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Round LED Driver

Discussion in 'Electrics UK' started by Paul-man, 30 Dec 2016.

  1. Paul-man

    Paul-man

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    We have a couple of ceiling fittings in our lounge which each take 10 x 12V G4 lamps. At 15W each, we decided it best to change to LED. Having done this yesterday - now running 10 x 2W LEDs in each fitting, we are experiencing flicker and occasional flash (off for about 0.5 secs).

    I noted in the review of the LEDs that someone had mentioned an LED driver and it seems that this is what is required to get the voltage stable.

    There is a round shaped transformer hidden in the "base" of the light fixture, which looks easy to change- the problem is, all of the LED drivers that I've found are rectangular and too long to fit within the light. (needs to be about 9.5cm diameter)

    I have found this: http://za.auroralighting.com/Lighti...20-60W-VA-Round-Electronic-Transformer-1.aspx which seems to go down to 20W, but it does state in the installation that it is intended for Tungston Halogen luminaires.

    Anyone know if this would be ok, or of a suitable alternative?
     
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  3. bernardgreen

    bernardgreen

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    Are the LED lamps 12 volt supplied with 12 volts from the round transformer ? If they are then in each LED lamps there is a driver to control the currrent through the LED element. These drivers operate with high frequency switching. The round "transformer" is a switch mode power supply that converts 230 volts AC to something like 12 volts that is OK for 12 volt halogen lamps. It has an average effective value of 12 volts but will almost certainly not be a smooth DC voltage having been produced by high frequency switching.

    The various high frequency switching functions interact with each other and create instability in operation pf the various items.

    If the construction of the fitting is suitable to have mains at each of the 10 lamps then convert to all 230 volt LED lamps.

    If that is not possible then if the output of the "transformer" is DC then a small value ( 0.1μF ) capacitor across the output of the "transformer" may solve the problem by smoothing the supply to the 10 LED drivers.
     
  4. Paul-man

    Paul-man

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    Bernard, thanks.

    The transformer currently (excuse the pun) in the fitting is the ktb-105: http://www.kaoyitransformers.com/ I cannot see specifically if the output is AC or DC.

    The bulbs are all 12V supplied with 12V from the transformer, so I am guessing I can't simply remove the transformer and convert them all to mains? I'm not sure if I mentioned that they are G4 bulbs and as far as I am aware you cannot get 230V versions of these.
    (These are they: https://www.amazon.co.uk/gp/product/B017R96NZC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1#Ask )

    Is there any value in changing to a transformer with a smaller output (such as the Aurora one I mentioned previously) or will this not help the instability?
    I suppose the capacitor would be a cheap option? I might give that a go if I can find one. I guess I just wire this in parallel across the output terminals?
     
  5. endecotp

    endecotp

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    The output of your transformer is AC (there is a ~ symbol I think), and your bulbs say they work on AC or DC, so it should work.
    Did the packaging with the LED bulbs also say that they work on AC or DC?
    Is there a dimmer?
    What happens if you remove most of the bulbs so only one or two are connected?
     
  6. endecotp

    endecotp

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    OK, I've looked more carefully at the ktb-105 transformer and it says "35-105W", so your problem is that your load is too low.
    Their ktb-60 says 20-60W so you could try that. Or the Aurora one that you linked to.
     
  7. endecotp

    endecotp

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    You could check by swapping one or two of the LEDs for the old halogens; that should take the load back above 35W.
     
  8. bernardgreen

    bernardgreen

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    The output is high frequency AC and not DC so a capacitor will not work.

    KTB-105A - Ungrouped from Dongguan Kaoyi Electronic Technologic Co., Ltd.
    KTB-105A

    Input voltage : 220 - 240V 50/60Hz
    Output voltage: 11.4V
    Output frequency : 39.8 Khz
    Normal power : 35 - 105W
    Line current (Amp) : 0.45
    Input terminal block(pairs) : 1
    Output terminal block(pairs) : 1
    Max,case temp tc : 80
    Max. a,boemt temp ta : 45
    Dimension (L*W*H) : 86/86/27
     
  9. winston1

    winston1

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    It is NOT even a transformer, nor are any of the other devices you have linked to, they are switch mode power supplies and unsuitable for driving LEDs.

    As you said in your first post you need an LED driver.

    Or you could of course get a real toroidal transformer as they can run on AC or even a DC power supply.
     
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  11. Taylortwocities

    Taylortwocities

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    Still got that bee in your bonnet, I see.
     
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  12. winston1

    winston1

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    ?
     
  13. bernardgreen

    bernardgreen

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    Winston, did you miss this bit of my post ?

     
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  14. Paul-man

    Paul-man

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    Thanks everyone... so a "smaller" (in terms of output) switch mode power supply / "transformer" is not going to help much?
    I note when looking at LED drivers that they seem to be described as either constant current or constant voltage. Does it matter which type I go for? Found a couple of round ones, but they seem to go up to 18W.
    Unfortunately, this is a downstairs room with no access from floor above, so I can't hide a driver in the ceiling- has to be max 90m length. I'll keep looking!

    I checked the packaging of the bulbs and they do indeed say suit AC/DC.
    I popped 1 halogen back in and it eradicated the flashing, but clearly the set-up isn't right for long term use.
     
  15. JohnW2

    JohnW2

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    Yes, it does. If the LED lamps are described as "12V" (which implies internal current control), then you would want a "constant voltage" source.
    Indeed, but it supports/confirms the suggestion that the flashing was due to the LEDs not providing as much as the minimum load required by your present "transformer".

    Kind Regards, John
     
  16. bernardgreen

    bernardgreen

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    The LED element, the bit that generates the light, requires a controlled current through it and controlling that current is the job of the LED driver. That driver may be part of the lamp ( driver and element together in one module ) or it may be external to the lamp.

    As your lamps are rated as 12 volt it means the LED drivers are built into the lamps. Hence those lamps require a supply that is regulated to be 12 volts. You do NOT need an LED driver external to the lamps. You need a 12 volt power supply.

    John got in while I was typing
     
  17. endecotp

    endecotp

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    On the contrary, that is exactly what you need; a transformer that goes down to 20W. See my post #5.
     
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