Car Headlights and PWM

Discussion in 'The Projects Forum' started by LipschitzWrath, Jul 6, 2012.

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  1. LipschitzWrath

    Thread Starter New Member

    Jul 6, 2012
    Hey guys, need some expertise here. I have a vehicle that has fancy new headlights, called "SmartBeam". Basically, it's an automatic high beam system. It worked really, really great before I started modding my vehicle. I installed HID's (high intensity discharge) lights. Each light is powered off its own fused +12V bosch relay.

    Here's where the trouble began. Come to find out, the Smartbeam system doesn't just turn the high beams on and off. When it senses a car far off in the distance, it first begins dimming the high beams with PWM. When it dims them down to a nominal (and unknown) level, it shuts them off entirely. The problem is the PWM section. Obviously, my relays don't like this PWM at all. They are erratic on when they finally shut off and they make a terrible buzzing noise during the entire PWM cycle as they open and close a billion times a second.

    I'd like to get rid of the PWM signal. There isn't a discrete wire in the car that I can pull off of thanks to the new CANBUS wiring system. I even tried the high beam indicator in the dash but it is a module. I have tried SSR's and they don't work. So I need some help. How do I do this?

    I thought maybe a transistor as its saturation voltage is much lower than the pull in or hold in voltage of the relay coil. Would that work? I don't know how a transistor would respond to having a PWM signal applied to its base.

    The other option is to filter it out with an R-C network right? Any ideas there?

    Now for the bad news. I don't know the duty cycle, decay rate, or frequency of the PWM signal. I don't have an oscilloscope either. I have a DMM and am quite handy with it.
  2. BMorse

    AAC Fanatic!

    Sep 26, 2009
    Your thread should be closed here in a few minutes since we don't deal with automotive modifications on this forum.... Might want to check out other automotive forums.... :)
  3. Wendy


    Mar 24, 2008
    he owners of All About Circuits has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:

    Another good forum that shares many of the same membership is . Good luck.
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