Low voltage causing breaker to pop?

[Steve]

One should be careful about making blanket statements.

Even if it does raise your post count.

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.

 

[ScottM]

One should be careful about making blanket statements.

Even if it does raise your post count.

I have no idea what you are insinuating, but yes you should.

But in the example that Hank wrote about that would be a current sensing device as well, not an under voltage device. He was very clear that it was the low voltage that tripped a circuit breaker.

Circuit breakers are devices that protect circuits and devices from an overload situation. Load in the electrical terms means power. If power is going to high it is either a high voltage or a high current as Power is equal to Current x Voltage. In neither of those cases did voltage go to zero.

As we discussed earlier when you see in the real world is that sometimes the sources cannot provide enough power and voltage will go down as a result of the higher current drain, but it is not the low voltage that is tripping a circuit breaker.

Low voltage detection uses different technologies that circuit breakers do. Because they are not sensing a high power situation.

 

[Dan Thomas]

But in the example that Hank wrote about that would be a current sensing device as well, not an under voltage device. He was very clear that it was the low voltage that tripped a circuit breaker.

Circuit breakers are devices that protect circuits and devices from an overload situation. Load in the electrical terms means power. If power is going to high it is either a high voltage or a high current as Power is equal to Current x Voltage. In neither of those cases did voltage go to zero.

Hank is referring to breakers used in inductive circuits. Electric motors, for example, have a certain current flow at their working RPM. As the armature spins and its windings (or bars) experience reversals in electron flow, their inductance (which opposes any changes in the amount of current flow, be it up or down) will control the amount of current they draw. If they are slowed down, either through overload or a drop in voltage, the inductance is reduced as the frequency of flow reversal is reduced, so they'll draw more current and maybe pop their breakers. This isn't maintainable right down to zero voltage, of course; there'll be reduction in current flow when the voltage gets low enough.

Inductance is what magnetos use to generate high voltages for the spark plugs. A magnetic field that is passed though a coil of wire will generate electron flow in that wire. Conversely, any coil of wire will create a magnetic field around itself when current flows though it, with the field getting stronger and larger as current flow increases, and if we reverse the direction of flow we'll reverse the polarity of the field. If we try to increase the flow, the expanding field cuts outward through the coil's wires and this action opposes the increase, slowing it down by trying to generate a flow in the opposite direction. Reducing the flow will have the opposite effect of boosting the flow as the field collapses through the wires. Stopping the flow real suddenly will collapse the field very rapidly, creating a sudden surge in flow that we use in the magneto to make the spark. This is a useful thing. But when you turn off your master switch with the radios still turned on, the solenoid's collapsing field generates a big voltage spike, too, that gets into the airplane's circuitry and can damage the radios. This is not a useful thing. Many airplanes have some means of protecting the avionics from this, but not all. Not the Citabrias, we have, for example, and not most old puddle-jumper airplanes.

So any inductive device (one having coils in it) will have different behaviour from a simple direct-current resistive circuit. Current won't follow voltage closely at all. If we through in some capacitance we can make things interesting indeed.


Dan

 

[ScottM]

Hank is referring to breakers used in inductive circuits. Electric motors, for example, have a certain current flow at their working RPM. As the armature spins and its windings (or bars) experience reversals in electron flow, their inductance (which opposes any changes in the amount of current flow, be it up or down) will control the amount of current they draw. If they are slowed down, either through overload or a drop in voltage, the inductance is reduced as the frequency of flow reversal is reduced, so they'll draw more current and maybe pop their breakers. This isn't maintainable right down to zero voltage, of course; there'll be reduction in current flow when the voltage gets low enough.

Inductance is what magnetos use to generate high voltages for the spark plugs. A magnetic field that is passed though a coil of wire will generate electron flow in that wire. Conversely, any coil of wire will create a magnetic field around itself when current flows though it, with the field getting stronger and larger as current flow increases, and if we reverse the direction of flow we'll reverse the polarity of the field. If we try to increase the flow, the expanding field cuts outward through the coil's wires and this action opposes the increase, slowing it down by trying to generate a flow in the opposite direction. Reducing the flow will have the opposite effect of boosting the flow as the field collapses through the wires. Stopping the flow real suddenly will collapse the field very rapidly, creating a sudden surge in flow that we use in the magneto to make the spark. This is a useful thing. But when you turn off your master switch with the radios still turned on, the solenoid's collapsing field generates a big voltage spike, too, that gets into the airplane's circuitry and can damage the radios. This is not a useful thing. Many airplanes have some means of protecting the avionics from this, but not all. Not the Citabrias, we have, for example, and not most old puddle-jumper airplanes.

So any inductive device (one having coils in it) will have different behaviour from a simple direct-current resistive circuit. Current won't follow voltage closely at all. If we through in some capacitance we can make things interesting indeed.


Dan

And how many of those are in a Cessna???

Are you guys going to offer anything germane to Kent's problem?

This is so Internet funny

 

[Ghery]

So any inductive device (one having coils in it) will have different behaviour from a simple direct-current resistive circuit. Current won't follow voltage closely at all. If we through in some capacitance we can make things interesting indeed.


Dan

But a purely inductive load still allows current to flow proportionally to the voltage applied. You have a phase shift between voltage and current with an AC voltage applied, but the amplitude of the current is still directly porportional to the applied voltage. Motors draw more current under a constant load if the voltage is reduced, but that is a different effect.

Anyway, Scott is right, this discussion has strayed off from the original question (that never happens here ). CBs pop when too much current flows through them for a period of time. The cause of the excess current flow needs to be found and fixed. And the cause on the circuit under discuss isn't low voltage.

 

[Steve]

I'm not the sharpest knife in the drawer, but I can make a "real world circuit breaker" trip without any wires connected to it, or even touching it.

No current required. There is a serious misunderstanding of circuit breaker operation to think only current causes one to trip one.

I have no idea what you are insinuating, but yes you should.

But in the example that Hank wrote about that would be a current sensing device as well, not an under voltage device. He was very clear that it was the low voltage that tripped a circuit breaker.

Circuit breakers are devices that protect circuits and devices from an overload situation. Load in the electrical terms means power. If power is going to high it is either a high voltage or a high current as Power is equal to Current x Voltage. In neither of those cases did voltage go to zero.

As we discussed earlier when you see in the real world is that sometimes the sources cannot provide enough power and voltage will go down as a result of the higher current drain, but it is not the low voltage that is tripping a circuit breaker.

Low voltage detection uses different technologies that circuit breakers do. Because they are not sensing a high power situation.

 

[rpadula]

I'm not the sharpest knife in the drawer, but I can make a "real world circuit breaker" trip without any wires connected to it, or even touching it.

No current required. There is a serious misunderstanding of circuit breaker operation to think only current causes one to trip one.

Don't keep us in such suspense -- I'm curious!

 

[Steve]

A circuit breaker like that found in homes and Cessnas is a simple device that utilizes a bimetallic strip. The differing coefficients of thermal expansion of the two metals is what the breaker design takes advantage of to operate. The breaker will respond to a temperature change regardless of the source of heat, whether it is heated internally through resistive heating on an energized circuit or heated externally by an ambient heat source. Add heat to an energized circuit and the total resistance will go up in the circuit. Add resistance in an energized circuit and additional heating will occur. Both will cause an increase in current in a DC circuit. An increase in current will cause the bimetallic material to deform due to resistive heating within. At some point the deformation is enough to change the state of the breaker (tripped). But the material will deform even if the source of heating is not internal resistance. Also, by heating one sufficiently a breaker's response to an overcurrent condition can be altered, too, to the point it does not protect at its rated setpoint.

In Kent's scenario the high likelihood candidate is a poor (loose, frayed, corroded, etc.) connection somewhere in the circuit, either on the "hot" side or the "ground" side. The ones on the "ground" side tend to get overlooked. The localized heating from the increased resistance is causing a current drain to which the breaker is responding by changing state (that bimetallic thing). When troubleshooting a circuit problem all parameters should be considered. Luck helps, but rigor and completeness always win.

...but it is possible to trip an electrical circuit breaker with no current present. B)

Don't keep us in such suspense -- I'm curious!

 

[ScottM]

A circuit breaker like that found in homes and Cessnas is a simple device that utilizes a bimetallic strip. The differing coefficients of thermal expansion of the two metals is what the breaker design takes advantage of to operate. The breaker will respond to a temperature change regardless of the source of heat, whether it is heated internally through resistive heating on an energized circuit or heated externally by an ambient heat source. Add heat to an energized circuit and the total resistance will go up in the circuit. Add resistance in an energized circuit and additional heating will occur. Both will cause an increase in current in a DC circuit. An increase in current will cause the bimetallic material to deform due to resistive heating within. At some point the deformation is enough to change the state of the breaker (tripped). But the material will deform even if the source of heating is not internal resistance. Also, by heating one sufficiently a breaker's response to an overcurrent condition can be altered, too, to the point it does not protect at its rated setpoint.

In Kent's scenario the high likelihood candidate is a poor (loose, frayed, corroded, etc.) connection somewhere in the circuit, either on the "hot" side or the "ground" side. The ones on the "ground" side tend to get overlooked. The localized heating from the increased resistance is causing a current drain to which the breaker is responding by changing state (that bimetallic thing). When troubleshooting a circuit problem all parameters should be considered. Luck helps, but rigor and completeness always win.

...but it is possible to trip an electrical circuit breaker with no current present. B)

What he is saying is that the extra current flowing through the breaker, as a result of the fault somewhere in the circuit, is heating up the inside of the breaker (the bimetallic strip) and it pops the breaker. The heat is a result of the higher current. Hence he is agreeing with me and my analysis throughout this thread.

My electrical-fu was faster and superior

I am still waiting for Steve to tell us about the reverse thermal coefficient bimetallic strips and how too little current will also trip certain specialized breakers. Those are types of breakers use current to to detect a low voltage. But again there are none of those in the panel of your average Cessna bug smasher. The CBs in your home and plane are detecting high current. The detection mechanism is that current heats an element that will trip the breaker. Nonetheless it is the current not the heat that is the controlling parameter for those types of breakers. Heat is just the byproduct of current converted to a mechanical property that enables the action to occur.

And they way you set off a high current type of breaker without touching it or hooking it up is to heat it.

 

[Tom-D]

OMG guys, just clean the Battery terminals, and get on with life.

 

[Steve]

Wait in one hand...

I wanted to see if posting ad nausem was something that could be recognized for what it was.

I got my answer.

 

[gkainz]

OMG guys, just clean the Battery terminals, and get on with life.

LOL!!!!

a mechanic, an engineer and a psychiatrist are discussing a breaker popping. The engineer wants to know why the breaker is popping, the phychiatrist wants to know if the breaker wants to be fixed and the mechanic cleans the battery terminals and the breaker is happy

 

[weirdjim]

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.
Dan

When I need a real answer I generally go to a source document and not wiki. In this particular case, RCA (which held the original vacuum tube patent) Receiving Tube Manual, 1961, page 4 discusses the three different types of filaments: tungsten, tungsten impregnated with thorium oxide, and tungsten indirectly heating "alkaline earths" (whatever that is).

Another 1961 source (ARRL Handbook) speaks to the tungsten and thoriated tungsten cathodes, but goes on to say that the "alkaline earths" are "rare earths", generally considered to be the Lanthanide series. I suspect the actual composition of the rare earths was somewhat of a trade secret as there is little, if any, discussion regarding the actual composition.

1961 was pretty much the death knell year for vacuum tubes. I worked my way through high school in a tv/radio fixit shop and remember (my senior year of high school) being trained by Magnavox (maggotbox) in their new superduper hi fi sets featuring (gasp) half a dozen transistors in the output stages.

Jim

 

[mikea]

LOL!!!!

a mechanic, an engineer and a psychiatrist are discussing a breaker popping. The engineer wants to know why the breaker is popping, the phychiatrist wants to know if the breaker wants to be fixed and the mechanic cleans the battery terminals and the breaker is happy

Telephone tech support says. "I have a breaker right here and it's working fine..."

 

[Tom-D]

Telephone tech support says. "I have a breaker right here and it's working fine..."

Why wouldn't it? its got clean terminals.!

 

[weirdjim]

OK, let me lay you out a likely scenario. Most modern dimmers use a switching regulator that is somewhere between 80 and 95% efficient, depending on how good the feller was that designed it. As opposed to the old analog dimmers that simply threw away as heat all the power that the lamps couldn't use, the switcher is actually a constant POWER device. That is, the lamps ask for power in watts, the switcher sucks that many watts (plus a small efficiency factor) from the battery bus.

Brother Ohm tells us that to consume a constant POWER, if the voltage goes down, the amps go up (power being the product of voltage and current). Thus, in attempting to deliver a constant power to the bulbs, when the battery bus goes a bit down, the current goes a bit up. How much a "bit" is is up to you.

Now given a small amount of corrosion on the breaker terminals, we have a heating effect given by the current SQUARED times the corrosion resistance. That SQUARED factor gets pretty large pretty quick, so indeed when the battery bus goes down, the current goes up and the heat goes up as current SQUARED.

And, as somebody earlier mentioned, the breaker internals have no idea what the current through the breaker is. All it knows is that if it gets too hot, it pops. Current SQUARED through both the breaker mechanism plus through the corroded terminal gets things a lot hotter a lot quicker than you might imagine.

I could be wrong, mindya {;-)

 

[weirdjim]

LOL!!!!

a mechanic, an engineer and a psychiatrist are discussing a breaker popping. The engineer wants to know why the breaker is popping, the phychiatrist wants to know if the breaker wants to be fixed and the mechanic cleans the battery terminals and the breaker is happy

A mathematician, a physicist, and an engineer are given the problem of fiinding the volume of a red rubber ball.

The mathematician carefully measures the ball's diameter and then uses the equation for the volume of a sphere and comes up with an answer +/- 1 cm^3.

The physicist carefully submerges the ball in a graduated cylinder and comes up with an answer +/- 0.1 cm^3.

The engineer simply reaches up onto his bookshelf and takes down the "Red Rubber Ball Handbook" ...


Jim

 

[Henning]

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.

Just a thought, with modern power supplies that work with various voltages and you have say a 24v system from which the radios draw say 5 amps to operate, so call it on a 7.5 breaker, now say the voltage drops to 12v and you key the mic, will it try to pull double the amps normal to maintain the same wattage and overload the 7.5 amp breaker?

 

[weirdjim]

Just a thought, with modern power supplies that work with various voltages and you have say a 24v system from which the radios draw say 5 amps to operate, so call it on a 7.5 breaker, now say the voltage drops to 12v and you key the mic, will it try to pull double the amps normal to maintain the same wattage and overload the 7.5 amp breaker?

Didja see what I wrote about switching power supplies about four messages down?

Jim

 

[Ghery]

OK, let me lay you out a likely scenario. Most modern dimmers use a switching regulator that is somewhere between 80 and 95% efficient, depending on how good the feller was that designed it. As opposed to the old analog dimmers that simply threw away as heat all the power that the lamps couldn't use, the switcher is actually a constant POWER device. That is, the lamps ask for power in watts, the switcher sucks that many watts (plus a small efficiency factor) from the battery bus.

Brother Ohm tells us that to consume a constant POWER, if the voltage goes down, the amps go up (power being the product of voltage and current). Thus, in attempting to deliver a constant power to the bulbs, when the battery bus goes a bit down, the current goes a bit up. How much a "bit" is is up to you.

Now given a small amount of corrosion on the breaker terminals, we have a heating effect given by the current SQUARED times the corrosion resistance. That SQUARED factor gets pretty large pretty quick, so indeed when the battery bus goes down, the current goes up and the heat goes up as current SQUARED.

And, as somebody earlier mentioned, the breaker internals have no idea what the current through the breaker is. All it knows is that if it gets too hot, it pops. Current SQUARED through both the breaker mechanism plus through the corroded terminal gets things a lot hotter a lot quicker than you might imagine.

I could be wrong, mindya {;-)

A light bulb isn't a constant power device. Neglecting the change in resistance due to heating, it is a fixed resistor. Power dissipated will be dependent on the voltage and current, and the relationship between those two is fixed with a fixed resistor. Lower the voltage, the current drops too. And dissipated power drops.

 

[weirdjim]

A light bulb isn't a constant power device. Neglecting the change in resistance due to heating, it is a fixed resistor. Power dissipated will be dependent on the voltage and current, and the relationship between those two is fixed with a fixed resistor. Lower the voltage, the current drops too. And dissipated power drops.

Well, either I'm not saying it right or you aren't hearing it right. Either one is possible.

Um, yes sir, at a constant voltage a light bulb IS a constant power device. At a constant voltage the light bulb will draw a constant current and the product of constant voltage and constant current is constant power.

That's what a voltage regulator does for a living, don'cha know? It keeps the output (lamp) voltage constant with varying input voltages (amongst other things).

Let's work through a numbers example. You've got the lights dimmed down to a nice 8 volt rosy late night glow. At this voltage the lamp(s) draw half an ampere. That's (8 * 0.5) 4 watts.

And, your generator is genning (or alternator alting) putting out a nice 14.4 volts to the battery bus. How much current (neglecting efficiency factor) is your switching regulator drawing? Power divided by voltage is current, so 4 watts divided by 14.4 volts means the power supply is drawing 0.28 amps.

But now you reduce the engine RPM so that the battery bus lowers to 12 volts. Now how much current is being drawn? The same 4 watts divided by 12 volts, or 0.33 amps.

0.33 amps divided by the original 0.28 amps shows that for this drop in voltage, you are drawing 20% more current at the low voltage than at the high voltage. If your breaker is running close to the limit this may be enough to trip it.

Okeh?

Jim

 

[Ghery]

OK, now you've pulled all the pieces together in one place. I see your point now. You're not talking about a bulb hanging off the "12 volt" bus, but instead one hanging off a switching dimmer, kept at a constant output with a varying input.