Noise using a dimmer

[Lyngarth]

Hi
Just had a text message from a friend asking for some help, so thought you guys might be able to help.

He has 5 x 12v downlighters in his sitting room, all working fine but he wanted a dimmer switch, so he fitted a 2 gang 400w switch, now he tells me the max on the switch is 315w on one side but when he turns it on he gets a buzzing noise , not from the switch but from the cu, with a normal switch all is fine and no noise.

The dimmer work fine and the lights dim its just the noise he is worried about.

So is there something worng withthe switch or does he need to get a different switch??

Many thanks,

Lyngarth

 

[Darkwood]

look up member sparkycpu hes done a post before about this which explains the issue as hes only done a few posts you should find it quickly

 

[Lyngarth]

Hi
did a search but could not find a member withthat name?? or I'm not doing the search right !!

Many thanks

Lyngarth

 

[Darkwood]

type in the search box 'Loud buzzing noise' then go down the list and clickon mcb loud buzzing noise when it opens hes on page 2 one of the last posts, let us know if you find it and if it helps

 

[Lyngarth]

Many thanks for that, not sure what I was doing, but have now got the info.

I will let him know and will let you know how he gets on.

Many thanks for the help,

Lyngarth

 

[amberleaf]

• This is common in modern but cheaply built dimmer switches. Since the Rheostat has been decommissioned in favor of a TRIAC circuit (variable transistor), the input voltage isn't wasted. Rather the TRAIC circuit turns the AC current flowing to the bulb on and off about 120 times per second. This "chopping" up of the voltage can result in a buzzing sound. A higher end dimmer switch will have both an inductor choke (a length of iron core wrapped in wire) and an interference capacitor. These two components store electricity to help smooth out the sharp voltage jumps caused by the TRIAC circuit.

 

[Christech]

Hi.
One thing i did notice from OP is that the dimmer is rated @ 400 Watts .When dimming LV transformed lumminaires the dimmer should have a VA rating and then be de-rated by 15-20% for transformer loses.Also check transformers against the dimmer to see if they are "Leading Edge or Trailing Edge" as they must be the same type.

 

[pushrod]

It seems that a lot of these problems are down to people not realising that the current is out of phase with the voltage because of the transformers and just doing true power / voltage calculations instead of apparent power/voltage. As a result they don't realise that mcbs, switches are stressed because the power factor means that the apparent power is greater than they realise.