Pre-wired 12v LEDs - Questions About Using Them

I have used these in various projects.  In my Bowser trolley's, I use them for head and tail lights, I have used the flashing ones for marker lights on cabooses.,  I have even put them in Flyer steam engines for head lights,  most of my Flyer runs about 13v anyway, so I have not noticed any problems..

Marty

banjoflyer posted:

This type of LED runs on 12 VDC. That means DC power. You can operate them with AC power but you will need to change the AC power to DC power with a bridge rectifier. From your link see this:

As to the white LED's in the lantern housings the same thing applies. The power to the LED needs to be DC power.

They look like this:

The AC power goes to the legs marked with a "~" sign (either AC wire goes to either leg).

The "+" leg goes to the red LED wire and the "-" leg goes to the black LED wire.

Try not to exceed the 12VDC rating or you'll shorten the life of the LED.

Hope that helps.

Mark

Banjoflyer,  Thanks for the reply.  I ordered some of these bridge rectifiers.  How do you "mount" them?  Is there a "holder" available?  Is it best to use one bridge rectifier for each LED?  Can I add another resistor to the LED so I can use them with higher Voltage - 16-18 volts?

Thanks for the help.

Truthfully, it's easier to light those with a simple diode, and it'll keep the voltage under control as well.

I like GRJ's suggestion.  You can share one 2-cent diode per controller or pair of LEDs.

By using a diode (vs. a bridge rectifier) you drive the LED half as often.  One can go thru the tedious equations but as it turns out, driving the LED with a bridge at 14V be similar brightness as with just a diode at 18V.  Then you don't have to fuss with adding/modifying a resistor.

If going with the bridge-per-LED approach, you should add or swap in a different resistor if operating at 18V.  I believe most 12V pre-wired LEDs have something like a 470 ohm resistor under the heat-shrink.  Probably easier to add an external resistor than messing with the existing one.  I'd suggest a 220 ohm, 1/4 Watt which is a common easy-to-find value.  Note that you can "share" one resistor between the two LEDs by placing the resistor where the diode is in the above photo.  The bridges would then be to the right.

As for your switch lantern, presumably this is the bayonet style bulb.  In which case I think it quite difficult to install an LED with supporting components if constrained by the bayonet socket.  There have been many threads on plug-and-play LED bulb replacements - for example here's one where you apparently participated!  So I presume the issue is one of cost as those LED bulbs run $2-3 or more?  Anyway, if can work out the mounting logistics you need to deal with the beam-angle of the LED.  The switch lanterns project light side ways or horizontally whereas a single LED bulb with rounded lens shoots a narrow conical beam upwards or vertically.  Look for so-called "flat top" or "wide angle" LEDs where the rounded lens has been modified to spread the beam.  You can actually grind/sand the plastic rounded lens yourself if desperate.

The current generation of plug-and-play LED replacement bulbs have multiple LEDs facing every which way to better mimic the "isotropic" omni-directional output of an incandescent.  But I don't know if these are available for switch lanterns that support the O-gauge AC voltage range.

Again, if you have too much time on your hands and like the smell of solder fumes, you can roll your own side-ways aiming LED replacement as I've described here.  This has 4 LEDs re-purposed from those 12V LED strips aiming side ways out each switch lantern lens so less than 25 cents in parts.

Since you are using the fixed-voltage plug option, yet another idea is to power the switches with DC voltage.  I seem to recall threads where it was confirmed that DC works fine - this could simplify some of the AC-DC issues with using LEDs.

If you lay out a simple PCB and go to OSH Park, you maybe can make that task easier.  I wonder if there's an LED package that would solder directly to a board and have it oriented like that?  Or, you could solder one end to the board and have a common wire around the top that connects them.

stan2004 posted:

I like GRJ's suggestion.  You can share one 2-cent diode per controller or pair of LEDs.

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I finally received my order of diodes and I'm trying to figure out the best way to solder the "very small" wires on the LEDs.  The first problem is stripping the insulation on the LED wires.   I tried to search for previous threads but must not be using the proper search words.  Any suggestions on the best way to do this?

Thanks

Did you check this thread?

Small diameter wire strippers

There are tons of options.

Thanks Gunrunnerjohn.  I read through quickly and there are lots of options.  Now to pick one and on to the next task - using magnifying glasses to see the small wire while soldering.

Thanks again John

Since my cataract surgery, I have to use a magnifier for all my bench work.   I guess that's better than not seeing at all!