If you have read my other blogs about GU10 mains voltage halogen lighting, you will know that I have mostly replaced these bulbs with LED equivalents. they cost more, but last longer, are cooler and use a fraction of the energy. a halogen bulb is typically either 35 or 50 watts. most LED bulbs are 3 watts.
While the bulbs in my house are predominantly GU10 mains halogens, I do have a couple of MR16 bulbs. These are a different type of halogen that operate from a 12volt supply. I should mention at this point that I don't have any dimmer switches in my house. Now some mains voltage GU10 LED bulbs are dimable (always check first).
MR16 bulbs have two pin connectors rather than the lugs found on GU10 bulbs. GU10's use a push and twist method of connecting to the socket. the MR16 simply push in place with metal clips also gripping the edge of the bin base.
They use a separate power supply , either a transformer (old type ) or a switch mode power supply(newer) to convert 250v AC mains to 12vDC. A transformer is a hefty box while most now use a switch Mode Supply, which can be made very cheaply. They are small light box, perhaps the size of two boxes of matches.
In the picture you can see one next to the vent hose in black. these transformers are often tucked away in the ceiling cavity. In my case the extract fan units were accessible , as the extract units vented up through the attic and out through dedicated tile vents via plastic hoses, the type used by tumble dryers
Because of the lower voltages, the MR16 bulbs are the type used in my shower fittings. You can see a common type of extract fan, with a central MR16 light.
Now I had tried LED MR16 equivalent bulbs in these fittings , but they either flashed briefly then went off or flashed repeatedly like a strobe light. Neither was ideal for showering.
The reason these LED 3 watts replacements didn't work is due to the power supply. the original power supply units fitted would only work with a minimum load of 20-30 watts. However the LED bulbs are only 3 watts. I have also read of people with a single power supply running a number of lights. When replacing with LED bulbs they found they had to keep at least one halogen in the circuit to keep the load high, or they would experience the strobing effect.
In my case these MR16 bulbs are fed from dedicated power supply units. the solution was to replace the power supplies with units designed for LED lighting. these can handle loads down to 1 watt. You need to ensure that the LED supply you choose can handle the correct load. In my case it's 3 watts from a single light. if you have a power supply driving multiple bulbs , which is normal too, you need to ensure the power supply has a maximum load sufficient for the total of the wattage of the bulbs i.e if you run 6 LED bulbs at 3 watts each , the power supply needs to have a maximum greater than 18 watts
in this picture you can see an LED driver or power supply, especially for LED MR16 replacement bulbs. Above it are two varieties of LED MR16 replacements, a Phillips Brand cost circa £20 at B&Q with 3 super-strong individual LED's and a Surface mount unit from SimplyLED for £11, who also supplied the driver for £8. Both provide good bright light. the SimplyLED is described as "warm white", meaning it has a slight yellow tint, they also do a "brilliant white" bulb which has a slightly bluish tint. This might be preferred by some, to my eyes fluorescent lights have a similar colour tint.
replacing the exiting transformers is relatively easy however
THIS PROCEDURE INVOLVES MAINS ELECTRICITY.DO NOT UNDERTAKE THIS IF YOU ARE UNSURE . IF IN ANY DOUBT CONSULT A QUALIFIED ELECTRICIAN. ALWAYS TURN OFF THE MAINS BEFORE ATTEMPTING THIS WORK. NEVER RELY ON THE WALL SWITCH TO ISOLATE THE CIRCUIT WHILE DOING ANY WORK. ONCE THE MAINS IS TURNED OFF REMOVE THE EXISTING HALOGEN BULB FIRST.
Once you have unscrewed the cover you can see that there are 4 screw terminal connections,
one set of two for the 240v mains input , labelled L for LIVE (Brown) and N for Neutral (Blue)
the other for the 12vDC output. the output is polarised, so the transformer indicates positive (+ve) and negative (-ve) outputs, though neither of the bulbs had any polarity markings and both appeared to work connected either way.
I simply disconnected or cut the wires from the old transformer inputs and outputs, stripped and prepared the wires correctly, and connected to the new transformers. I double checked that no copper wire was visible, and that the screw terminals were not binding on the insulation. I then gently pulled each wire to see that the connections were sound. I then put the covers back on.
I also tried a different type of transformer on another light. This kind I purchased from ScrewFix for £12. exactly the same procedure except that the inputs and outputs were at opposite ends.
once I was sure of all the wiring, I put the new LED bulbs into their sockets before turning the mains back on. Had I left the original high wattage halogens in the light fittings, I might have damaged the new power supplies with the heavy loads. It was then a simple case checking the bulbs illuminated correctly from switch on, which they did
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