House Electrics - Question on mysterious Buzz

blazesoftware

Hi,

Not sure what the subject should be but here it the problem. I've moved into a house thats been rebuilt and everything is perfect. I've noticed though that the micorwave and to some degree the TV have a buzzing sound louder then normal which happens ONLY when I turn on the lights. The Microwave is completely silent but when I turn on the kitchen lights for example it starts to imit a buzzing sound. Its not overly load but is noticable. When the lights go off sometimes it stops and if not, does stop shortly afterwards.

I'm told that the electrical lines are completely independent so there shouldnt be any interference between plug sockets and lights but I'm not convinced. Its just strgange that the sounds only happens when lights are switched on. All the lights are on dimmers if that matters. As I turn the dimmers up the sound does seem to change.

Is there any cheap equipment I can buy to test the current in the plug sockets to see if it fluctuates or anyone have any ideas?

Thanks

Hoagy

It's very unlikely that the microwave is buzzing.
Are the lights low voltage downlighters on dimmers?
If so, it's probably the transformers in the ceiling producing the sound, particularly on the TV, since there is probably a bit of RF (radio freguency) noise being produced as well.
I suppose it might be possible for the microwave to vibrate a bit in sympathy.
The cure for this would be to change the downlighters to mains voltage GU10 type.
If you don't have downlighters, you should get it looked at.

johnnyrotten

Dimmer swiches are b!tches for it too!

blazesoftware

Hi,

Its definately not the downlighters. I can hear a hm from the dimmer switches but I expect that with Dimmers.


I am 1000% sure it is direct from the Microwave. Its actually coming from the internal part where the light is as it is louder when the door is open but u can hear it with the door closed.

All the lights are downlighters and are all in dimmer swiches. I know each downlighter has it own transformer.

Its like there is interference but I keep getting told its not. Its not just me. I've asked alot of people and they can all hear it and if it not happening and I turn on one set of the kitchwen lights it starts.

Thanks

Hoagy

Might seem a silly suggestion, but could you try it with the microwave unplugged?
Could it be vibration through the worktop, maybe from underpress fluorescents?

Sonnenblumen

Reminds me of the story of the built in oven with intermittent sounds emanating from clock area, they discovered after huge checking and re-checking that atiny mouse was trapped inside.

Check your microwave for bees!

blazesoftware

Ok forget the buzzing, humming sounds. Can anyone suggest a cheap piece of equipments that I can use to test the current in the sockets etc to see if there are any surges or would that have to be only carried out by an electrican.

byte

http://www.epanorama.net/documents/lights/lightdimmer.html

There's a techy thread on dimmers. From what I can gather, the humming is probably coming from the filament in the microwave bulb itself, though I thught dimmers should only affect the bulbs they're wired to. Buzzing can be caused by poor filtering.

blazesoftware

Byte,

Excellent thanks. Thats exactly what the problem is.


"Buzzing bulbs are usually a sign of a "cheap" dimmer. Dimmers are supposed to have filters in them. The filter's job is to "round off" the sharp corners in the chopped waveform, thereby reducing EMI, and the abrupt current jumps that can cause buzzing. In cheap dimmers, they've economized on the manufacturing costs by cost-reducing the filtering, making it less effective. "


I gues the builder is using cheap dimmer and is causing conflict with the Mircowave bulb although the Microwave wasnt cheap.

Thanks again. Now I can go back to the Electrician.

Auslander

The Dimmer switch is Chopping the 230V Mains supply, This is causing harmonics on the fundimental frequency, i.e 50Hz.

This RFI is being picked up by the microwave, power supply, and yes you can hear a humming, thats because at certain frequency ranges, i.e. 300Hz - 3.4kHz Humans can 'hear'.

The humming is a harmonic of the fundimental frequency which lies in the audiable frequency range.

Normally a dimmer will have a scrubber circuit to cut out audiable RFI.

Changing for better quality dimmers

OR

insuring that the load on the dimmers matches the rating of the dimmers is also linked to humming.

i.e.

Rating of dimmer 500W ( written on a label on the back)

= 10 x 50Watt lamps


also insure that a Low Voltage( LV) dimmer is being used

Auslander

Buzzing bulbs is caused by worn terminal connections on the Low Voltage (LV) bulbs.

The noise is generated by slight 'welding' between the holder contacts, and the bulb contacts.

You can see this for yourself, by taking down a bulb that is humming (only LV bulbs) And look at the pins, you will see slight charring on the pins.

The solution to type of humming is to replace the bulb pin holder.

blazesoftware

Auslander

Thanks for that. I can live with the buzzing but I just want to make sure its not dangerous. Its not the dimmer lights that buzz its the inside of the mocrowave. Coming from where the internal light is. Its a new microwave and the whole house has been redone and we put dimmers in all over it with Low voltage downlighters.

Thanks again