Transformer

  1. Parm

    Parm I have fun doing stuff

    Messages:
    10,075
    Location:
    Towcester
    Can someone provide a link to a cheapish plug in transformer

    240v to 4v at around 0.75a

    need it for a clip on LED light

    all the ones I can find are around 15 to 20 quid Mark.
     
  2. mtt.tr

    mtt.tr Member

    Messages:
    1,381
    Essex England
    Usb is about 5v
     
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  3. Spark plug

    Spark plug Member

    Messages:
    3,403
    Location:
    Durham, England
  4. slim_boy_fat

    slim_boy_fat Forum Supporter

    What about an old phone charger? I have a few kicking about if it'd work.
     
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  5. eddie49 Member

    Parm likes this.
  6. Parm

    Parm I have fun doing stuff

    Messages:
    10,075
    Location:
    Towcester
    Are they 4v?
     
  7. Parm

    Parm I have fun doing stuff

    Messages:
    10,075
    Location:
    Towcester
  8. optima21 Forum Supporter

    Messages:
    2,663
    Location:
    halifax, England
  9. slim_boy_fat

    slim_boy_fat Forum Supporter

    I'd have to check, I'll be our to to the cave so will check then.
     
  10. The_Yellow_Ardvark

    The_Yellow_Ardvark Member

    Messages:
    11,267
    Location:
    England
    @Parm .
    Let me check my pile of items.
    I may have. Plan of cunning.
     
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  11. Parm

    Parm I have fun doing stuff

    Messages:
    10,075
    Location:
    Towcester
    :thumbup:
     
  12. the snooper

    the snooper getting older by the day

    Messages:
    20,133
    Location:
    Hull UK
    I would also use a phone charger 750ma upwards
     
  13. Wany Member

    Messages:
    40
    Location:
    Gloucester, UK
  14. EBME2 Member

    Messages:
    30
    Location:
    UK Preston
    You could use a 5V power supply and a feed through a diode usually drops about 1V through the diode, something like a 1N4004 would probably do
     
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  15. slim_boy_fat

    slim_boy_fat Forum Supporter

    @Parm Sorry, forgot about this :ashamed:

    I have a TomTom charger lying here [along with all the extras, screen mounts, remote control etc and the head unit, which didn't like being dropped from 3' onto the pavement, they don't build stuff like they used to.....:rolleyes: ] - rated at 5V if that's any good for your needs?
     
  16. m_c Member

    Messages:
    120
    Location:
    East Lothian
    I'm guessing the LED lamp is designed to run of a single cell Li-Ion/LiPo battery, given the 4.2V requirement.

    If it's something you don't mind risking melting, you could try it on 5V from a USB socket. Given it'll be designed to run of a ~3.0 to 4.2V supply, it will have some kind of regulator built in, so there is a reasonable chance it'll run fine on 5V.
    However, if you don't want to risk it, @EBME2 's suggestion of adding a diode would work. Although personally, I'd probably go for the slightly bigger 1N540x series just so it's got a bit of bigger surface area for dissipating heat, and use two in series, as the voltage drop over a silicon diode is only 0.7V, which should give about 3.6V from a 5V source.
     
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  17. gerrymoore

    gerrymoore CNC expert (well, getting there!)

    Messages:
    845
    Location:
    Wirral UK
    Hi Parm 4 volts seems a very strange amount for an LED?? Either try it with a 5 volt charger (can't see an extra volt causing any harm) or put a small resistor in series after doing ohms law - someone help here !!!
     
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