One Last Shorty

[Odyknuck]

In lieu of all the additional rework, could you have just put a resister in series with the LED to dim it down.

[Steggy]

In lieu of all the additional rework, could you have just put a resister in series with the LED to dim it down.

LEDs don’t work like that. While series resistance is often used in LED circuits, its purpose is to limit the LED current to a safe level within a given range of supply voltage.

Current flow through an LED is exponentially related to applied voltage, which means there is a narrow voltage range in which an LED will non-destructively emit light. The voltage transition from light emission to no light emission is rather sharp, which makes regulating the light output of an LED purely with series resistance difficult. LED lamps that can be dimmed are controlled with pulse-width modulation (PWM) to vary the average current flow and brightness. The effect of PWM is to rapidly cycle the LED between off and on, with the pulse rate high enough to prevent flickering.

[ccvstmr]

In lieu of all the additional rework, could you have just put a resister in series with the LED to dim it down.

Ody...Steggy provided an explanation of what it takes to power an LED. Me, I pushed the EASY button, and decided to use readily available 9 volt battery(ies) as needed. Slightly lower voltage = less light output. Best part...suited my purposes. Carl B.

[ccvstmr]

DETAILS- Illumination, Part 4

Might as well wrap up the car #7 observation deck light. Last time, was in the process of making the lamp lens ring bezel.

Here's how the lens and lens ring turned out. Left the fit slightly loose. Didn't know if temperature variations would be a problem while storing the car in an outdoor storage structure.

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Looking thru the ceiling opening, can see how the LED clearance lamps was centered under the opening.

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The wiring for the LED came out of the ceiling cavity. Eventually, a light shield would be fabricated from a piece of aluminum sheet metal to cover most of the roof rib elliptical opening. Think the light shield was in place in one of the earlier roof p

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Painted some oval head wood screws gloss black while the lens ring was sprayed with gloss, polyurethane clear coat. The lens is captured in the wood lens ring bezel and the bezel screwed to the deck ceiling. In short, the lens won't going anywhere...except for a ride down the rails.

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And last but not least, how did the entire observation deck lighting turn out? Had some back lighting outside the shop door seeping in, but overall, the deck lighting was somewhat diffused by the lens that was fabricated. Far as I was concerned...it was time to move on.

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As long as the car lighting has been explained, there's one more electrical matter to cover...and that's the marker lamps. Will pick up there next time. Carl B.

[NP317]

Beautifully done!
RussN

[ccvstmr]

Beautifully done!
RussN

Thanks Russ...but don't go away, there's more goodies to come. Carl B.

[ccvstmr]

DETAILS - Marker Lamps, Part 1

Moving right along like molasses flowing downhill during a Chicago winter in February...there's one more electrical item to describe before moving ahead...the marker lamps.

Had to start by establishing some criteria for the car #7 marker lamps. Here's what I came up with...

1) marker lamps had to be hinged. Why? #7's car body is 15" wide. Train club storage dimensions limit users to 16" wide envelopes. With marker lamps sticking out approx. 1.5" on each side...needed a way to satisfy the width limitation...without having to unplug the marker lamp wiring and remove the lamps BEFORE the cars were pushed back into the car barn. Figured a hinged marker lamp bracket would satisfy.

2) FAMC provided 12 volt grain of wheat light bulb...which wouldn't do. Not bright enough. Was planning to use the shorties for card order mixed-train switching. The remote brake unit in the last car (now to be #7) would be used to illuminate the marker lamps when the rear end train brakes were set. The lamps had to be bright enough in strong sunlight to know if the rear train crew was awake...and releasing the brakes before trying to leave town. As such, would replace the grain of wheat bulb with a high output LED.

3) wanted the marker lamp to have (4) lenses instead of the normal (3). Red to the rear. Green to the front. Yellow to the sides. Wanted some extra lenses too, in case I changed my mind about the lens configuration.

4) lastly, wanted the threaded stem mount to be located at 45 degrees off center so the lamps would hang on the rear corners of the car body.

Nothing like a short list of needs is there? Figured car #7 should get a "nice" looking marker lamp to follow the train around. Ended up talking to Joe Ed Gaddes at FAMC - Franklin Automatic Machine Corp in Brentwood, TN. Joe Ed makes marker lamps (among other things) that are CNC machined. Discussed my needs with Joe Ed and he was able to amend his #83 marker lamp to satisfy the needs listed. Paid extra for the above described changes...but marker lamps are one of those things that get noticed...even if they're at the back of the train. So, felt the added cost would be worth it.

Once the marker lamps were received, talked Honest Dave into fabricating the hinged brackets. Resurrected a car body mock up made a few years ago when Honest Dave's Central Pacific passenger cars were built. Dave wanted to know how the red color would look on the wood planked car siding. Since the mock up corner had a 1/2" quarter round trim...this would help Dave develop the marker lamp hinges.

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The tricky part was replacing the long 10-32 threaded marker lamp stem with the parts needed to hold the marker lamp on the hinge.

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Dave's solution involved a short stem, threaded 10-32 on the outside to screw into the marker lamp...and an internal 6-32 thread for a screw to fasten the bracket to the marker lamp. Then, make new "spool" pieces to fit between the bracket and lamp with the proper radii to engage the marker lamp and bracket on either side. Next photo shows the orientation of the various parts. What's not shown is the holding clip Dave made to be screwed to the car side.

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Here's a photo showing the marker lamp "snapped" into position during train operations.

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Here's another photo showing the marker lamp swung back and out of the way for storage.

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Lastly, here's an overhead view showing how well the bracket curvature followed the trim work on the car corner. As usual, Dave did a great job with his brass work!

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Okay, the first requirement was satisfied...a hinged marker lamp mounting bracket that could be "latched" for train operations and swung out of the way for storage. Next time, will describe the LED upgrade. Carl B.

[Odyknuck]

Pretty slick Carl

[ccvstmr]

Ody...ain't that the truth? Had a goal in mind and was able to accomplish that. Last thing needed was to back the train into the car barn and wipe those marker lamps off the side of #7 'cause I forgot to pull the lamps in! Carl B.

[ccvstmr]

DETAILS - Marker Lamps, Part 2

With the marker lamp hinged brackets out of the way, was time for a lighting upgrade. Actually, might have done the lighting upgrade before the brackets were completed. The FAMC marker lamps are provided with grain of wheat bulbs for lighting. The marker lamps on #7 were intended to operate in one of two ways: 1) on steady for night time running or 2) on periodically for card order switching operations while the rear end train brakes were "set".

In the next photo, can see FAMC's grain of wheat light bulb and the FAMC machined light bulb mount. On the left...my LED solution using a 1 watt, what I call "bubble LED". As with any LED...DO NOT put voltage directly to the LED to check the brightness without a voltage dropping resistor (unless you have a power supply of the rated voltage). Else, might as well throw that LED away.

Needed to make a similar mount for the LED that could be inserted thru the base of the marker lamp body. The Nylon/Delrin mount was designed to put the LED bubble at the same approximate height as the Fresnel lens center...or slightly below. Wires needed to "hug" the sides of Nylon or Delrin base and get soldered to the bent down LED tabs...while noting the LED polarity. Then, put a dab of GOOP automotive contact cement on top of the mount and pull the wires back and let the GOOP dry. Done.

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The big question was...how well would the bubble LED light up the marker lamp? Why? Engineer needs to see the lamps from the front of the train in direct sunlight to know if the brakes were released (lamps off) at the back of the train (rear brakeman responsibility. Besides...gives him something to do). Sorry...the digital camera did not do well capturing the light intensity. But can say...it WAS bright!

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Calculated that I'd need a 30 ohm, 5 watt resistor to get the voltage down to an acceptable level for this LED. Also wanted to make sure the resistor would NOT overheat. Opted to go with a finned aluminum housed resistor.

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Next photo might be jumping ahead a bit, but here's how the marker lamps look after painting...which I'll cover in the next post. Carl B.

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[ccvstmr]

DETAILS - Marker Lamps, Part 3

As long as I'm seated here, might as well pump out the next post. This time, marker lamp painting. Once again, wanted a finish that would really make the marker lamp stand out.

First step in the finishing process was to remove the lens rings. These can be pryed off...CAREFULLY...so they're not deformed. Will get back to the lens rings in a bit. Decided to glass bead blast the marker lamp bodies. This is not as harsh a cleaning and surface preparation compared to something like a Black Beauty abrasive grit. Did my best to prepare both the outside AND inside of the lamp bodies.

Carefully masked the lens ring mounting surface. There wasn't much for the masking tape to hold on to. Then, used Rustoluem gloss black appliance epoxy spray paint. Wanted a hard, durable surface for the lamp exteriors.

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Next, used a small brush to paint the lamp body interior with gloss white enamel paint. Why white? White surfaces reflect more light than other colors. Might as well "push" as much illumination out thru the lenses as possible.

While I don't have any photos, believe I modified the bottom lamp "plug" to get the LED light wiring out the bottom of the lamp housing and file any sharp edges to avoid cutting the wire insulation.

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Made several arbors from some scrap aluminum to hold the lens rings snugly...so the rings could be polished with a bugging wheel. When satisfied with the polishing effort...wiped the lens rings clean with lacquer thinner. And then, used a crystal gloss clear coat to hopefully, preserve the shine.

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With the lenses in place, used Loctite #290 (per FAMC) to affix the lens rings to the marker lamp body. Loctite #290 is a "wicking" product. Not anywhere near as viscous as thread locker products. Put a dot of #290 on the inside of the ring and it just filled the entire lens ring lip. The rings were set in place to hold the lens and any excess wiped off.

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There was no need to paint the marker lamp mounting stud as that would be hidden by the "spool" piece between the lamp and bracket. However, the spool was painted with the same paint as the lamp body. The marker lamp mounting bracket and clip would be bead blasted and painted with gloss Hunter Green like the sides of car #7. Fully expected the paint on the clip would get chipped away due to use. Can always go back and touch that up...and then watch that get worn away over time.

Next time, to close out the chapter on the marker lamps, will get the lamps mounted and show the lighting control panel made for the 2 modes of marker lamp operation. Carl B.

[Steggy]

As with any LED...DO NOT put voltage directly to the LED to check the brightness without a voltage dropping resistor (unless you have a power supply of the rated voltage). Else, might as well throw that LED away.

An LED is a constant-current device, whereas bench-top power supplies are (theoretically) constant-voltage. Unless an LED is designed be directly connected to a power source (not the case with the LEDs used by Carl), series resistance must be present, even thought the power supply’s output voltage is the same as the LED’s forward voltage. The correct choice of resistor will cause the LED to self-regulate over a reasonable applied voltage range.

An LED is very sensitive to applied voltage. Once the avalanche (forward conduction) voltage is reached, the relationship between current and voltage is predicted by Shockley's diode equation. Shockley's equation establishes that the change in forward current is exponentially proportional to the change in applied forward voltage. The result is a trivial increase in forward voltage will cause a large increase in current. Hence the importance of a ballast resistor to limit current to a safe level. Without any resistor, forward current flow will be limited only by the capacity of the power source, wiring resistance (usually negligible) and the LED’s forward voltage drop. The LED will immediately go into thermal runaway and burn out.

With insufficient resistance, forward current flow will exceed the LED’s rating, causing it to overheat and eventually go into thermal runaway. Prior to failure, the LED’s apparent color will be abnormal, tending toward white, which is a sure tip-off there is too much current flow.

Although it’s possible to “Easter Egg” to determine the correct resistance for the ballast resistor, it’s much safer to compute it using standard Ohm’s Law equations. Different-color LEDs avalanche at different voltages, so what will work for a red LED won’t be correct for a green or blue one. Recommended operating current and tolerable forward voltage limits are specified by the manufacturer and should be used to compute the correct ballast resistance.

As the voltage drop across the ballast resistor represents wasted power, the resistor’s wattage rating must be commensurate with the operating conditions. The LEDs used by Carl pass fairly large amounts of current, necessitating the use of a power resistor in his application. The greater the difference between the LED’s forward voltage and the power source voltage, the more wattage dissipated in the resistor. That will translate into more heat.

While it is tempting to have several LEDs share a common ballast resistor, that is a no-no. Identical LEDs will not have identical current vs. voltage curves. Two such LEDs in parallel can differ enough that one might fail to light and the other might go into thermal runaway. Always provide each LED with its own resistor.