LV Halogen downlights

[Bill Gardener]

Sorry if these questions have been asked before, me and Google groups just do not get on! Some of us don't find this computer stuff easy you know.

The other half wants halogen downlights in the kitchen, why woman just can't be satisfied with what they've already got I will never know.

I am thinking of seven 20w 12v bulbs giving 140w of light in the Kitchen. First question: Is this enough light for a medium sized kitchen?

Screwfix have the following transformer rated at 150w, so can I connect all

7 lights to this?

what kind of cable is required to connect all lights and transformer together, I already have some 1.0mm T&E. Is this suitable?

Thanks,

Bill

[Angela]

groups just

That doesn't sound enough to me. My kitchen is 5.5m x 3.5m and I have 6 x 50w LV halogen downlighters and this is just right, though I do sometimes have to supplement it with under cabinet lighting as I do find that the halogen does mean you can end up casting a shadow over where you are working. The kitchen is one place you don't want poor lighting.

Angela

[Roger Mills]

According the instructions which come with Screwfix transformers (I have several!) if you connect a lot of low power bulbs (i.e. more than 5) to one transformer, you need to downrate the transformer by 20% - which would mean only using 120w with a 150w transformer - so that 7 x 20 isn't on.

I don't know what size your kitchen is but I would suggest maybe 6 x 35w lamps. You could technically run these off 2 x 105w transformers - but 2 x

150w would give a bit more margin.

1 mm cable should be ok for the mains side. I would use something a bit bigger (at least 1.5mm) between the transformer and lamps - and keep the runs as short as possible - because you cannot afford any appreciable voltage drop at the LV high current end!

Roger

[Bill Gardener]

Thanks Roger, a lot clearer now, I assume I connect each light in parallel ?

Bill

transformer

[Lawrence]

Are these electronic transformers or wound transormers.

If they are wound (are they heavy) you need to keep the load close to rated otherwise the voltage rises and a 1/4 volt rise on a 12v halogen will reduce its life.

On the other hand the electronic ones can generate a lot of RF interference (they have an oscillator at circa 40Khz). Keep the wires as short as possible. You will probably find it impossoble to use an older (analgue, NON DECT) type cordless phone anywhere near them.

I think the level of lighting required is very personel. I have a kitchen about 4m *2.5m (minus a larder and shower!) and use 5 20w lamps in there, I like the warmer colour of the lower power lamps.

If I had cupboards >

Lawrence

usenet at lklyne dt co dt uk

[Steve Firth]

I have 10 x 20W in a large kitchen. If you pay attention to where you install them it will give more than adequate light. We have them arranged in a rectanle inset from the walls by the depth of a wall cupboard + 50%. Four along the long side of the rectangle, three along the short. I trid it with 10 x 50W and the light was extremely good, but

10x20W is more than adequate.

[Roger Mills]

Yes. When D did mine, I made up a sort of harness - with the output from the transformer going to a junction box, and with 3 or 4 cables (one per lamp) connected into this - with the lives connected together in one screw terminal, and all the neutrals in another. [LV lights don't have earth connections].

Pre-wiring it was particularly useful for an upstairs installation - so that I only had to make one electrical connection in the confined roof-space.

Roger

[Harris]

I was once told that halogen bulbs after a while draw more power? if thats the right thing to say? anyway it basically means that a while a

20w bulb will start to use more power, e.g. 23w which means your transformer would not be able to cope.

I've always installed 1 transformer per light, purely because my mate is an electrician and not only does he get them cheap but thats what he did in his own house....

[The Natural Philosopher]

Thats 300W in 20 square meters, or 15W/square meter.

I have 9 50s on 3/4 of 6x5m and thats not nearly enough, although I can cope as the work areas are well lit. 20W/ square meter.

I'd say the average kitchen would need about 7 50W units.

It pays to look at bulb cost as well as unit and transformer cost. In teh end bulb cost will dominate the overall cost, and I THINK the 50W stuff is the cheapest on bulbs, so I'd go for 7 of those on as wide an angle (or eyeball lamps) as you can....If you can space them on teh ceiling evenly, you can get away with less than if you have clusters angled all over the place. But I would still reckon on 20-25W per square meter.

Yes, I totally agree. I have poor lighting in mine, but only in the dining and door area. The work tops and cookers have enough.

[The Natural Philosopher]

It pays to use teh transformers at or near to rated output, because thats where they are specced.

I have a mixture of electronic and toroidal, some single, somne multiply connected. All work well. There is very little difference in cost between e.g 3 50W transformers and one 150W transformer.

In the end what you pick is a matter of convenience. If there is plenty of room in the ceiling and existing switched mains lighting wiring, its easier to tap into that and use a transformer per, stuffed in the celing.

If starting from scratch, sometomes a big central trasnformer can go in a cupboard or stud wall, and star wires to the lamps can be run. Easier to get at if it blows.