Instant Full Brightness headlights?

Discussion in 'FAQs' started by AN_Modeller, Jun 27, 2006.

  1. AN_Modeller

    AN_Modeller New Member

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    Hi all, sorry for this.. another headlight squestion. i have been looking around a fair bit to try and solve my answer, but i only get mixed answers. what i would like to do is have it so my headlights come on instantly, at full brightness when the train is only getting a little bit of current, i want to have a power source in the loco for the headlights, (im thinking some of those small 3v button lights) and i want it so somehow there is some sort of electronic switch that automatically turns the headlight on when current is detected in one of the rails. i was thinking maybe a transistor of some sort, but i am unfrmiliar with these.
    Any input welcome, Thanks

    *Note, i understand this is easy with DCC, however i cannot currently afford this with buying decoders and all. so for now i want the above setup ^

    Thanks
  2. ezdays

    ezdays Out AZ way

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    First of all, welcome to the Gauge.

    In order for your lights to light full brightness when running at any speed, especially at startup, you will need a constant voltage source. You will not get that from the tracks so you will need another source such as a battery. The battery will need to provide enough power to run your light for a period of time. You may not get that with a button battery, and they're not rechargable. Now, you could use a transistor to trigger that source, but even then you will need the rail voltage to reach some pre-determined level before that would turn on the transistor. It takes power and at low voltage levels you'd have to draw a lot of current to do this. There are current-sensitive relays, they're expensive and still requires power.

    This is just speculation on my part based on what I know, so maybe someone here has done this. If so, let's see what they have to say.
  3. AN_Modeller

    AN_Modeller New Member

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    ok, i was thinkin more than 1 button battery, (maybe 3) that will be trial and error. the only think that is holding me back is a way to make it come on autimatically with the train, and off again,
  4. ezdays

    ezdays Out AZ way

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    I'm not saying it can't be done, you could trigger the trasistor with say one volt, but you'd have to limit the current to it as the voltage increased. Someone here surely will know of a circuit that will do the job, I haven't done it and I'd have to design something from scratch. I hate to reinvent the wheel though..:D

    I would still consider a different battery. Button cells don't last that long, they are designed for very low current drain for long periods and they are expensive to replace. I would think about a couple of AAA, cheap enough and you can use the rechargable ones.
  5. AN_Modeller

    AN_Modeller New Member

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    yeh, about the batterys, its for HO, so, space is an issue here, but modifications are possible, at first i thaught this would be easy, but now ive hit a wall, basically, i want a light that comes on at full brightness as soon as the train gets current, any design welcome that'll fit in an HO loco, and automatically comes on and off.
  6. MasonJar

    MasonJar It's not rocket surgery

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    I think what you are looking for is called "constant intensity lighting" or something along those lines. It is a relatively common thing with DC-powered layouts. It involves some electronics that ensure the light(s) use the first power available. The lights will only go out when the powerpack/throttle is set to zero. However, if you are used to the engines moving out at a very low setting, this will of course change that...

    Try a google for "constant intensity lighting HO scale" or something like that. If you strike out, I will try to wade through my collection of bookmarks... :rolleyes: ;) :D

    Andrew
  7. MasonJar

    MasonJar It's not rocket surgery

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  8. ezdays

    ezdays Out AZ way

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    There's one other solution I can think of offhand. Using a low voltage lamp, say 1.5 volts, and a 1.5 volt zener and a voltage-dropping resistor, you could essentally use the rail voltage to turn the light on full whenever the rail voltage reached 1.5 volts or higher. Anything over that, and the resistor would dissapate the power. A simple circuit and batteries not required.

    Just another thought.:D
  9. Woodie

    Woodie Active Member

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    AN Modeller,

    I note your Australian National G Class?? is it? Powerline? Most of the later Australian models (Powerline, Austrains etc) have probably the best constant brightness lighting you'll get when using DC. That's why most use 1.5V DC globes, not 12V DC globes. They have a "contant brightness" circuitry built in, with diodes for directional capability. Forget Lima. You'll need to build our own.

    Found this website that lists some parts etc (from Dick Smith) and uses LEDs instead of globes.

    http://www.pollensoftware.com/railroad/index.html

    Also this thread on the rail-page forum.

    http://www.railpage.com.au/f-t11304123-0-asc-s0.htm

    See what ya reckon.

    However, it costs it out at about $10 per light (each end of loco), when you can get a basic DCC decoder for $20, that does all what you want and more. But you need the DCC command station as well, of course.
  10. jim currie

    jim currie Active Member

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    :wave: welcome to the gauge:wave: I use LED's for headlights and on most of my loco's they come on bright ( not full but bright) before the locos start to move as most LED's need only 2.7 to 3 volts.
  11. 60103

    60103 Pooh Bah

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    One way is to put 2 diodes (rectifier) in series with the motor -- one in each direction, then wire a 1.5V bulb with one lead each side of the diodes. The diodes create a 1.5V drop (but no more) which powers the light. Using a LED will give you directional lighting. The lights will come on at full brightness at 1.5V of power, then the additional power will eventually start the motor. Your loco will not get more than 10.5V at maximum.
    (I' seem to remember two diodes in series. Comments?)
  12. AN_Modeller

    AN_Modeller New Member

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    Could you please draw a bit of a diagram? and what diodes u recommend?
  13. Ray Marinaccio

    Ray Marinaccio Active Member

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    Here's a link to a diagram of a constant lighting circuit.
    http://www.mrollins.com/constant.html
    I would be interested in a battery powered circuit that is turned on by and charged by the track voltage to light passenger cars.
    A simple delay circuit could be added (capacitor and resister) to keep the transistor energized over dirty track.
  14. MasonJar

    MasonJar It's not rocket surgery

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    Ray,

    One of the guys from the local NMRA group has a little (tiny!) Mack railbus that he put a decoder in. Since there are not a lot of wheels to pick up, and the railbus is very lightweight (due to the full interior), he created an uninterruptable power supply for the decoder using some sort of capacitor that is "recharged" by track power. Carries the little bus across dirty spots without stopping or resetting...

    Andrew
  15. Ray Marinaccio

    Ray Marinaccio Active Member

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    That's a possible solution Andrew.
    A bridge rectifier, memory backup capacitor and ultra bright white LEDs.
  16. ezdays

    ezdays Out AZ way

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    Ray,

    It seems like maybe an isolation diode would do if you're not reversing polarity. Otherwise a bridge would be required. Still, there's a need to regulate the voltage somehow.

    That circuit with those diodes doesn't impress me. This guy is using two diode drops to regulate the 1.5 volts to the lamp and is using the motor as a sink for the excess voltage. That's going to reduce the DC to the motor and I don't think that's a good way to do things. I would still go with a zener and a dropping resistor and probably use LEDs. You'd need two circuits, one for each direction for DC.
  17. Ray Marinaccio

    Ray Marinaccio Active Member

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    Don,
    I have a zener diode lighting circuit similar to the one you described. It does work nicely. I do have to change the value of the resister as it gets hot when running at full throttle.
    There is a current regulator (LM334Z) that I want to try to light LEDs with. All that is required is the regulator, a resistor to set the current and the LED.
    http://www.pollensoftware.com/railroad/index.html
  18. ezdays

    ezdays Out AZ way

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    Ray,

    That's a good choice, especially in the smaller package. If the center leg is tied to common, then it will put out a regulated 1.5 volts. You can change that with two resistors and choose any voltage you want, as long as it is 1.5 volts lower than the input. Again, on a DC circuit where the polarity of the rail voltage can change, I would use a blocking diode to keep the polarity from reversing, or a full-wave bridge to keep it positive regardless. Then the diode drops come into play. :rolleyes: