Led hooked to motor leads?

The amount of resistance you need varies with the voltage supplied to the motor. a quick work-around would be to use a small voltage regulator as part of the circuit to provide a constant 5V off the motor leads. An example can be found here. Since it's likely the motor will get more than five volts at any given time you'd only need a small resistor for the LED. You're talking about a Williams locomotive here, so it's running on DC can motors so you already have a DC source. A diode for each regulator would prevent reverse voltage from coming through.

Hope this helps some. Good idea by the way.

Thank Matt..  I tried it without the CV board with just a resistor, It sort of worked but too much flickering when the direction was reversed. Would a capacitor eliminate the flickering??  I think I may just hook  both head and  back up  lights  up to  track voltage.  Perhaps a  couple of extra leds (red & green) for class & marker lights.   Not sure  yet.  Always "on"  .

On my large scale trains I simply hook the LED leads to the motor as Gregg mentioned.  Of course I do have resistors in place.  Since the power is straight DC, there is no issue with voltage convertors and such.   The LED headlights illuminate according to the direction of the loco.  I have no clue about what size resistors I use, it just works, no matter what size LED I use, i.e. 5mm, 3mm, straw hat type, rounded type, etc.    

Dan Padova posted:

On my large scale trains I simply hook the LED leads to the motor as Gregg mentioned.  Of course I do have resistors in place.  Since the power is straight DC, there is no issue with voltage convertors and such.   The LED headlights illuminate according to the direction of the loco.  I have no clue about what size resistors I use, it just works, no matter what size LED I use, i.e. 5mm, 3mm, straw hat type, rounded type, etc.    

The LED active component is very small. The sizes are all just the cases designed for different applications. The key is the voltage requirements.

I added LED headlights on a high-speed battery power railcar and they kept going haywire and burning out, apparently from voltage spikes off the motor -- even though the LED's had correct nominal voltage through a resistor from the fixed battery voltage. Problem solved with a filter capacitor across the LED leads. I forget the values, I used salvaged components.

Use a 1uf 50V NP cap across the motor, then a 470 ohm 1/4w resistor in series with the LED's.  If you want the ultimate protection, add a reverse polarity protection diode to each LED.

gunrunnerjohn posted:

Use a 1uf 50V NP cap across the motor, then a 470 ohm 1/4w resistor in series with the LED's.  If you want the ultimate protection, add a reverse polarity protection diode to each LED.

We're getting close. NP?   does that mean non- polarised?. I just have enough electrical knowledge to get in  big

trouble.  

Sorry, yes, non-polarized.

The trick is to use back to back diodes in series with the motor leads. Each diode has to carry full motor current so say 5 amp rating to be safe. It will depend on the stall current of the motor(s). Then place your LEDs with series resistors across the diode pair but reversed from each other. The diode drop is around .7 volts. Most standard LEDs require at least .6 volts to light. Your series resistors can be small like <100 ohms. This techinique has been around for a half century for 1.5v incandescents but require 4 diodes, two pairs in series and then the pairs wired back to back (anode to cathode) to get the required 1.5 v drop.

Pete

White LED's require close to 3 volts to light, you'll need four or five diode pairs to light them.  You can get away with 3A diodes, hard to imagine you will draw more than that continuously, but still that's probably ten diodes!

I've wired a number of conventional ones with the three components I described.

Gregg posted:

 I tried it without the CV board with just a resistor, It sort of worked but too much flickering when the direction was reversed. Would a capacitor eliminate the flickering??  I think I may just hook  both head and  back up  lights  up to  track voltage.  Perhaps a  couple of extra leds (red & green) for class & marker lights.   Not sure  yet.  Always "on"  .

 

What do you mean by too much flickering when direction was reversed?  

If you are using a conventional reversing-unit board the LEDs will obviously be off in Neutral if the LEDs are powered by the motor.  With further clarification of what you have it may be practical to tap into the reversing-unit circuit to obtain the direction "information".  As for capacitance, super-capacitors can power an LED for seconds or minutes so the LED(s) could be on even when you press the Direction button.  Yes, more components, more soldering, and a few more dollars but once committed to hooking up the diodes, capacitor, resistor, perhaps worth the incremental effort to get a better effect.

If class and marker LEDs are on the table why not work that out now.  Plan twice, solder once!

Hi Stan.. THE 3 volt white led with resistor  attached to the can motor leads  seem to work fairly well in one direction.  Isn't an LED a diode and should only light up in one direction? Anyway when I reversed the  motors the led still  flickered.

This is an old Lionel engine GP-9  with the can motors in the trucks.  It was at one time a Rail scope engine . No head or tail lights  ever as far as I can tell.  The wiring is a little weird.... With 4 wire coming out of trucks, you would think the red & black would be the power pick ups. Nope! the blue and yellow are the pick ups and the red a nd black are  the motor leads.  Anyway it runs but now needs some lights.. I have all the stuff including fibre optics,  red , green  and white leds to work with .   I need to find a cap from all the other board junk board (stuff) I have stored away. 

Gregg posted:

Hi Stan.. THE 3 volt white led with resistor  attached to the can motor leads  seem to work fairly well in one direction.  Isn't an LED a diode and should only light up in one direction? Anyway when I reversed the  motors the led still  flickered.

OK, so if I understand it the LED is solid-on when in, say, Forward.  But in Reverse that same LED flickers (probably faintly) as the motor is running.  My guess is you're getting intermittent track power contact (dirty wheels, track, whatever).  During the brief interruptions in track power, the current flowing thru motor winding suddenly loses its return path to the track and looks for another escape route which happens to be the LED (of the opposite direction).  You've probably seen/read about how you're supposed to put a diode across a DC relay coil to clamp the voltage spike when the relay turns off?  Well, here you have a motor "coil" that is intermittently turning off; and your clamp diode happens to be one that emits light (!) when current flows thru it.  Hope that makes sense.

Anyway, I still suggest you lay out the scope of the project to plan a complete solution...though I appreciate the idea of learning-as-you-go attacking one thing at a time.

gunrunnerjohn posted:

Use a 1uf 50V NP cap across the motor, then a 470 ohm 1/4w resistor in series with the LED's.  If you want the ultimate protection, add a reverse polarity protection diode to each LED.

This seem to have done  the trick  however I had to put the cap  directly across the led leads. Anyway It's working and thanks to all . Would you believe  I found 2 new caps never used in my  junk stuff. Probably from Digital dynamics. We have a great bunch on this DCS part of the forum.

What did you end up with as a configuration?