 

Pretty sure there hasn't been a new airplane built in a long time that has a vacuum pump...there really are some good reasons for that...

https://airfactsjournal.com/2017/04/death-knell-vacuum-pump/  

 

[Nokomis449]

21 hours ago, EricJ said:

I do think it's a little odd that the JPI primary displays don't have battery backup.   

Re: battery backups:  Interesting tidbit I found while perusing the AV-30-C Flight Manual Supplement:

5.2 Required Battery Charge Status for IFR Operations
The internal battery on the AI must show 95% or greater prior to departure into IFR, or planned IFR conditions.

Re: single points of failure:  As for learning at the Redundant School of Redundancy, a friend had a nice experimental that he thought had redundant systems like a normal plane until one day he was out flightseeing and the engine just quit.  He landed in a bean field without damaging self or property (paid the farmer for the beans).  Inspection determined that there was a single point of failure in his ignition switch that shuts off everything when it fails.  He ended up donating the perfectly good experimental to the Southern Museum of Flight in Birmingham (KBHM) and bought a Carbon Cub.

[RobertGary1]

3 hours ago, JimB said:

Pretty sure there hasn't been a new airplane built in a long time that has a vacuum pump...there really are some good reasons for that...

https://airfactsjournal.com/2017/04/death-knell-vacuum-pump/  

 

But no one is suggesting installing a new vacuum pump system. 
 

but the last Cessna t206h I delivered from the factory did have a vacuum back up attitude indicator. 

Edited March 2, 2021 by RobertGary1