This might interest some who like using LED's.
http://www.trainelectronics.com/LED_Articles_2007/LED_104/index.htm
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Good stuff. If there's room, this eliminates all guesswork, and the LED will be fine no matter if your track voltage is 12V or 18V. Should work in DC, once the track voltage gets above the minimum for the LED plus whatever drop the constant current source eats up. For DCC, you'd use the function wire plus blue wire as the input source. Blue is positive.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I wonder if this will work with half-wave power straight off the track? Since it's steady once a certain voltage is reached, if it does it would be ideal for things like cab lights and firebox flicker which can stay on all the time, thus you don't need to use up functions to turn on and off applications that'll be left on anyway.
Mike Lehman
Urbana, IL
The CL2N3-G is DC only, so you'd also need a rectifier and filter to run it off track power.
'half wave' usually refers to using the function lead and one rail pickup instead of the functiona nd blue wire, so it still needs a function lead.
Randy,
OK, I can see needing the rectifier with the CL2N3-G if it needs straight DC.
If you need on-off or other control over the attached LED, yes, you will need to use a function to use half-wave for that. But if it's a constant-on circuit, like firebox flicker or a cab light, there's no need to use a function for it. I added headlights to a Walthers wedge plow this way, just the resistor and the LED. It's hooked directly to DCC track power via wipers. It's always on when on the track, but doesn't need a decoder to work.
If a bridge rectifier is needed with the CL2N3-G, then it's probably cheaper to just do this with an ordinary resistor, of course.
I was just pointing out that the term "half wave" when applied to DCC lighting means using the rail as the common and the function wire, as opposed to the normal way of using the blue as the + common and the function wire.
If indeed the light will always be on, you can wire it right to the track - but a regular LED should have either another one or a regualr diode hooked up anti-parallel to protect it from too much reverse voltage - white LEDs in particualrly cannot stand much reverse voltage, even if it is current limited by the resistor.
For firebox flicker, might as well use a function, to make a flicker you would need a circuit, which will likely require DC, so rectifier again.. plus some decoders can vary the firebox flicker based on the load (using BEMF to sense it) so you get brighter/more flicker depending on how hard the loco is working.
Uh, yes, gotta still have the resistor even without the LED being in circuit with the decoder to use power direct from the track. Always good to emphasize that. I've blown a LED or two in my time just forgetting that tiny detail inadvertently.
On the firebox flicker, I've got some red "tower" LEDs that supposedly have self-contained flicker, maybe just a variation on the LEDs we're discussing here. I haven't had the time to try them, but a buddy of mine, Laurie McLean MMR, does them up like this. True, you won't get simulated variance according to the load on the engine, but works OK if you're easily wowed like me by them just flashing down under there at all.
mlehman Randy, Uh, yes, gotta still have the resistor even without the LED being in circuit with the decoder to use power direct from the track...
Uh, yes, gotta still have the resistor even without the LED being in circuit with the decoder to use power direct from the track...
I htink you missed Randy's point, I believe he was pointing out that in addition to the resistor you should have an additional regular DIODE to protect the LED from reverse voltage, something many people neglect since an LED is a diode. LED's are not designed to withstand high reverse voltages, and while you may get away without the diode, you also may drastically shorten the life of the LED.
mlehman ... On the firebox flicker, I've got some red "tower" LEDs that supposedly have self-contained flicker, maybe just a variation on the LEDs we're discussing here...
...
On the firebox flicker, I've got some red "tower" LEDs that supposedly have self-contained flicker, maybe just a variation on the LEDs we're discussing here...
You might want to give some of these a try:
http://evilmadscience.com/component/content/article/189
They are supposaed to simulate a candle flicker. Here is a video showing one of them:
http://www.youtube.com/watch?v=753-lkao8l0
CSX Robert mlehman Randy, Uh, yes, gotta still have the resistor even without the LED being in circuit with the decoder to use power direct from the track... I htink you missed Randy's point, I believe he was pointing out that in addition to the resistor you should have an additional regular DIODE to protect the LED from reverse voltage, something many people neglect since an LED is a diode. LED's are not designed to withstand high reverse voltages, and while you may get away without the diode, you also may drastically shorten the life of the LED. SNIP
SNIP
Wouldn't the bridge rectifier provide protection in lieu of another diode in the case of the installswith this new voltage regulator?
For my simple constant lighting circuits, I tend to use plenty of resistance with my LED installs anyway, because I prefer a dimmer headlight in most cases, so that may be helping dampen voltage spikes. I also have DCC track voltage turned down to 12.5 volts.
I've only applied these in a couple of installs, but noticed no shortened life issues. The plow doesn't see much track time, so not a good test there. The other is a recycled license plate lamp assembly I use for a light source in a remote staging area. It's obviously happy at anything from 12.5 to 14+ volts. Also has some onboard resistors embedded in resin, maybe there's a diode hiding in there, too? so again not a good test.
Yes, the bridge rectifier would provide the protection against reverse voltage, the extra diode is for when the LED is wired straight to track power. Also, if you have two LED's wired back-to-back and sharing one resistor(such as directional lighting on DC), then you don't need the extra diodes.
We're getting complictaed here, and I didn;t mean to. My actual point was that the term "half wave" for DCC lighting means it still uses a function lead.
AN LED wired tot he track with a bridge rectifier needs a resistor, nothing more. But if you are going to fo that, it takes less space to just put another diode anti-parallel with the LED and use the resistor, no bridge rectifier needed.
What we have is 4 ways to hook things up:
LED, didoe, resistor directly to the track pickups
bridge rectifier to track pickups, LED and resistor to DC terminals of bridge
LED and resistor with one side to function wire on decoder, other side to either track pickup
LED and resistor betweeb decoder function wire and decoder blue wire.
The first two will be on any time the track is powered, the second two use a function output ont he decoder to control the LED.
And of course some decoders come with the resistor already included so you might not need to add one.
Why not just an LED and resistor for direct track power on a DCC system?
Richard
Richard,
That's exactly what I'm doing when I was describing my snowplow install wiring. No protective diodes in mine, just the LED and resistor. YMMV is probably at work here. I've not had any issue with them like this, but I suppose there could be was the caution.
mlehman Richard, That's exactly what I'm doing when I was describing my snowplow install wiring. No protective diodes in mine, just the LED and resistor. YMMV is probably at work here. I've not had any issue with them like this, but I suppose there could be was the caution.
You're likely right since it's "pulsing" vs constant. I used to avoid doing it this way for that reason, but it's so simple and the LEDs seem to last--I've not done or researched a study on it. One thing I liked on the website link was adding the cap. However, I've been putting my efforts into improving track pickup methods for all wheels. Like Ring Engineering wheel sets.
It's in most white LED specs, a limit on reverse voltage of typically no more than the max forward voltage, unlike a rectifier didoe which can have 50, 100, 200 or more reverse voltage limit. However, they don;t mention current usually, and lots of people have done it with no protection diode, so perhaps with a 1K resistor, which limits a typical white LED to under half the max current (about 9ma vs a 20-25ma rating), it might be ok - the difference in life might be 90,000 hours instead of 100,000 so not really a big deal.
That squares with my experience. I typically run headlights with at least 1k resistance, oftentimes more. Can't recall what I did on the plow right now, but I'm sure it's at least 1k.
I just realized that the device in the circuit is 5 volts minimum.
Below is a link on how to do this with DC only operated locos.
http://www.pollensoftware.com/railroad/index.html
I for one fail to see the usefulness of this device. Looks to me like a solution that is searching for a problem.It's not like the voltage in any permanent circuit is constantly changing, at least not in my circuits.Why spend 2 quarters on this device when you can get away with pennies for a smaller resistor instead?
Kyle.
Dr.Gonzo62 I for one fail to see the usefulness of this device. Looks to me like a solution that is searching for a problem.It's not like the voltage in any permanent circuit is constantly changing, at least not in my circuits.Why spend 2 quarters on this device when you can get away with pennies for a smaller resistor instead? Kyle.
You completely missed the point.
Some today want constant lighting in DC locos. There are still some who only want DC. Many DCC people hate that.
Turn up the power pack a little and the lights are on. I remember many years ago when I first saw that in a MRR magazine.
The older constant lighting used 1.5 volt bulbs with a full wave bridge rectifier and today some want LED's. Bulbs do have a shorter life than LED's.
They could even have marker lights using SMD LED's. Not anything I would care to do but there are some who will go down that path.
richg1998You completely missed the point.
Apparently I did. I had glanced over the thread and the word DCC seems to come up a lot.
Sorry.
Here's the problem with doing it on DC (sort of like the problem with having sound on DC - but not QUITE as bad) - a white-flavor (golden white, sunny white, whatever-white) LED needs a bit over 3 volts - some are as low as 3.1, but ,any are 3.4 or 3.5. So to be able to turn the power pack up and have the lights come on before the loco moves, you have to drop at least that m,uch voltage fromt he motor circuit. That's definitely going to impact top speed, and also shortens the control range, since you've already turned the knob som amount before the loco even starts.
It works better with 1.5V bulbs, because you cna get away with putting just 2 diodes per direction in the motor circuit, a 1.4V drop.
You can 'cheat' if the DC power system uses pulses, but what works with one may not work with another - I installed a constant light circuit for someone back when I belongs to a club, and on one line we had one of the big MRC walkaround power systems, and it worked fine there (unless you turned off pulse). The other line had a CMI walkaround, and the constant lighting would not work on that one (could be the other way around, it's been 20 years).
It REALLY works on a system that uses PWN liek the Aristo, because with PWM the amplitude never changes, just the pusle width,a nd you cna filter that and charge a capacitor int he circuit to near peak even with short pulses - providing full power to a lighting circuit while the motor still doesn;t turn.