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    AC to DC rectifier bridge

    I'm trying to convert the tail light on a snowmobile from incandescent to LED to conserve power (brakes dim headlights). The electrical system is ~12v AC. My problem is that the system uses 3 wires and has 2 filaments in the bulb. One common wire, one which is always powered for running lights and one that is powered when the brake lever is pulled. I wired up a rectifier bridge for each filament and tied the common from the AC to the two rectifier bridges and the other AC wires to a rectifier each. I bridged the two DC output grounds together and fed them up the common wire to the light and each of the positive wires to a separate filament.

    So, it worked but I don't think it is working correctly. It seems just as bright as the LED's running on the AC current and a multimeter shows that there is still AC on the output at the bulb so I'm thinking there is weird "feedback" going on between the two rectifiers. If I remove one of the rectifiers the AC voltage disappears at the light socket.

    I drew everything out and can see how it could feed back through the rectifier but admit I'm very limited in my knowledge and I cannot figure a way to resolve the issue. Any help would be GREATLY appreciated! I want to see this winter on the trails :)

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    Re: AC to DC rectifier bridge

    In this vehicle is there a Battery ? (as I am not familiar with this type)
    If yes, you are not needed to put the rectifiers. If NO (means no Battery) then Yes you have to put the Rectifier but in that case I will not recommend the Bridge rectifier but Simple Diodes separately for both filaments (one for each side). Reply my question, so I may guide you on the connections.


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    Re: AC to DC rectifier bridge

    Yes there is a battery for the electric start but it does not feed the electrical system; meaning when the engine stops, all lights go out.

    If I just put the diodes, won't the light effectively PWM to whatever the cycle (I think 50 on this system) of the stator is? Like I said, it works just plugging the bulbs into the stock housing on AC but the brightness difference between the brake and running lights doesn't seem to be very big but if I run the bulb off of a 12 v dc supply there is a much bigger difference.

    Thank you so much for your help!



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    Re: AC to DC rectifier bridge

    There is another solution
    If you are using 5 LED for tail lamp, place another 5 LED in board which will glow for break switch. no PWM required in this case.



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    Re: AC to DC rectifier bridge

    Quote Originally Posted by shamikrudra View Post
    There is another solution
    If you are using 5 LED for tail lamp, place another 5 LED in board which will glow for break switch. no PWM required in this case.
    I'm not sure what you are saying. The sled uses 3157 wedge style automotive bulbs. I purchased replacement 1 watt 3157 dual intensity LED bulbs.

    I removed my rectifier bridges and messed with diodes. I found that If I put a diode on the running light wire but not the brake wire, the running light didn't get dimmer but the brake circuit got MUCH brighter. I soldered and taped it all up and installed it back on the sled (I was bench testing with a wall wart) and find that it works great at idle but if I rev the engine up the running lights go out but the brake light always works fine. My guess is the diode I used which I had laying around is not rated for this type of application?



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    Re: AC to DC rectifier bridge

    can you upload LED bulb circuit diagram?


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    Re: AC to DC rectifier bridge

    Hi Moxified,
    How your LEDs are connected, series or parallel /. If not aware just tel me please what is the working voltage of the LED bulb ?
    Normal Diodes won't work, as the AC frequency is much higher when you throttle the engine. You need here FAST diodes. Best is let me know the working voltage I will give you complete circuit with safety, so your LEDS do not fuse away on High voltage when the throttle is high.
    Hope it helps.


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    Re: AC to DC rectifier bridge

    Here is a page from the service manual for the snowmobile. [Page 310] Polaris IQ Service Manual 2007-08 PN 9921044.pdf I know there is a lot of other stuff on there but just follow the stuff for the brake switch and the tail light.

    The system is really simple (in my uneducated opinion), power to bulb to ground for running light and power to bulb through switch and to ground for brake light. The only weird part is that they tap off of the brake wire and run that to a reference on the regulator. Best I understand it is that will be the path to ground in the event that the brake switch isn't pulled. When the regulator sees 12v ac on that line, it turns the brake indicator light on the dash OUT.

    What I have done currently is placed a diode in line with the brown wire and placed a 10k resistor between the yellow and orange wires (gives a path to ground for the brake indicator wiring to regulator mentioned above).

    This is a 12v AC system and the two tail light bulbs are wired in parallel. See the diagram attached for wiring path. Let me know if I can help clarify as I have been all over this electrical system over the last few days.

    Thank you so much!



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    Re: AC to DC rectifier bridge

    OK moxified,
    All circuit is now clear to me. Just I want to know is the LEDs Bulb (you purchased) working voltage. Please confirm me and as soon as you confirm I will upload the modification circuit for you.



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    Re: AC to DC rectifier bridge

    The LED is from superbrightleds.com. 3 Watt Luxeon 3156/3157 Bulb with Lens Specifications

    Here is their specifications:

    Part NO: 3157-R3W
    Color: Red
    Operating Voltage Range: 9~14.5
    VDC Current Draw @ 12 Volts in mA: 65 / 240
    Luminous Flux: 35 / 90
    Doominant Wavelength / CCT: 617
    Beam Pattern: 320

    These are of course dual circuit bulbs for running and brake. There are 2 of these bulbs in parallel on the sled.

    Thanks!



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    Re: AC to DC rectifier bridge

    search for automotive class rectifier. ready made available for bikes which uses DC supply for its tail lamp and flasher lites.



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    Re: AC to DC rectifier bridge

    Quote Originally Posted by shamikrudra View Post
    search for automotive class rectifier. ready made available for bikes which uses DC supply for its tail lamp and flasher lites.
    I'm not finding much for "automotive class rectifiers." Do you have a link to an example to help me in the search? I also looked for super fast diodes but don't know how fast I need.



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    Re: AC to DC rectifier bridge

    Thanks for the links. Those are basically what I did though, especially the last one, that is exactly what I did. I was talking with an electrical engineer today and he suggested that my diode is actually not acting as a diode so to speak but rather a resistor in that it is lowering the current and therefore the brightness of the running light filament. So, I'm thinking if I replace the diode on the running lights lead with a resistor, it will reduce the brightness but not at the exponential rate that the diode is reducing with respect to engine speed. I don't know if this makes sense.



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    Re: AC to DC rectifier bridge

    Going by your initial post.

    You originally had 12V incandescent bulbs. These do not start to light until you apply a few volts. So the original circuit may allow some harmless miscellaneous current through a bulb even when it is 'off'. It allows simplified design where multiple bulbs and filaments are involved.

    LED's on the other hand start lighting up just by applying a milliamp.

    So your new installation may have been free of electrical mistakes. However LED's have their own tricky side to them.



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