Why do capacitors and transformers make audible noise?

[Special K]

I have noticed that right after I take a picture with a flash, I can hear an audible, high-pitched "charging" noise as the capacitor inside is recharged. Why/how does this make an audible noise?

Also I have noticed that medium to large sized transformers emit an audible hum. Why is this? I have used isolation transformers before and when I put my hand on them while they were plugged in, I could feel them vibrating. What causes this?

 

[PottedMeat]

http://en.wikipedia.org/wiki/Magnetostriction

 

[bobsmith1492]

The forces from the moving magnetic fields make the wires physically move at the same frequency; when they move, they move the air, creating sound waves that you hear.

 

[Tiamat]

Originally posted by: bobsmith1492
The forces from the moving magnetic fields make the wires physically move at the same frequency; when they move, they move the air, creating sound waves that you hear.

Is it bad (in terms of electrical properties) if you put some sort of glue or coating onto the vibrating wires to kill the vibration?

 

[bobsmith1492]

No, if you look in a power supply, the output inductors are often coated in hot-glue gun - like glue. It could make it less effective at transferring heat from the wires, though... did you have a specific application you wanted to try?

 

[Tiamat]

Originally posted by: bobsmith1492
No, if you look in a power supply, the output inductors are often coated in hot-glue gun - like glue. It could make it less effective at transferring heat from the wires, though... did you have a specific application you wanted to try?

Same application but on motherboard. I have coil whine/buzz. Id have to think about the heat consequences though.

From my minimal understanding, the buzz is an inefficiency where the energy is converted to vibrational then acoustical energy and heat. So, even if I dampen the vibrational energy, then potentially, I think there would be more heat emitted to conserve the same amount of energy loss.

 

[BrownTown]

Yes, its part of the losses, but don't worry, modern power transformers are on the order of 99% efficient, so you really aren't wasting much energy on the noise.

It is kinda cool though, I don't know how many of you have ever been around 500kV substations or power plants, but the 60Hz hum comming off of the equipment at those voltages is pretty darn loud, its almost like you can feel all the power going threw the equipment (just to quantify that, a big 500kV substation has enough power going threw it for a million people, were talking billions of watts).

 

[Special K]

What about the capacitors in cameras? Those emit a high-pitched chirp noise. That's not the same effect as the transformers is it?

 

[Mark R]

Originally posted by: Special K
What about the capacitors in cameras? Those emit a high-pitched chirp noise. That's not the same effect as the transformers is it?

The noise is almost certainly from the transformer that is used to step-up the battery voltage to the 400 V needed for the flash bulb.

 

[icarus4586]

Howstuffworks explains how camera flashes work, and why they whine. Here's the link: http://electronics.howstuffworks.com/camera-flash3.htm

 

[Qacer]

I look at it this way. E = m*a / q , where E= electric field, m = mass, a = acceleration, and q = charge. The electric potential is related to the electric field by some integral. Anyway, the higher voltage you have, the higher the electric field. This also means that the acceleration increases if the mass and charge stay constant. With the electrons being accelerated at greater values, the impact force would also be greater, which in turn produces a more noisy environment. This would explain why you hear high voltage lines humming.

 

[gerwen]

Originally posted by: Mark R

Originally posted by: Special K
What about the capacitors in cameras? Those emit a high-pitched chirp noise. That's not the same effect as the transformers is it?

The noise is almost certainly from the transformer that is used to step-up the battery voltage to the 400 V needed for the flash bulb.

You can't step-up DC voltage with a transformer. A transformer is an AC device.

Now i'm off to Icarus' link to find out what kind of circuit they use to charge and fire a camera flash.

** edit ** wow, I sorta stand corrected. They use an oscillator to turn battery dc into ac, then a transformer to step up the voltage, then a rectifier to turn the high voltage back to dc to charge the cap which drives the flash. Amazing, and sorta kludgy.

 

[bobsmith1492]

Originally posted by: gerwen

Originally posted by: Mark R

Originally posted by: Special K
What about the capacitors in cameras? Those emit a high-pitched chirp noise. That's not the same effect as the transformers is it?

The noise is almost certainly from the transformer that is used to step-up the battery voltage to the 400 V needed for the flash bulb.

You can't step-up DC voltage with a transformer. A transformer is an AC device.

Now i'm off to Icarus' link to find out what kind of circuit they use to charge and fire a camera flash.

** edit ** wow, I sorta stand corrected. They use an oscillator to turn battery dc into ac, then a transformer to step up the voltage, then a rectifier to turn the high voltage back to dc to charge the cap which drives the flash. Amazing, and sorta kludgy.

Two words: switching supply.

 

[Born2bwire]

Originally posted by: Qacer
I look at it this way. E = m*a / q , where E= electric field, m = mass, a = acceleration, and q = charge. The electric potential is related to the electric field by some integral. Anyway, the higher voltage you have, the higher the electric field. This also means that the acceleration increases if the mass and charge stay constant. With the electrons being accelerated at greater values, the impact force would also be greater, which in turn produces a more noisy environment. This would explain why you hear high voltage lines humming.

The collision of electrons with nuclei or phonons does cause vibrations, but this only manifests itself in the form of temperature. The hum of transformers and inductors are due to the fact that the magnetic field lines up the domains in the ferromagnetic material, slightly altering the physical shape, back and forth as the AC voltage changes polarity. As for high voltage lines, I would think that the noise associated with them might be due to the corona discharge since the lines are not ferromagnetic.

 

[jjzelinski]

Originally posted by: bobsmith1492

Originally posted by: gerwen

Originally posted by: Mark R

Originally posted by: Special K
What about the capacitors in cameras? Those emit a high-pitched chirp noise. That's not the same effect as the transformers is it?

The noise is almost certainly from the transformer that is used to step-up the battery voltage to the 400 V needed for the flash bulb.

You can't step-up DC voltage with a transformer. A transformer is an AC device.

Now i'm off to Icarus' link to find out what kind of circuit they use to charge and fire a camera flash.

** edit ** wow, I sorta stand corrected. They use an oscillator to turn battery dc into ac, then a transformer to step up the voltage, then a rectifier to turn the high voltage back to dc to charge the cap which drives the flash. Amazing, and sorta kludgy.

Two words: switching supply.

Diode, rectifier + regulator, etc..

 

[jjzelinski]

Originally posted by: Born2bwire

Originally posted by: Qacer
I look at it this way. E = m*a / q , where E= electric field, m = mass, a = acceleration, and q = charge. The electric potential is related to the electric field by some integral. Anyway, the higher voltage you have, the higher the electric field. This also means that the acceleration increases if the mass and charge stay constant. With the electrons being accelerated at greater values, the impact force would also be greater, which in turn produces a more noisy environment. This would explain why you hear high voltage lines humming.

The collision of electrons with nuclei or phonons does cause vibrations, but this only manifests itself in the form of temperature. The hum of transformers and inductors are due to the fact that the magnetic field lines up the domains in the ferromagnetic material, slightly altering the physical shape, back and forth as the AC voltage changes polarity. As for high voltage lines, I would think that the noise associated with them might be due to the corona discharge since the lines are not ferromagnetic.

Nice explanation

As for the lines, are we sure it's the lines we're hearing or is the all of the transformers?

 

[Mark R]

I must confess I've never heard HV lines hum or buzz. Although when it's raining, you can often hear them sizzle (not sure whether this is due to water shorting out the insulators and boiling due to the current, or the fact that the wires are so hot from the massive currents flowing through them, that the water sizzles when it hits them).

 

[BrownTown]

Well, I don't know what you consider "high voltage", but the 500kV lines I've been under hum VERY noticably. I beleive that is due to corona discharge though, so lower voltages likely won't have the same problem.

 

[Mark R]

Originally posted by: BrownTown
Well, I don't know what you consider "high voltage", but the 500kV lines I've been under hum VERY noticably. I beleive that is due to corona discharge though, so lower voltages likely won't have the same problem.

Never noticed it with the 275 and 440 kV lines - so maybe it's only at the very highest voltages.

 

[BrownTown]

Well I would think that would be enough, maybe where you are they just take more care to minimize corona discharges. However I guess it could be that I'm just mistaking the sound of the transformers as comming from the lines. I'm trying to remeber, but I do feel like it was the incomming lines, and I've touched 500kV transformers that were live before, and don't really remember them being so noisy that they would still sound very loud from 100m away. I guess the problem is that the 500kV transformers I've been closest to had the lines going down the side of a mountain where you couldn't get clsoe to them to hear anything. But the 500kV lines I've been under were at a nuclear plant where the transformers along with the rest of the swtchyard were behind a 2ft thick conctrete wall with barbed wire and break rocks in front of them, so obviosuly they aint letting people just walk up and see how loud they are, so its possible they were just alot louder than the other ones and therefore their sound carried alot more so that in the parking lot it still sounded loud enough for me to mistake it as comming from the lines. Having said that I am pretty sure that it was the lines making the noise, but it is always possible my memmory is flawed. Although apparently wikipedia agrees with me that corona discharges make audible nosies on high voltage lines. Perhaps the ones you have been under were very tall, or there was other background noise that you just didn't hear it?

EDIT: the 161kV lines deffintely didn't have nearly the same amount of noise, so its possible 275 wouldn't be all that loud, but I doubt the difference between 440kv and 500kV would be enough to make a large increase in volume. It could be current though, the nuclear plant was at 2400MW, so thats at least 4800/sqrt(3) Amps total going through the 5x500kV lines, and maybe more if power is just going through the plant to other locations (IE: 2 of those 500kV lines go to another nuclear plant, an another to a 3000MW coal plant).

 

[Born2bwire]

Originally posted by: Mark R

Originally posted by: BrownTown
Well, I don't know what you consider "high voltage", but the 500kV lines I've been under hum VERY noticably. I beleive that is due to corona discharge though, so lower voltages likely won't have the same problem.

Never noticed it with the 275 and 440 kV lines - so maybe it's only at the very highest voltages.

Humidity might play a factor. Isn't BrownTown out in Arizona? Water vapor increases the dielectric constant of air, so maybe the drier climate where he is allows for more occurances of discharge than moister England.

 

[IEC]

Originally posted by: BrownTown
Yes, its part of the losses, but don't worry, modern power transformers are on the order of 99% efficient, so you really aren't wasting much energy on the noise.

It is kinda cool though, I don't know how many of you have ever been around 500kV substations or power plants, but the 60Hz hum comming off of the equipment at those voltages is pretty darn loud, its almost like you can feel all the power going threw the equipment (just to quantify that, a big 500kV substation has enough power going threw it for a million people, were talking billions of watts).

Heh, you don't even have to be close to hear that nice 60Hz hum

You can even hear it in smaller transformers. The wikipedia link explains it pretty well.

 

[Qacer]

Yes, the hum on the high voltage lines is due to corona discharge. But isn't corona discharge related to very high electric fields accelerating electrons at such high speeds to the point of dielectric breakdown? I haven't touched on this subject for a while, so I may be wrong.

 

[Born2bwire]

Originally posted by: Qacer
Yes, the hum on the high voltage lines is due to corona discharge. But isn't corona discharge related to very high electric fields accelerating electrons at such high speeds to the point of dielectric breakdown? I haven't touched on this subject for a while, so I may be wrong.

Acceleration need not be involved for dielectric breakdown, just like in the case of electrolytic caps.

 

[futuristicmonkey]

How's this for 500kV hum....look about a third of the way down the page. Good explanation there, too: Text