Low voltage lighting and dimmers

[bill1]

Hello everyone,

I am looking at putting some undercabinet lighting in the kitchen (like these here).

Is it ok to use the above with a normal dimmer switch. I read in another post that 240V halogens are easier to dim than low voltage (12v). Can both voltages be used with a normal dimmer?

 

[Softus]

I am looking at putting some undercabinet lighting in the kitchen (like these here).

Very nice!

Is it ok to use the above with a normal dimmer switch. I read in another post that 240V halogens are easier to dim than low voltage (12v). Can both voltages be used with a normal dimmer?

If you use low voltage lighting with a dimmer then you need to get a dimmable transformer. For normal lighting with a dimmer just make sure that the switch you get can support the total power of the bulbs that you're going to use.

And get a good quality dimmer - you gets what you pays for.

 

[ban-all-sheds]

Can both voltages be used with a normal dimmer?

Not necessarily.

Firstly, the lamp voltage is irrelevant, because with ELV lighting the dimmer goes on the LV (i.e. mains) side of the power supply, not the ELV (i.e. 12V) side.

Secondly, the "transformer" (in quotes because they aren't actually transformers) needs to be suitable for dimming and the dimmer switch needs to be suitable for use on ELV power supplies and you need to match the characteristics of the dimmer to what the power supply needs - some dimmers are what is called "trailing edge" and some are "leading edge", and different power supplies will be happy with one sort of dimming or the other. http://www.google.co.uk/search?sour...n&q=+"leading+edge"++"trailing+edge"++dimmer*

LV halogens on the other hand are easier to dim, as they don't have an electronic power supply and therefore don't care about which bit of the AC waveform is chopped out. What the dimmer cares about is the load that it sees, and a characteristic of halogen lamps is a very low resistance when cold compared to traditional incandescent lamps. This means that when you first switch them on they draw a very large current surge, which can b*gger a dimmer if you've put the full load on, e.g. 200W of lighting on a 200W dimmer as the surge is equivalent to a lot more than 200W. Increasingly manufacturers are making their products with LV halogens in mind, or are specifying their ratings for the two different types. If you have a dimmer and they do not say what it is rated at for halogen lamps, then you should derate it by 30-50%, i.e. a "200W" dimmer should only be used to control 100 - 140W of LV halogens.

 

[delmel]

Bill although they seem nice, beware they take a capsule lamp and are well enclosed. These produce lots of heat and with that type of fitting they can overheat if left on for lng periods. This will not be a danger but hope you like changing lamps. I would suggest flor for undercupboards.