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Technical Using LEDs on 6v positive ground

Discussion in 'The Hokey Ass Message Board' started by A_Burly_Wind, Dec 25, 2017.

  1. Anyone here done this? Cant seem to fund much info on this. Any specific place that sells bulbs for 6v stuff?

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    chryslerfan55 likes this.
  2. G-son
    Joined: Dec 19, 2012
    Posts: 874

    G-son
    Member
    from Sweden

    Buy "loose" powerLEDs on metal backing (for cooling), mount them where you need them and add your own current control - a simple resistor works okay, a more advanced regulator is better with efficiency and varying voltage. Done correctly with quality components it should outlast the car, no need to keep using a socket for easy replacements.
     
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  3. blowby
    Joined: Dec 27, 2012
    Posts: 8,062

    blowby
    Member
    from Nicasio Ca

    They have tail/stop light bulbs for old British motorcycles.
     
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  4. orange52
    Joined: Feb 21, 2003
    Posts: 456

    orange52
    Member

    Probably not what you're looking for but I used the guts of an led light from Harbor Freight, fitted it to a 52 Chevy pickup tail light and now its the 3rd breaklight in my back window. I'm running a 6V system and I think this light is 4V with the batteries.
     

    Attached Files:

    loudbang likes this.

  5. Depends on what you are doing with the LED's. If you are replacing existing bulbs, the LED replacement plug-ins will be configured for negative earth. If you are , say, trying to light up an instrument panel, you can wire in an LED with a resistor in series with one of the legs. It doesn't matter which one has the resistor, but you have to connect the ANODE (long lead) to ground.
    A standard LED will need roughly 300 ohms series resistance.
     
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  6. pitman
    Joined: May 14, 2006
    Posts: 5,151

    pitman

    At what voltage? (6V). For a 12V system I usually strung 4 bulbs in series, as they were +/- 3.5V each.
     
  7. ...i've heard LED's don't work on positive ground,,,?
     
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  8. tinkirk
    Joined: Jan 16, 2017
    Posts: 111

    tinkirk

    I've experimented with them and the ones I've tried seem to work fine as is
    I'm planning on using them on my 29 with positive ground


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  9. BJR
    Joined: Mar 11, 2005
    Posts: 7,251

    BJR
    Member

    Just make sure the + on the LED is connected to the + on the car. They will not light if hooked up backwards.
     
  10. G-son
    Joined: Dec 19, 2012
    Posts: 874

    G-son
    Member
    from Sweden

    The problem with that is that you get no control over the current running through the LEDs. Unlike lightbulbs, electric motors etc. LEDs require more or less precise control of the current, while the voltage simply is allowed to become what it has to be.

    If we use water flow and pressure to demonstrate current and voltage, a regular lightbulb is like a bucket with a small hole in the bottom. The more water we put in, the higher the level, the more pressure at the bottom where the hole is, and we get more water flowing through the hole.

    The LED on the other hand, works more like the bucket w/o a hole. No matter how high the water level (voltage) is, nothing happens - until it reaches the edge, and then just a small increase causes a huge flood coming over the buckets edge.

    LEDs do have a "working voltage", but it is not stable - it varies a little with temperature, manufacturing tolerances and so on, so LEDs should never be fed from a source without current control. Small changes in voltage causes huge variations in current, going from an almost empty 12V battery at 11V to a full battery getting charged at normal 14.4V is MORE than enough to go from almost no light to overloading and cooking uncontrolled LEDs.

    Always, always, always use something to control current through LEDs. If you use the very simple method of putting a resistor in series and the voltage in the system can vary quite a bit as in a car, put around half the total voltage on the resistor to reduce the effect of varying voltage. With more advanced current control or a more stable voltage less safety margin is needed.
     
  11. tinkirk
    Joined: Jan 16, 2017
    Posts: 111

    tinkirk

    I would think that a 12 volt light running on 6 volts is enough of a resistor you won't need to worry about it


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  12. G-son
    Joined: Dec 19, 2012
    Posts: 874

    G-son
    Member
    from Sweden

    I'm afraid you're missing the point of how LEDs work if you think that. Bare LEDs always need current control - although "12V" LED bulbs already has built in current control - sometimes they work on 6V, somtimes that's just not enough voltage. Depends on how they're constructed.
     
  13. tinkirk
    Joined: Jan 16, 2017
    Posts: 111

    tinkirk

    I try not to think or over think things such as this
    I'm more of a trail and error type of person


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  14. gimpyshotrods
    Joined: May 20, 2009
    Posts: 19,225

    gimpyshotrods
    ALLIANCE MEMBER

    I would try a 12V alternator or generator, a ground polarity switch, and avoid the error of 6V negative ground LED's.
     
  15. G-son
    Joined: Dec 19, 2012
    Posts: 874

    G-son
    Member
    from Sweden

    Trial & error is good. But the error bit is best to avoid with safety equipment such as automotive lights. Do it right, or don't do it at all.
     
    gimpyshotrods likes this.
  16. If you use these- image.jpeg
    Basic wiring diagram-

    image.jpeg
    The LED has 2 legs- Anode (+) and Cathode (- ). The Cathode is the shorter lead ( you can't see from the picture, but one is slightly shorter), and has a flat area on the housing (have a look at the fourth red LED in the pic, on the RHS, you can just make it out.
    Wire them up just like in the lousy sketch- if they are supplied backwards they wont light up. If you run 12 volts, use a 470 ohm resistor (1/4Watt), for 6 volts you can use 330 ohms. (R)
    This will give you a forward current of about 20mA. If you happen to put 12v straight across the LED, make sure you have your safety glasses on, as it will instantly overheat, and may physically explode. As mentioned above, some already have a limiting resistor inside.
    These things are cheap, grab a handful, and some resistors, and have a fiddle around with them. There are many colours available and they can be used in lots of places in a car.
    The bigger wattage LED's like this-
    image.jpeg Need a heatsink, are very bright, and are used for headlights, home lighting etc. ("CREE" LED's).
     

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