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12v minimum power - help please

  1. Sep 29, 2009 #1
    hi all,
    im sorry if this is a very basic question,
    i am installing a aftermarker HID kit on a vehicle with daytime running lights.
    the hid kit requires a 9-16v input.
    vehicles headlights have a power of 12v
    the daytime running lights give less than 9 volt, i believe it is 6 volts to the halogen bulb and 12 when headlights are on.
    what i want to do is somehow block anything under 10volts from getting to the ballast.
    when the daytime running light power is sent to the ballast it causes the headlights to flicker and this will blow the bulbs or ballast quickly.

    would adding in a resistor on the positive wire block the power to the ballast if it is less than 10volts?

    i am basically attempting to disable the daytime running lights feature.

    thank you
  2. jcsd
  3. Sep 29, 2009 #2


    User Avatar
    Science Advisor

    You could have a relay that pulled in on more than 10 volts and connected power to the headlights.

    If it didn't pull in, no power.

    The contacts on the relay would be carrying the full current of the headlights, so it would need to be a good quality one.

    It would still draw some coil current during normal running, but this would still be less than running the lights, even at reduced voltage.

    Attached Files:

    Last edited: Sep 29, 2009
  4. Sep 29, 2009 #3
    with the relay, is there something to drain the unneeded power? i could in theroy add a small light bulb to draw off any unneeded power and it would be ok if i had to...

    i understand this but im not sure how it will all line up...

    i just found this...can someonene do dome sort or sketch of what the lines would look like....also if it would work.
    Option 3: HID's are OFF with switch in Position 1 or 2 and ON in Position 3

    This variation has the same overall effect as Option 2 above, but is much more stable, works with all relay types and there is no guesswork about resistor/inductor values...

    1) Buy an HID kit that has a wiring harness, relay AND extra 9006 cable
    2) Install everything as normal in the HID kit
    3) With the HID's on, use a voltmeter to determine which wire on the remote turn on lead is ground and which is power (in my case Blue was Power and Black was Ground)
    4) Buy the following components from an electronics parts store: IRF510 MOSFET, 50kohm resistor, 28kohm resistor, 2.2uF (anywhere from 2uF to 10uF should work) 25V (or higher) Electrolytic Capacitor
    5) The MOSFET has 3 Terminals (in order) - Gate, Drain and Source:
    6) The capacitor has two terminals and a marking down the side indicating which terminal is negative
    7) Resistors have 2 terminals (they are interchangeable)
    Your 9006 cable has two ends, the female side plugs into the car 9006 harness and the male side plugs into the HID remote turn on lead - you can cut this cable in half so you have a female end with two wires and a male end with two wires - CONFIRM your polarity in Step 3 before continuing
    9) Solder time! Be very careful to include ALL of the connections below:

    - POSITIVE Terminal of Capacitor TO Gate of MOSFET
    - NEGATIVE Terminal of Capacitor TO Source of MOSFET
    - Drain of MOSFET TO Male 9006 Ground Wire
    - Female 9006 POWER wire TO one end of 50kohm resistor AND TO Male 9006 Power wire
    - Female 9006 Ground wire TO one end of 28kohm resistor AND TO Source of MOSFET (which also has the capacitor on it)
    - JOIN the remaining two free ends of the resistors together and solder TO Gate of MOSFET (which also has the capacitor on it)
    10) Isolate, insulate and wrap all the connections with electrical tape or shrink tubing
    Last edited: Sep 29, 2009
  5. Sep 29, 2009 #4
    is there a power drain on this?

    i have heard of a harness that just boosts the signal to the balasts, w had that on the car and blew 2 ballasts in 1 week...it was a home made one and i think the guy cheaped out on the parts because i looked up the design and it looked correct...but sloppy.

    im trying to clean up someone elses mess at the same time as findig a solution.

    thanks for your reply, greatly appreciated.
  6. Sep 29, 2009 #5


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    Science Advisor

    is there a power drain on this?

    Yes, a small current for the relay. Maybe 1 amp when the headlights are on and about 3/4 Amp when they are off. Depends on the relay.
    The daytime lights would have taken a lot more than this when they were working.

    with the relay, is there something to drain the unneeded power? i could in theroy *** a small light bulb to draw off any unneeded power and it would be ok if i had to...
    You don't need to get rid of unwanted power. The alternator of the car will be a little easier to drive, so the car will use slightly less gasoline.
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