Disclaimer: if you decide to copy any of the things I did here, you do so entirely at your own risk. If you are not completely confident you know what you are doing consult a qualified electrician.

Not only do we now have to contend with noisy low voltage down-lighting, there is now also a proliferation of low voltage pendant lights that have a similar noise issue with the switch-mode supply built into the ceiling rose. We have three lights in our house that were obtained from Next retail which exhibit this problem. The largest of the three is shown below (after modification):


I decided I would have a go at replacing the built in switch-mode supply with a transformer. The light shown above uses ten 10W/12V bulbs and the others use five 10W/12V bulbs, so I would need 50VA and 100VA rated toroidal transformers. I used a MCTA100/12 transformer that is rated at 100VA for 49deg C temperature rise and a VTX-146-050-112 transformer that is rated at 50VA for 42deg C temperature rise. Both are manufactured by Multicomp, and at the time of writing are available from Farnell as order codes 1675057 & 9530479 respectively. Their dimensions are such that they will just fit inside the ceiling rose once the switch-mode unit has been removed. Both units have two 12V outputs that must be paralleled to achieve the full VA rating. I have since also discovered the MCTA060/12 transformer from Multicomp (Farnell code 953-0428) which is rated at 60VA for 48deg C temperature rise, and also fits inside the rose. This would run cooler, but I haven't experienced any issues in this respect.

First, the switch-mode unit must be removed, and then the transformer is installed in its place, as shown below:

The mounting disc requires enlargement of the hole to use the central thread and nut to secure the transformer in place. The central thread must not create a shorted turn, so the protection earth wire must connect below the transformer and come round the side.

For added safety, you can add a bi-metallic thermal protection switch, such as Microtherm part No. T11V10005U200L, available from Rapid as order code 26-5165. Wired in series with the mains connection, this will disconnect the transformer from the mains supply if a fault condition occurs and the transformer overheats. In the photo above, the switch has been located in the void underneath the transformer, which helps secure the wiring, as well as being the hottest place.