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Discuss 12v MR16 LED bulb question in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    A (plumber) mate of mine, has changed a standard 12v downlight to a LED downlight - he tells me that the first bulb he tried flickers a few times before coming on and the 2nd bulb is worse. The original standard bulb is back in so the transformer is OK.

    The lamp is fitted into one of those light/extractor fan devices.

    Any ideas what's going on?

    Its been a long day and I'm tired!
     
  2. Megavolt
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    Megavolt Electrician's Arms

    Location:
    Zoo
    The LED MR16 will work on most standard low voltage transformers. however some transformers are 20-60 VA and can cause problems with this lamp. If this is the case it is best to replace the transformer With a LED comparable one
     
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  3. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Just thought I'd bounce this back into "play" to see if I can get more opinions rather than start a new thread.
     
  4. La Poste
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    La Poste Electrician's Arms

    Location:
    South east
    Check the transformer to see if it has a minimum required load to function properly.

    Do you know what brand the LED bulb is, maybe for best results it should be run with an LED driver, they cost about £10.

    I'm new to this LED game.
     
  5. drew35
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    drew35 Guest

    But there's constant current or constant voltage to choose from, get the wrong one and they don't work properly???

    240v is king!
     
  6. La Poste
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    La Poste Electrician's Arms

    Location:
    South east
    Drew have you some examples of constant current or constant voltage drivers?

    Could you elaborate a bit more on what you are saying, what do you mean by constant current and constant voltage drivers and what is the difference?

    Thanks.
     
  7. Richard Burns
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    Richard Burns Respected Member

    Location:
    Cambridgeshire
    Business Name:
    Richard Burns
    Just some of my ideas about the situation:

    A standard cheap electronic lighting transformer will only start to work correctly once the minimum loading is reached, before that level is reached the transformer might only flicker or not operate at all.
    This is something to do with the two sides of the transformer needing to reach (a term which escapes me at the moment I am thinking hysteresis but this is not right, think synchronous amplitudes) and then it will start working.

    LEDs as a component require a minimum voltage to operate and also require a constant current because without any control they will continue to conduct higher and higher current until they burn out.
    There are various electronic controls in an LED lamp (variable depending on manufacturer).
    A 240V LED will generally have a current limiting resistor and a rectifier, usually with smoothing capacitors at minimum so it is internally controlled. (the smoothing capacitors are why they can flicker under induced voltage because the capacitor charges and then, once charged enough, discharges to the LED and it briefly lights)
    A 12V LED will usually rely on the transformer controls to operate correctly as 12V dc is much closer to the supply they actually need.
    Using standard lighting transformers supplying 12V the current is not closely controlled and the LEDs can be overloaded and eventually fail. Normally if the load is sufficient for the transformer to operate then they will work but the lamp lifetime is shortened considerably.
    LED drivers are, as Drew says of two types, one providing a closely controlled output voltage, where the current will be controlled by the lamp, and one providing a closely controlled current so that the LEDs are operated at the optimum current and have a long life time.
    It is particularly important where the LEDs are in a series string that the current is evenly distributed so that one LED does not burn out causing a cascade failure.

    Overall using the appropriate transformer for the lamp type allows them to operate correctly and to maximum life (and costs loads to keep changing transformer, which then fail and cause more cost.)

    Oh but 240V, no problems!
     
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  8. La Poste
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    La Poste Electrician's Arms

    Location:
    South east
    Well I'm working on the assumption that the more components you have in an LED bulb the more chance it has of going wrong.

    If you can get 12V bulbs without the rectifiers and voltage regulators inside that run off a constant supply the better, they will be simpler in design. The driver will be a separate unit that can run let's say four bulbs for each driver.

    The driver will house the SMPS, rectifiers etc and if it goes wrong all you will have to replace is this unit. This should actually work out cheaper if you are fitting a few bulbs and should overall be a more reliable system.

    I saw some LED's online that were designed to run in a car off a 12V battery and they had virtually no components inside them at all and hence less to go wrong.

    I agree that 230 Volts Halogens are more reliable than 12 Volt with an added transformer but when it comes to LED's I think the opposite is true.

    Please feel free to shoot my logic down.
     
  9. Richard Burns
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    Richard Burns Respected Member

    Location:
    Cambridgeshire
    Business Name:
    Richard Burns
    I think I would prefer to be able to replace one lamp that fails rather than have all my lighting go at once and have to rewire a new transformer costing twice the price and probably less accessible.

    I agree that as a component an LED is reliable (if powered correctly) and it is the additional components that usually fail, however there will always be components in an LED lamp and any may fail (particularly current limiting resistors that take a lot of current), I would prefer one point of failure as opposed to two.
     
  10. trydan
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    trydan Guest

    Hi
    Small current leakage can make the LED flicker. Mostly on the cheaper versions.
     
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