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12v dimmable transformer query

Discussion in 'Electrics UK' started by Deansplit, 20 Aug 2017.

  1. Deansplit

    Deansplit

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    Hi, I bought a set of x10 10W halogen low voltage starlights (probably about 12 years ago now but didn't have a use for them until now!)

    Bit confused though as the transformer says dimmable (made buy 'Ring' Model DET-105) but the instructions say 'WARNING' Not advisable to use with a dimmer switch.

    Err, why???
     
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  3. Taylortwocities

    Taylortwocities

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    12 yeasr ago, dimmers were made to dim general tungsten lamps which is mostly what we got then.

    It may depend on the 'transformer'. Is it a big heavy thing that feels like its a lump of metal - in which case its mostly a lump of metal. Most dimmers cannot cope with that.

    If it's an electronic thingy then the (100W) load will not be eanough for most dimmers to work properly.

    Post a pic of the transformer thingy. so we can revel in nostalgia.

    These days there are lots of low-wattage LED lights and its easy to buy an LED-compatible dimmer.
     
  4. Deansplit

    Deansplit

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    See attached pics, it's the usual type of transformer I'm used to seeing with light TBH...?

    Now you mention the dimmer 'switch' load, I wanted to actually have the lights working off of an existing dimmer switch which has a ceiling pendant (breakfast bar light with 5x 40w G9's – the star lights were to form a circle around the main light)... so is that not advisable then?

    IMG_8235.JPG IMG_8234.JPG IMG_8236.JPG
     
  5. Taylortwocities

    Taylortwocities

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    Most dimmers should work with that electronic transformer. Give it a try.
     
  6. stillp

    stillp

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    The lamps are halogen, which will have a shortened life when used with a dimmer.
     
  7. Deansplit

    Deansplit

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    Oh, so change bulbs to LED then and sorted...?
     
  8. 333rocky333

    333rocky333

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    Not that easy, you may weigh out for led lamps, only to find they are unstable or flicker with that transformer.
    Your unlikely to even notice if the halogens have a shorter life, and are cheap to replace anyway and despite the halogen ban they will not just vanish overnight.
    You can likely get a set of 10 decking leds complete with driver for less than the cost of 10 decent G4 Led capsules
     
  9. winston1

    winston1

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    Terminology is important here. Low voltage generally refers to above 50 volts. Your lamps are probably 12 volts which is generally referred to as extra low voltage. You really need to tell us the voltage as low voltage is meaningless.

    What you refer to as a transformer is almost certainly a switch mode power supply. If they say not advisable to use with a dimmer don't do so.
     
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  11. winston1

    winston1

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    So a total of 5x40 + 100 = 300 watts. Probably more than your dimmer can handle. But 300 watts in a kitchen? Glad I don't pay your electricity bill.
     
  12. Deansplit

    Deansplit

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    This is one of 9 circuits in a 47m sq m room, sod the bills, it's about the look! ;)
     
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  13. JohnW2

    JohnW2

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    As we've discussed before, there seems to be some confusion/uncertainty about this.

    For what it's worth, what I have read is that, whilst dimming will prolong the life of any filament bulb/lamp, in the case of halogens (for which a high envelope temp is need for proper working of the 'halogen cycle') the prolongation of life is not as great as it would be for a non-halogen bulb/lamp. Whether that is true, I haven't got a clue.

    Kind Regards, John
     
  14. winston1

    winston1

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    With such a large room you would be better turning some off rather than dimming the lot.
     
  15. ericmark

    ericmark

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    The power supply you show I think is rated 35 - 105 VA which I always questioned when used with mutli-lamps as really at 10W each it should have been rated 10 - 105 so it would continue to work with only one bulb still intact, it was designed to run 4 to 10 x 10W bulbs, as it states the transformer device can be dimmed and it also correctly states you should not dim halogen lamps specially that small, the whole idea of a halogen lamp is the envelope is so hot that the tungsten from the filament will not be deposited on the envelope but instead back onto the filament, over time the tungsten will not be re-deposited in an even manor so it will develop thin and thick bits and in the end the thin bit will rupture. If the lamp is not kept hot enough you will see the quartz envelope go black inside.

    At 1 to 2 watt each maximum wattage would be around the 20 watt mark which is too low for that transformer, and at around £2.30 each 10 would cost around £23 plus new transformer at say £6 so it would cost in the region of £30 to convert to LED.

    However you also state main lights are G9 these should also not be dimmed, as quartz lamps, so option is to change all to LED with new transformer or get rid if the dimming.

    As stated 300 watt is a fair amount of heat, likely OK in the winter, in fact likely will if heating is all electric reduce the heating bill because inferred heating does not heat the air directly so you can reduce air temperature to 18°C but the room will feel as if air is at 20°C but 300 watt is over 1A and unlikely you can find a dimmer to take that load at a reasonable cost and also in the main we use ceiling roses as junction boxes which are rated at 6 amp so the fuse/MCB/RCBO for lights is just 6 amp, and likely for the whole house. So you need to consider if you have a large enough supply.

    In the summer you may want the ability to switch off some of the lights, so consideration must be made as to if the lights should be split into two circuits, this is common in Europe so in your case you could have 100W or 200W or 300W with just two switches, you would not really need a dimming switch if set up like that.

    I think the whole idea of heating with lights may be more economic, that is something which can be debated, but 15 quartz bulbs in one room would be high maintenance, every week you would be renewing bulbs, and in the end you will be forced to swap anyway as the supply of quartz bulbs is phased out, it is a lot of work to fit those lamps correctly and build or fit the fire proof boxes or hoods around each lamp, unless of course on the top floor, so personally I would not fit them.

    I fitted pods in my bathroom, got them cheap, thought they looked good, but rarely were all four working, one bulb at least also seemed to be out so did not really look that good, I was lucky powered with a proper wire wound transformer I have been able to move to LED, in fact most of the house now LED, that has resulted in near maintenance free lighting, and also released a cupboard which was used to store replacement bulbs.

    In the last year I have replaced just one lamp, a 6 foot fluorescent in kitchen, and when I came to replace it seemed it was simply disconnected and really did not need a new tube, pre LED I would replace around 100 bulbs a year, a task I am pleased to have lost.
     
  16. bernardgreen

    bernardgreen

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    His "obsession" is more a case of pointing out that refering to a switched mode power supply ( SMPS ) as a transformer can give rise to problems if the person installing the SMPS is under the impression that the SMPS will operate in the same way as an inductive ( non electronic ) transformer. Hint : radio frequency radiation.
    12 eff.jpg

    Just what is the AC frequency of the AC output of this SMPS ? And what does the eff in Sec:12V eff: mean ?

    Ring do make good quality SMPS units.
     
  17. EFLImpudence

    EFLImpudence

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    Why would he think that?

    Do 'electronic' things generally work the same as the earlier 'electric' or mechanical things?
     
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