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Chasing down an electrical anomaly


alexress99
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Wondering if anyone has had something similar happen to help focus what needs attention.

Symptom: Turn the ignition to START and the entire electrical system goes dead. 

This has happened three times spread apart by months (dozens of starts).  The first two happened on the ground trying to start the engine.  The third most recently attempting a restart in the air.  The scenario is that I'm getting ready to start the engine, master switch is on and everything is powered normally such as the radio/intercom and Dynon.  Discharge light is on since the engine is not running.  As I rotate the key to the START position, everything goes dead.  No indication of power to the starter.  Radio/intercom go dead.  Discharge light is not illuminated.  Despite cycling the battery selector switch between 1, 2, 1 and 2, and off, no change to power status.  Cycling ignition and master switch also provides no change.

In all three instances, after returning to the airplane in as little as 15 minutes, the electrical system operates normally and the engine starts fine.  The third occurrence happened this week while attempting a restart after engine-off soaring.  This resulted in an uneventful out-landing and now the eventual fix to the anomaly.

Hopefully no one has had this issue but I'd appreciate any insight into the eventual fix.

Aloha,  Alex

If anyone is visiting Oahu, Hawaii, contact me if you'd like to go flying (after eventual fix of course!)

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Is there self-resetting circuit breaker in the system? Perhaps you are using a lithium battery with BMS that might cut off the battery voltage?

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Thanks for the ideas Eric. I’m not aware of such a circuit breaker from the factory.  I feel fairly certain that the first owner didn’t modify it as he only flew it a few times. 
I’m thinking even if one of the batteries was unhappy and isolated itself, the other battery wouldn’t be affected right?  BUT,  I will look into those as I could be totally wrong. 

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Hi Alex,

Intermittent failures like this can be very puzzling and frustrating. You’re probably gonna end up having an A&P or avionics tech look at this, but in the meanwhile there are several things that you could do that will make the job easier and familiarize yourself with your Phoenix.

It’s always helpful to do a system trace and mapping with this type of fault. I would start with the battery and work my way to the starter through the hot leads and the grounds. Make sure you disconnect both leads to both batteries when you do this. Start with the positive connection to the battery and check the continuity of each wire as it moves through the system mapping as you go. Unfortunately the diagram in the Phoenix maintenance manual is very sparse in detail, so it’s only a little help. You should be able to work your way through the master switch, the ignition switch, the battery contactor relay, the starter relay, and the starter itself. Test the switches as well. You don’t have to test any of the accessories on the main bus at this point, just focus on the path to the starter. Do the same thing for the ground path starting at the battery negative lead and trace all the way to the ground strap on the engine. Every time you come to a connection evaluate it for any corrosion and clean it if necessary.

I know this sounds tedious, but it’s probably what the A&P or avionics tech is going to do anyway, and you can save a good bit of money if you can present a wiring diagram and some data. You may even find the problem, and it may be something obvious once it’s illuminated. I’m not aware of any self setting breaker in the loop, and the battery management system would have to do this for both batteries simultaneously if that were the source. It’s very puzzling, but my guess is that you’re going to find an intermittent connection with some corrosion or interruption either in a wire attachment or a switch itself. Because you live in a saltwater environment your plane may have more exposure to this than most, so I’d think about a good physical examination to see what you can find. 

The other benefit for you is that you’ll have a much better understanding of your electrical system, and it’s kind of fun to do the Sherlock Holmes work. Share what you find with the group and we can provide some celebratory congratulations or condolences.  :)

good luck with your hunt!

Ed  U15/05

 

 

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Thanks Ed.  I look forward to getting to know the Phoenix better and will let everyone know if I find anything definitive.  The intermittent problems can be challenging.

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Hi Alex,

There are two things that can create this blackout and then successful start a few minutes later.  The first is trying to start the engine with a low battery voltage.  Always look at the battery voltage before starting the engine.  If it is below 11.8 volts do not attempt the start.  If voltage is insufficient, it will create the blackout event that you have experienced.  I don't know why the plane starts a few minutes later on the good battery and not right away.  There is no resetting circuit breaker.

Note which battery you are using for the start every time so that you can diagnose further if there is a problem.  A bad cell in a lithium battery can create an intermittent failure even with good voltage.

The other thing is a starter switch (the key switch) going bad.  You might see some black arching residue on the back of the switch, but maybe not.  They don't cost much from Aircraft Spruce.  I recommend that you order the switch and install it.  If it happens again you have a bad battery (and a spare switch).

I have seen this exact thing happen to another plane due to the battery problem, and I have had this happen to me on the ground due to the bad switch on my plane.

cheers,  Jim

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Good points, Jim. I am not in the habit of starting one battery, but I will do that in the future. A weak battery will be much more likely to show up that way.

Eric

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  • 2 weeks later...

Hi Alex,

Just wondering if you ever figured this out? I’m still puzzled about the mechanism that would’ve produced this given the symptoms you shared. The fact that the engine can start in as little as 15 minutes after the failure makes me think that this isn’t a battery problem. It takes a lot of cranking amps to turn over that engine.

I still think it’s possible that it might be an intermittent engine grounding problem. The reason is that it’s the only common connection to all of the events that you’ve described, i.e., all the current has to get back to the battery somehow, and there’s only one wire through which it flows with the engine block being the common ground.  If you haven’t looked at it yet, simply take an ohmmeter and measure between the negative battery terminal and the engine block. It should be just a few ohms. Move the wire a bit near the connection points to see if the resistance changes. There’s a lot of amperage returning through this wire, and I’ve seen invisible internal damage to the ground cables in some automotive engines.

Also, check the battery terminal attachments with particular attention to the black wire negative, especially where it attaches to the battery and engine block. It might be prudent to disconnect and clean up the ends of the cable both at the engine and battery terminal. It doesn’t take much corrosion to create a significant resistance.

Good luck, and let us know what you find.

Ed

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There is nothing I'd like to be writing more than to tell you what the smoking gun was.  Because of the intermittent nature of the issue, that is difficult.   A bad ground would be a welcome find and I will try the test you mentioned Ed.  I appreciate the posts above.  The videos, mostly form the EAA, on aircraft electrical issues all seem to emphasize the ground.  Interesting to me that there was no split washer or anything on the negative battery terminal to keep the nut from backing off.  I love to shut down the motor so that connection will be an emphasis item for me in the future.

Another rabbit hole I'm in is what replacement battery to use.  It's very interesting but it's keeping me out of the sky.

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  • 4 months later...

I have gotten more data on the electrical problem I started this thread with.  Bottom line up front, it's just like Jim Said, "There are two things that can create this blackout and then successful start a few minutes later.  The first is trying to start the engine with a low battery voltage.  Always look at the battery voltage before starting the engine.  If it is below 11.8 volts do not attempt the start.  If voltage is insufficient, it will create the blackout event that you have experienced.  I don't know why the plane starts a few minutes later on the good battery and not right away."

I have been able to recreate this now by letting a battery drain down below 12v as displayed on the Dynon.  I select start and watch the battery voltage go to zero in about 1 second.  The Dynon power starts counting down as it is only powered by its backup battery and the battery discharge light goes out.  I can switch to the non-drained battery, off, and both but nothing changes the blackout until I try again approximately 15 minutes later and then everything powers up fine.

This situation is inconvenient in the air and I will do as Jim suggests and not attempt a start with a battery showing low voltage.  I'm surprised this hasn't been more widely discussed.  Still love the airplane, just beginning to learn.

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