Proto 2000 and White LED Headlights

I'd like to put a White LED headlight in my FA1 Proto2000 locomotive. The circuit board provides 1.5 volts for a headlight, but the White LEDs I have want 3 volts.

How can I go about doing this? Are there reasonable sources for 1.5V White LEDs, or does someone make an inexpensive kit to support this?

Puckdropper

Reply to
Puckdropper
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Puckdropper skriver:

You can not get 1,5volt white LED's.

How is the 1,5 volts created ? I guess that it is diodes in series with the motor, adding more diodes will cause a higher voltage drop and higher voltage for your diodes.

Du you run digital or analog ?

Klaus

Reply to
Klaus D. Mikkelsen

Are you saying the white LED you have will not conduct or the light is not bright enough for you. I have white LEDs that will light with 1-1/2 volts.

Reply to
Jon Miller

"Jon Miller" wrote in news: snipped-for-privacy@corp.supernews.com:

The LED will not visibly light up. I know it works, as I've tested it in a different circuit.

Puckdropper

Reply to
Puckdropper

Well as someone suggested you can add some more diodes or go to DCC !

Reply to
Jon Miller

Puckdropper spake thus:

Yes, there is another, better way to go: use a current regulator.

This is actually a superior way to drive LEDs, as it limits the current through the device. The current reg is a cheap, small-package semiconductor. You also need a small resistor. I can't recall offhand what type it is; I have a bunch here, but don't want to get up to check just now. I think others here can supply that info if I don't get a round tuit soon.

I intalled one in my Bachmann Spectrum Mountain, and it works fine. Easy to put in.

Reply to
David Nebenzahl

Puckdropper wrote:

You should not think of LED's as having a voltage,like incandescent lamps do. Think of them as semiconductor diodes that just happen to emit light when they conduct. Once a diode is forward biased enough to conduct at all, it switches ON and looks like a closed switch. A closed switch connected from plus to minus of a voltage source is a short circuit. It conducts and conducts until something lets go, a fuse, the diode itself, an over current protection circuit in your power pak. You have to have a separate resistor in series with a LED to limit the current to 20 milliamps (mA) or less. Most ordinary LED's will glow brightly with 20 mA and glow brightly enough for model railroading purposes with as little as 10 mA. Plain old silicon diodes need 0.7 VDC of forward bias to switch them on. LED's need a bit more, anything from 1.2 to 3.something, depending upon the individual diode. But once ON, the LED MUST have a resistor in series with it to avoid destruction of the LED. For your Proto FA-1's (nice locomotive, I have an ABBA set of FA2's) you want a 560 ohm resistor in series with each LED. That will give full brightness at full speed (12 volts) and dimmer as you reduce voltage. That's the bare minimum to make the LED's work at all. To compute the LED series resistor, you can ignore the LED forward bias voltage. Just divide your source voltage by 0.02 amps to get the needed resistance. This will give a resistor value close enough for model railroading work. Then you have to get the LED polarity right, so the LED is forward biased when the locomotive is moving forward, otherwise the LED will be reverse biased (dark) when going ahead and forward biased (ON) when going in reverse. LED's don't like reverse bias. Many of them will only withstand 6 volts reverse bias, which means you need to protect the LED with an ordinary diode in series to take the reverse bias. Ordinary diodes will take 50 to 500 volts reverse, much more than they will ever see on a model railroad track. For extra credit, you can go for a constant brightness circuit that gives a nice bright headlamp for all track voltages high enough to move the locomotive. This needs a full wave bridge rectifier, and a current limiter circuit. The current limiter can be as simple as a single transistor, or some IC regulator chip. I've done tings like this, using parts from my electronic scrapbox, each circuit is a little bit different depending upon what parts I happen to have at the moment.

I used to have a wonderful book by Peter Thorne with all the model railroading circuits you could ask for, but it seems to be missing in action right now. There are some railroading web sites with circuits as well.

Final thought. I prefer incandescent lamps for headlights because the color is realistic. I have yet to see a LED headlamp that wasn't terribly blue.

David Starr

Reply to
David Starr

Agreed. Or gold. Just awful.

Reply to
<nospam

snipped-for-privacy@sbcglobal.net spake thus:

Gold might actually be better to simulate oil lamps on old steam locos. But agreed, blue is pretty hideous. I try to ignore it on my LED-equipped loco.

Reply to
David Nebenzahl

in article 45c4ffdf$0$6836$ snipped-for-privacy@news.adtechcomputers.com, David Nebenzahl at snipped-for-privacy@but.us.chickens wrote on 2/3/07 1:38 PM:

For "white" leds in a variety of temperatures, go to Richmond Controls:

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I have also purchased "warm white" leds from ledtronics in the past, but be aware that many of their products have minimum order quantities:

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They have domed and cylindrical (flat on the front) leds in 3mm and 5mm sizes; the cyl. Ones are almost the right size just to put into a headlight housing directly with no lens. But their minimums are 100 units at 90 cents each. Sigh...

Loys Toys also sells the Richmond control golden and sunny white leds:

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Reply to
Edward A. Oates

David Nebenzahl skriver:

LM317

Klaus

Reply to
Klaus D. Mikkelsen

Klaus D. Mikkelsen spake thus:

No, that's not it: the 317 is a voltage regulator. I'm talking about a

*current* regulator (constant current source): different critter.

It's the LM334Z:

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They come in a TO-92 package (little bitty transistor size), so fit nicely in any loco.

Reply to
David Nebenzahl

David Nebenzahl skriver:

Belive Me, the LM317 is both voltage and current regualtor, for using it at current regulator it only requires one resistor, just like here:

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Just like the LM317

Klaus

Reply to
Klaus D. Mikkelsen

Klaus D. Mikkelsen spake thus:

Nope, the 317 is in the larger TO-220 package (unless you get the surface-mount varieties). That's the one with the heat-sink tab.

Reply to
David Nebenzahl

David Nebenzahl skriver:

Very odd, what is the the LM317 in to92 housing I have in My garage ?

Try to google LM317 to92

Klaus

Reply to
Klaus D. Mikkelsen

Snip:

I've been able to get good color using filters or transparent paint. To me though, all the LEDs I have seen don't look realistic -- just a pool of bright light where incandescent lamps have a realistic point of light source. It might be possible to expose the point of light on an LED by trimming the lens back -- haven't tried it. I'd think the LED point of light would be a bit large to be realistic in most situations.

Jim Bright

Reply to
Jim Bright

Jim Bright spake thus:

You bring up an interesting point. Yes, you can trim LEDs back: I've done it by grinding them with a Dremel, very carefully; just be sure not to get too close to the active element, which you can easily see (under magnification). And it does seem to improve the way they look.

After grinding, I polished up the end so the light wouldn't be diffused.

Reply to
David Nebenzahl

Klaus D. Mikkelsen spake thus:

Odd indeed: National Semicircular* doesn't list that package in their availability chart:

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I'll take your word that you have one in your garage, though.

  • Someone I knew who used to work @ National called it that, long time ago.
Reply to
David Nebenzahl

You probably want to make the estimated voltage a bit higher, depending on the power source. Some of the pulsed DC power packs put out 20 volts at the peak of the spike.

For tail lights in a caboose, I just used rechargable batteries. This keeps the lights on even when the motor power is cut. It also prevents any reverse bias problems, pulse problems, etc. In fact, I got away without even using a resistor. The voltage drop of the LEDs was so close to the battery voltage (battery voltage is 1.2 volts per cell, or 2.4 total and the LED voltage is about 2.3 volts) I just used some *very* small gauge wire (electric magnet wire for small motor armatures) and the distance between the battery box and the LEDs was enough to create the resistance I needed.

In this particular case, because the voltage drop across the LEDs and the power supply is so close, I did want to take into account the LEDs. In my example, voltage supply = 2.4 v, LEDs = 2.3 v. 2.4v - 2.3v = 0.1v is the actual voltage that would be across the resistor. The resistance requied is 0.1 v / 0.02 a = 5 ohms resistance needed. 5 ohms resistance is easy enough to create with enough small gauge wire.

The magnet wire that I used not only has very high resistance, but because it is so small in diameter it looks like HO scale wire. I ran it outside the caboose to the marker light, and it looks just like an HO scale wire powering the light as it would in real life.

One of the very good things about LEDs is the very low power consumption. Thus, even the very small batteries used in my caboose will last long enough for my needs before needing a recharge. If you have the space, you might want to consider the battery power route just because it means a constant brightness constantly on headlight no matter what else (including a power failure!) happens.

If you decide to go the bridge rectifier route, if you have the space consider adding a low voltage rated but fairly high value capacitor across the output of the bridge rectifier. This will keep the LED lit for a brief period even if the power is completely turned off to the locomotive.

Reply to
gl4316

David Nebenzahl skriver:

Perhaps they have removed it from production. At least Texas makes it as TL317

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Klaus

Reply to
Klaus D. Mikkelsen

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