halving voltage from low voltage transformer

Discussion in 'General Electronics Chat' started by myckts23, Apr 21, 2018.

  1. myckts23

    Thread Starter Member

    Feb 27, 2011
    15
    0
    Thank you in advance -
    looking for the part I need to order to wire in line with "red" - the application is a lamp with one 50W 12v Sylvania bulb - halogen - the Transformer is a LET 60W . - lightech - the wiring in foto allows me to operate bulb with existing 3 pin 2 position (technically 3 position - off, lo, hi) rocker switch - And i know that I can get a rectifier/multiplier to multiply but I want to halve voltage for lo lighting - I believe I can wire in series - splicing the blue between red red and txfmr - but I need the part - never done this before.
     
  2. Alec_t

    Expert

    Sep 17, 2013
    10,259
    2,508
    It is tempting to use a diode to half-wave rectify the transformer output, but this would risk destroying the transformer. This thread is worth a read.
     
  3. myckts23

    Thread Starter Member

    Feb 27, 2011
    15
    0
    ....ok
     
  4. MisterBill2

    Distinguished Member

    Jan 23, 2018
    3,697
    723
    What I see in the picture is probably NOT A TRANSFORMER in the sense of windings and an iron core. It looks like an electronic switching power supply, and so none of the things that work with a transformer would be applicable, nor would they work. If there is room for a second bulb in the system then you could put two bulbs in series to provide a dimmer light. Another option is to get an actual transformer and add it to the package and use a lower voltage to get less light.
     
  5. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    8,151
    2,020
    And it may actually be a DC output. The halogen bulbs wouldn't care whether it was AC or DC.
     
  6. Reloadron

    Distinguished Member

    Jan 15, 2015
    4,457
    2,184
    First glance I saw a SMPS but caught the word transformer partially obscured in the picture. This is what they seem to have and it is in fact a transformer. Here are the specifications:
    • Item Halogen Transformer
    • Input Voltage 120VAC
    • Output Voltage 11.7VAC
    • Input Power 64W
    • Power Output 2.5 to 60W
    • Input Current 0.50A
    • Output Current 5A
    • Power Factor 0.96
    • Height 0.79"
    • Length 2.09"
    • Width 1.3"
    • Ambient Temp. Range 0 to 50 Degrees C
    • Standards RoHs Compliant, UL Recognized, Class 2
    The Black and White are Line and Neutral input respectively and the two blue wires are output of about 11.7 VAC for a 120 VAC input. I do not get or understand the switch wiring configuration as pictured? You would normally want an Off/On switch for the AC Mains and then a Low/High switch depending on how the lamp is configured.

    Ron
     
  7. MisterBill2

    Distinguished Member

    Jan 23, 2018
    3,697
    723
    OK, it might be a transformer, but it might not. Now for a high-low switching arrangement just connect a diode across the two wires from the switch, with the center of the switch connected to one side of the SECONDARY, instead of controlling the primary. Then the lamp is connected between one of the switch end terminals, probably the red wire, and the other side of the secondary. Then in one position the light gets full AC, while in the other position it get half wave rectified DC. This would be about half brightness, probably a bit less. But the diode would need to be good for the lamp starting current and at least 50 PIV. And the best part is that it won't matter what that module is. And it will be cheap to do.
     
  8. ebp

    Well-Known Member

    Feb 8, 2018
    2,332
    812
  9. myckts23

    Thread Starter Member

    Feb 27, 2011
    15
    0
    '''' input 120V - output 12v - lightech 60W for halogen lamps - pretty sure this is a step down small transformer - I was wondering if a prtoperly sized resistor would bring one leg to 6V?
    so interesting the idea that it "might be or might not be.."
    Am I using the incorrect language -
    this is a low voltage lighting application - very common - 120V to 12V transformation - how can this not be a transformer? Always seeking to learn - so thanks -
    and what size Diode? the unit )LET 60W -
    output is 11.7V 5A - so if i wire in a 3A with 50PIV - will this reduce the lighting?
    I am replacing the transformer unit that came with the light - we have had it ffor 15 years or so - gift and thus the questions - I can make it work at one level - but would like to provide the spousal unit with the same 2 choices.
    RECTIFIER DIODE 3 A MP / 50 PIV . 3 gfor 60 cents - but I can remove the 4 that were in the original transformer
     
  10. dendad

    Distinguished Member

    Feb 20, 2016
    2,921
    810
    As you no doubt know, a transformer is a pair (or more) of windings on a magnetically permeable core, and the varying magnetic field of the primary induces a voltage in the secondary.
    A lot of lighting power supplies I've seen are labeled as "transformers". Yes, they do transform the 110 (or 240) volts to 12V or whatever, but the terminology is misleading. Probably done by the advertising division. It would be better to have them as power supplies.
    They will mostly have a transformer in them as one component of the power supply, but it will usually be running at a high frequency to get the size down.
    I agree with ebp above, it looks way too small to be a 60W power transformer.
    Some more investigation is needed.
    Can you measure the DC resistance of the primary and secondary?
     
    Reloadron likes this.
  11. Reloadron

    Distinguished Member

    Jan 15, 2015
    4,457
    2,184
    Yeah, reading the small print in the second link:
    "6 0 W Class 2 electronic transformer. Low 2.5 wattage minimum load makes it suitable for AC LED MR16s. Check compatibility with AC LED MR16 manufacturer. Potted. 120V input. Current: AC".
    The wording "electronic transformer" and the weight leads me to believe it is a SMPS which is potted.

    As to the actual lamp, would it have two terminals or three terminals. Meaning a common terminal and a low and high terminal or is it simply a two terminal lamp?

    Ron
     
  12. dendad

    Distinguished Member

    Feb 20, 2016
    2,921
    810
    It sounds like you want to dim the halogen lamp. That is not really recommended.
    http://www.teklight.com/faq_s.html
    If you want dimming, maybe you should go to LEDs?

    The power supply is labeled as "dimmable" so a light dimmer in the mains should work to lower the volts.
     
  13. myckts23

    Thread Starter Member

    Feb 27, 2011
    15
    0
    2 terminals on Sylvania lamp - on the side - let me state the lamp had been operational for years more than 10 and it is on its second lamp - very relaible- the bulb is hi and low - rocker switch is 3 position - off hi lo -
     
  14. myckts23

    Thread Starter Member

    Feb 27, 2011
    15
    0
    small - 3ohms - does this sound correct
     
  15. MisterBill2

    Distinguished Member

    Jan 23, 2018
    3,697
    723
    The reason that it might not be a transformer is because there are all kinds of switchmode supplies around, and mostly they are cheaper to produce than a good transformer. In addition, there has been a lot of complaints about the switch-mode power supplies used for lighting. THAT is the reason for my statement that it might not be a transformer. I have wall-wart power supplies rated 5 volts and 3 amps (15watts) that are smaller than transformer wall warts rated at 9 volts but only 100milliamps (0.9watts). That is my explanation for asserting that the device might NOT be a regular transformer.
     
  16. myckts23

    Thread Starter Member

    Feb 27, 2011
    15
    0
    tired of effing with it tonight - I will reproduce with diode - another time - thank you all for education and assistance
     
Loading...