headlight failure (H7)

Discussion in 'General Motoring' started by Mike Marlow, Mar 17, 2008.

  1. Mike Marlow

    Mike Marlow Guest

    Good stuff Dan. Thanks for posting this. Why bother waiting a week though?
    That won't really show you anything, so why not just go ahead and install
    the second diode now and start the clock ticking?

    Mike Marlow, Mar 17, 2008
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  2. Mike Marlow

    Dan K Guest

    Well, I actually did something about it this weekend. This is what I

    With 2002 XG350 running:
    V battery = 14.2 v
    V at headlight = 13.43 v
    V headlight + to battery - = 13.55 v

    This tells me there is a 0.12 volt drop in the ground wiring (seems
    reasonable), and a 0.65 volt drop in the positive side which probably
    includes wiring, a fuse, and a switch of some sort (relay, transistor, or

    So I placed a 10 amp diode in the passenger side headlight circuit. It now
    reads 12.8v (headlight + to battery -). This should imply that the voltage
    measured at the headlight is now around 12.68v (I did not measure this). As
    I installed the diode and placed it in and out of circuit while watching the
    headlight intensity, you could tell the difference, but only because you had
    the 2 to compare. Its virtually impossible to tell by looking now that the
    passenger side headlight is a little dimmer than the driver side. My plans
    are to run this for a week or two and then install a diode on the drivers
    side. I will then see how long it takes to burn out a headlight or two. If
    they still burn out in under 3 months I might try a second diode in each
    side - which should drop the voltage at the headlight down to right around
    12.0 volts.

    I'll post updates as they occur.

    Dan K, Mar 17, 2008
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  3. Mike Marlow

    Dan K Guest

    The thought was that if something weird occurred, like the diode went out
    for some strange reason, it would not take out both headlights. As soon as
    I convince myself that this is a stable configuration, through multiple
    startup - drive - turn off cycles and a number of hours of run time, then
    I'll go ahead and do the other side. What could possibly go wrong with a
    simple diode I hear you ask? I've been an engineer too long and seen too
    many instances of the impossible happening to ever ask that question "what
    could possibly go wrong?"

    Dan K, Mar 17, 2008
  4. Mike Marlow

    mykey Guest

    the voltage drop through a diode
    will be about 1 V or less and install
    them in series until you get 12 volts.
    measure across the filament for 12 Volts.
    or use a Zeener 10W diode
    for example a 1.5V zeener will give
    you almost exactly what you need,
    they come in all different available
    voltages, such as 2 volt, 1.5 Volt,
    1.8 volt....
    some are stud mount for more secure
    mounting. that would be recommended.
    OK make sure it's an isolated stud.
    Yes any electrical circuit has a voltage
    drop, thats normal.
    Well halogen lights are well known for
    short life, over-voltage won't help that's
    for sure. But a good alternator shop can
    adjust the output voltage easily.
    you might as well install diodes to get
    12volts on both sides now.
    you are right, over-voltage will fry the
    filaments, no question.
    That's funny, the headlights on my accent
    have lasted 70,000 miles, 5 years. why
    won't Hyundai do something to fix the
    bug? Is there Xenon replacements?
    mykey, Mar 17, 2008
  5. Mike Marlow

    mykey Guest

    OK wait a second, how many watts is the bulb?
    Low AND high beam...
    let me know and I'll try to help here.
    using load and voltage we could calculate the
    watts load on the diode. You have apparently
    overheated the diode. But don't forget there are
    industrial diodes that can take the heat, heat sink
    included, chassis mount or stud mount.
    You have a good idea, just need better hardware.
    Also industrial voltage regulators. cheap if
    the bulbs go out every 3 months!
    Interesting project, can't wait to see how it turns out.
    mykey, Mar 17, 2008
  6. Mike Marlow

    Darby OGill Guest


    pardon my question, if it has been answered in earier posts, but is the
    voltage at the lamp known to be abnormal-too high? If every other of the
    1000's of like cars and bulbs are at that figure, maybe heat or vibration or
    some other thing more unique to your vehicle is the culprit ? Good luck !

    (as an aside, I've changed one headlamp in 2 yrs/60k mi, 06 sonata)
    Darby OGill, Mar 17, 2008
  7. Mike Marlow

    Dan K Guest

    That's just it, nobody knows for sure what the problem is. There are a lot
    of Hyundai cars out there with H7 bulbs that go through them like popcorn.
    I own two XG350's (his and hers) that both have had the alternator replaced
    once, so that's 4 alternators and the H7 bulbs seem to last 6 months if we
    are REAL lucky. So if its an over voltage problem, I suspect its a design
    flaw and not due to a failed piece of hardware. I'm use to the old cars
    that needed a new set of headlights once in their entire life (of coarse
    that was only 100,000 miles)...You never thought to buy a spare
    headlight...with the H7's I wouldn't dream of going anywhere without a
    couple spare bulbs in the trunk!

    So, anyway, this is a first attempt to see if a lower voltage will fix the

    Dan K, Mar 17, 2008
  8. Mike Marlow

    Vic Garcia Guest

    One thing to remember, while we usually use the term 12V battery, it
    really means 12.6V, no-load voltage battery. That's the normal voltage
    for a fully charged lead-acid battery under NO-load condition.
    With the car running, the alternator has to provide a higher voltage to
    recharge the battery, so the voltage should be 14.4V plus or minus 0.4V
    depending of the load.
    The bulbs manufacturers take this into account.
    For what you measure, your car is at the low-level of the range, so
    over-voltage does NOT seem to be the problem.
    Have you tried another brand of bulbs ???.
    BTW, Elantra GTS 02, Santa Fe LX 03, both still original lamps .... so
    no, I do not have any problem.
    Vic Garcia, Mar 17, 2008
  9. Mike Marlow

    hyundaitech Guest

    The voltage is okay in this case (14.2V). That's normal alternator output.
    In my opinion, the culprit is the H7 bulb itself. For whatever reason, it
    seems to burn out quickly.

    Dan's theory, however, is that if we reduce the voltage to the bulb but
    still keep it high enough for proper lighting, bulb life may be
    significantly increased. Hopefully, he'll report back when he's been able
    to conclude something.
    hyundaitech, Mar 17, 2008
  10. Mike Marlow

    jusme Guest

    I used to have these halogen headlight bulbs burn out very rapidly,
    until I learned that you cannot touch them with your bare hands when
    you are installing them, as the natural oils on your fingers will
    cause them to fail prematurely. I started wearing cotton pallsbearer
    gloves when I change my headlight bulbs and the early failure problems
    went away completely.

    My .02 cents, ymmv

    jusme, Mar 17, 2008
  11. Mike Marlow

    B Crawford Guest

    Although I never checked the voltages across the headlights on my 2001
    XG300, the 14.4V or so to the battery on charging sounds like mine.
    That said I still have the original battery & I have never yet, touch wood,
    changed a headlight on that car! The only bulbs to burn out have been the
    licence plate marker & the glove box light. The other consideration here is
    my car is Canadian & has always had daytime running lights on (all lights on
    but reduced intensity during day).
    B Crawford, Mar 18, 2008
  12. Mike Marlow

    John Guest

    For what its worth I work in medical electronics and I never buy any lamp or
    battery from a certain country. No names mentioned but I,m sure you could
    guess.(not Korea)
    I,ve done comparative studies of different brands to
    justify it. Even Panasonics who used to make excellent batteries shifted
    manufacturing to this country and now they are just as bad as the others.
    John, Mar 18, 2008
  13. Mike Marlow

    Mike Marlow Guest

    This is a very well known issue with any high temp bulb. Perhaps there are
    people who still don't know about it and are handling their bulbs
    incorrectly, but the real problem is that for the people who do know about
    it, the problems with H7 bulbs persist. Your bulbs will fail also, unless
    you've found a brand that is a bit longer-lived, in which case we'd all sure
    like to know about that.
    Mike Marlow, Mar 18, 2008
  14. Mike Marlow

    Mike Marlow Guest

    Well..... that all by itself is useless, unless you tell us where you have
    found good bulbs.
    Mike Marlow, Mar 18, 2008
  15. FWIW, I've had Hella Optilux XP bulbs in my Elantra for over 8 months
    now, which is longer than any other bulb I've tried.
    Brian Nystrom, Mar 22, 2008
  16. Mike Marlow

    Mike Marlow Guest

    Good input Brian. Thanks.
    Mike Marlow, Mar 22, 2008
  17. I'll try to keep everyone updated on these bulbs. So far, so good.
    Brian Nystrom, Mar 23, 2008
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