Most of the power supplies for the 50W quartz halogen are pulse width modulated or switch mode two names for same thing. As a result they have both a minimum and maximum so swapping to LED will likely mean your drawing below the minimum rating. Also LED stands for light emitting diode and if you combine diodes and inductance together at a high frequency it can turn into a transmitter. If the transformers are the old heavy type toroidal transformers then likely you can simply swap, but with the lighter smaller "Electronic transformers" which are not really transformers then chances are you will have problems. You could remove some of the electronic transformers and power 4 lamps instead of one lamp of each and it may work. But also it can still cause problems.
The whole idea of the 12 volt quartz halogen was you have a thicker element in the bulb and a very precise voltage so the quartz envelope is held at a precise temperature. With LED there is really no advantage in using extra low voltage the low voltage (230v) work a lot better. So in the main it is better to swap the MR16 G5.5 lamp for a MR16 GU10 lamp and move to 230 volt.
If the LED bulb cost 50p then the idea of try it would be valid, but at £4 each you clearly want it to work. So in real terms either swap to 12 volt DC power supplies often called drivers although not really a driver as a true driver is fixed current not fixed voltage and you want fixed voltage. Or move to GU10 type and swap to 230 volt and do away with all the transformers. The latter is the better idea and cheapest but more work to convert wiring to 230 volt.
Also consider the difference in angles of the LED to Quartz halogen. The MR16 stands for multifaceted reflector at 16/8 of an inch, not a clue why not called 2 inch. These reflectors create the spot of light often aimed at a white surface which then gives a shadow free lighting to the room. Often angled to bounce light off the walls. Unfortunately some people have not realised this and fit them shining off a dark floor and whole room looks like a planetarium. With the LED there is often no reflector so really are not MR16 lamps, the LED does however naturally have a beam of light, but often not with the hard cut off point of the old halogen seeing a 25~35 is common where most of the light is in 25 degrees but some also spreads out to 35 degrees. Using one of these to replace a 60 degrees halogen will give a much narrower beam of light, reflected from a white wall still OK but against a dark floor really not what you want.
I saw one guy who has used GU10 to E14 adaptors and fitted candle bulbs in the holders to get the spread of light. If you are changing to GU10 then think are recessed lamps the best option anyway? Since LED does not get very hot you can get lamps which are surface mount and they may do a better job.
Google "surface mount LED lamps" then click on images and look at the options most will cover the existing hole many are a complete lamps the LED is not renewable when in 10 years time it falls then fit a new lamp, Although rated at 30,000 hours I expect most will exceed that time, I would not be surprised if double that time.
You may also want to look at 2D lamps, these are fluorescent lamps often 12 inch round or square which are nearly as efficient as LED and also surface mount.
Hi ericmark - many thanks for a prompt and detailed explanation
The transformers to each of the 11 halogens are "20-60va electronic transformer for LV- halogen lamps". I got this off the transformer itself. Reading between the lines would I be right in thinking that I could simply cut off each of the old transformers and wire in a new GU10 light bulb without any transformer? I have 11 halogens and each has its own transformer so I would buy 11 GU10 bulbs and wire them in after cutting off the old transformer.
If I'm right in thinking I can do that should I get 4 watt GU10s as a direct replacement with a "warm light" bearing in mind the kitchen floor is a cream colour?
The GU10 lamp holder does not have an earth but the whole fitting may need an earth when you swap from extra low voltage to low voltage. Although you can buy the GU10 lamp holder on its own I am wary there could be a safety problem due to no earths. Having not seen your lamps I can't really say if there is or is not a problem in your case.
But yes I would get rid of the transformers and wire direct using GU10 fittings.
As to size of bulb this is a hard question. I can only say what I found in my own house and let you decide if the same could be true for you.
So main living room when we bought house new had two lamp holders with two 100W bulbs. My wife wanted a triple lamp fitting instead of the two bulbs and we seemed to alternate between 6 x 60W and 6 x 40W standard bulbs depending on if I changed them or my wife. As the compact fluorescent lamp arrived largest bulb we could get seemed to be 11W so we used 6 x 11W CFL in the room. Then to get nicer looking bulbs the fittings were changed to 5 bulb fittings and we got 10 expensive globe CFL 8W each from Philips bulbs facing up and we were disappointed it was around 3200 lumen for the room and they started up rather red and slowly got whiter as they warmed up. They should have lasted 10 years but they did not last 2 years we had done the dining room as well so my wife found 6 bulbs again 8W and globe but cheaper and we used the bulbs out of dinning room as spares for the living room. Then reached the point where no more spares and Lidi were doing some candle LED bulbs at 1.4W each which I stuck in as a temporary fix. We were impressed these 1.4W bulbs looked brighter than the 8W they replaced, next time Lidi did bulbs I got 8 at 3W each and replaced the whole lot with LED. The room looked far brighter despite the fact we had dropped from 3200 lumen to around 2400 lumen and we were very pleased with the result.
However some weeks latter the lamps no longer seemed as bright, I think they are it is just we have got use to them. However we found we needed standard lamps to read with, also LED 3W MR16 spots with a E14 fitting.
What I realised on reflection was being so white 3000k made us think they were brighter but in real terms we now only have 2400 lumen of light so we need the extra to read with. The use of lumen is misleading as it does not take into account the whiteness of the light. Neither does it allow for the fact the new bulbs all shine up to the ceiling and the light is defused where the old bulbs also emitted some direct light.
So a 50W halogen is around 800 lumen but colour temperature around 2700k and an LED gives out around 60 to 100 lumen per watt so doing the maths you will need 8 ~ 10 watt LED's to get same lumen output, but in real terms likely you will find 5W are ample if the spread of light is the same. With 11 lamps you have a massive 8800 lumen remember my living room has 2400 lumen. My kitchen has an extension on it. The original old kitchen has a 5 foot fluorescent tube giving out some 5800 lumen using a 68W tube it is very bright, the extension part the fluorescent tube has been replaced for an LED tube at 24w and 2400 lumen not as bright as the fluorescent but plenty bright enough.
Looking at my GU10 bulbs the 2W are 120 lumen each quite poor at 60 lumen per watt and the 5W is 350 lumen at 70 lumen per watt the latter is a 25~35 angle the 2W is a 30 angle I have used them with my camera and what ever the speck says at 3 foot away there is no difference for the exposure rating. It is likely due to the wider angle. I bought cheap bulbs from B&M bargains although the 5W is an Osram bulb. The 5W has a single chip with a defuser built in the 3W have three chips so the spread is very different.
As said my kitchen extension 2400 lumen and twice the size of my sons kitchen he has 5 x 7W LED's so about the same lumen output, but I needed a touch to read his boilers meters. The light simply does not reflect off his light wood floor.
I personally think the MR16 GU10 is a great lamp to read with when in bed, I have one either side of the bed. But in the main useless for general lighting. Having said that as an experiment I twisted the bed side lamps to light the ceiling and it worked well. If I was doing the kitchen again yes GU10's aimed at counter tops but main lights would be 12 inch 2D lamps at 28W each giving a bright general light. In fact mother has a single 2D 28W lamp for whole of kitchen. She has counter lights and hob light but never used.
A 28W 2D is rated at 2150 lumen so really ample for a kitchen if you have counter lights to remove shadows cast by your body.
thanks again for the comprehensive reply ericmark - I am going to wire into the mains the GU10 5w bulbs I have just bought rather than use a driver with the existing MR16s - will let you know how I get on
That is how I would do it. Don't like extra low voltage except where you have to like in some bathroom lighting. Out of interest the GU10 is a MR16 lamp. The 12 volt lamp is a G5.3 which refers to the connection pins, you can even get E14 MR16 lamps. The MR16 refers to it having a multifaceted reflector and being 16/8" dia.
The bulb holder fittings I have have an L shape coming off and I have some earth wire, so bearing in mind the comments you made in your post about earthing the fitting I propose to take and earth wire attached to the L shaped metal bulb holder and attach it to the earth wire coming in with the live and neutral wires from the ceiling
To earth or not to earth that is a real hard question. In the main the double square which denotes double insulated means you should not earth, however the wiring regulations still require an earth to be brought to the lamp even if not connected.
I had a real problem when PAT testing, the unit was called a rota broach which was a magnet base holding what was really a standard drill adapted to use a special cutter to drill large holes in steel. The magnet was class I that means it has an earth, the drill was class II that means you are not to connect an earth. But the two units were bolted together so it was impossible to earth one without earthing the other one. So pair had to be earthed.
However with some equipment earthing can introduce more danger than not earthing. With extra low voltage we have three classes SELV must not be earthed, PELV must be earthed, and FELV can either be earthed or not earthed. However with low voltage Class I is earthed and Class II is not and there is no third class.
To my mind one does not change bulbs with the lights on so really in your case it does not matter. Just use common sense.
Hi once again ericmark - I hope you don't mind me keeping you busy!
I have had a look at the fittings - there is no double square on the fitting so I have bitten the bullet and taken an earth from the metal fitting( which now houses the new LED bulb) and connected it to the earth terminal on the block in the ceiling which houses the live an neutral, I've switched the lights on an all Ok, no shocks from the fittings!
Incidentally, when changing over the halogens for the LEDs I noticed the old fitting wasn't earthed, not sure if this makes a difference to what I've done now i.e. in earthing them, but I'm going with my initial thought that earthing to the light fitting would make them safer???
Any further thoughts would be welcome and thanks once again
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