LV downlighters. Wire-wound or electronic transformers?

[Nick]

Currently have 9 mains voltage GU10 50W tungsten downlighters arrayed in a bank of 3 x 3. Each bank separately switched, for good reason. Mains voltage tungsten is a PITA, changing lamps every five minutes, tripping mcb on lamp failure etc.

The plan is to convert these to LV GU10, 12 volt. Three 50w lamps @ 240v = C 1.6A. Three 50w lamps @ 12v = C 12.5A Distance from transformers to lamps 2.0m maximum. There is plenty of space to recable with 1.5mm or even 2.5mm t+e. Dimming not required.

Would I be better off with wire-wound or electronic transformers? I would have thought wire-wound but would appreciate some advice. Also, any recommendation for decent/long-lived transformers ? Thank you,

Nick.

[Tabby]

Electronic are cheap. Wirewound are very reliable.

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[mick]

Electronic transformers have a couple of advantages. They are much lighter - easier when you are working from a pair of steps! They often incorporate soft-start to increase the life of your lamps. Many of them are dimmable using ordinary dimmers, without needing to derate.

OTOH they are always something else to go wrong.

Wound transformers are heavy, sometimes Very *Heavy* indeed! You need either special dimmers or much derated ones. They can have a hefty switch-on surge, which doesn't help switch contacts. They are probably as reliable as you can get.

You pays your money and takes your choice. I personally would recommend dimmable electronic ones and make sure that you leave access to them. It gives the option of adding dimmers later and the cost difference isn't much. Try to mount them so that the secondary wiring is as short as possible, no matter what you decide on.

IIRC when I did my kitchen I put 3 dimmable units in. 2 were fed from the same dimmer and had 4 lamps each. The third (lower rating) had it's own dimmer and just fed 2 lights over a breakfast bar.

[Adam Aglionby]

Wirewound need held on their loading, torrodials especially have terrible regulation, lose a lamp and voltage to rset rises. Only tend to use them for open suspended cable sytems where electronics would either not work or use the cables as aerials.

Mode and IBL make excellent electronic transformers.

Cheers Adam

[Roger Mills]

In my lounge, I've got 3 arrays of 4 x 50w lamps, each driven off a 200w electronic transformer from Screwfix. I've only had one transformer fail in about 9 years (only to find that it wasn't as accessible as I thought it was - and I had to remove some floorboards above it to get at it!)

In my kitchen - which was done more recently (about 2 years ago) I've got 8 x 50w lamps, each with its own individual built-in transformer. These are readily accessible by pulling the whole lot through the hole in the ceiling - and don't give a single point of failure. In other words, if a transformer fails (which it hasn't, yet) you lose only one lamp.

I would definitely adopt this (second) approach in future - and it makes sense when replacing mains lamps because you don't have to modify the wiring.

[John Rumm]

Agreed, it makes sense when retrofitting. Also has an advantage if you have a ceiling void with insulation in it - since it keeps the power dissipated by the transformer down, and hence the temperature as well.

I usually find that electronic transformers (at least upto 250W power handling) can usually be pushed through the hole of a standard downlighter making replacement fairly simple even if you have one transformer feeding several lamps.

[Roger Mills]

Yes, but I then went and screwed the bloody thing to a joist (to support it while the ceiling was nailed up) and then found that I couldn't reach in far enough through the hole to unscrew it when it failed 9 years later!

In the event, the replacement transformer was different from the original in that it had 4 sets of output terminals - with a current limit on each - whereas the original had a single 200w output to which 4 lamps were connected via a junction box. So I did away with the junction box and connected the individual lamps direct to the transformer. This would have been difficult or impossible to do through a hole in the ceiling.

I'm a convert to individual transformers - for new work as well as retro-fits!