LED downlighter puzzle

Discussion in 'Electrics UK' started by sparkypenguin, 3 Nov 2021.

  1. sparkypenguin

    sparkypenguin

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    Hi all,

    Over the past few years I have had regular issues with my 12 kitchen downlighters due to replacing the standard 12v lamps with 12v LED's and leaving the old transformers in place.
    As I understand it, the issue is that the transformers require a minimum wattage to be drawn to work correctly.
    Therefore I finally decided yesterday to simply remove all of the transformers and replace with 1 transformer.
    However this has not worked as only some of the lamps do not come on and when I fit some lamps others dim.
    I have attached a sketch showing the set up and would appreciate any help as I cannot understand why this will not work.
    Could it be anything to do with LED sometimes requiring an initially higher current?

    Any help much appreciated.
     

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  3. winston1

    winston1

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    There is also the issue that those power supplies (they are NOT transformers by the way) operate at tens of kHz not 50Hz. 12v LEDs are typically designed for DC or 50/60Hz AC. Either get a real wire wound transformer or a proper LED driver.
     
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  4. bernardgreen

    bernardgreen

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    If a lamp is rated as 12 Volt or 240 Volts then it requires a suitable power supply and not an LED driver. The driver that controls the current through the LED element(s) will be integral to the lamp.

    Winston you have been told many times that almost all lamps using LED elements have an integral driver.
     
    Last edited: 3 Nov 2021
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  5. securespark

    securespark

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    For my money, I would do away with all drivers/ supplies and run 230V direct to each fitting and use 230V LED GU10 lamps.
     
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  7. sparkypenguin

    sparkypenguin

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    Thanks everyone for their answers (y)

    From the above 2 replies I think the 2nd is correct and I do have a "transformer" that is probably a "power supply" and it is designed for LED's so I am confident that it is the correct piece of kit.
    However since my original post I have discovered that the maximum length of the output cable is stated as 2m and hence I am exceeding that significantly.
    Does anyone know why this would make a difference?
    Could it be due to increased impedance?


    I was actually thinking of doing this so I have ordered some GU10 leads to replace the GU5.3 leads in the current lights.
    All of the cabling is already 1.5mmT&E so the change over should be fairly simple (hopefully!).
    Are there any downsides to using the higher voltage lamps as I have always used the low voltage ones in the past?

    Thanks again (y)(y).
    Mark.
     
  8. bernardgreen

    bernardgreen

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    Many power supply units use high frequency ON-OFF-ON-OFF switching to control the voltage on the output. With long leads there are two main problems.

    The high frequency switching creates radio frequency ripply on the output, this radiates from the cabling and can interfere with radios and other wireless items.

    The external capacity between the cores of the lead can affect the stability of the circuits controlling the voltage.

    A power supply produces power with a controlled voltage. This power is then fed to a driver which controls the current that is driven through the LED element(s) of the lamp.

    An LED driver provides a controlled current which feeds the LED element(s).

    Many items are mis-labelled

    upload_2021-11-4_8-25-14.png

    It is described as an LED Driver It is NOT a driver but it is a power supply. If it were an LED driver it's output would be a rated CURRENT but as can be seen this item has an output that is rated as a constant VOLTAGE.

    If you connected this directly to an LED element then the LED element would be destroyed.
    This item is intended to supply power at 12 volts to a driver inside a lamp.
     
    Last edited: 4 Nov 2021
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  9. winston1

    winston1

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    You don't .
    1. From your diagram in post 1 you show a supply with an output of 35 to 105w. Real transformers don't have this minimum restriction, it is typical of halogen power supplies.
    2. Real transformers don't have a 2 metre restriction on their output cables. Halogen supplies operating at switch mode technology in tens of kHz generate radio interference. The shorter the cable the less of this interference is radiated.
     
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  10. sparkypenguin

    sparkypenguin

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    Thanks to everyone for your help. (y)(y)
    I can't say I totally understand how this all works but now appreciate that it is not just a simple case of matching voltage and wattage as the frequency plays a large part.
    So I will try the GU10's instead!
    Is it just a simple case of swapping the GU5.3 leads with GU10's?
    Does the actually holder have to be earthed?
     
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