american flyer running on dc transformer adding led lights

[wjstix]

"The most common way to limit the current that is allowed to flow through an LED is to place a resistor in series with the LED and its power source."

http://www.trainelectronics.com/LED_Articles_2007/LED_104/index.htm

 

[Laurastom]

To have a constant intensity light with variable track voltage (conventional operation) a regulator is required. There are several sources of these LED Regulators designed specifically for model trains. The most common application is passenger car lighting, but they are small enough to fit in a Gilbert engine. Henning's trains sells a constant current one that works well, it is a JW&A 20110 LED Lighting Regulator. The catch is all the ones I am familiar with are for AC track power only.

[ADCX Rob]

wjstix

In a Command Control system, like DCC, there is a constant amount of current in the track.

Not quite. DCC operation is constant voltage, the current varies quite a bit(from zero up the maximum capable from the power supply).

wjstix

You can uses resistors to allow power to go to the light before it goes to the motor - so like, power doesn't go to the motor until it reaches 3 volts of track power because of a resistor,

Well no on this too. Resistors are current limiting devices, not voltage.

Reading up on Ohm's law may help clarify some of this.

[wjstix]

In a Command Control system, like DCC, there is a constant amount of current in the track. You can then turn on the headlight and it will operate separately from the motor. 

In a system where track voltage (whether AC or DC) itself determines how fast the engine moves, the light is going to change based on the amount of power. When track power is zero, the light will be off. As track power ramps up, the light becomes brighter.

You can uses resistors to allow power to go to the light before it goes to the motor - so like, power doesn't go to the motor until it reaches 3 volts of track power because of a resistor, but track power can go directly to the LED. As long as you set track power to more than 0 volts but less than 3, the light could be on but the engine not moving.

The difference in light intensity might be less noticeable with an LED than a regular bulb. I like Evans Designs LEDs, they come pre-wired with diodes and resistors so can be wired up to any AC or DC system up to 16 volts.

[rlassoc12]

I am using the bridge rectifier in the engine to eliminate the e-unit so that I can change the direction of the train by changing the polarity of the the voltage out of the transformer. By using the bridge rectifier on the engine I am in essence making the motor a dc motor.

[Astrolite]

I probably won't be much help, new here and new to AF. I've had AF since 1957, but its spent the last 60 years in a box in the closet. I too am running my AF on DC. It was my understanding that the motors were "universal motors" and would run on either AC or DC without any modification. Since a bridge rectifier is used to convert AC to DC I'm not sure why you need that in the loco. The locomotive should't need it and since you are already running DC, your LED lighting shouldn't need it. I would think what you need is a a resistor to lower the DC voltage to the level needed by the LED and a capacitor to eliminate the flicker. As far as providing a constant voltage, so that the brightness does not change with throttle setting, I do not know. It would seem to me the only reason to have a bridge rectifier would be to protect the LEDs if you ran the loco on AC power.

Take what I say with a grain of salt as I find this AC/DC stuff confusing!

[rlassoc12]

I am running an AF 302 on a DC tranformer with a bridge rectifier in the engine. The + and - outputs of the rectifier are attached to the coil of the motor. I assume that I should power the led light from these connections since they don't change polarity. How will the intensity of the light change as the power supply voltage is changed? I am trying to get the light to not change like the incandescent bulbs do with voltage change.