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Bulb Protection

Discussion in 'LEDs and Optoelectronics' started by bharathmanogna, Dec 9, 2011.

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  1. bharathmanogna

    bharathmanogna

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    Dec 9, 2011
    Hi,
    I have a bike which uses a 12V 35/35W Bulb(1 gnd and two supply points one for High beam other for low beam) ,the supply (12V) is generated by a static plate and a rotor(AC Voltage basically) which is rectified to deliver 12V output.recently i have been facing this issue of Bulb damage(2 times),every time i replace the bulb it functions properly for some time (while functioning i have noticed sudden increase in brightness several times) and then goes bad(especially when switching between high beam and low beam).i presume the rectifier section is at fault , i am reluctant to opt for replacing the rectifier section as it costs more.so i thought i might use a NTC resistor in parallel with the Bulb so that it suppresses the current spike,i also thought of using a TVS diode.i need some assistance in calculating the values of an NTC or TVS, as i am not familiar with the parameters that need to be considered for these component selection.please provide your suggestions and views.....
     
  2. davelectronic

    davelectronic

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    Dec 13, 2010
    Hi bharathmanogna.
    Welcome to the forum.
    Thats odd the voltage does not need to be DC i dont think, but if thats the way its designed then thats how it is, mind you saying that i loved my bikes once, to ill to ride now days, yes mine where DC perhaps it gives better efficiency to the lights, ie no flicker etc.
    If you go from low beam to high i think the voltage changes, or is the bulbs element finer meaning brighter, less power to make it bright. Any way if the voltage is stepped up on high beam, or kept lower for low beam a NTC might run into rating issues, as to its resistance when warmed up affecting brightness, and i am not sure about the diode idea, could the switch not be at fault, how about a modest capacitor and resistor to make the transition from low to high beam smoother. :)
     
  3. duke37

    duke37

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    Jan 9, 2011
    If the bulbs are blowing, you are peddling your bike too fast!

    The rectifier may not be just a rectifier but also a voltage regulator. Get a circuit diagram to check. If it is a regulator, it will need an earth reference, check for bad connections to the frame.
     
  4. davelectronic

    davelectronic

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    Dec 13, 2010
    I thought motor bike, peddling bicycle, 35 watt lamp, or is it one of the electric type cycles you see about ? :)
     
  5. bharathmanogna

    bharathmanogna

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    Dec 9, 2011
    Dave its a motor vehicle its name is bajaj pulsar ..and the three terminal(1-gnd 2-high 3-low .connection at a time may be between 1-2 (high) or 1-3(low)) bulb is rated 35/35W i believe that it means 32 watts for both high beam and low beam at 12V that why i was thinking of an NTC.and regarding the switch are you suggesting that switching transients are causing the damage if so would placing an RC network in series to both the terminals 2 and 3 solve the problem???
     
  6. bharathmanogna

    bharathmanogna

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    Dec 9, 2011
    .

    thanks duke ,it has a regulator too,but would the reference earth be connected to the chassis(metal body of the bike)?? can you please explain how this might affect the voltage regulation. and its not a peddle bike its a motor vehicle (bajaj pulsar)
     
  7. duke37

    duke37

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    Jan 9, 2011
    I am not familiar with motor cycle electrics but assume they are similar to car electrics. The alternator will produce a voltage proportional to its rotational speed and will need some form of control to keep it within bounds. There will be two output connections, one will go to the switches and one will go to the frame of the bike. At the light, one wire will come from the switch and the other connection will be the frame.

    In England where the weather is often wet, corrosion of contacts is common and so voltage drops occur in the most unexpected of places and give strange effects. If you have a regulator set to 12V but there is a voltage drop on the frame connection of say 6V, then you will get an output of 18V and bye bye bulb.

    You have an intermittent problem so I would think that the parts are working but there is an intermittent, possibly loose, earth connection.

    Can you get a circuit?
     
  8. duke37

    duke37

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    Jan 9, 2011
    I have done a Google and see that the Pulsar has had electrical problems. There is a circuit diagran on the web and it shows a B/Y (black/yellow?) wire from the regulator to frame. This is the one I would look at first.

    Best of luck.
     
  9. davelectronic

    davelectronic

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    Dec 13, 2010
    I have totally rewired a motor bike once, to cut a long story short i was in a head on with a taxi, could have killed me, i was lucky, not the same for my bike, an old sypmson made in the former Yugoslavia, any way i needed a second hand frame and built up from scratch, i also had some electrical issues at the time, got there in the end.

    I think its probably as Duke said a wiring fault, look at it like this, the machine was not designed with an NTC or a special RC network, though there may be the latter, its worth using a meter see if you can find the fault, it may take a while, but its probably going to be a defective component or wiring fault, while the NTC / RC network might cure blowing bulbs, its really only masking the real fault, and sooner or later another problem will arise.

    Go down Dukes road, i think thats the way to, i am no expert, but what he says makes sense. :)
     
  10. bharathmanogna

    bharathmanogna

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    Dec 9, 2011
    hi duke37 i checked out the regulators ground connection it is intact(no corrosion or loose connection)and regarding you comment "you have a regulator set to 12V but there is a voltage drop on the frame connection of say 6V, then you will get an output of 18V and bye bye bulb" i did some experimentation with a new bulb which has the same ratings 12V 35/35W i connected it to a 30/12V 100mA DC power supply(aplab) in separate iterations and noticed that the filament did not explode when i connected it to 30V,100mA so i presume no matter what is the voltage, current is the damaging factor.i also connected it to a 5V,2A even then no damage (but the intensity of light was more for the same current( say 100mA) at higher voltages(30V)) so i thought of two solutions
    1)connect a bulb with higher rating 12V 55/60W(the bulb will of course not glow to its maximum potential but may not get damaged due to high currents).
    2)use a TVS diode rated for 12V to bypass the bulb in case of over currents.

    express your opinion about this......
     
    Last edited: Dec 11, 2011
  11. duke37

    duke37

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    Jan 9, 2011
    Do not get mixed up between voltage and current. A 12V 35W bulb will take about 3A., if you do not have the ability to supply 3A then the voltage will be lower than you think.

    With your 100mA supply, the voltage would be very low.
    With your 5V supply the voltage is low and the bulb MAY be taking more than the rated 2A. (The bulb resistance goes down as the voltage goes down)

    You only get high currents through the bulb if you supply high voltages.
    1. Using a more powerful bulb may overstretch the regulator.
    2. A TVS diode will suppress short transients but will overheat if the overvoltage persists. You will need to go above 12V to give some leeway. The diode passes current when the voltage exceeds its rating, it does not control current.

    Do as Dave says and get some voltage measurements otherwise you are working in the dark, paricularly if the bulb has blown!

    Vibration is a big killer for filament bulbs but if the light became very bright before failure, then this is unlikely to be the cause.
     
  12. bharathmanogna

    bharathmanogna

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    Dec 9, 2011
    Hi Duke , please forgive me for repetetively reasoning in the same manner,but i am really a bit confused :confused:now by looking at the above statements of yours, as i think they may be contradicting , can you please describe a bit more on how the regulator is overstretched(say a regulator can deliver 2A at 12V even if i connect a bulb of 12V 55/60W which require about 4.5/5A then only the bulb will not be glowing to its optimum capacity how would this affect the regulator?)and what adverse effectes it may have on the circuit.

    and regarding the TVS , i will definetely consider your suggestion of providing some leeway (may be somwhere greater than and close to 12V). i think i didn't communicate my view properly about connecting the TVS, i was thinking of connecting the TVS in Parallel to the Bulb so that it can bypass the bulb in case of overcurrents.....

    i am also looking into getting some voltage measurements of the bulb circuitry,but until that time we may have to just rely on theoratical presumptions:)
     
  13. duke37

    duke37

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    Jan 9, 2011
    A device can be designed to supply a certain current, if you take more current than it is intended for, then it may fail due to overheating. A sling used with a crane is rated at a certain maximum tension. If this is exeeded the sling may break.
    Your regulator can happily supply 3A but may overheat if asked to supply more than this. It may be protected by internal current limit or over temperature limit but I wouldn't bet on it. Car alternators have current limitation by leakage inductance designed in, yours will probably be the same but you do not want to melt any wires due to excessive current.

    Laboratory power supplies can have a voltage and current control to set the output. If the current draw is more than the current setting, then the voltage is reduced. In the motor bike case, there may be no current limit other than melted metal.

    The TVS should be connected as you say but does not bypass the bulb in the case of overcurrent, it passes current if there is overvoltage. You would not control the speed of your bike by using maximum throttle and applying the brake to get rid of excess energy. This would be expensive in fuel and the brakes would overheat.
     
  14. bharathmanogna

    bharathmanogna

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    Dec 9, 2011
    are you reffering to 55/65W bulb when you say "using maximum throttle" .

    and also my confusion arose from reading a datasheet on an LED which indicates an minimum current limit to acheive the rated luminous intensity,if current is lesser than that the led will glow but not at the rated luminous intensity , i just wanted you to know this because the 12V 55/60W bulb which i am thinking of replacing requires 4.5/5A to obtain its peak luminous intensity .my understanding is it does not draw 4.5/5A to work ,it works on whatever current it derives from the regulator and glows with relative luminous intensity.i still fail to see how it would overload the regulator .since my case includes an intermittent spikes of overcurrents ,the 12V 55/60W bulb must be capable of handling this.

    i think if i connect 12V 55/60W bulb ,in normal conditions when the regulator is outputting 12V,3A the bulb will glow but not at its maximum capable luminous intensity, when overcurrents occur (say some x value above 3A and below 4.5/5A,if i am lucky) this bulb will be operating as per the ratings... or am i foolishly missing something ,please comment...
     
    Last edited: Dec 12, 2011
  15. duke37

    duke37

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    Jan 9, 2011
    You are still confused between current and voltage. A led outputs an amount of light roughly proportional to the CURRENT, the voltage changes little, it is not similar to a bulb.
    A bulb works by heating a wire and on low voltage, the wire is not hot and gives out no light. Efficiency rises as voltage (and current) rises until the wire melts.
    If the alternator/regulator are sized for 3A and you try to draw more than this then bad things can happen. A 60W bulb will take 5A.
    The regulator is set to produce 12 to 14V and if it is producing much more than this and you then limit the output voltage with a TVS the current will rise to a high level. This may be all right with a short transient but not for long.

    You must monitor the voltage and make sure the regulator is earthed and replace it if faulty.
     
  16. electro_pa

    electro_pa

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    Aug 14, 2011
    Hi bharathmanogna,
    Bulbs will fail from both excess voltage and current.
    Your test with 30V/100mA supply did no damage, as that power supply cannot supply enough energy to make the filament glow even dimly, I suspect. A bigger current supply, will do damage at 30 volts!
    Most likely you have lost control of the voltage from the regulator, so the alternator output is too much for the bulb. Maybe regulator is faulty. Can you test the voltage with multimeter, while engine is revved?
    If regulator does not limit voltage to less than 14 volts, bulbs will fail often.
     
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