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Yesterday all of my AC/DC power supplies began making strange buzzing, crackling noise (quickly and intermittently repeated pops). First I thought that my computer's power supply is dying. So I switched to laptop, to my surprise its power began to make the very same noise when I started the laptop. I checked the outlet and there was not problem.

I tryed other wall outlets in the flat too. All of them making this noise. I looked around the house. Other AC/DC converters making this noise too (eg. the main door bell).

But something is strage, the DC appliances and computers still working no signs of overheating or crashing, incandescent light bulbs NOT blinking, AC appliances (like hair dryer) works like before.

Also no electric smell anywhere inside building, pylons seem and sound to be ok. The local transformer just humm.

This crackling noise is quite annoying at night, and it's worrying.

So what can be the source of the noise? And how to fix it? (at least in theory as I rent the flat and I have no tools).

Some technical details: I live in Hungary, the voltage between one phase and ground is 230V, between two phases it's 400V. It seems only one phase installed in the house but I'm not sure.

UPDATE:

Uploaded a Youtube video of the phenomenon:

https://www.youtube.com/watch?v=zrWAY0XMB_E

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I'd ask my neighbors if they noticed anything similar to rule out your house versus the grid –  Steven Dec 10 '12 at 2:17
    
Assume they don't have the same problem. Wouldn't the power company able to detect these kind of problems somehow? –  Calmarius Dec 10 '12 at 12:09
    
If its an issue with a local transformer I doubt they could detect it –  Steven Dec 10 '12 at 13:06
    
Have you checked the frequency of the outlets? Are they 60Hz? Even better, could you look at it with an oscilloscope? Maybe there is something wrong with the transformer and your house is out of phase... Just an idea. –  kjmccarx Dec 20 '12 at 0:38

2 Answers 2

up vote 8 down vote accepted
+100

You have an arc-over somewhere in your power supply system. Electric arcs produce a broad band signal with precisely that noise pattern.

Cracked or dirty insulators on the power poles, transformer with an internal primary circuit fault, loose connections between the transformer and meter, or compromised underground feeder cables that are leaking current between the conductors will probably be the source of this EMI.

Heaven forbid that the source is anywhere in the house, that's a dangerous situation.

Determining where it comes from

Given the noise that can be heard in the video, this should be transmitting a pretty nasty interference on AM radio frequencies to the point you should have no problem using an AM radio as a source detector.

First steps are to make sure this isn't something in the house that is suffering from a loose connection, ground leakage or arc fault. Turn your radio on and with it somewhere mid band between stations, see if you can hear the noise. Now go through the breaker panel or fuse panel and cut power to each circuit till you have cut all power to the house.

If the noise goes completely away from powering off a circuit, then start looking for appliances, switches, lighting fixtures powered by that circuit that that have failures. At this point, if wiring starts being the possible culprit, you're getting into electrician territory, so get a qualified electrician if you're exceeding your technical expertise or what you're allowed to do under your local laws.

Using this method, I had found that the people who wired my house up had used a crimp ground ring to complete a power circuit in the bathroom which explained the radio noise and the dim lighting that would flicker every so often. Removing the electrician's tape off the odd looking connection revealed that the crimp ring (improper use, only supposed to be used in the ground circuit) had worked loose and the copper wire was being slowly eroded from the arcing in the loose connection.

If the power down only slowly diminishes the noise till the last circuit is cut off, then you need to make sure the power entrance and cabling to the breaker panel/fuse panel are intact to clear your residence (qualified electrician time, you do not want to be messing with this).

Once you have cleared your residential wiring, then you need to get the power company involved in hunting down where the noise is emanating from. It's in their best interest to fix it if its a bad splice, cracked insulator or transformer getting ready to blow.

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Yeah, I've just bought an AM radio for the purpose. And yes, on the first floor at the electric meter box it began to receive this noise. I will contact the owners of those appartments soon. –  Calmarius Dec 20 '12 at 12:52

First of all, try to locate the root of the problem. From what you wrote, I guess this can be your home electric wiring failing to provide the quality the energy provider is giving to your home, or a low quality of the service. You said all the plugs at your home do the same thing, so it is not an isolated problem in one room or one device, like an old computer.

How can you know which one is the root? It's not easy to know, because you normally don't have access to the wiring out of your home, it could be illegal in some places, and also very dangerous if you don't know what you are doing. Most countries have a set of rules about the quality of the electric service (the name may vary, but you get the idea). If your company fails to provide a good quality of service, they should improve it or pay you for any damage this could cause. The best way to know is inform yourself about these rules and then call the company, telling them that you are having serious quality problems. They will come to your address and check it, it won't be their fault or may be the rules will not be very strict, so don't keep your hopes up about getting any money from them.

If it is your home installation, you probably live in an old house with old wiring. I have that same issue and it's not very nice. Years ago, electric wiring wasn't taken so seriously and many rules didn't apply. You might find very thin protected wires and very noisy AC signals in an old house. How old is your home electric installation? Do light bulbs last shorter than you should expect?

I am understanding that the noise is IN the transformer and not the plug itself, check if I'm right, because the first might be harmful for your equipment but not dangerous, the second can cause a fire easily.

There are two kind of noises in a transformer, humming (which can go up to buzzing) and cracking. Humming is a "natural" noise caused by electromagnetic interaction of the transformer, it should be kept as low as possible, but if you listen carefully enough, you will always hear it in any transformer. Humming might go louder if you charge the transformer too much, but this is not very common and you don't seem to be doing it. Cracking sounds happen when the transformer is not working on its design values. Design values are voltage and current (or both) at which the device is meant to work. If you go too high or even too low, you might hear some noise. This means your transformer is doing extra work and it might significantly shorten its life. The sound in the transformer is (very) rarely caused by arcs, it normally comes from the semiconductors, which are the "switches" that let the AC pass in a way it goes out as DC.

One way to make this less critic is installing some kind of filter or protecting device that guarantees the quality of the signal received by a device. This units might seem expensive, but they can save you a lot of money on the long term if they protect 2 computers, for instance.

I hope I didn't make this very long and you can now understand what's happening. Unfortunately, there's no easy way out of this kind of problem.

(Sorry about my English, it's not my first language and I usually don't use it on this field, if you find it necessary to make any corrections to any technical term I didn't find, please do is to I can learn the right word for it).

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Just to clarify, when I said "noisy AC signals" I was talking about electric noise, that is, if you could see the wave generated, it would be "curly", not the perfect sin(x) wave. Not the noise that you can hear now and is worrying you. –  Rubén Cabrera Dec 10 '12 at 20:54
    
Yes the house is pretty old and I believe the wiring is quite old too... And yes the source is the AC/DC transformer. Even my speakers make this noise quite loudly when the signal cable is not plugged in. I don't experience overheating yet. Maybe it's due to undervoltage? –  Calmarius Dec 11 '12 at 9:14
    
The fact your speakers are making noise without any signal suggests a radio interference problem that might be caused by an arcing wire somewhere. This would not explain the transformer noise, though. Is all the sound coming from the speakers? And is aggravated by touching the transformer? That would suggest a problem with the shielding on your audio set up. –  Tim Quinn Dec 11 '12 at 11:28
    
If it is a loud RFI, can the coils in AC/DC adapter pick that up and make it audible? btw, the noise in the adapters in load dependent. For example the mobile charger does this buzz too, but when I attach the mobile to charge it, it does it louder, the same is true for the computer's power supply too. –  Calmarius Dec 11 '12 at 12:54
    
I recorded a video about the problem, added the Youtube link to original post. Did you mean something like that noise? –  Calmarius Dec 19 '12 at 11:05

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