Led lights and transformers

[whistler]

My bathroom has three 50w 12v downlights with individual transformers marked 10 - 60w. I am planning to fit new ip65 rated down lights with led bulbs rated around 4 or 5 watts. I understand that my existing transformers won't drive these low wattage bulbs.

My question is.

Is is acceptable to use just one of my existing transformers to drive the three bulbs wired in parallel, or should I fit three new led rated transformers?

 

[bernardgreen]

You should fit "transformers" that are recommended by the supplier / manufacturer of the LED lamps.

The "transformers" you have are almost certainly switched mode power supplies ( SMPS ) designed to supply a resistive load which is the filament lamps you have now.

The LED lamps will have LED drivers internally and these are not resistive loads but also a form of switched mode power supply.

One SMPS ("transformer") feeding another SMPS ( LED driver ) can result in un-stable operation of one or both of the SMPSs which can then result in un-stable illumination with lamps flickering, fading up and down or pulsing.

 

[ericmark]

In theroy it should work. In practice it depends if the LED bulbs will be damaged by the wave form from the transformer which is not a simple transformer but uses electronics to increase the frequency and clips the wave form to control the RMS voltage.

Consider RMS is an average voltage but not a peak voltage and there could well be peaks of 20 volt with a 12 volt system. Some bulbs will take this others will not and the problem is as the user we don't know which are which.

With a DC power supply the voltage is smoothed and there will be no peaks. The lighting industry seems to call DC power supplies "drivers" but they also call current regulated supplies "drivers" so it is easy to end up with the wrong device.

In the main the easy way out is to convert from extra low voltage to low voltage and do away with any voltage reducer. You would need to change bulb holder from GU5.3 to GU10 and the cable would need to be suitable for low voltage (230 vac) but you are then certain it will work.

 

[winston1]

My bathroom has three 50w 12v downlights with individual transformers marked 10 - 60w. I am planning to fit new ip65 rated down lights with led bulbs rated around 4 or 5 watts. I understand that my existing transformers won't drive these low wattage bulbs.

They are not transformers and they won't drive LEDs.

Best thing is to replace the fittings with GU10 types and use 240volt LEDs.

 

[DaftPunk]

They are transformers.

 

[bernardgreen]

They are transformers.

The industry refers to the switched mode power convertors as "electronic transformers" as this label requires less education of the mass market the devices are aimed at.

If we on this forum use the correct terminology when giving advice then there will be a few people better informed about the different and non compatible type of devices marketed as "transformers".

Otherwise the advice on this forum will descend to the same level as the "advice" given by profit driven sales people who will say anything to get their product sold to the public.

 

[winston1]

They are transformers.

No they are not. The OP clearly said they are marked 10-60w. Transformers don't have minimum loads like this. They are clearly switch mode power supplies.

 

[RF Lighting]

Electronic transformers have a minimum load.

 

[ericmark]

They are transformers.

They likely contain a transformer but so does my TV and I still call it a TV not a transformer.

The switched mode power supply does to main things it reduces the voltage and it isolates the output from the input.

The simple transformer also does the same.

But the switched mode power supply also controls the RMS voltage to far closer tolerances than the transformer and to reduce weight and cost of the transformer it contains also increases the frequency.

The whole idea of switched mode is we change the ratio of on time to off time it's called the mark/space ratio. There is a minimum time it can be on for and that in turn means there is also a minimum output.

In theroy the poster is correct as long as it draws 10W it should work so putting a few LED lamps on the same supply should in theroy work.

However since the output of the transforming device is not a sinusoidal output but a series of pulses and the LED lamp has to reduce the current to each LED using electronic components they is a chance that one device will upset the other.

To remove all the spikes easy was is to turn into DC again in theroy fitting a rectifier and a capacitor would mean DC but get a simple 12 volt RMS transformer and rectify and use smoothing capacitor and likely the output would be 16 volt not 12.

So the turning to DC must be done with in the device and the device will control the DC output.

Most people would call this a power supply be it designed to run a computer or a set of LED lights it is really the same device.

However raw LED's have to have the current controlled not the voltage. A simple resistor can control the current or another switched mode supply with in the package containing the LED's to differentiate between voltage regulation and current regulation we call current regulation devices "Drivers".

However it would seem lighting manufacturers are calling all devices that power LED's drivers be they voltage of current regulated.

So instead of using a simple name we have to read the specification on the device. If it says 10 - 60 watt its a switch mode device. If it says 12 volt output it's a power supply. If it says 20 mW output it's a driver.

The manufacturers say it's to make it easy but to my mind we should call a spade a shovel.

 

[winston1]

Electronic transformers have a minimum load.

No such thing as an electronic transformer. They are switch mode power supplies.

 

[JohnW2]

Sigh

 

[whistler]

I decided to just fit the new light fittings with the supplied 12v 50w bulbs. My original reason for asking this was that the salesman said it was ok to simply replace them with led bulbs. Obviously he was wrong!

Thanks for the replies.

 

[Chris61]

Sigh

+1

 

[ban-all-sheds]

They likely contain a transformer but so does my TV and I still call it a TV not a transformer.

 

[JohnW2]

They likely contain a transformer but so does my TV and I still call it a TV not a transformer.

True, but if it's sole purpose were to convert one voltage to another, and isolate input from output, I presume you then wouldn't call it a TV!

I don't think that this new term "electronic transformer" (with which the dictionaries haven't yet caught up - but they will!) has got anything to do with what components it contains (wirewound transformers or otherwise) - but, rather, it's a question of the functionality of the device (i.e. if just regarded as a 'black box' with input and output terminals).

Kind Regards, John