Circuit breaker popped

[PPC1052]

Last night, the circuit breaker for my alternator popped. (1976 C177 B ).

We pushed it back in, and everything seemed to work ok. Any ideas what might be the culprit and how to trouble shoot it?

 

[Norman]

Which circuit breaker; alternator field or 70 amp bus breaker?

 

[Cpt_Kirk]

When was the last time the airplane flew?

 

[PPC1052]

Which circuit breaker; alternator field or 70 amp bus breaker?

60 amp for the alternator. Also, there is an over voltage warning light. I attach a copy of the page from the POH with the electrical diagram. On the right side, there is a description of the over voltage sensor, and that it will turn of the alternator under such conditions. Seems to have worked as intended. We turned off the battery and alternator switches, and reset the breaker. It operated normally.

I am just wondering about the underlying cause. Also, do I keep flying, or does this thing need to be grounded? Obviously, no night time, or IMC until we get this sorted out. But am I okay VFR day close by the airfield?

 

[PPC1052]

When was the last time the airplane flew?

Two weeks ago.

 

[poadeleted20]

I would point out that a few years ago the FAA changed its recommendations on pushing c/b's back in after they pop. Used to be they said "Push it back in and see if it pops again, and if it does, leave it out." Now, after some fatal accidents involving electrical fires, they've changed that to "Do not reset a popped c/b unless it is necessary for the flight, and even then, don't push it back in more than once."

Now, because it was a night flight, maybe you were in a situation where that alternator was essential, but having been that route myself and had smoke in the cockpit as a result, if I was day VFR, I'd probably leave it alone and land visually.

 

[Dan Thomas]

60 amp for the alternator. Also, there is an over voltage warning light. I attach a copy of the page from the POH with the electrical diagram. On the right side, there is a description of the over voltage sensor, and that it will turn of the alternator under such conditions. Seems to have worked as intended. We turned off the battery and alternator switches, and reset the breaker. It operated normally.

The overvoltage sensor doesn't pop the breaker. It shuts off the regulator, killing the alternator.

If the 60-amp breaker popped, it's either because the alternator was putting out more than 60 amps, and that might be a short in the output cable to ground, or, less likely, the regulator overvolted, which usually gets looked after by the overvolt sensor. The most likely problem in an older airplane is a breaker whose contacts have become oxidized, generating resistance in the breaker, making it heat up and fooling it into thinking there's an overcurrent situation.

I'd look for chafing of the alternator output cable between the alternator and breaker, and if there's nothing there, replace the breaker.

Dan

 

[PPC1052]

I would point out that a few years ago the FAA changed its recommendations on pushing c/b's back in after they pop. Used to be they said "Push it back in and see if it pops again, and if it does, leave it out." Now, after some fatal accidents involving electrical fires, they've changed that to "Do not reset a popped c/b unless it is necessary for the flight, and even then, don't push it back in more than once."

Now, because it was a night flight, maybe you were in a situation where that alternator was essential, but having been that route myself and had smoke in the cockpit as a result, if I was day VFR, I'd probably leave it alone and land visually.

It was not a "night flight". It was after work, so it was in the evening (around 6:45- 7:00), but not dark yet. Sunset here is pretty late (almost 9:00 o'clock right now.) At that time of day, in those lighting conditions, I do like to have my strobes and nav light on.

 

[PPC1052]

The overvoltage sensor doesn't pop the breaker. It shuts off the regulator, killing the alternator.

Yes.

If the 60-amp breaker popped, it's either because the alternator was putting out more than 60 amps, and that might be a short in the output cable to ground, or, less likely, the regulator overvolted, which usually gets looked after by the overvolt sensor. The most likely problem in an older airplane is a breaker whose contacts have become oxidized, generating resistance in the breaker, making it heat up and fooling it into thinking there's an overcurrent situation.

I'd look for chafing of the alternator output cable between the alternator and breaker, and if there's nothing there, replace the breaker.

Dan

Great thoughts.

 

[poadeleted20]

It was not a "night flight". It was after work, so it was in the evening (around 6:45- 7:00), but not dark yet. Sunset here is pretty late (almost 9:00 o'clock right now.) At that time of day, in those lighting conditions, I do like to have my strobes and nav light on.

I like that, too, but not at the expense of a significant possibility of an electrical fire, so that would not be sufficient to motivate me to reset that c/b in the air since the things Dan cited can all lead to a really unhappy day.

 

[Norman]

The overvoltage sensor doesn't pop the breaker. It shuts off the regulator, killing the alternator.

If the 60-amp breaker popped, it's either because the alternator was putting out more than 60 amps, and that might be a short in the output cable to ground, or, less likely, the regulator overvolted, which usually gets looked after by the overvolt sensor. The most likely problem in an older airplane is a breaker whose contacts have become oxidized, generating resistance in the breaker, making it heat up and fooling it into thinking there's an overcurrent situation.

I'd look for chafing of the alternator output cable between the alternator and breaker, and if there's nothing there, replace the breaker.

Dan

Precisely what I am thinking.

 

[PPC1052]

I like that, too, but not at the expense of a significant possibility of an electrical fire, so that would not be sufficient to motivate me to reset that c/b in the air since the things Dan cited can all lead to a really unhappy day.

Ron, I appreciate your thoughts. I was not trying to suggest anything to the contrary. I just was pointing out that it wasn't a night flight, which I think further supports your thinking. Certainly, the possibility of an in flight fire was in the back of my mind, but honestly I was not thinking about leaving the breaker alone to try to mitigate the risk. In retrospect, what you say does make a lot of sense.

As my instructor and I were walking away from my hangar, he apologized that I didn't get to work on the training issues we set out to do. I responded that this issue was itself a fantastic training opportunity that, unlike flying approaches, you can't just plan to go do whenever you want.

 

[poadeleted20]

Ron, I appreciate your thoughts. I was not trying to suggest anything to the contrary. I just was pointing out that it wasn't a night flight, which I think further supports your thinking. Certainly, the possibility of an in flight fire was in the back of my mind, but honestly I was not thinking about leaving the breaker alone to try to mitigate the risk. In retrospect, what you say does make a lot of sense.

"Learning" is a change in behavior as a result of experience. Since it seems you've learned from this, I'm happy with the result.

 

[gismo]

Precisely what I am thinking.

I have a somewhat different explanation. Contrary to popular wisdom the CB for the alternator output isn't there to protect the alternator from overload. Alternators (unlike generators) are by design inherently current limited and in many airplanes that limit is reached any time you turn on most or all the big electrical loads (landing lights, pitot heat, flap motor, landing gear motor).

The real purpose of this CB is to limit the current flowing from the battery to the alternator diodes or it's output lead if there's a short to airframe ground from either.

So chaffing on that lead is definitely a possibility as is anything that could cause a short from the output terminal on the back of the alternator.

Another distinct possibility is that the CB popped for some reason besides excessive current. One such issue is a poor connection between the CB terminals and the main bus or the wire leading to the alternator. The poor connection causes the terminal to heat up and the high temp trips the breaker. CBs also can fail in a way that makes them trip when they shouldn't although that's fairly rare if the breaker isn't subjected to several real overcurrent trips.

 

[kontiki]

Circuit breakers protect wires plain and simple.

If you have a short circuit, you want that breaker to trip before the wire turns red and ignites something. The 60A breaker protects the wire from the alternator.

The only way you have more than 60A draw from a 12VDC system is the resistance of the load(s) drops (as in a short circuit) as the alternator and voltage regulator hold the system at 12 V.

I just had a similar problem after leaving my master switch on and letting my battery carry the beacon for an hour or so while I stopped for coffee.

The load imposed by charging the battery (after it did start) was too much for the breaker, needle on the amp meter (which deflected in correct - charge direction) didn't indicate any way near full scale when it tripped. I just replaced the CB.

If you have a failed rectifier diode, I'd say its unlikely your alternator can put out the 60A it rated for.

 

[kontiki]

The overvoltage sensor doesn't pop the breaker. It shuts off the regulator, killing the alternator.

Dan

Actually, in an old Grumman, there is a Zener diode in the field circuit that is used for overvoltage protection. If the voltage goes above say 16V, the diode just bypasses current opening the 5A breaker on the field circuit.

 

[dtuuri]

I attach a copy of the page from the POH with the electrical diagram.

Although a lousy mechanic, I love this stuff. To start with, all the diodes are drawn bassackwards except for electrical engineers.

I like to visualize the ammeter like this:

If you then look at the diagram, other than a bad ALT CB as mentioned, any high load circuit would be suspect. What was going on at the time? Fuel pump? Landing lights on? Flaps? Even the starter might be engaging or not disengaging after start--a perilous and common problem on some planes (after starting, a verification of starter disengagement is a good SOP).

One other thing to note here is the feeder between the ALT CB and alternator--there's no feeder fault protection there. A chafed feeder can cause a fire and won't blow the CB. You don't want to accidentally drive a sheet metal screw into that wire. But I'll defer to just about anybody with technical competence, since I have near zero. Their ball...

dtuuri

 

[N801BH]

I would point out that a few years ago the FAA changed its recommendations on pushing c/b's back in after they pop. Used to be they said "Push it back in and see if it pops again, and if it does, leave it out." Now, after some fatal accidents involving electrical fires, they've changed that to "Do not reset a popped c/b unless it is necessary for the flight, and even then, don't push it back in more than once."

Now, because it was a night flight, maybe you were in a situation where that alternator was essential, but having been that route myself and had smoke in the cockpit as a result, if I was day VFR, I'd probably leave it alone and land visually.

Now paging a Mr Ricky Nelson... Please crawl out of your grave and pick up the white telephone for an important message..........

 

[Dan Thomas]

Although a lousy mechanic, I love this stuff. To start with, all the diodes are drawn bassackwards except for electrical engineers.

I long ago learned to think in terms of electron flow instead of current flow. Makes things much more consistent, though some folks get uneasy when they realize that electrons flow out of ground, through the load, and back to the bus and battery or alternator.

Current flow was dreamed up by Ben Franklin or one of those early guys who though that whatever it was moving through a conductor was moving from a surplus (+) to a shortage (-). Positive to negative. Later it was discovered that electrons flow the other way. Positive pulls.

The battery and alternator are in a tug-of-war. When the alternator isn't running or has died, the battery is doing the pulling and the ammeter shows a discharge. The battery is winning the tug-of-war. When the alternator goes to work, it generates a higher voltage (more pressure, or more pull) and it wins the tug-of war, and the ammeter shows a charge. The battery ends up getting electrons pulled through it the "wrong" way, which breaks down the dead-battery products of lead sulfate and water and turns them back into lead, lead peroxide and sulfuric acid, making the battery like new again.

Dan

 

[kontiki]

A chafed feeder can cause a fire and won't blow the CB. You don't want to accidentally drive a sheet metal screw into that wire. But I'll defer to just about anybody with technical competence, since I have near zero. Their ball...

dtuuri

I agree. The breaker only protects the alternator feeder if the short is at the bus, or if you add too many loads onto the bus.

I know my own airplane had a lot of mods and I didn't see a load analysis anywhere in the records. I'm working one up as I go through it. In addition to my own tripping 60A breaker, I discovered that pulling the ALT breaker did not stop the alternator from charging, pulling the Audio AMP breaker did. I'm in the process of tracing through my alt field circuit now.

 

[kontiki]

I long ago learned to think in terms of electron flow instead of current flow. Makes things much more consistent, though some folks get uneasy when they realize that electrons flow out of ground, through the load, and back to the bus and battery or alternator.

Current flow was dreamed up by Ben Franklin or one of those early guys who though that whatever it was moving through a conductor was moving from a surplus (+) to a shortage (-). Positive to negative. Later it was discovered that electrons flow the other way. Positive pulls.

Dan

Not trying to sound condescending, but I used to get caught up in this before I went back to school and got an EE degree. Now I'm OK either way. It's a math based model for something that can get way more complex. So you pick a signage scheme for a direction, use it consistently everywhere in the circuit and the math and model will always work out. Is it electrons moving, well it's probably deeper than that?

I like to use the light example. Sometimes light is modeled as a particle, sometimes as a wave, so which is it? Those are models. Models allow us to understand and predict the behavior of something we cant see or really understand without tools. Sometimes the wave model is applicable sometimes the particle model is applicable, but in reality, what we're looking at is probably neither.

Same with electricity, the simple OHMs law is a special case "circuit theory" analysis that could also be modeled using field theory and Maxwell's equations. Lots more math, not required for a 12VDC system, but it will handle that as well as RF transmission through a radome.

 

[weirdjim]

Why is everything in here such a MAJOR catastrophe that we should IMMEDIATELY ground the airplane and if we don't the thing will FALL OUT OF THE sky and maim THOUSANDS of innocent children on the playground.

For crying out loud. You popped a circuit breaker. FOr all we know some errant electron decided that this was the day to swim upstream and take elevendy billion of his friends with him.

WHen it happens again in a week or so come talk to us about it. Until then it is sort of like the old maxim that it isn't the first time you can't do it the second time that is the problem, it is the second time you can't do it the first time.

When it happens again, let us know. Until then, have a good flight.

Jim

 

[Jay Honeck]

On Cherokees, if your Alternator CB popped it was almost always caused by a loose wire on the back of the alternator. Happened in my 151 and 235. I'd check there before spending a dime.

 

[weirdjim]

Not trying to sound condescending, but I used to get caught up in this before I went back to school and got an EE degree.

Like a few hundred of us on this board didn't get that degree but aren't braggin' on it.

"I'm an engineer. But please don't tell my mommy. She still thinks I'm playing piano in the cathouse."

Jim

 

[kontiki]

Like a few hundred of us on this board didn't get that degree but aren't braggin' on it.

"I'm an engineer. But please don't tell my mommy. She still thinks I'm playing piano in the cathouse."

Jim

Actually I think that you are usually discussing your own problems when you address me. I notice the list of credentials in your signature has grown like peacock plumage.

The things you accuse me of, you typically demonstrate.

I don't really care what your problem is, I suspect you just a flipping A-hole running around looking for fights, although I can't for the life of me figure out why?

Occasionally you do dispense some ill considered advice too.

I don't think you know as much as you think you do at all. Yes you ported your hobby ham radio interest to Experimental aviation. So what.

I don't really think you have a clue otherwise. If you did, you wouldn't reek of insecurity.

 

[RotorAndWing]

Actually I think that you are usually discussing your own problems when you address me. I notice the list of credentials in your signature has grown like peacock plumage.

The things you accuse me of, you typically demonstrate.

I don't really care what your problem is, I suspect you just a flipping A-hole running around looking for fights, although I can't for the life of me figure out why?

Occasionally you do dispense some ill considered advice too.

I don't think you know as much as you think you do at all. Yes you ported your hobby ham radio interest to Experimental aviation. So what.

I don't really think you have a clue otherwise. If you did, you wouldn't reek of insecurity.

 

[Norman]

I have a somewhat different explanation. Contrary to popular wisdom the CB for the alternator output isn't there to protect the alternator from overload. Alternators (unlike generators) are by design inherently current limited and in many airplanes that limit is reached any time you turn on most or all the big electrical loads (landing lights, pitot heat, flap motor, landing gear motor).

The real purpose of this CB is to limit the current flowing from the battery to the alternator diodes or it's output lead if there's a short to airframe ground from either.

So chaffing on that lead is definitely a possibility as is anything that could cause a short from the output terminal on the back of the alternator.

Another distinct possibility is that the CB popped for some reason besides excessive current. One such issue is a poor connection between the CB terminals and the main bus or the wire leading to the alternator. The poor connection causes the terminal to heat up and the high temp trips the breaker. CBs also can fail in a way that makes them trip when they shouldn't although that's fairly rare if the breaker isn't subjected to several real overcurrent trips.

Diodes are one way valves, if you will, that prevent the back-flow of electrons. A circuit breaker will not. Back to electricity 101.

 

[kontiki]

Actually I think that you are usually discussing your own problems when you address me. I notice the list of credentials in your signature has grown like peacock plumage.

The things you accuse me of, you typically demonstrate.

I don't really care what your problem is, I suspect you just a flipping A-hole running around looking for fights, although I can't for the life of me figure out why?

Occasionally you do dispense some ill considered advice too.

I don't think you know as much as you think you do at all. Yes you ported your hobby ham radio interest to Experimental aviation. So what.

I don't really think you have a clue otherwise. If you did, you wouldn't reek of insecurity.

I'm going to apologize for personal comments I made in this post. This sort of tit for tat rubbish is not what I'm about. This guy Weir is frequently critical of the way I present certain explanations, I don't get anything out of his comments beyond that fact there are similarities in our backgrounds and he doesn't like something I said and he expresses it poorly.

The only reason I mention getting a degree is because it was only after working out another zillion circuit problems on paper did It finally dawn on me what the math models were and were not. The only reason I did that was because I was directed to by the curriculum for a 4-5 year engineering degree. Much of that additional problem solving was working out problems that contain fewer unknowns than what is usually taught in technician schools.

I don't mind admitting I really don't know enough about circuit breakers and circuit breaker design. I've actually looked for books to purchase on circuit breaker design, but can't really find anything beyond maybe a Klixon device selection guide.

Most small aircraft breakers are heat activated devices which are affected by environmental heat and sometimes wire temperature; as is the case with sink back heating. The time before a breaker trips is also function of the design and of course multi phase breakers might also trip as a result of imbalances on phase legs. I think I've seen in a complex systems with multiple distribution bus levels each protected by circuit breakers, where an errant load does not trip the closest breaker, but does cause a breaker installed a bus or two higher to trip because of the effect the environment has on the time to trip.

Those were weeks long troubleshooting efforts on intermittent problems seen in large aircraft systems, where we didn't have all the design data, but needed to come up with an answer to move the plane. In a cost sensitive strict regulatory environment, tolerance build ups you can't explain can really send you down the rabbit hole over things that seem simple to a management team, but are not. Breakers do trip for reasons that are often not apparent. In every case the physical laws of nature are never violated.

I've had enough of this for today.

 

[poadeleted20]

I hope in the aftermath of the electrical engineering class conducted by several folks above that nobody has missed the point I raised earlier -- that resetting a c/b even just once has resulted in fatalities, and that's why the FAA is so concerned. I urge all of you to read the SAIB on this subject they issued five years ago and be very cautious about resetting even once any c/b which trips in flight until you get on the ground with your mechanic watching.

 

[N801BH]

I hope in the aftermath of the electrical engineering class conducted by several folks above that nobody has missed the point I raised earlier -- that resetting a c/b even just once has resulted in fatalities, and that's why the FAA is so concerned. I urge all of you to read the SAIB on this subject they issued five years ago and be very cautious about resetting even once any c/b which trips in flight until you get on the ground with your mechanic watching.

Agreed......

Which is exactly why I posted the "Ricky Nelson" blurb.....

 

[poadeleted20]

Agreed......

Which is exactly why I posted the "Ricky Nelson" blurb.....

For those unfamiliar, see NTSB AAR 87/02. The Ricky Nelson accident starts on the page 32/48 of the .pdf file.

 

[Fearless Tower]

I hope in the aftermath of the electrical engineering class conducted by several folks above that nobody has missed the point I raised earlier -- that resetting a c/b even just once has resulted in fatalities, and that's why the FAA is so concerned. I urge all of you to read the SAIB on this subject they issued five years ago and be very cautious about resetting even once any c/b which trips in flight until you get on the ground with your mechanic watching.

If I'm not mistaken, the impetus of the SAIB was the NASCAR 310 crash.

 

[3393RP]

Agreed......

Which is exactly why I posted the "Ricky Nelson" blurb.....

The NTSB report says nothing about a faulty circuit breaker. It is suspected the cabin heater caused the fire but that was not proved.

While it could not be established that the fire originated in the cabin heater, there is no doubt that the fire did originate in the area of the heater. If the copilot's statement about the repeated attempts to relight the cabin heater are accurate, then the captain's repeated attempts to trouble-shoot and relight the heater apparently resulted in a fire in the area
of the heater.

There were other potential ignition sources in the area of the heater, such as airplane electrical wires; however, after examination of these systems, none could be identified as having ignited the fire.

 

[N801BH]

If I'm not mistaken, the impetus of the SAIB was the NASCAR 310 crash.

Yeah... The NASCAR 310 going down in the Sanford Fla neighborhood was the most recent in flight fire caused by repeated resetting of the radar breaker.... IIRC......

 

[N801BH]

The NTSB report says nothing about a faulty circuit breaker. It is suspected the cabin heater caused the fire but that was not proved.

It has been awhile, but I seem to remember the flight crew specifically saying they reset the heater breaker numerous times so the people in the back would stop complaining about it being so cold back there..,,,

 

[weirdjim]

I'm going to apologize for personal comments I made in this post.

Probably good idea.

This sort of tit for tat rubbish is not what I'm about.

I've got tats. You???


This guy Weir is frequently critical of the way I present certain explanations, I don't get anything out of his comments beyond that fact there are similarities in our backgrounds and he doesn't like something I said and he expresses it poorly.

I've said it the same way I'd tell an errant student that kept making the same mistake over and over. There is nothing similar in our backgrounds with the exception of the fact that I worked my way through engineering school WORKING for the airlines and you went to engineering school and think you are a 90 day wonder because you caught on with a cargo carrier without any real life experience.

You seem to be like one of my students who think they can be an engineer wannabe by bragging that they built their house with a micrometer. THe house isn't all that great and the rest of the world thinks you a fool.


The only reason I mention getting a degree is because it was only after working out another zillion circuit problems on paper did It finally dawn on me what the math models were and were not. The only reason I did that was because I was directed to by the curriculum for a 4-5 year engineering degree. Much of that additional problem solving was working out problems that contain fewer unknowns than what is usually taught in technician schools.

Good lord save us. Another engineer that needs to work out the "math models".

I don't mind admitting I really don't know enough about circuit breakers and circuit breaker design. I've actually looked for books to purchase on circuit breaker design, but can't really find anything beyond maybe a Klixon device selection guide.

PreCISEly the problem. Never hung under the instrument panel (or behind the breaker door) sweating in 120F and the aircraft is due to be dispatched in 15 minutes and YOU are the holdup trying to figure out what is going on. I daresay the Klixon selection guide isn't going to be of much use.

But DAMMIT, don't come on here trying to tell somebody why their circuit breaker isn't working when you have not a CLUE how the real world of breakers is coming down.

Most small aircraft breakers are heat activated devices which are affected by environmental heat and sometimes wire temperature; as is the case with sink back heating. The time before a breaker trips is also function of the design and of course multi phase breakers might also trip as a result of imbalances on phase legs. I think I've seen in a complex systems with multiple distribution bus levels each protected by circuit breakers, where an errant load does not trip the closest breaker, but does cause a breaker installed a bus or two higher to trip because of the effect the environment has on the time to trip.

Jeezus. You get a C on your term paper, just barely. Suggest strongly that you don't take any of my graduate level classes.

Those were weeks long troubleshooting efforts on intermittent problems seen in large aircraft systems, where we didn't have all the design data, but needed to come up with an answer to move the plane. In a cost sensitive strict regulatory environment, tolerance build ups you can't explain can really send you down the rabbit hole over things that seem simple to a management team, but are not. Breakers do trip for reasons that are often not apparent. In every case the physical laws of nature are never violated

Yadda, yadda, yadda ....

I've had enough of this for today.

I've had enough of you for fall semester.

Jim

,,,,,

 

[dtuuri]

I'm going to apologize for personal comments I made in this post. <snip>

There was no need to apologize. It just invited more of the same. Oh, wait a minute! Maybe you were baiting him to reveal more of himself? In that case, well played sir!

dtuuri

 

[kontiki]

There was no need to apologize. It just invited more of the same. Oh, wait a minute! Maybe you were baiting him to reveal more of himself? In that case, well played sir!



dtuuri

He does make assumptions and presents them as fact. Buffoon to the end.

 

[RotorAndWing]

He does make assumptions and presents them as fact. Buffoon to the end.

 

[poadeleted20]

If I'm not mistaken, the impetus of the SAIB was the NASCAR 310 crash.

That may have been the event which pushed the FAA to actually act, but there was a significant history of such events (like the cited "Ricky Nelson" accident) which had brought the FAA to the edge of that action already, needing only one more push to move them to act. IOW, the 310 accident was not an isolated incident might otherwise be ignored or downplayed. This is real "threat to life" stuff, so please take it very seriously -- if a breaker pops, don't reset it unless you really need it, and then reset it only once before landing. Otherwise, put this in the latter half of the "if it ain't broke, don't fix it, but if it ain't fixed, don't fly it" category.