Power buzzing after 5pm, help please!

[willcocks]

Right - this has been going on for too long now!

Between 5pm and midnight every day my electricity supply is faulty and items such as my TV and computer buzz from their power supplies. This is loud enough to stop me watching tv

We've had two electricians look at the property and both have deemed the wiring inside the apartment to be okay. We've had an electrician from the power board check their side, which he said was okay.

So what is causing the buzzing noise? Could it be the communal tv booster? Surely that wouldn't cause noise between 5pm and midnight only?

The letting agency have washed their hands of us as the wiring inside the property is "okay". Very frustrating.

Help! this is driving me mad - is it damaging my equipment? Anybody know what could be causing it?

 

[333rocky333]

This is only a possibility.

We once had a lady complain of interference each night.

she done some observation and noted the nearby pub outside lights came on at the same time it started.

We traced it to a worn out lamp in a son fitting high up on the pub.

Where it was trying to strike the igniter was continuously trying, and it was that causing the problem.

we relamped the fitting and all was ok after that.

Best thing then is to see if anything locally occurs at similar time.
Especially discharge lighting or similar

 

[willcocks]

Thanks for the suggestion. I have had a look around before for things that could be causing it but I couldn't find anything unfortunately. I'm quite close to a taxi rank and a train station though.. do you think they could be at cause?

Nothing I can see comes on around 5-6~pm and goes off at midnight. It's very strange.

I have tried various ferrite cores to no avail. My voltage fluctuates between 235v and 240v so I guess that is not stable. Could that be what is causing it?

 

[electronicsuk]

Fluctuating supply voltage doesn't really prove anything substantial, you'd need an oscilloscope to display your incoming waveform to see what's really going on. We had a problem similar to what you describe at my place of work a couple of months back, although the buzzing was constant. It was traced to an old, faulty UPS that was introducing all sorts of harmonics and noise into the supply.

Still, I'm not sure how far the use of a scope would go in helping you to find what's actually introducing the problem in the first place.

 

[Taylortwocities]

Just a long shot. Do you have any dimmers in your lighting circuits?
Sometimes they can cause the contact breakes in a fuseboard to make a noise if the circuit is heavily loaded.

Another long shot:
When you get the noise, turn off the circuits on the fuseboard (consumer unit) one at a time and see if any one circuit is causing the problem.

If it does then you can then narrow down the search.

 

[willcocks]

Nope unfortunately we dont have any dimmers. Have tried turning everything off at fuse board apart from the plugs, even swapped fuses around to no avail.

Am completely at a loss to explain what is causing it.

Although at the moment the noise has stopped, and my power meter is registering a more stable 240-242~. the Hz reading is 50, when the noise occurs its 49.8/49.9. Is that all normal? It's just everyones [the electricians, the electricity board] telling me it's fine - when it clearly isn't!

Not really sure what to do.

I have uploaded the noise it makes incase anyone can recognise what makes this sort of noise. Also have analysed the spectrum, incase anyone can guess what commonly produces this frequency! (long shot I know!!)

http://rapidshare.com/files/146985579/1844.wav.html

 

[Softus]

Could you put an oscilloscope on your supply and have a look at the waveform(s)?

 

[BS3036]

I'd second the oscilloscope suggestion. (With suitably voltage rated probe!) The sound waveform looks (by eye) like short bursts of around 7kHz, 100 times a second. So something is injecting current on the peaks of the rectified voltage.

By the way the mains frequency is rather a universal thing, so can't have anything to do with the problem.

In the old days when we still had an empire; if you complained to the post office about interference, a man would come out with a directional wide band radio receiver and wander around with it to try to locate the source. Basically a medium wave transistor radio, tuned to a blank spot on the band should be roughly equivalent. You could wander around outside to try and localise the noise.

 

[tim west]

Trouble with inductors(coils) such as in the power supplies you mention is they have a habit of filtering out noise in the supply (they vibrate the laminations they are mounted on) as may be caused by switching of heavy loads ie Invertor control of motors (triac switching) Have they recently installed any such like equipment at the train station?
Explain to the Electricity supplier your problem and ask for them to check the condition of your supply between these times using monitoring equipment, if they dont agree then consult a regulatory body, you may also wish to "hire" said equipment to monitor your supply checking your appliances by unplugging whilst monitoring to prove its not your stuff causing the problem and therefore gain evidence to produce to the supplier for them to action, remember that no company must be running equipment that causes excessive detrimental effects to the supply as they can be heavily fined for doing so.

 

[mattylad]

How close to the train station are you?
It would not hurt to have a walk over there & ask if they have had anything new installed at the time this all started?

 

[333rocky333]

. Basically a medium wave transistor radio, tuned to a blank spot on the band should be roughly equivalent. You could wander around outside to try and localise the noise.

Heard this before, worth a try.

 

[mikethesparky]

have a look for any neon signs on a local chip shop or pub, it may not be lit but still being turned on every night

 

[willcocks]

Right,

Today the buzzing started at 4pm and stopped at 4:50pm. This is very strange. It will be back later I am sure.

I've looked for neon signs but there arent any unfortunately.

Unfortunately I can't get hold of an oscilloscope. The train station also isn't electric and they haven't had any new equipment installed - though we have only been here for 3 months. It has been like this the entire time we have been here. The woman was unhelpful also!

I have also tried walking around with AM radio tuned to a blank spot - can't seem to find anything.

The buzzing is only noticeable when you are drawing over 100watts of power. My Xbox360 power brick has died.. so I am assuming it has caused that to go.

I had a listen in the meter cupboard earlier - only us and another flat were buzzing (out of 8 flats). Either we are the only two using power, or there is a fault - since both meters are next to each other.

Communal management refuse to check the TV booster because "nobody else has a problem". I have also been strongly encouraged not to "encourage them to have a problem".

argh

edit: we have had two YEDL electricians out and two others. Pretty sure they are either not looking in the right places or the wiring is actually fine.. so it has to be interference? or not? im not sure.

 

[333rocky333]

Does the block have communal lighting or stairlighting via photocell and timer or a door entry system.

Some door entry systems have a timer to allow tradesmen/milkmen in at certain times, usually early AM but could be set wrong.

Can you find the booster and turn it off a moment just to eliminate it.

You can hire a unit that plugs in and and analizies the supply, it is not cheap though.

The supply has to be within certain tolerances
I think the electric board will fit one temporary if you keep on to them.

 

[willcocks]

Ok it's started buzzing again, at the same time as usual. Strange for it to start and stop earlier on a Saturday though.

Yeah we have communal lighting - think its light activated. theres also an automatic gate/door entry system. The fuse box for it is in the same cupboard. The door control box (outside near the actual door) also buzzes (loudly) when it's unlocked at any time of the day - isn't this normal though as it's a magnetic lock?

This is how the meters are set up

1 2 3 4 8 5 6 7

It is strange how 8 is out of place. 5 + 8 are the only two that buzz. So surely it can't be interference? 8 does have something written above it about distance.

I have kept on to YEDL but they are not interested as the noise comes from the fuse box near the meter and they say that it's not their problem.

edit: not mentioned to them how it comes from the big grey box also, but have only just discovered that! they have also sent two electricians (only one of which looked at teh wiring - i dont think he even opened the grey box though. Is that their responsibility?

Who's responsibility is the fuse box with the on off switch on next to the meter? It's not the fuse box for the property as we have another inside.

edit: I can find the booster however would like to avoid touching anything - and I cannot see how only 5 + 8 would buzz if it was the booster.

edit2: theres also some buzzing from the big grey thing with "415 Volts" written on it. All the cables come from there.