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MR 16 questions ( I have looked )

Discussion in 'Electrics UK' started by aveatry, 14 Apr 2020.

  1. aveatry

    aveatry

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    I am converting my garden 12v lighting to use 12V MR16 leds.
    Am I right in thinking all the MR16 12v bulbs are actually DC but some can run off AC because they have extra electronics in them.
    I am looking at these in screwfix https://www.screwfix.com/p/lap-gu5-...ck/728fh#product_additional_details_container problem is they do not state if they are DC only or AC/DC others are asking the question that is not being properly answered there.
    My transformer is an older 12V 150W AC. I have 12 7w (rubbish] T15 wedge bulbs at the moment.
    20200412_181110.jpg_thumb.png
     
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  3. winston1

    winston1

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    All the MR16 12v LED type lamps l have seen can run on DC or 50/60 Hz AC. Your transformer will outputs 12v at 50Hz so will be OK.
     
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  4. ericmark

    ericmark

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    G5.3 MR16 lamps can be AC/DC, AC or DC. Many are marked 50 Hz which means AC, we assume they will work with DC, but there will be double the current through a rectifying diode which likely they can stand, but in real terms we don't know, there is also a problem with high frequency AC, if the power supply has minimum output low enough it likely will work but with kHz output it could end up being a radio transmitter, again unlikely a problem unless long extra low voltage supply leads which can act as an aerial.

    Some bulbs are clearly DC this firm specialises in 12 and 24 volt DC lights, well in fact most are 10 - 30 volt so very good for boats and caravans, as to what ripple they will stand I don't know, they are designed for connection to a battery and the question is will a switch mode / pulse width modulated power supply interfere with a second switch mode / pulse width modulated power supply built into the bulb?

    As to screwfix site link is blocked, but this is a picture I copied earlier temp.jpg you can clearly see 12V 50Hz so that is a AC bulb. I will guess your transformer is a wire wound heavy device in which case there will be no problem with screwfix G5.3 MR16 bulbs, I agree the screwfix site is rather poor missing out vital information, but most UK over the counter outlets are the same, they only read what is on the packet.
     
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  5. aveatry

    aveatry

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    Thank you.
    The transformer is a heavy wire wound one. Do you think teher will be a problem with the LEDs being too low at 2.6 W - there will be 15 of them = 39W total.
    I did not know the link was blocked but these are the ones I am looking at and there is no writing on those one to see here are the screenshots lapre.JPG spec.JPG
     
  6. ericmark

    ericmark

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    Personally I would take a chance, unlikely to be a problem.
     
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  7. bernardgreen

    bernardgreen

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    Wire wound transformers do not require a minimum load to operate properly, the output can be left open circuit without causing any problems.

    It is Switched Mode Power Supply ( SMPS ) "transformers" that can become unstable when the load on them is too small
     
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  8. winston1

    winston1

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    Transformers don't have a minimum load. However regulation is often not all that good, so the output voltage could rise with only a 39 watt load on a 150 watt transformer. However I would not worry about it, the rise will be fairly small.
     
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  9. 333rocky333

    333rocky333

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    The Dc only ones I think are marked + and - otherwise you would not know which way round the lamp fits and are expensive and for specialist use.
    I have used standard Mr16 lamps that normally run from transformers, in my van for years off the 12 volt Dc battery
     
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  11. bernardgreen

    bernardgreen

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    An LED lamp that runs on AC or DC will have a full bridge rectifier between it's input and the LED element's driver. The driver controls the current driven through the element and requires a DC supply.

    If the lamp is fed with 12 volts DC then the driver will get about 11 volts. ( 12 volts less the forward voltage drop of the bridge rectifier. )

    If the lamp is fed with 12 volts AC then the driver will get about 16 volts DC due to the 12 volt RMS AC supply having peaks of 12 x 1.4 volts.

    RMS = Root Mean Square
     
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  12. aveatry

    aveatry

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    Thanks every one. Great info.
    So its unlikely that a MR16 12v led bulb will be DC ONLY - so most of them are AC/DC and none of them are AC only :unsure:
    It doesn't help not knowing the manufacturer of the LAP screwfix ones so I could check there.
     
  13. bernardgreen

    bernardgreen

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    Some could be AC only, these use a capacitor to limit / control the amount of current driven through the LED element, these will not work on DC.
     
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  14. aveatry

    aveatry

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    In that case I want to try and avoid investing in AC only bulbs ( need 15 ) because some time in the future I may need a new transformer and that then could be a proper driver instead.
     
  15. winston1

    winston1

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    That is highly unlikely. Transformers like that generally don't die. Even if it did you could get another like that.
     
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  16. Speakercon

    Speakercon

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    Looks like a Ring select-a-light Transformer from B&Q.
    [​IMG]

    And the lights are like this?

    [​IMG]

    You might struggle to get the MR16 lamps to fit in the T15 fitting (I've tried).
     
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  17. aveatry

    aveatry

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    Yep that's the one apart from my lights are like this. I have done one and replaced the T15 with an MR16 fitting very successfully there is even a round recess just bigger than the MR16 porcelain which I hot glue melted in place.
    I will convert another and take pictures at each stage. ( I have got 15 to do ) those 7 w T15 bulbs are rubbish. I looked at replacing with T15 LED bulbs but some of the reflectors have lost a lot of the chrome, it doesn't matter with brighter MR16 bulbs as they don't need the reflector to bang out the light as they are the reflector 20200412_done.jpg_thumb.png
     
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