LED Help please

Discussion in 'General Electronics Chat' started by jj_dude, Jun 29, 2009.

  1. jj_dude

    Thread Starter New Member

    Jun 29, 2009
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    0
    Hi guys,

    I need some direction here from the experts on an LED strip I am trying to install on my Harley. I want to use it as a brake/tail lamp. I bought it off ebay as being just that and if I hook it up to just a battery it works fine, I have a lower tail mode and then a higher brake mode. It came with three wires to it, tail , brake and ground.

    The problem is when I wire it into my motorcycles tail/brake light circut. When I installed it the lower tail light did not work but the higher output brake side did. I then tested my wiring on another LED tail/brake light that I had for a trailer. Worked perfect. So I knew my wiring was good. I then put the strip I wanted to use back on the bike.

    Now heres the kicker, I then just randomly disconnected my incandesant tail lamp bulb and on went the LED strip. It worked perfect in both tail and brake mode. I plugged back in my tail lamp and out it went. What would the connection be with my incandescent tail light? Whats happening here and is there anyway to fix it? Thanks for the input in advance.
     
  2. Lanz

    Active Member

    Oct 30, 2008
    153
    0
    Im not an expert but i think maybe the current is not enough to drive the LED.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    LEDs are quite different animals from incandescent light bulbs, and generally take a lot less current.

    Have you read this? LEDs, 555s, Flashers, and Light Chasers

    Can you show us a schematic of what you're trying to accomplish?
     
  4. Lanz

    Active Member

    Oct 30, 2008
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    I just give my opinion.
    Sometimes electronics are hard to be understandable.
     
  5. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    Can you measure the voltage at the tail lamp when the incandescent light bulb is in and when it is out?

    The presence of the bulb may reduce the voltage low enough that the LEDs do not light, i.e. there may be resistance in the line that lowers the voltage across the bulb to get the reduced brightness. Without the bulb, there is less current draw and the voltage at the LEDs is higher, enough to light the LEDs
     
  6. jj_dude

    Thread Starter New Member

    Jun 29, 2009
    3
    0
    I have very limited knowledge of electronics so please bear with me. By plugging in my incandescent tail lamp, is that not like adding a rather large resistor to my circuit? It is a rather large bright bulb (brighter than an automotive bulb) and certainly uses a fair amount of current. If I measure from any power source to ground with that light on, I get a reading of about 150 ohms. I would think this is because my blub is a "path" to ground. As soon as I unplug it my reading drops to zero and the dim mode of my LED strip works.

    What is changing in the circuit that is causing this to happen?

    I don't know the construction of the unit I purchased, so I can't really post a schematic. I would have to destroy it to get at the components. Sorry I can't give that piece of the puzzle. The only thing I can say is I am wiring it in parallel with my other lights, should I try it in series with an smaller incandescent running lamp.

    Thanks for the help, its great to try to solve problems like this....mikes life interesting.
     
  7. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Can you measure the voltage from the tail wire to the ground wire on the while the lights are on? If you can, measure it twice, once with the bulb connected in parallel with the LEDs and another time with the LEDs by themselves. It is better to do a voltage measurement rather than a resistance measurement.

    Is the end goal to get the LEDs to work with the bulb or to replace the bulb with the LEDs?
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    u know the secret little thingy that none of you came across but I have since I like repair my own motor bike from top to bottom. :D
    The thing is tail light and brake uses two different voltages. Tail light is powered from the alternator so to say it is AC, and some how to make things a bit awkward does not light LED's. So u need it to change to DC.
    But brake light is from battery direct.

    Got it. I am like very proud now since I am familiar with motor bikes and none of the electronics geeks here are . hehehe :p

    Rifaa
     
  9. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
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    I will definitely say that I did not know that.

    That is probably what the LEDs are counting on then to give the reduced brightness for the tail light, a pulse width modulation (PWM) of sorts.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    OK, if you can't post a schematic how about a link to your parts. Without knowing what you are using anything we say is just a guess.

    BTW, you can always post a schematic. Schematics are the language of electronics, even if you draw a box for something unknown.
     
  11. jj_dude

    Thread Starter New Member

    Jun 29, 2009
    3
    0
    Well I tried some things and I got it to work. I put a diode in series with the lower output side of the led bar and it now works. For some reason this solved my problem. I am not sure why but it work right away.

    Thanks for all the help, you guys are great.

    One thing to clarify in this thread, my bike is a Harley and they have NO ac any where on the bike to be used for lighting. Both the tail and brake are 12 volts DC and share the frame as a ground. They light seperate elements in the tail lamp bulb.

    Thanks again for the help!
     
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
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    Better put a capacitor to smooth out the DC.
    Either way by putting a diode and if the led's light then what you have is AC not DC. Don't you think?

    Rifaa
     
  13. BobaMosfet

    Active Member

    Jul 1, 2009
    109
    11
    Er, nevermind my other post, you got it working. I'd love to put an oscilloscope on that and see what it sees with and without the diode.
     
    Last edited: Jul 1, 2009
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