Two similar LV circuits; one dimmer buzzes, the other doesn't (much)

[Michael Brewer]

I see that issue of buzzing dimmers has come up many times before on this ng, but I couldn't see anything which would explain this.

I have two separate lighting circuits as follows:

1) MK Logic Plus LV dimmer 60-400W ; 8 x 50W Aurora LV halogens, each with their own individual Aurora transformer (60W rated I think)

2) MK Logic Plus LV dimmer 40-240W ; 11 x 20W Aurora LV halogens, divided into groups as: 3-3-3-2; with each group having an Aurora transformer (60W rated)

Now, the thing is that the dimmer for circuit (1) doesn't buzz much (a little, but only if you hold your ear close enough to the switch that it is scalded), while the dimmer for circuit (2) buzzes quite loudly, as do each of the four transformers in the circuit. The buzzing is about the same loudness right down to being almost off, when it vanishes.

Can anyone shed any light on why this should be the case? As far as I can see, the components used are much the same brand/type, loaded to pretty much the same level.

Many thanks!

Mike

[Christian McArdle]

You've got these dimmers loaded up to the eyeballs. Many types need derating for halogen, so they're probably both well overloaded. There is a maximum of

4 transformers for the dimmer. So you are running this switch with precisely the maximum load and precisely the maximum number of transformers. It's probably a miracle that the other dimmer doesn't buzz. I'd buy a 400W dimmer for the buzzy bank, really, and see if that improves things. (Actually, I'd rip the whole lot out, as I'd rather have 20W compact fluorescent lighting in a room, rather than 240/400W of Bangladesh submerging carbon dioxide emmisions).

Christian.

P.S. the non-buzzy 400W is overloaded, as there is a stated 5 transformer limit.

[Michael Brewer]

Hang on a second. How can they be "probably both well overloaded" and at "precisely the maximum load" at the same time? The MK Logic Plus Dimmers (the LV "intelligent" variety) are specifically rated at

40-240W / 60-400W for LV. So, by having 11x20W, I'm 20W under; and by having 8x50W, I'm bang on 400W. When something is rated between X and Y surely that means you can go up to Y without problems; otherwise they would rate it at X to Y-Z (and then, do you go up to Y-Z, or is it really only safe to go up to Y-Z-W?). How much power do the transformers consume? Would that tip it over? I also appreciate that a 50W rated bulb may consume slightly more (or less) than that, but I would be surprised if this wasn't within the tolerance of the switch. If it really is the case that my 240W switch is overloaded, and that is the cause of buzzing, would the buzzing quieten when turned down to half max? In my case, this doesn't happen, it buzzes with the same loudness.

The main query I had was why one buzzes and the other doesn't; both are loaded roughly to the same level relative to their max rating. If anything, the 400W switch is more loaded and is also over the max number of transformers. This is why I am curious. If they both buzzed, I probably wouldn't have questioned it; if they both didn't buzz, I probably wouldn't have noticed it. I would like to understand why one does, and the other doesn't.

Thanks! Mike

PS Thanks, too, for the environmental lesson. I'm saving Bangladesh by not having a very big house and hence not many rooms to light. Personally, I don't like fluorescent light.

[Christian McArdle]

Whoops. For some brain fart reason I calculated 11x20 to be 240W!

That's basically down to the internal design and layout of the dimmer. You've proved that the 400W one doesn't buzz so much, so I'd be tempted to swap the buzzy one for that.

TBH, I've never seen a dimmer switch that doesn't buzz like crazy, so you've been pretty lucky with the 400W one.

Christian.

[Michael Brewer]

Perhaps you're right. BTW, the four transformers powering the 11x20W LVs buzz just as much as the switch. It's like being in a flipping bee hive (well, without the stinging).

Mike

[Andy Hall]

Are you not using electronic transformers?

.andy

To email, substitute .nospam with .gl

[The Natural Philosopher]

Alternatively, get some 30 minute epoxy, opemn up the dimmer, and smear the toroidal choke with the epoxy. Stops 90 of the buzzing.

[The Natural Philosopher]

Smear the choke in that with epoxy too. Cheap crap.

[The Natural Philosopher]

Obviously he is. Toroidal mains transformers don't buzz. Irts those tacky ferrite ones that do.

[Martin Angove]

Not doubting the latter, but I had a torroidal which buzzed when dimmed (not when on full whack). It was 180VA running 5*35W bulbs, very short output leads, running from a 250W LV dimmer (the sort that ramps up over a second or so when switched on). When dimmed to any degree it and the dimmer both buzzed, but you could only hear it if everything else was quiet. Below about 1/4 brightness it was easily audible even under normal background noise levels.

Just occurred to me that this was an "unbalanced" lighting circuit - the live went directly to the switch, and the neutral to the light - with this light the only thing on the circuit. I wonder if the substantially different L and N path lengths might have made some kind of difference as other dimmers I've used didn't buzz so obviously...

Hwyl!

M.

[Michael Brewer]

I've heard of this fix before. To me, it begs the question: if it helps so much, why doesn't the blimming manufacturer use his own epoxy to avoid us having to do it? I can't imagine it would increase the cost by more than a few pennies and it would result in a quiet dimmer. Or am I missing some logic? It's not as if the MK Logic Plus dimmers are overly cheap anyway.

Mike