I have a Lionel LCRX installed in a K-line MP-15 dummy and would like to use LED lights. I use Christmas light LED's with a 1K ohm resistor on my other engines but this set up does not work with the LCRX. The LED's with work if I add a 18v light.
So I installed a 680 ohm resistor between the (+) and (-) wires before the 1K resistor and on the (+) wire before the 680 ohm resistor I added a 1001N1 rectifier diode. The will work from track voltage of 18v. but not with the LCRX.

The LCRX puts out approx 10volts to the headlight and the 18v light has a resistance of 12.2 ohms.

Do I need to put the 680 ohm resistor after the 1K resistor? Do I need a 12 (+) ohm resistor and not the 680 ohm.

(+) -1001N1->-----1K ohm-----

|                  |

680 ohm           LED

|                  |

(-)-------------------------------

thanks

Last edited by CBS072
Original Post

Sorry I am confused as to the need for a 680 ohm resistor across. Not sure of the voltage input of the LCRX. Only if it is AC do you need the diode, If it is DC you do not even need the diode, just a proper resistor.  If the diode is in proper polarity it wont hurt anything though.

To replace the bulb with an LED use ohms law. Voltage drop divided by amperage. So for a typical LED (20ma., 3.2 volts) 10-3.2/ .02 amps equals 340 ohms,minimum resistance required.. Next standard resistor value is 360 ohms. So that or anything more than that should work. Use a higher ohm value if you want to dim the LED. Wattage used by the resistor is 6.8 X .02 or .136 so a quarter watt resistor is fine. There are resistor calculators on the web that will do this for you.

Dale H

I believe it is half rectified AC and it can change polarity via direction change.  Have you tried swapping leads?  G

Originally Posted by Dale H:

Sorry I am confused as to the need for a 680 ohm resistor across. Not sure of the voltage input of the LCRX. Only if it is AC do you need the diode, If it is DC you do not even need the diode, just a proper resistor.  If the diode is in proper polarity it wont hurt anything though.

The 680 ohm resistor is required to give the triac enough "leakage" current to fire, it won't fire without some sort of resistive load.  This is common and happens on the R2LC as well.

You can get AC out of the light output in conventional mode, or when the locomotive thinks it's in conventional mode, so you need the diode.  I mistakenly omitted the diode in early LED conversions, and after a few months the LED's started dying, apparently from reverse voltage spikes in excess of their reverse voltage ratings.

You need both the resistor and the diode.  Also, as GGG says, for some firmware you could reverse polarity on lights, I don't know if that applies to the LCRX as well.

Thanks for all the help.  Still could not get the LED's to work. May have burned up the lights output on the LCRX.

Going to plane "E"

Plan "E" is install a ERR Mini Commander EX in the MP-15 dummy and use the LCRX in a F7B for railsound(no lights in the F7B)

I have had good luck using my LED's in ERR DC Commanders so the LED's should work with the Mini Commander.

Thanks again

The Lionel lamp drivers are strange and will not drive

LEDs directly. Try connecting a 12v filament lamp across

the output then connect the LED and resistor in

parallel with the filament lamp.

You can try the regular lamp to see if you blew the triac.  Easy to replace.  They should work with the diode and 1K resistor.  If your ok with them on all the time you can connect them to pin 3 of the RS connection this is 5VDC and the Ground wire Pin K.  G

Originally Posted by pa:

The Lionel lamp drivers are strange and will not drive

LEDs directly. Try connecting a 12v filament lamp across

the output then connect the LED and resistor in

parallel with the filament lamp.

They will drive an LED, but you have to provide the resistive load I mentioned previously.  I have many installations with LED lighting using the Lionel lamp drivers.

Note that the ERR stuff apparently has the resistor on the board as they don't require the load resistor.

John & Dale H,

I am having a problem understanding why this will not work, if I can put LED lights

like I do, into my old 711 or 072 Lionel switches and they work, why is he having problems using the same LED lights in his engine?

PCRR/Dave

It's not that they won't work Dave, it's just that you need a resistive load for the triac on the R2LC or LCRX to trigger and light the light.  The bulbs you put into your 711 already have the diode and resistor that is also needed to run LED's off the 12V coming from the Lionel lighting circuit.  So, you need the series resistor and diode to protect against excess current and reverse voltage, and you need the other load resistor to trigger the triac properly with the LED.

John,

So what you are saying is that I will not be able to just put the LED lights I use in my 711 switches into one of my engines without some additional engineering work.

PCRR/Dave

If you put one of the standard screw or bayonet base bulbs in the lighting circuit of the Lionel R2LC or LCRX, it won't light unless you put the load resistor across the lighting output, that's correct.  Nature of the beast, but hanging a 680 ohm resistor across the output isn't exactly "engineering".

They're correct, but he doesn't explain why you'd want to "pull current" from the lamp output.

These are my old drawings from 12 years ago when they were blowing these boards out in the Geep upgrade kits.

There was a question back then about how develop a voltage drop across the output to drive LEDs using resistors or resistive loads so I sketched these up.

I guess when they designed those boards, there was no thought about LED's running off of them.

So how do you determine the value of the parallel resistor in the above circuit?

Seat of the pants.  I normally use a 510 ohm 1/2 watt resistor.  I found that a 1k resistor wouldn't always work, so I just reduced below what I found to be a reliable value.

gunrunnerjohn,

Thanks for the knowledge, I appreciate it very much.

PCRR/Dave

Thanks for all the help on this. I've been gone today from the railroad and hope to work on the LED problem Thursday or Friday.

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