Transformers for LED Downlighters

[Hysteresis]

OOPPS!!!!
Spoke too soon. I connected 5 - 6.5W LED down lighters to one Electronic Transformer rated 20-60 W so 32 W load. All worked fine. Left lights on for an hour and then all went out. It appeared that the transformer tripped out possibly on over temperature. A few minutes after apparent cooling, lights were able to be switched on for a few minutes then tripped out again. I heard the sound of a click coming from the transformer suggesting a trip of some sort.
What is odd here is that the Transformer was OK for years with a 60 watt load with two 30W halogen down lighters with no hint of temperature trips in over 14 years of use.
So I thought I would now split the load into two transformers, one feeding two 6.5 W LED/sand one feeding three 6.5W LED's. The two LED loaded transformer seamed OK but the three LED Transformer tripped after about 80 minutes. This is weird as the load on the two LED transformer is only 13W which is below the bottom limit of the rating of 20-60W, and the three LED loaded transformer is only 21.5 W which is well with in the power rating.
These transformers were no problem with a 60W load so what is the problem with an LED load. Just doesn't make sense to me.
My next step is to re-establish three transformers with Two LED's on two of them and one LED on the third and see what happens.
A load of a few Watts to LED's is surely the same as a load to a halogen light and any wave form problems are not apparent as the LED's operate perfectly satisfactorily for well over an hour.
The transformers did feel warm when they tripped and I can only account for the rise in temperature due to losses in the electronics of the transformer, but these losses would be the same irrespective of the Load.
Any switching transients are not apparent when switching on the LED's so there appears to be no problem there.
If my present arrangement fails I will have to bite the bullet and replace the down lights with 240V G10 LED's, but I hate the unexplained failure characteristic of these damn Electronic transformers. The damn things are being used below their specification, so what the hell is going on here.
These 12v LED's are being sold by the High Street outlets as replacements for 12v halogen lights and the 12 V in a domestic installation has to be derived fron a transformer of some sort and most likely an electronic one, so presumably everyone who tries to replace the Halogen lights will have exactly the same problem as I am having.
So electricians out there get ready for a lot of work coming your way from unsuspecting households. Save time and install 240 V G10 units at a fraction of the cost of solving the problem.
Happy days

 

[Jackrae]

Unlike incandescent lamps (tungsten, halogen etc) LED lamps themselves contain a bunch of electronics to control the current through the LED chips. So the load they impose on the supply is not "smooth" and can cause havoc with whatever is feeding them. Having an "electronic" transformer (aka switched mode power supply) feeding an indeterminate electronic load is basically asking for problems. If you are happy using 12 volt LEDs then I suggest you get hold of conventional wound transformers; your only problem there is finding them as the chinese electronic ones seem to be ruling the market. Alternatively, as has already been suggested, change the LEDs for mains operated ones.

Edit : As a quick and simple guide to unmarked transformers, "electronic" ones are very light, wound ones are relatively heavy.

 

[winston1]

These transformers were no problem with a 60W load so what is the problem with an LED load. Just doesn't make sense to me.

A load of a few Watts to LED's is surely the same as a load to a halogen light and any wave form problems are not apparent as the LED's operate perfectly satisfactorily for well over an hour.
The transformers did feel warm when they tripped and I can only account for the rise in temperature due to losses in the electronics of the transformer, but these losses would be the same irrespective of the Load.
Any switching transients are not apparent when switching on the LED's so there appears to be no problem there.
If my present arrangement fails I will have to bite the bullet and replace the down lights with 240V G10 LED's, but I hate the unexplained failure characteristic of these damn Electronic transformers. The damn things are being used below their specification, so what the hell is going on here.
These 12v LED's are being sold by the High Street outlets as replacements for 12v halogen lights and the 12 V in a domestic installation has to be derived fron a transformer of some sort and most likely an electronic one, so presumably everyone who tries to replace the Halogen lights will have exactly the same problem as I am having.
So electricians out there get ready for a lot of work coming your way from unsuspecting households. Save time and install 240 V G10 units at a fraction of the cost of solving the problem.
Happy days

Halogen lights are essentially resistive loads. LEDs are not. They may even have some sort of SMPS in them to reduce 12v to around 2v that LEDs actually run at. They will certainly have a bridge rectifier in them and are not designed to run at several kHz.
The SMPS sold to drive 12v halogens are not designed to drive LEDs. Either use a proper wound transformer or a dedicated LED driver.
But as has been noted there is no advantage of 12v LEDs over 240v ones.

 

[Hysteresis]

Halogen lights are essentially resistive loads. LEDs are not. They may even have some sort of SMPS in them to reduce 12v to around 2v that LEDs actually run at. They will certainly have a bridge rectifier in them and are not designed to run at several kHz.
The SMPS sold to drive 12v halogens are not designed to drive LEDs. Either use a proper wound transformer or a dedicated LED driver.
But as has been noted there is no advantage of 12v LEDs over 240v ones.

The load can only be Resistive, Capacitive or Inductive, LED's are a semi-conductor Diode and as such are Highly resistive . As you suggest the LED unit will have a Bridge 'Rectum Fryer' built into it as the LED's requires DC to drive them. The Bridge Rectifier will probably have a smoothing Capacitor and maybe a wave clipping circuit to produce a 2V dc smoothed output to drive the LED's. But the electronic Transformer will essentially see a highly resistive/capacitive load with only the resistive component contributing to the power consumption. So I am still at a loss to understand why the Electronic transformer is effectively over heating (I think) when the load is well within it's specification.
Clearly I do not know the circuitry of the Electronic Transformer or the LED unit, but just considering the Power consumption characteristics of the circuit, the understanding of the problem is beyond me.
With respect to there being no advantage to 12V Led's to 240v LED's, After my experience there is a great advantage to the 240 v variety as they do not require a transformer to drive them, the necessary transformation and rectification is achieved by the unit itself. One very big advantage in my view.

 

[bernardgreen]

They may even have some sort of SMPS in them to reduce 12v to around 2v that LEDs actually run at.

The LED driver controls the current flowing through the LED element and not the voltage applied to the LED element.

Either use a proper wound transformer or a dedicated LED driver.

You have no option but to use a LED driver suitable for the LED element(s) used in the lamp. Most LED lamps have the necessary driver fitted as part of the lamp.

But as has been noted there is no advantage of 12v LEDs over 240v ones.

A compact LED driver with a 12 volt input is easier to design and manufacture at low cost than the design and manufacture of the same thing with a 230 volt input.

If the price to market is the same then the 12 volt unit will ( normally ) be more reliable ( and maybe safer ) than the 230 volt unit.

 

[ban-all-sheds]

These 12v LED's are being sold by the High Street outlets as replacements for 12v halogen lights and the 12 V in a domestic installation has to be derived fron a transformer of some sort and most likely an electronic one, so presumably everyone who tries to replace the Halogen lights will have exactly the same problem as I am having.

If everybody returns them for a refund because they are not fit for purpose the sellers will soon get fed up.

 

[Hysteresis]

If everybody returns them for a refund because they are not fit for purpose the sellers will soon get fed up.

I agree totally, I think the public needs to be aware that the 12v MR-11 LED down lighters are not suitable for being powered from an electronic transformer designed specifically for Halogen lamps. They would be OK (I think) if the original fitting was powered from a wound transformer, it depends on what was fitted originally. I suspect most Halogen installation would be installed with an electronic transformer.
As long as the purchaser is aware of the problems, and I doubt it, as such most would expect the the MR-11 Led's to be a direct replacement for the Halogen bulbs, but it 'Aint .
My exercise has certainly been educational, hopefully helpful to readersof DIYnot.com.

 

[JohnW2]

I agree totally, I think the public needs to be aware that the 12v MR-11 LED down lighters are not suitable for being powered from an electronic transformer designed specifically for Halogen lamps. They would be OK (I think) if the original fitting was powered from a wound transformer, it depends on what was fitted originally. I suspect most Halogen installation would be installed with an electronic transformer.
As long as the purchaser is aware of the problems, and I doubt it, as such most would expect the the MR-11 Led's to be a direct replacement for the Halogen bulbs, but it 'Aint .

I essentially agree with all that - in particular that I would imagine that 12V LEDs ought to be fine with 12V derived from a wound transformer. However, what I'm less sure of, since I have very limited experience of trying to undertake the transition, is how inevitable it is that a particular 12V LED will not work with a particular 'electronic transformer' (SMPS). Although I don't know for sure, I suspect that some such LEDs will work with some 'electronic transformers' (depending on exactly what is coming out of the 'transformer'), but that some such combinations won't work (at all, or satisfactorily) - which, if true, would make it very much a 'hit and miss' business for unsuspecting consumers.

... add dimming to the equation and the whole business obviously becomes even more iffy and unpredictable.

Kind Regards, John

 

[Hysteresis]

I essentially agree with all that - in particular that I would imagine that 12V LEDs ought to be fine with 12V derived from a wound transformer. However, what I'm less sure of, since I have very limited experience of trying to undertake the transition, is how inevitable it is that a particular 12V LED will not work with a particular 'electronic transformer' (SMPS). Although I don't know for sure, I suspect that some such LEDs will work with some 'electronic transformers' (depending on exactly what is coming out of the 'transformer'), but that some such combinations won't work (at all, or satisfactorily) - which, if true, would make it very much a 'hit and miss' business for unsuspecting consumers.

... add dimming to the equation and the whole business obviously becomes even more iffy and unpredictable.

Kind Regards, John

That is also my conclusion to all of this. I seem to have mine working apart from one down light which occasionally fails to illuminate. Switching off and then immediately back on has always been successful so far, but as you say the whole thing is rather unpredictable.
I think 'Hit and Miss' is the conclusion and I whole heartedly agree with your comments.