Doesn't matter.
Bob Nelson
Thanks Bob. Moving the common for the LED's to the other side of the field coil worked. While this problem was simmering in the back of my mind today, I had already decided to give this a try.
Kind of makes sense if you consider that the armature and field coils are analogus to a pair of resistors in series - the classic, basic voltage splitter.
Connect one side of the incandescent lamp to the outside rails, through the locomotive frame. Connect the other side to one of the brushes. When done with an incandescent lamp, this works because the lamp receives the full track voltage in one direction and only the field-coil voltage in the other direction. The field voltage is so low that the lamp doesn't put out any significant light.
The same trick can work with an LED circuit if the field voltage is low enough not to reach the LED's forward voltage. But it might; and the LED might light up a bit. If this doesn't work, try connecting one side to the ungrounded end of the field coil, the end that connects to the e-unit, and the other side to one of the brushes as before. The LED circuit will get less voltage when it is on; but it will get zero when it should be off.
That is how I've got mine wired. My error might be where I'm taking power from the motor/e-unit combination.
It's because of the AC current. With the diode in place the LED can work both ways regardless of how the wires are connected. Shown are two LEDs3 and 5mm on AC current.The 3mm has a 470 ohm resistor and the 5mm has 330 ohms. I kept them uninsulated for show.
.. ..
Linited sucess. The first victim was my #600 NW-2 switcher, mainly because the headlight housings are the right size to use the 5mm LED's available at Radio Shack.
I ended up using Radio Shack #276-0017 high brightness white LED's and resistors worth 400 ohms. I also have IN4001 diodes across the LED's to protect them from the reverse polarity portion of the AC voltage. The + side of the diode is connected to the - side of the LED and vise-versa.
I had to enlarge the headlight openings in the body shell to a #8 drill to allow the LED's to fit. The openings started at about a #16 drill size. Since this is a 50+ year old plastic casting, I enlarged the holes in several passes, using a #14 drill, then a #12 drill, etc., until I got to the #8 drill - less chance of snagging and cracking the body shell with a drill that way. Everything is tucked up out of site in the body shell with spots of hot glue. A Futaba servo extension cable cut in half provides a mineature plug and socket to allow for removal of the body shell.
So far, so good. These LED's are definitely bright and definitely on the blue side of white. It was too late to take pictures tonight. I'll post some later.
The part of this project that did not work out too well was my attempt to get directional lights. Sometime back on this forum, I remember reading that if you powered one headlight off of the motor brush that makes the motor run forward, and the other headlight off of the motor brush that makes the motor run reverse, you will end up with directional headlights.
This does not seem to work with the LED's. I've wired them up that way, but they are both on whenever the motor is running - direction does not seem to matter. Is this because of the low current draw of LED's?
HaH!!! Good score with the Digi Key catalog! There are a few places that sell "warm" white LEDs. But you can get the same effect cheap or free....depending on if you already have the stuff....tinting the LED with and amber/orange marker or fairly diluted paint. I've used a medium point amberish colored Sharpie...works quite well.
underworld
Try looking for a Mouser catalog as well. I've bought a few unusual things from them for my old radios that the local electronics store doesn't stock. Post some pictures when your done. I just installed a 3mm LED w/ a current limiting resistor in the switch for the auxiliary windbird at the scope. Got to play w/ a neat device called an Ohmranger to test the ohm rating I needed. In a hammered metal case from Ohmite industries in Skokie, Illinois.
Bob
Tucson, AZ (aka the Ol' Pueblo)
Home of the Mt. Graham & Arizona Eastern Boiler Shops
Thanks Bob. I'll look that source up.
A happy coincedence today at work - a new load of Digi-Key catalogs arrived in tha mail. Somebody tossed one in the recycle bin, so I recycled it home with me. Large selection of LED's there form a variety of manufacturers. Resistors and mineature plugs and sockets too. I'm sure there is other useful stuff in there too.
That should be enough. The LED itself is narrower than that and, in any case, can be mounted with its nose through the shell. The diode is almost microscopic and the resistor not a whole lot larger. But they don't even need to be up there--you can put them anywhere you have space.
I've been thinking about doing the same for a Williams GP38: the bulb for the headlight is located under the low hood in the nose while the dual beam headlight lens is located just under the cab hood. The bulb in the nose throws a little light into the cab and none at all through the headlight. I'm going to have to fit the LED and diodes under the cab roof and don't have a lot of room since the vertical motor and flywheel take up a lot of space in the cab - does anyone have any thoughts as to how much space i'm going to need - thinking that I have no more than 1/4" inch of free space under the roof.
Otherwise the GP38 is great (new Bachmann production) - slow speed operation is very smooth and the motors and gears are nearly silent.
If someone from Bachmann is reading the Forum - this may be an opportunity for a nice upgrade kit (HINT).
Thanks,
Mike
Bob is right. Three millimeter LEDs are also standard; but 5 is usually close to headlight size. You can reshape the plastic case in moderation. I have slightly reduced the diameter to directly replace the headlight light pipe on Lionel locomotives and flattened the spherical tip to a more realistic curvature. Toothpaste makes a good final polish after this work.
I have avoided the usual bluish-white LEDs for headlights after I discovered those sold by Richmond Controls. "White" LEDs are actually blue, with some (not enough!) phosphor added to create the rest of the spectrum. The Richmond Controls ones have orange-tinted plastic bodies that filter out enough of the blue to make their light resemble incandescents'.
http://www.richmondcontrols.com/
The size is easy. 5mm. The choice is in brightness. Most keychains lights use a 5mm. The newer they are, the more brighter they get. At a dollar store, or 5 and Below, they sell for a buck. are white or blue, and throw a good beam.
Thanks guys.
The replacement LED bulbs won't be quite right for what I want to do. The three victims for this activity are a Williams GP-9, a Williams BL-2, and a Lionel #600 NW-2. I'm wanting to place LED's in the headlight openings in the body shell. The real trick will be finding the right size and color LED.
8N, You may want to check the places like "Town and Country" and some of the other suppliers as I believe they sell direct replacement bulbs that have LEDs in them. Some are bayonet mount, some are screw in. OF course if you are wanting to experiment....
Dennis
TCA#09-63805
Diodes are rated for forward current and reverse voltage. Practically any small signal diode will do for this application, where the voltage is less than 50 and the current less than 20 milliamperes. Common types are 1N914 and 1N4148. Here are some: http://www.radioshack.com/product/index.jsp?productId=2062587&filterName=Type&filterValue=Diodes
Thanks, Bob.
Size the shunt diode the same wattage (are diodes rated in watts?) as the load resistor? Use Ohm's law to calculate the current, and use it and the operating voltage to size the shunt diode?
I know, I'll start small, and keep replacing them with bigger dioeds until they quit smoking
Yes, you can and should put in a regular diode to replace the second LED. An alternative approach is to put a diode in series; but the shunt diode is a little safer, since semiconductors tend to fail shorted.
What Doug describes is a good idea for directional lighting, and what I use in the few can-motored locomotives that I have. The circuit is actually the same as for AC. That is, you need that extra diode to protect the LED from reverse voltage when the locomotive is running backwards (unless it has a headlight at each end, in which case both diodes are LEDs).
Forgot where I saw it, senility , but it was on one of the train forums about wiring the LED's to the connections on the vertical can motors. According to the respondents you gained directional lighting and there was no need for an AC/DC conversion since the can motors are already receiving DC power. Hopefully Bob will read this and give some input on their assertions.
Remember the Veterans. Past, present and future.
www.sd3r.org
Proud New Member Of The NRA
I have a couple of Williams locomotives that have unimpressive headlights. Comments on another post got me to thinking about how to install LED's. A reference to Bob Nelson's article in the Sept. 2008 CTT and a trip to Radio Shack got me enough bits and pieces to experment a little.
I was sucessful on the bench, answering my questions about varying voltage, and gave me an idea about what types of LED's to look for for my conversions.
One question for Bob - in your article, you reccomended running LED's in pairs when using AC. If I only wanted one, LED, could I replace the second LED in the pair with a regular diode and maybe an extra load resistor to protect the single LED from the reverse polarity portion fo rthe AC power?
Or is it better to use a full wave rectifier to convert the AC to DC for a single LED?
This electrically challenged mechanical engineer thanks you in advance.
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