Low voltage causing breaker to pop?

flyingcheesehead

flyingcheesehead

Taxi to Parking
Joined
Feb 23, 2005
Messages
25,044
Location
UQACY, WI
Display Name
Display name:
iMooniac
Hello,

Having an odd problem. I noticed today that the Cabin Lights breaker in the 182 (instrument and radio lights too) was popped when I went to leave. I reset it, flew all day, started flying a bit at night, but landed before the sky was completely dark. I was running the lights for a while, however.

Then, on my landing roll, the breaker popped again. As I pulled off the runway, I reset it. Then, I noticed that when I was all the way at idle, the lights got much dimmer, fairly suddenly. At 900-1000 RPM's they went back to normal brightness. Then right before I shut down I tried it again - 600 RPM idle, the lights got much dimmer, flickered a couple of times, and the breaker popped again.

Is this one of those "Doc it hurts when I do this/Well then don't do that" kind of things, or an indicator of a more serious problem?
 
flyingcheesehead said:
Hello,

Having an odd problem. I noticed today that the Cabin Lights breaker in the 182 (instrument and radio lights too) was popped when I went to leave. I reset it, flew all day, started flying a bit at night, but landed before the sky was completely dark. I was running the lights for a while, however.

Then, on my landing roll, the breaker popped again. As I pulled off the runway, I reset it. Then, I noticed that when I was all the way at idle, the lights got much dimmer, fairly suddenly. At 900-1000 RPM's they went back to normal brightness. Then right before I shut down I tried it again - 600 RPM idle, the lights got much dimmer, flickered a couple of times, and the breaker popped again.

Is this one of those "Doc it hurts when I do this/Well then don't do that" kind of things, or an indicator of a more serious problem?
Click to expand...

It can certainly be.

Recently I flew in an airplane where the Wingtip strobe CB would pop on takeoff only.

I told the student-owner he should leave the Strobes off until he had them checked

After a couple of trips to the avionics shop, the tech pulled the wires. Not good.

Whoever ran the wires to the strobes did not use the dedicated channel, and ran them over the wing braces, where they rubbed for years until the insulation was worn through.

When the airplane took off, the slight change in dihedral angle was enough to move the wire so the bare wire portion made contact and shorted out the circuit.

Bare wire shorting out inches from the fuel tanks!

The only indication was the CB popping on takeoff.
 
Last edited:
I'm also in the camp if it may be a more serious problem. Intermittent problems like you describe are harder to track down but they can still be serious. I feel circuit breakers that pop indicate a serious issue.

I'm no electrician, A&P, and I haven't stayed at a Holiday Inn Express in months, but the problem sounds similar to what Dan describes. IF you choose to fly it again and IF you have a current wiring diagram, you may try to isolate the problem with an ohm meter as a short will show low resistance.

I'm sure someone will chime in with better advice....
 
I agree. With the lights dimming, flickering, and then the breaker popping..... you have an intermittent short circuit. I hope you get lucky, as these problems can be a bi**h to find. but find it you must!

-Skip
 
CBs do not pop from low voltage, they pop from high current. A short somewhere in the circuit is causing a high current draw, one of the results may be a low voltage indication as the high current is dragging down the voltage on the bus.

This could be several things from a broken wire to a voltage regulator or even alternator problem itself. Have it looked at.
 
I've yet to see a POH that allowed for resetting a breaker more than once. A second pop should be addressed as soon as possible.
 
Kent I know this is a bummer since you are on your great adventure but please do have it looked at. I suspect that you can't use the radios with out the radio lights so that may preclude operating with the CB popped. Does teh problem affect the Radio reception, volume and transmission as well?
 
All you electricians will probably jump all over me for stating it this way but here goes.

when you cut the voltage down the amperage goes up, amperage is heat heat pops the C/B.

When you drop to 900/1000 RPM, your alternator drops the load,( that is the function of the voltage regulator) and the battery does the job after that. you probably have a high restance connection to the battery, causing the voltage to drop below circuit requirements.

My suggestion, clean the terminals/connections to the battery. see what happens.
 
AdamZ said:
Kent I know this is a bummer since you are on your great adventure but please do have it looked at. I suspect that you can't use the radios with out the radio lights so that may preclude operating with the CB popped. Does teh problem affect the Radio reception, volume and transmission as well?
Click to expand...

Most all radios will operate fine down to about 9 volts, light circuits won't, because they are direct current draws, and don't have transformers in them.

On circuits that are direct current draws the rule of thumb is when you cut the voltage in half, you double the amperage to do the same work.

Doubling the amperage will pop the C/B.
 
NC19143 said:
Most all radios will operate fine down to about 9 volts, light circuits won't, because they are direct current draws, and don't have transformers in them.

On circuits that are direct current draws the rule of thumb is when you cut the voltage in half, you double the amperage to do the same work.

Doubling the amperage will pop the C/B.
Click to expand...
The radio s are also DC so they do not have power transformers in them (they may have audio and/or RF transformers). Transformers only work with AC. But the radio do have voltage regulators in them to help stabilize the voltage fluctuations. Since the displays are probably working off of 5Vdc on the radio you do not see a fluctuation when the bus voltage drops to 9Vdc. The output power of the radio is probably a bit lower though!

Voltage and Current are related by Ohm's law. That is Voltage/Current=Resistance

All of those terms are dynamic. A decrease in circuit resistance could be a decrease in voltage with a corresponding increase in current. That is probably what Kent is seeing with his problem. Some device is starting to fail. It's resistance is decreasing towards a short. Eventually the current goes up enough to trip the circuit breaker.

Since it is just one CB you have to figure out what is on that circuit that could be failing.
 
NC19143 said:
On circuits that are direct current draws the rule of thumb is when you cut the voltage in half, you double the amperage to do the same work.
Click to expand...
That is not a rule of thumb that is the law, Ohms law.

NC19143 said:
Doubling the amperage will pop the C/B.
Click to expand...
Depends on the capacity of the CB. If you are drawing 5 Amps through a 15 Amp circuit breaker doubling it to 10Amps should not trip the breaker.


One other thing that could also be wrong for Kent is that the breaker itself has gone bad. But if that is so I would not expect to see the Voltage sag he is seeing, that indicates a high current draw from something.
 
NC19143 said:
All you electricians will probably jump all over me for stating it this way but here goes.

when you cut the voltage down the amperage goes up, amperage is heat heat pops the C/B.
Click to expand...
Nope.

Look at this circuit
200px-Ohms_law_voltage_source.svg.png


If I cut the voltage in half the current will also drop by half as the resistance has not changed.

Voltage is the pressure to push current. Current is the actual motion of electricity. Resistance is a push of resistance opposite tot he direction of current. Think of it as the conveyor belt to the 'airplane like' like electricity ;)


In Kent's case it is more likely that the resistance is changing. It is going down, that is pulling more current and the voltage is moving down as the system cannot supply anymore force. Eventually if the CB did pop you would see current max out and Voltage go close to zero.

Theoretically current would go to infinity and voltage would go to zero but this is the real world and our aircraft electrical system jsut cannot do that.
 
Last edited:
Electrical Theory and Application 101 is a good course, but the most likely cause for a CB popping is that the circuit is somehow compromised (i.e. a short).

This is never good in an airplane and should be addressed by a qualified A&P.
 
NC19143 said:
Most all radios will operate fine down to about 9 volts, light circuits won't, because they are direct current draws, and don't have transformers in them.

.
Click to expand...

Tom my thought was that even if the radios worked he couldn't see the numbers on the read out to see what frequency he was or or dialing into. I guess you could count clicks but thats kind of a PIA
 
Tom you are correct if the load is an electric motor. With less voltage, the motor will run slower (and because of lower back EMF) draw more power = more amperage. However, lights are purely a resistance load and lower voltage will result in lower amperage. -Skip
 
breakers are not switches, even tho sometimes they're used as such. Popping one a few times can and will weaken it and it will pop with less load, which is not a bad thing - you've got a problem that needs to be resolved to use the circuit - either something causing higher load, short in the wiring, or a bad breaker. Continually resetting it will not make it better (but could identify any possible short in the wiring - just follow the smoke to the bad spot!) - not recommended, btw.
 
Like I said you electricians would jump all over me.

but take my advice, clean the battery terminals see what happens.

The big clue is, it happens at the time the alternator kicks off and the battery takes over.

If the terminals aren't bad, the battery is.
 
Skip Miller said:
Tom you are correct if the load is an electric motor. With less voltage, the motor will run slower (and because of lower back EMF) draw more power = more amperage. However, lights are purely a resistance load and lower voltage will result in lower amperage. -Skip
Click to expand...

It happens the same way with bulbs, the lower the voltage, the dimmer the bulb.

I'll wager that here is a connection between the battery and the buse, that will get hot when the circuit load gets heavy.

find it, and clean, it and the problems goes away..

BTDT way too many times. it is very typical of aircraft electrical problems.
 
What Tom is alluding to is the the circuit resistance is becoming high, the stuff on the circuit is still drawing the same power. BTW power in the DC world is Current times Voltage. Each of those dirty contacts that are resistive are also drawing power. Eventually the whole circuit is drawing a lot more power than it normally would and the higher current required to supply that power trips the breaker.
 
NC19143 said:
It happens the same way with bulbs, the lower the voltage, the dimmer the bulb.

I'll wager that here is a connection between the battery and the buse, that will get hot when the circuit load gets heavy.

find it, and clean, it and the problems goes away..

BTDT way too many times. it is very typical of aircraft electrical problems.
Click to expand...
I have no doubt that cleaner connections will help. I also think we are both right. As your corroded connections heat up, the resistance of those connections changes. So it becomes a dynamic system with many things changing at once - with unknown and probably variable results.

-Skip
 
Skip Miller said:
I have no doubt that cleaner connections will help. I also think we are both right. As your corroded connections heat up, the resistance of those connections changes. So it becomes a dynamic system with many things changing at once - with unknown and probably variable results.

-Skip
Click to expand...

I've found the battery feed wire at the bus corroded inside its crimp terminal. This gets hot and resistance builds and the lights dim and so forth, but the heated terminal, which is often attached to the bus using one of the breaker screws, also heats the breaker involved and since those things use heat to trip them, it will pop off.
Old breakers get a film of oxide on their contacts. More resistance that causes heat and it will pop earlier than it should.
Electricity is fun. You can't see it leaking out at a short or piling up at a bad connection, so until you learn to think it out it can be a real pain for you and a good source of income for someone who's good at it.

Dan
 
smigaldi said:
Also are you hearing any sort of hum in your audio circuits that changes frequency with the engine RPM?
Click to expand...

No, but my #2 radio was causing some "issues" last night (noise in the intercom, even when Com2 wasn't selected), so I turned it off.

But then this morning I discovered that Nav2 was still selected in the audio panel, so it may have been picking up a far-away VOR just strong enough to break squelch.

:redface:
 
AdamZ said:
Tom my thought was that even if the radios worked he couldn't see the numbers on the read out to see what frequency he was or or dialing into. I guess you could count clicks but thats kind of a PIA
Click to expand...

Well, the 430 doesn't need the lights, and I don't think the MAC 1700 does either but I had it turned off at the time so I don't know. :dunno:

But, my next night flight may be the last leg back into MSN anyway.
 
AdamZ said:
Kent I know this is a bummer since you are on your great adventure but please do have it looked at. I suspect that you can't use the radios with out the radio lights so that may preclude operating with the CB popped. Does teh problem affect the Radio reception, volume and transmission as well?
Click to expand...

I don't know... The problem didn't happen until the landing roll at an uncontrolled field.
 
Dan Thomas said:
Electricity is fun. You can't see it leaking out at a short or piling up at a bad connection, so until you learn to think it out it can be a real pain for you and a good source of income for someone who's good at it.

Dan
Click to expand...

"Leaking out at a short?" "Piling up at a bad connection?"

As one of my EE profs was fond of saying, "Uncle Kirchoff's plumbing law says that the sum of the currents into a paper bag is 0."

What's that mean? Take any node in a circuit, however you wish to define it, and the amount of current entering will equal the amount of current leaving. There is no such thing as a current sink. Going back to the orginal quotes - if you have a current source (battery) and X amperes of current leave it, X amperes of current will return on the opposite terminal. It has to be that way. A short circuit is simply an alternate path for current to return to the source. Usually undesired. And as the impedance is in parallel with the intended load, the total current increases. Add enough current flow through the CB and it pops.

If this is an intermittant problem, have fun finding it. I hate troubleshooting intermittants. Good suggestions in this thread. And Scott is correct, voltage goes down in a resistive circuit, current goes down. And power dissipated in the load goes down. And Skip is right on about motors.

Didn't this start out as a problem on a single CB? I'd start looking on the load side of that CB, not back at the battery. But that's just my approach.
 
Ghery said:
"Leaking out at a short?" "Piling up at a bad connection?"

As one of my EE profs was fond of saying, "Uncle Kirchoff's plumbing law says that the sum of the currents into a paper bag is 0."

What's that mean? Take any node in a circuit, however you wish to define it, and the amount of current entering will equal the amount of current leaving. There is no such thing as a current sink. Going back to the orginal quotes - if you have a current source (battery) and X amperes of current leave it, X amperes of current will return on the opposite terminal. It has to be that way. A short circuit is simply an alternate path for current to return to the source. Usually undesired. And as the impedance is in parallel with the intended load, the total current increases. Add enough current flow through the CB and it pops.
Click to expand...

We know all that. I was just making a point: you can't see electricity, only what it does, so troubleshooting an electrical problem is much more difficult than figuring out where the water in your plumbing is going when you turn on the tap and nothing comes out but the meter's going round and round.
Finding shorts can be most difficult, mostly because they often happen in inaccessible places and can be intermittent, and the suspect circuit must be disconnected at the supply and resistance taken while moving the wire around or banging on things and so on. We once had a 150 that would pop its nav light breaker, even in the daytime when the lights were off. The service manual schematic showed the fuel gauges conected to the same breaker, and sure enough, they'd go dead, too. We looked hard at the wire between the breaker and nav light switch, at the switch itself, the breaker, and the feed to the fuel gauges, but nothing showed up. It finally turned out to be a small brass nut that had fallen into one of the gauges (they're a wide-open-frame thing in old 150s, no gauge case), probably gauge securing hardware that got away from the mechanic and couldn't be found, and it would move around a bit and unpredictably short the gauge's hot side to the frame.

Dan (CPL/Instructor/Aircraft Maintenance Engineer)
 
smigaldi said:
hmmm So when I see lightning that is not electricity?
Click to expand...

You're seeing superheated air, not the electrons flowing through it. Same as the spark of a spark plug or an arc welder. Something to do with the ionization of the air's molecules, stripping off and adding electrons as it flows along and generating a heap of heat in the process. Or something. Very, very hot.
When I learned electronics a long time ago we were still fooling with vacuum tubes. Those things are variable valves that control the flow of electrons between a cathode and an anode within a vacuum. All you see inside is the glowing filament that heats the barium-oxide-coated cathode so that it releases electrons easily; you never see the electrons themselves as they fly across the tube between cathode and anode.

Dan
 
Last edited:
I thought you could only see photons...:goofy:


Dan Thomas said:
You're seeing superheated air, not the electrons flowing through it. Same as the spark of a spark plug or an arc welder. Something to do with the ionization of the air's molecules, stripping off and adding electrons as it flows along and generating a heap of heat in the process. Or something. Very, very hot.
When I learned electronics a long time ago we were still fooling with vacuum tubes. Those things are variable valves that control the flow of electrons between a cathode and an anode within a vacuum. All you see inside is the glowing filament that heats the barium-oxide-coated cathode so that it releases electrons easily; you never see the electrons themselves as they fly across the tube between cathode and anode.

Dan
Click to expand...
 
Dan Thomas said:
All you see inside is the glowing filament that heats the barium-oxide-coated cathode so that it releases electrons easily; you never see the electrons themselves as they fly across the tube between cathode and anode.

Dan
Click to expand...

Um, that would be a THORIUM coated cathode. That's why vacuum tubes are a hazardous waste. The thorium is mildly radioactive.

Jim
 
weirdjim said:
Um, that would be a THORIUM coated cathode. That's why vacuum tubes are a hazardous waste. The thorium is mildly radioactive.

Jim
Click to expand...

I had to go look that up. Wiki (which might be wrong, of course), says that transmitting tubes used thorium, while (later) receiving tubes used barium oxide.
http://en.wikipedia.org/wiki/Vacuum_tube

This site agrees with Wiki: http://mysite.du.edu/~etuttle/electron/elect27.htm

Not that any of it matters anymore. Tubes are only seen now in a few guitar amps and in a few audio amps aimed at folks with money, like the one I see in a shop that has a couple of tiny tubes atop it, neither big enough to deliver more than a couple of watts nor offering more than three or four stages of amplification for a single channel in any case. There has to be a chip hidden inside, along with some power transistors.
http://www.alibaba.com/catalog/11490928/Vacuum_Tube_Amplifier.html

Dan
 
smigaldi said:
CBs do not pop from low voltage, they pop from high current. A short somewhere in the circuit is causing a high current draw, one of the results may be a low voltage indication as the high current is dragging down the voltage on the bus.

This could be several things from a broken wire to a voltage regulator or even alternator problem itself. Have it looked at.
Click to expand...

I am not an expert on aircraft breakers but I am an expert on the breakers we used on the electric power plant and those most certainly do trip on low voltage--technically it is over-current, but what is happening is that the load draws a certain amount of power. Power= voltage*current, hence for a given power drawn, as voltage goes down, current goes up and the breaker trips.
 
hankrausch said:
I am not an expert on aircraft breakers but I am an expert on the breakers we used on the electric power plant and those most certainly do trip on low voltage--technically it is over-current, but what is happening is that the load draws a certain amount of power. Power= voltage*current, hence for a given power drawn, as voltage goes down, current goes up and the breaker trips.
Click to expand...
Even in that case it is the current that trips the breakers.

If circuit breaker were voltage controlled and tripped on low voltage you would never be able to set them when they are not hooked up to anything as there is zero voltage on them. Ever see circuit breakers popping when they are sitting unconnected on the lab bench? Do all your house circuit breaker pop during a power outage? How about when you turn off your plane and let the voltage on the circuit breakers go low, zero Volts, do all the breakers pop? Nope, so they must not be popping on low voltage.
 
Last edited:
There are under-voltage protection devices that will pre-emptively trip circuit breakers on low voltage at 0 current. I suspect Hank has worked on a few.
 
Steve said:
There are under-voltage protection devices that will pre-emptively trip circuit breakers on low voltage at 0 current. I suspect Hank has worked on a few.
Click to expand...
There are those, I agree. But what we are talking about are the common circuit breakers that people find in their homes, airplane, etc. Those mostly work with a heat detecting element that will trip the circuit when current is too high. The high power world of electricity is another game altogether with some interesting devices. But to say that Kent's circuit break was detecting an under voltage situation is simply not true. The cicuit breakers in a Cessna are ALL current sensing devices. It tripped due to high current.
 
You must log in or register to reply here.
Back
Top