Energy Matters Forums

[Sandivee]

Hi All,

Recently I had an issue where I was trying to replace a halogen downlight 50W 12V with a 5W 12V LED replacement. MR16 fitment.

I did the replacement but the light would only flick on for a second and then turn off.

After looking at the transformer there seems to be a minimum 20W load for the transformer to transform hence not being able to make the 5W LED work.

Does anyone know of a way to trick the transformer into thinking there is a 20W load but only consuming 5W or less?

Any help is much appreciated.

[emilia_iacovino]

You need to replace transformers with LED drivers

http://lightingpro.com.au/catalog/produ ... cts_id=444

http://www.neco.com.au/lighting/led-driver

Although, you have to pay for these, they loss less energy than the old mechanical down light transformers (which loose up to 10W each) so you will save even more energy.

[Sandivee]

Right, so there is no way to retrofit straight lights.

=(

O well. Thanks a lot for the information I will look at it tonight.

[gully]

You don't need special high-tech LED drivers. Ironically, the older (iron-core) transformers are perfect for LED downlights. The downfall is they may not have over/undervoltage protection or soft-on functions. In this case you have 2 options, run one transformer to many lights (ie. in the same room, eg. 5 in the bathroom, for example). As long as the total combined wattage is over the minimum required on the transformer, it will work fine.

Most have minium of 20 watts to run, as this is the lowest halogen downlight you can buy.

Or, you can make it even more efficient, and just get GU10 240v LED downlights and fittings!
No transformer required.

[Sandivee]

Thanks for your replies. It has helped a lot.

[emilia_iacovino]

Gully is correct. You could connect multiple LED to the one iron core transformer, but miss out on the extra safety features incorporated into new transformers and will still loose 10W per transformer. Also you can't insulate close to the old transformers (or halogen globes) so you end up with a condition called "thermal bridging" where all the heat in the room with down lights will go through the ceiling in the spot where the transformer (and down light) is, reducing the benefit of having insulation and increasing your heating bills.
Personally I would do the complete changeover to either the new electronic transformers or down lights that run on mains power, as Gully as suggested, or get rid or them completely and go back to ceiling mounted lights, which can look as good or better than down lights, and mean there are no holes in your ceiling or insulation where the warm air can escape in winter.

[SR76]

I can tell you what I did (but this might not help)...

I had 5 * 50W halogen lights in my kitchen, 2 on one switch and 3 on another. Each had a nasty old iron core transformer.

I bought 5 * IOGEAR 5W LEDs and 2 Osram Redback transformers off the net, but after I bought them I found that the recommended load for the transformers was 20-60W. I phoned Osram to check what happens under 20W... answer was: not sure - they might not start up?

Anyhoo: I decided to give it a burl, and wired 2 LEDs in parallel to one transformer and 3 to the other. Both worked, but the set of 2 was quite flickery.

Then I got some heavy duty resistors (used ohm's law to work out the equivalent required to mimic a bulb) and put one in parallel with the set of 2 (to mimic a 3rd bulb). Better. Still a tiny bit flickery but not bad.

OK, so there's 5W wasted but considering:

5 * (50 + 15) = 5 * 65 = 325W (old transformers ~ 15W)
2 * (5+5+5+2) = 2 * 17 = 34W (Redbacks ~ 2W, Led OR resistor = 5W)

I'm still well ahead.

I could even probably put 5 on a single transformer (take out one switch) as there are very few times that I run one group without the other.

Of course... if I ever want to sell the house I would probably need to pull everything out and start again with the (*spit*) halogens. Wiring standards, building codes... best not to electrocute future generations.

[Bthree]

A question please SR76,

These 5watt LED's, can you comment on the light output as a comparison

Are you happy with the new colour range and brightness ?

Thinking of going this way myself !

[SR76]

I got the warm ones and I like them. However the brightness is nowhere near the full brightness of the 50W halogens. I would estimate (no scientific basis) they are somewhere between 50-75% as bright. For where I have them, it's exactly right (halogens were TOO bright).

They won't please everyone, though, if you were trying to replace something just right.

Cheers,

-SR

[Sandivee]

I guess it depends on what you want them for - if you actually going to be lighting up specific things then it may be a good idea to go for the cool white colour.

Either way 90% energy saving is too good to pass up in my opinion.

and I did think of connecting 4 or more lights together from the one transformer but for the application it is not viable.

Thanks all for your comments.