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Dash warning light indicator polarity problem

Discussion in 'Automotive Electronics' started by kenloen, Jul 14, 2016.

  1. kenloen

    kenloen New Member

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    Hi,

    New here, and I have a problem,

    I have just replaced the dash warning bulbs on my car with led lights. However this has created a issue with the indicator lights.

    depending on which direction you choose to indicate, the dash warning light gets fed from either wire. No problem with a bulb, it just lights up, but I have just changed my warning lights to LED's. With the standard wiring if I turn left, everything works and the new dash LED light blinks, turn right and the dash LED doesn't flash. However, if I swap the wires round to the LED and turn right then this works normally and left turn has no dash light.

    to get around this I added a relay to switch a +12v when needed and used a common ground, (poor diagram below),

    [​IMG]


    problem is, when I use the Hazard lights everything lights up but if doesn't flash... any ideas be most grateful
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Put a full-wave bridge with the LED across the DC output...

    9.png
     
    Last edited: Jul 14, 2016
  3. kenloen

    kenloen New Member

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    cheers that got me thinking and i have resolved. I used both indicator feeds to the relay rather than a feed to earth, I figured if a bulb lights up from either direction then the relay would fire from the same feeds. Tried it and it works..
     
  4. dave

    Dave New Member

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  5. crutschow

    crutschow Well-Known Member Most Helpful Member

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    You can avoid the relay if you use Mike's circuit.
     
  6. kenloen

    kenloen New Member

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    what value diodes should I use? the ticking of the relay is loud and will irritate in no time at all... I will leave as is for today as the MOT is tomorrow, but I would rather the circuit solution..
     
  7. alec_t

    alec_t Well-Known Member Most Helpful Member

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    That could be an advantage: a reminder to cancel the indication.
     
  8. crutschow

    crutschow Well-Known Member Most Helpful Member

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    A 1A or larger bridge rectifier should work.
     
  9. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Last edited: Jul 17, 2016
  10. kenloen

    kenloen New Member

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  11. spec

    spec Well-Known Member Most Helpful Member

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    Hy Mike,

    In your above circuit you have assumed that the turn signals (presumably V1= turn left and V2 = turn right) switch between 14V and 0V. But, in my experience, the turn signals switch between 14V and open circuit. If this is the case the circuit will not work.

    spec
     
  12. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    In my experience, the "flasher" is a formA switch, followed by a center-off formC switch (the lever arm on the steering column). The turn lamps have a low resistance to frame ground, so the simplistic dashed box with the two ideal voltage sources in post#2 is an adequate model of what is in a car...

    If you insist on me actually showing that I can simulate the upstream stuff in the typical car, here it is:

    380.png

    LTSpice has a voltage-controlled switch, so we define time-dependent control voltages Vflash, Vright, Vleft that are >0V when we want their respective switches to be closed. I show both the "flasher", as well as the self-cancelling, center-off steering column switch (which is really two switches). I replaced the full-wave bridge shown in post #2 with the two-pin bi-lateral LED I mention in post #8. What is important is the direction of current through the current-limiting resistor, R3.

    I could also develop a model for the thermal flasher, if you insist... Here I took a short-cut, making the flasher time-based, instead of load current-based.

    The important thing about modeling in LTSpice is to come up with the simplest model that reflects reality, without worrying about the insignificant stuff. For example, most cars have another switch between the battery and the flasher (ignition switch) which I didn't bother to model...
     
  13. spec

    spec Well-Known Member Most Helpful Member

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    Thanks Mike,

    The fact that the turn bulbs are used as an earth return is crucial to the operation of your circuit. Had you showed this important point in your circuit it would have been clear to see.

    All the same many cars in the UK anyway have separate teller lamps on the dash and the line switches from open circuit to 14V.

    I too could give lectures about the use of simulators including meaningful real world labeling and circuits.

    I have not 'insisted' on anything.

    spec
     
    Last edited: Jul 16, 2016
  14. kenloen

    kenloen New Member

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    diagram of turn circuit if this helps

    [​IMG]
     
  15. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Thought it was obvious. A voltage source can switch between 14V and 0V with ease...
    Not according to the schematic that kenloen just posted. His looks like what I expected and modeled, with the exception of the four-way flasher switch...
     
  16. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello,

    I dont see why a circuit that runs a bulb in BOTH current directions will not work with a full wave bridge and some other resistance besides a bulb.

    Since the LED lights in either condition but not both, it seems reasonable to assume that the current is reversing and we need to have the current in the same direction for the LED but not for the bulb. To put it another way, adding a full wave bridge with a bulb would just mean the bulb would always get the same current flow direction. Changing the bulb to LED just means a different resistance, which in itself could be a problem, but since it works one way then it should work with the bridge rectifier.

    So my reasoning is that if the LED works in mode 1 and not in mode 2 and we switch the polariity of the LED and it works in mode 2 and not in mode 1, then full wave rectification should make it work in both modes, provided the two diode drops dont bother the voltage too much for the LED.
     
    Last edited: Jul 17, 2016
  17. spec

    spec Well-Known Member Most Helpful Member

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    Hy kenloen,

    You have a Nobel M12 :cool::cool:

    Feel like posting a picture?

    spec
     
  18. kenloen

    kenloen New Member

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    Hiya,

    Yeah I bought as a Cat C damaged car a few years ago and had it repaired (GRP clamshell). Its a early car, a 2.5 with TDS and LSD.

    I don't have many pics but here is 1 from when I was car papped enroute to LeMans a few years ago..
    [​IMG]
     
    • Like Like x 1
  19. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Hey nice car.
    My only question then is do you ever park it unattended, and if so, where? (Just kidding :) )
     
    • Funny Funny x 1
  20. spec

    spec Well-Known Member Most Helpful Member

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    Wow. :cool:

    spec
     
  21. picbits

    picbits Well-Known Member

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    We've got an M600 in at work at the moment (Nobles own car). Stunning looking motor :)
     

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