LED Transformer

Well I learn something new everyday.... Although not cbus exactly - you guys are just so experts you might be able to help out...

I bought some recessed LED path lights to put down the side of the house, to brighten up the dull side entrance. They are 12V AC Max 1.2W each.

So I thought I'd try them out with one of my spare transformers I have that I have previously used with halogen lights - well they are 12V AC 60W... tried a couple of different brands.

Each one gave the strange reaction - plugged them together, the LED would flash on and then go straight off...

Then upon closer inspection of the viper and other transformers I had, noticed that although they are typically rated to a maximum of 60W or whatever, they are also rated for a minimum level too ! Typically 20W each.

Corr - I had always worried about the upper limit of being so importance, I never realised they had a lower limit !!! Doh! dum dum me!

So I tested it - put a 50W halogen on the load, with 3 of these LED lights - perfect ! Works well, the LED lights sine nice and bright - dont get hot - its exactly what I wanted...

Now I need to find a 12V AC transformer to use... I will have 4 circuits of these controlled via a cbus relay each. The largest circuit is likely to have 8 of these led lights, the smallest is likely to have 5. As each LED unit is 1.2W - it means I am probably looking for a transformer with a minimum load of (5*1.2) or 6W.

No I dont want to hide a halogen somewhere to increase the load - I was trying to be a bit greenish here in going with the LED's - well that was before I learned about the transformers... always make life difficult!

So do I just go off to jaycar and buy a plugpack ? I was really wanting to wire it in hardwired, like the possum / Viper transformers...

I have looked over the net for iron core / electronic / magnetic - but quite often the spec detail on these things is not available or incomplete...

Anyone have a clue on a transformer with a low low minimum output level - that is rather small that could be enclosed into a wall cavity?

TIA

 

Hello,
I am not to sure what kind of LED lights you have, but in my
experience most LED'S use a driver not a transfromer.And some times
they need to be wired in series not parallel.

Hope that helps.

Choppa.

 

Choppa,
It looks like the driver circuitry/current limiting resistor has already been taken care of, like most store-bought stuff is. There is no such thing as a 12 volt LED, so there would have to be some kind of circuitry built into the fittings already.

Impact,
You have a few cheap and easy options.
The cheapest, but most energy wasteful route is to just buy a normal iron-core downlight transformer, and use that, it will meet your needs no problem at all.

In the middle we have buying a smaller 12v AC iron-core transformer from somewhere like Jaycar. Estimated price would be about $8 per 6w of lights (or per circuit) that you wanted to run, however I'd recommend putting them in a ventilated enclosure, so that might be another $15 or so.

Another option would be to have your sparky put a GPO for each circuit in the roof, or inside a junction box as close to the outside lights as possible, buy some switchmode plugpacks from Jaycar or Dick Smith, (Just make sure they are rated at 12v AC, with a minimum of 1000mA or 1A rated output), and plug those into the GPO's and then connect to the lights.
Being switchmode, these would probably be the most energy effecient (green) method, as they will use the least power in the long run. They would also mean you could do the wiring without needing a sparky, because you can just unplug them and plug them in as you need.

Final option would be to get some proper DIN-rail mounted switchmode power supplies, put them inside an IP56 or higher rated enclosure, and put them as close to the lights themselves as possible, running 240v TP+E from your CBUS gear to that point.
However that would be the most expensive option by a LOOOONG way... (Estimated costs $90 per circuit for DIN-Rail PS's, $60 for enclosure and DIN-Rail, plus mains cabling, conduit, and sparky's labour)
Like I said, thats the best option, but certainly not cheap.

HTH,
Darpa

 

johnC whre are you????

 

What's in a Transformer?

Hi All
I don't quite agree with Darpa. My understanding is the problem is the power supplies, as Impact mentions the viper / possum (redback & all) do not work because of the minimum loading. These electronic transformers are "switchmode" style, if they are not in fact switchmode transformers.

The LED's Impact mentions do not sound like the fancier new generation type, but more like plain old ones that are quite robust and will probabally run best on a small wirewound transformer, these do not have minimum load requirements, the voltage just rises without much load. You don't want too big a transformer because the load is only small (100mA/led).

Any transformer has losses, wirewound (magnetic) type tend to have more than electronic, for example an old "TM-50 type" wirewound transformer for a halogen downlight has a loss of about 10w, the electronic (mouse / possum) types have 3-6w loss.

For such small loads I suggest using a small wirewound transformer for each circuit, (so off to dicksmith / jaycar as you had already determined). Switch these with your c-bus relay so they are only on when required (dont switch the LED cicruits on the LV output of a transformer). In any case you will be saving many more watts as opposed to installing 10-20w lamps for your path.
Regards Matthew

 

Sorry, I should have been more specific, the switchmode supplies I was talking about are not the regular downlight ones (20-105w), I was talking about either plugpack ones, or very low-rated ones that are DIN-rail mountable, and only rated for 500mA-1.5A.
And I agree that cheap iron-core transformers from DS or Jaycar will do the job just fine, same as an iron-core "downlight" tranny, except with the DS or Jaycar ones, you'll need an enclosure for them.

Darpa

 

Lighting transformers are a prescribed item, and it is not legal to use a transformer from Jaycar or Dick Smiths in a lighting application.

Just buy a Atco TM50 or rip one out of another project. There are literally millions of them out there. Or buy a downlight kit and throw away the downlight.

 

I bought a TM50 - and it works beautifully.... Im just a spoiled newbie who is used to electronic transformers - that TM50 is a big bulky heavy item !!! Oh well at least if the economy really goes badly, maybe iron will increase in price and Ive got something to sell at a profit!

Thanks JohnC - I knew that about the jaycar transformers - the tm50 works like a charm