LEDs from low voltage

Discussion in 'General Electronics Chat' started by boatsman, Dec 29, 2014.

  1. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
    165
    390
    I have an electronic transformer input 220VAC output 12VAC 50W made for use with 12v halogen lights. I connected it to the mains and checked the output voltage as I wasn't sure that the gadget was OK. When I checked the output voltage I got a reading of 7.12v. When I reversed the test probes I received a reading of 9.3 volts. I had connected the output wires of the transformer to cable connectors and had pressed the probes down firmly on the screw heads which were tight on the output wires of the transformer. I repeated this test several times and received the same result. What's the explanation? I want to use the transformer via a bridge to power a series of leds that were originally supplied by a 6v supply. Which way of connecting should I use?
     
  2. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,150
    205
    A LED with a Vf of 3.6 V won't work on a 3.6 V supply. Vf has a range of voltages as well.
    When driving with a solid state device you also have to account for that drop too.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Welcome to AAC!

    A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own.

    This was split from
    Might be a stupid question to most...
     
  4. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
    165
    390
     
  5. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
    165
    390
    Sorry that I erred. It was completely unintentional. I just thought it fitted in with the title of the thread.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Electronic transformers are really a switch-mode power-supply, and some do not work if run unloaded. You should repeat your tests with a test load to simulate the halogen lamp(s) that would otherwise be connected.
     
  7. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
    165
    390
    Thank you I will try it again with a 12 v halogen lamp. Is it possible to reduce the voltage and use it via a bridge to power a set of leds with input voltage of 6vdc or is the type of power produced not suitable for powering leds?
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Do you have a part number for the supply. It is possible that it is doing PWM for soft-start or dimming of the halogen, in which case, it may not be well suited to LEDs.
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    I presume that your meter was on a AC V range? Only thing that comes to mind for strange readings is if transformer wewe ferro-resonate & was screwing up the waveform. A bridge rectifier will not care of AC connection. if you no not filter output,& under load ( 5 to 8 A ? ), output might be close to 6 V of pulsing DC.
     
Loading...