The LION is into building SUBWAY TRAINS (see monks.assumptionabbey.com/Lion).
Subway passengers do not like riding in the dark. They do not like lights that go off every time the train stops. They could get mugged, you know. So it becomes incumbent upon me to provide lighting in my subway cars, and eventually in all of my passenger cars. Constant lighting.
DCC would be nice, but I do not have that, and could not afford to put it in all of my locomtotives, besides, I have no idea how many locomtives I actually have anyway.
My plan is to use LEDs in the cars, I thought to use a capacitor circuit such as was found in this month's MR, or also in the APR-98 issue. But these will only stop flickering, and will not keep the lights on in the stations.
I have been told that batteries are a good choice. I was thinking of using NiCad or something, and have them charge off of the track power. Does anybody have a CHEAP circuit that will work, and that a LION can build. (Lions are all claw, you know)
Thanks for your thoughts and better yet, your help!
The Broadway Lion,
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
For a start:
Track power through a bridge (takes care of reversing direction issues). Bridge DC ouput through a resistor to the Battery and LEDs'. Choose resistor to limit charge current to a safe value at max track voltage. If battery voltage is higher voltage than LEDs you need a second resistor between it and them. It would be a good idea to use one in any case.
Lithium Ion is another option to NiCads. Less instantaneous current (not at issue here) but nicer to the environment and cannot be overcharged.
That's about as cheap as you can get.
The mind is like a parachute. It works better when it's open. www.stremy.net
Thanks. OK, I made a drawing. Is this what you were trying to suggest to me? What values should I try for the resistors. As you can see, I plan to light three cars from one power source which will be hard wired between the cars. (Subway trains use drawbars, you know) Maybe each set of LEDs needs its own resistor, that is also easy to do.
Thanks, Elias
In this circuit the battery will only charge when it's really low and the track voltage is high.
You might want to use a lower voltage battery and more parallel shorter strings of LEDs.
Battery voltage should be less than (lowest track voltage - 1.4 volts)
Otherwise, the general circuit will work..
Resistor values depend on LEDs used and their voltage drop. Let's take a theoretical example with each LED "drops" 2.5 volts.
4 LEDs in series will drop 4 x 2.5 = 10 volts. The battery supplies 12 volts so the resistor has to drop 12v - 10v = 2v across itself at the proper current.
Selecting 10mA for LED current, the resistor carries 3 x 10mA (3 parallel branches) or 30 mA.
Ohm's Law: E=I*R 2 Volts = R x .030 Amps , R = 2V/.030A = 67 ohms.
P = E * I = 2V x .030 amps = 0.06 watts. Double this for safety. A 1/8th watt rating should do.
R1 should carry the charge current of the battery (which depends on the battery and how much you want to steal from the track).
Use similar formulas: V track - V battery - 1.4V (for the bridge) = V-resistor. R = V-r / I
I would think that 300 - 600 mA would do the trick and make the additional current draw of the LEDs at low battery trivial.
I hope that this is clearer than mud.
Karl
Hi
A couple of thoughts...
I am running DC, but my throttle adds a pulse to the output - I can vary the frequency and width of the pulse. Does 2 things, it improves the Loco response at low throttle settings and also provides enough power to keep the lights lit..
For powering the lights, the bridge and voltage rectifier is the way to go - however, what I do is use a LM317 (to92 version) wired as a current regulator to power a string of leds. The advantage of this approach is that you only need a single resistor, and it doesn't matter how many leds you have in series (as long as your peak voltage is greater than the total voltage needed to light the leds).
Wire up the 317 as a current regulator by connecting a resistor to the output pin, the other lead from the resistor goes to the led string & the adjustment pin on the 317. The 317 will adjust the output voltage so that the difference in voltage between the adjustment pin & the output pin of 1.25V. So, if you want 1 ma of current, the resistor value will be
1.25/.001 or 1250 ohms - or the closest realistic value.
One led will draw 1ma, 2 in series will draw 1ma etc - until you have too many for the max output voltage needed.
Using this approach also means that you don't need differing resistor sizes depending upon the number of leds that you are driving...
Villy