Fitting a dimmer switch to a floor lamp - No Earth

[colin.j.brown]

Hi,

we have a floor lamp that makes the room far too bright when on, and leaves the room too dark when off. So, we asked our unreliable handyman to fit a dimmer switch, which he did, a normal click on/off dimmer in a plastic housing, by cutting the main cord, and putting it inbetween the plug and lamp.

He left the job muttering something about "it buzzes because there is no earth". The thing did buzz, and the lamp flickered as well, and eventually after a week or so, there was a reasonbly loud bang, and the lamp stopped working.

How do I do this properly without the above problems?

Many thanks Colin

[mark_yh]

I've fitted in cheap Ikea in-line dimmers to table lamps with no earth connections, and no problems. Can't see the problem..

[fred]

In article , [e-mail] writes

The buzzing has nothing to do with the earth, it's a symptom of a shit dimmer with a loosely wound inductive filter. As to the failure, is the floor lamp a halogen uplighter perhaps? If so, your dimmer may require to be derated quite a bit for the linear halogen bulb, perhaps a 400W dimmer for a 250W bulb.

[meow2222]

He's talking bs.

fitting a lower power bulb might make more sense. Dimming kills energy efficiency, and filament bulbs are already bad.

NT

[chris French]

In message , [e-mail] writes

alower wattage bulb?

[The Natural Philosopher]

Earth is irrelevant.

Apart frim safety.

He fitted a crap dimmer thats all.

SOME onterference may be larger without an eath, but the buzzing is just a very crap dimmer.

[John White]

Does this lamp have a low voltage halogen bulb in it?

The buzzing noise, flickering and final bang symptoms suggest that the lamp has (or had) a built in transformer or power supply unit that is unsuitable for dimming.

If you have such a fitting then you would need to replace the power supply unit with one that can be dimmed.

John

[colin.j.brown]

Yes it is a halogen floor stander, with 10 flexible arms each with a halogen bulb at the end of it.

So from what you are saying I will actually have to change the internal workings/power supply of the lamp, in order to get it to work and its nothing to do with earth or a crap dimmer switch?

[Dave Plowman (News)]

You need a dimmer stated to be suitable for 'low voltage lighting' use.

[The Natural Philosopher]

Is it a low voltage array?

[John White]

That's right. A lot of these fittings have a power supply that objects to the chopped or pulsed waveform that comes out of most dimmers.

In extreme cases the electronics in a switched mode power supply can get very confused - and go bang.

There are replacement power supply units (often called transformers) which are specifically designed to work with dimmers. You also need to be certain that you get an appropriate unit for the total wattage of the bulbs. Most units have a minimum wattage specified as well as a maximum, so the old idea of getting a big one just in case does not always apply.

Also, as other posters have said, the dimmers themselves normally have to be rated at a higher wattage when used with halogen lights rather than incandescent bulbs. This is because halogen lamps take a higher current when first switched on. Typically 250 Watts of halogen lights will need a 400W dimmer.

John

[colin.j.brown]

Thanks for all the responses by the way -- very good of you.

So from this, we are saying that it won't have been the dimmer switch that went bang, but the actual transformer in the lamp, meaning the lamp is now knackered?

So whats my plan of action? There are ten bulbs, each labelled 12V10W, so what transformer should I replace it with in order to

(a) allow the lights to work (b) ensure we dont get any more load bangs (c) be able to fit a dimmer switch

?

Cheers Colin

[colin.j.brown]

Also below the actual bulbs on each arm, is a sticky label stating "G4 MAX 10W". Does this mean I can get other "G4" bulbs, that are less than 10W that would be dimmer than the current 10W ones?

[blaildyors]

Yes, A quick google (g4 bulbs) gave:

Halogen should be quite a lot dimmer. Will be pricey if you need ten though!

[e-mail] wrote:

[John White]

No problem

Well it could be either or both, it's a bit hard to be certain without actually seeing them.

You need a replacement transformer:

- with an output of 12 V (either AC or DC)

- with a maximum load of at least 100 W (e.g. 120 W)

- with a minimum load of less than 100 W (e.g. 50 W)

- that is labeled as suitable for use with dimmers.

Such as:

also need a dimmer switch that is labeled as suitable for use with low voltage lights, and which has a rating of at least 100 W.

You may find it difficult to get an in-line dimmer that is suitable.

John

[John White]

Like this?

may exist but I don't know of any G4 bulbs less than 10W..

John

[Rumble]

Sorry to be picky, but halogen bulbs *are* incandescent. "Ordinary" light bulbs (i.e. with a filament in inert gas, but not halogen, etc) are usually referred to GLS or General Lighting Service lamps.

This is because halogen lamps take a higher

It is true that halogen lamps take a higher current when switched on, but the use of a dimmer masks this inrush for low-wattage lamps. The very act of placing a dimmer between the supply and the lamp creates a soft-start effect which has the advantage of prolonging the life of the lamp. The primary reason for de-rating the dimmer is to allow for inrush/inefficiency in the transformer(s) not the lamps, per se.

HTH

[The Natural Philosopher]

And you need a LV transformer that is 'suitable for being dimmed'

Toroids can work..but electronic ones that are able to handel the waveforms work too.

[Dave Plowman (News)]

Any transformer can be 'dimmed'. Some SMPS not - or at least by a usable amount.

Since the OP didn't complain about the dimmer not actually dimming the lamp I assumed it has a PS that can be dimmed. ;-)

[Andy Dingley]

That's a rather risky statement. The extra harmonics from the average phase choppng dimmer are going to increase losses in an average transformer core, leading to excess heating. It's "dimmable" but you need to allow for potentially a large derating in output, hot running and a loud buzzing noise.