12V LED downlighter transformer question

[Vortex3]

In my home I have about 20, 20 Watt Halogen downlighters all with MR16/GU5.3 lamps. I want to reduce my energy consumption so these have to be replaced with something more efficient

Over the past year I have purchased a few sample LED alternatives, but until historically these have proved to have completely inadequate light output. In fact absolutely pathetic in many cases.

Last month I finally identified a candidate LED lamp replacement, that is genuinely bright enough for the job but only about 3W power consumption.. In fact pretty impressive. (ebay 130328613774 for more info), not cheap but I purchased 4.

I have now encountered the problem that the PSU's in my lighting circuits won't "start" with a pure LED load. They need to have at least one incandescent lamp (minimum 20 Watts) to work properly.

Q. Does anybody have experience or opinions on the best 12V transformers for LED circuits? If so what do I need to look out for?

I see from TLC I can purchase a simple linear transformer like

which I am sure would work ...and allow use of a dimmer.

But I also see

which claims

0-50 Watts. Is there any reason this would NOT work? It's a good price.

Any/all wisdom appreciated.

D

[Dave Plowman (News)]

If you look at the spec for an electronic LV lighting transformer it usually gives a minimum load. An 'ordinary' trasforner won't have this limitation. A better solution would be to use dedicated LED drivers. These produce a series of high frequency pulses that allow an LED to produce more light and increase the efficiency. But I dunno if this will work with LEDs designed as LV lighting replacements as they must already have some form of electronics built in. A basic LED requires a constant current DC supply which an LV lighting transformer doesn't supply.

[Dave Liquorice]

=A354.15 to save 68W. Say 10p per kWhr, =A354.15 buys you 541,500Whrs at=

68W that's 7963hrs, 331 days with the lamps *never* switched off.

Assuming that these are only on during the evening for say 6hrs then you are looking at over 3 1/2 years to break even assuming they are on *every* evening for 6hrs.

This doesn't factor in the cost of replacing halogen bulbs over the expected life of the LED replacement, which will reduce the payback time. However the ebay description is a bit inconsistent on the expected life of the LED bulb, 35khrs or 50khrs?

To me it's borderline economic sense. The cost and number of halogens required over the life of the LED would be the determining factor not the power saving.

I see in the description on ebay:

"Note: LED bulbs should not be used with dimmer switches."

[dennis]

The 12v LED lamps in Lidl last week stated that they were unsuitable for electronic transformers. The last time I tried one with an electronic transformer it just flashed at about 10 Hz.

[NT]

Use a toroidal transformer. Or you might have a square 12v ac transformer sitting in your junkbox.

NT

[Vortex4]

£54.15 to save 68W. Say 10p per kWhr, £54.15 buys you 541,500Whrs at 68W that's 7963hrs, 331 days with the lamps *never* switched off.

Assuming that these are only on during the evening for say 6hrs then you are looking at over 3 1/2 years to break even assuming they are on *every* evening for 6hrs.

This doesn't factor in the cost of replacing halogen bulbs over the expected life of the LED replacement, which will reduce the payback time. However the ebay description is a bit inconsistent on the expected life of the LED bulb, 35khrs or 50khrs?

To me it's borderline economic sense. The cost and number of halogens required over the life of the LED would be the determining factor not the power saving.

I see in the description on ebay:

"Note: LED bulbs should not be used with dimmer switches."

[John Rumm]

Typical LV electronic transformers have a minimum load that needs to be connected before they work correctly. If you look at the OPs second link you will note that is *not* a typical electronic transformer, and claims to work from zero load up to its maximum.

[Vortex4]

I just ordered one to try it out!

Seems to be a pretty popular make and model but nowhere on t'interweb is LED suitability mentioned....so I will adopt the empirical approach.

[Rob G]

Interesting. Anyone any idea how these bulbs are configured ?

One option (are there others?) - 12v supply and one diode voltage of say 2 v suggests 8 banks of 6 diodes in series, with 26ma therefore passing through each bank. The design of these diodes must have come a long way to produce that amount of light from 26ma / diode.

What happens when one diode fails - does the whole bank go out, or will they be like xmas tree lights and have some bypass system when a bulb fails ? I notice that LED traffic lights fail in blocks.

Rob

[Rob G]

I went off to look at bulb outputs, and found this website

measurements are for 50w bulbs so it would seem that the 240 lumens claimed is pretty good and hence meets Vortex's subjective measurement.

One of the interesting things is that halogen MR16 have been measured at the centre of the beam which is much narrower than the 120 degrees from the LED ones. If indeed these LED bulbs are subjectively good with this much wider beam then it does look as if things are going in the right direction.

Rob

[Andrew Gabriel]

Note that lumens is the total light output from a lamp summed in all directions. (In theory, it's measured by using what's called an "Integrating Sphere", which sums the light output in all directions to calculate the total lumen output.) So the lumen output is unaffected by things like beam angle. Intensity of a beam is candella (which is effectively lumens per solid angle, i.e. within a cone) and intensity of a lit surface is lux (which is effectively lumens per area).

Many of the LED lights around have quite high intensity beams, but an extremely small solid angle, so the total lumen output is tiny. That's why they look bright when you stare back up the beam, but don't manage to light up anything much bigger than an ant crawling directly under them on the floor, never mind a whole room.

[Vortex3]

These LED lamps use SMD components without lenses so are not very directional compared to traditional LED's, but there is less light loss because of the lack of lenses and also less heating. Lower junction temperature means more light. Positive things.

They are "warm white" which is achieved by using a yellowish filter, this does cost some brightness....and cause additional heating. I've not tried the "daylight white" ones yet. I suspect they take a little getting used to.

From ceiling height a tratitional halogen GU10 delivers an intense pool of light about 2' diameter at counter level. Tweaking 3 of them to illuminate - say - a breakfast bar is a bit of a compromise. IMHO these LED lights are much less directional.

D

[Dave Plowman (News)]

Last warm white ones I tried (Luxon) were a bilious shade of green. On balance I preferred the 'blue' white ones. Warm white to me has more red.

[stan]

Who could have anticipated that 'lighting', could get so complicated! What with LV starting circuits, LED and transformers, halogen down lighters etc. etc.! Interesting though. Here, for the moment sticking with plain old 115/120 volt incandescents, costing about 25 cents Canadian (about 14 new pence) each, in packages of four. Nice simple technology. The wasted lamp heat, now that temps have dropped below 12 degrees C (about 50 deg F) at night just aiding the electric heating, along with wasted heat from the TV etc. until we go to bed. Oddly the only bulb that failed in any spectacular manner was a 230 volt low wattage that I brought back (new) from the middle east, and placed above the work bench to monitor the 230 volt feed (115 plus

115) for some 230 volt tool/items there. It 'went off' with quite flash and tripped a 30 amp breaker! In workshop/garage we have quite a supply of used four foot, two and four tube fluorescent fixtures. Some are not cosmetically perfect but clean up well and work fine even in low temperatures. Also have a back up supply of used ballasts and tubes so can also keep neighbours fixtures supplied. Main fluorescent string fixtures in downstairs workshop have 'electronic ballasts' and are from a school refurbishing. They were just chucking em out; so went in and asked if could take a few. Their only question was "Can you take all of them; save us a trip to the dump/tip?". Seek and you shall find; I guess.

[Appin]

The message

from stan contains these words:

That'll be at the usual ration of one 60w bulb per room? :-)

(Traditioinal Canadian practice with a four-lamp ceiling fixture with only one bulb inserted with the result that Stygian gloom pervades the room)