# LED's Using [DCC] V-AC Track Power..



## ED-RRR (Jun 4, 2015)

LED's Using V-AC Power..

Warning:
This does "NOT" apply to a "Locomotive Decoder Lighting".. 

LED's:
- 2 mm / .079" Dia. (Tower)
- 3 mm / .118" Dia. (T-1)

Usages:
- passenger cars
- caboose marker lights
- crane flood light
- unlimited other usages

Special Note:
LED's are much cheaper ($'s)..
LED's have almost an "unlimited" lifetime..
When adding LED/LED's into rolling stock
electrical wheel wipers are required..
On the internet there are posted images
and home made projects..
I personally prefer this one.. 
Wheel Wipers
http://www.sbs4dcc.com/hoscalewheelwipers.html

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Most small LED's operate between 1.8/2.0 V-DC @ 20.mA 

Calculation (Required Resistor)
Example: (HO Scale)
(14.V-DC) (2.V-DC) (20.mA)

LED calculator: (current limiting resistor value)
http://led.linear1.org/1led.wiz
Source voltage [14]
diode forward voltage [2]
diode forward current (mA) [20]
= 680 Ohms, 1/2 Watt, 5% Resistor 

You can actually buy 680 Ohms, (1/2 Watt), 5% Resistors.. 
Requires 5% resistor or a "lower" #%..
LooK --> 680 Ohm resistor

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Caution:
When wanting a "white" color light
do "not" use a "clear" LED..
A "clear" LED gives off a "blue" tint..
Instead use a "warm white" LED
that has a light yellow color..

=============================================

Hardware Required:
- (x1) LED
- (x1) resistor [1/2 Watt, 5% or less] 
- (x1) small diode [1n4001]
- (x1) small wire (#22 or #24 AWG) 
- (x1) mini on/off switch (optional) 
- (x1) electrical wheel wipers sets (optional) 

=============================================

Caution: (Passenger Cars)
Resistors are rated in "Tolerance" ranges..
Different tolerance ranges effects LED's brightness..
When adding LED's into more than (x1) passenger car
the required tolerance must have the "same" Ohms..
Use a multi-meter set at 2000 Ohms..
Check all resistors and group them into Ohms ranges..
I recommend using the "maximum" Ohms range
to keep the "brightness" down..

......


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## DonR (Oct 18, 2012)

For passenger cars I prefer the LED strip lights that
come on a roll. You can cut them in 3 LED strips that
run on 12 V DC. They have self adhesive backing and draw
very little current. The light they produce has the
appearance of florescent tubes that were often used on
the silver side and similar cars. They do need a
rectifier though, and I use a capacitor to limit
flickering through turnouts and crossings. I've found
that individual LEDs seem to have a 'focused' ray
out their tips. They don't distribute the light well. 

Don


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## wvgca (Jan 21, 2013)

ED-RRR ...quote: 
LED calculator: (current limiting resistor value)
http://led.linear1.org/1led.wiz
Source voltage [14]
diode forward voltage [2]
diode forward current (mA) [.02]
= 680K Ohms, 1/8 Watt, 5% Resistor 

your numbers are off, by a factor of 1000 times...
both on calculated resistor value [ as compared to normal usage],
and definitely the led current [again as compared to normal led specifications], 
placing a 680k in series with a 'normal' led will give ZERO light emitted ..
sorry


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## wvgca (Jan 21, 2013)

sorry ED=RRR , I was a bit abrupt in previous reply, doorbell was ringing ...
anyways ... from your posted formula that I previously quoted, it seems that you specified current draw in mA [normal], but entered the value in Amperage, not mA, which skews the actually draw by 1000 times less ... which results in a calculated resistor value of 1000 times MORE than what would normally be required for full brightness .. leds that draw .02 mA do not exist as far as I know..


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## Mark R. (Jan 26, 2013)

I see a number of errors in addition to what was already pointed out. White LEDs require 3.2 to 3.4 volts to operate, not 2.0 volts. 2.0 volts would be for colored LEDs such as yellow, green or red.

The term "clear" is rather misleading. Clear refers to the epoxy casing and is ofter referred to as water clear, as opposed to opaque casings. "Color" refers to the color of light emitted and there are usually three classes of white. You will find white, pure white and warm white. White usually has a slight blue cast to it - much like a flourescent light - which can be useful if you are wanting to represent that. Pure white is just that - a solid white with no blue over-tones. Warm white is a yellowish white much like that produced by an incandescent bulb.

You "can" run LEDs off AC voltage, but it's not a "best practices" method. I use them (red and green) straight across my DCC track joints in a reversing section to indicate "polarity" in the reversing section, and DCC is a like form of AC. If possible, it would be recommended to use a bridge rectifier to convert the AC to DC to run your LEDs.

Mark.


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## gregc (Apr 25, 2015)

Mark R. said:


> You "can" run LEDs off AC voltage, but it's not a "best practices" method.


While it is typical to provide a constant DC voltage to an LED, it is also very common practice to control the intensity of an LED by switching it on and off with a varying duty cycle (PWM). A very simple approach is to use full or half wave rectified AC to cut the intensity in half.

If a certain resistance is required to limit the current thru an LED with constant DC power, only half the resistance is needed if power is applied only half the time, as with DCC.



Mark R. said:


> If possible, it would be recommended to use a bridge rectifier to convert the AC to DC to run your LEDs.


another approach is to simply wire half the LEDs with reverse polarity through a common resistor. If the concern is the reverse voltage across the LED, a reverse biased diode across would protect it (and cheaper than a bridge). But a 2nd LED could just as easily be used.


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## ED-RRR (Jun 4, 2015)

*Thanks*



wvgca said:


> ED-RRR ...quote:
> LED calculator: (current limiting resistor value)
> your numbers are off, by a factor of 1000 times...
> both on calculated resistor value [ as compared to normal usage],
> sorry



Thanks for the friendly heads up..:smilie_daumenpos:
That's what buddy's do.. 
It is 20.mA
I always get screwed up when using mA..

I have corrected my calculations..
......


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## wvgca (Jan 21, 2013)

for me it easier to take the voltage drop, [ source minus led forward voltage], and multiply by 50 [based on 20ma draw] .. quick and no calculator needed .. gives a minimum resistor value, but i usually increase the value to around double that, gives a less bright more realistic illumination ... in your initial example you may also want to factor in the 2/3 volt drop across the diode ..won't matter much either way ..


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## ED-RRR (Jun 4, 2015)

*Hi*



DonR said:


> For passenger cars I prefer the LED strip lights that
> come on a roll. You can cut them in 3 LED strips that
> run on 12 V DC.
> Don




Caution: (Your Track Voltage)
As per N.M.R.A. (Track Voltage) 
[N] = 12.V
[HO] = 14.V 
[O/G] = 18.V



DonR said:


> I've found that individual LEDs seem to have a 'focused' ray
> out their tips. They don't distribute the light well.
> Don


You are 100% correct..
That is why I use (round diffused milky white lens)
for my track signals.. 
Viewing Angle: 140 ~ 160 Degrees..
......


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## gator do 65 (Jan 27, 2014)

gregc said:


> While it is typical to provide a constant DC voltage to an LED, it is also very common practice to control the intensity of an LED by switching it on and off with a varying duty cycle (PWM). A very simple approach is to use full or half wave rectified AC to cut the intensity in half.
> 
> If a certain resistance is required to limit the current thru an LED with constant DC power, only half the resistance is needed if power is applied only half the time, as with DCC.
> 
> ...


Could you please clarify this last paragraph with a schematic? I believe I get it but....


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## ED-RRR (Jun 4, 2015)

*Our Calculations (x3)*



wvgca said:


> for me it easier to take the voltage drop, [ source minus led forward voltage], and multiply by 50 [based on 20ma draw] .. quick and no calculator needed .. gives a minimum resistor value, but i usually increase the value to around double that, gives a less bright more realistic illumination ... in your initial example you may also want to factor in the 2/3 volt drop across the diode ..won't matter much either way ..


Hi Again::smilie_daumenpos:
Here is another LED "resistor" calculation..
(Power Supply) "minus" (LED Voltage) "divide" (mA) = rough calculation..
(14) - (2) / (.02) = 600 ohm resistor..

I have tested this small diode [1n4001]
1A, 50V, Signal Diode, DO-41
At 12.V there was only -.5V drop

Sorry, but I prefer the computer calculation..
Also supplies the "minimum" Wattage required..
......


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## gregc (Apr 25, 2015)

gator do 65 said:


> Could you please clarify this last paragraph with a schematic? I believe I get it but....


in the diagram below from the original posting, a simple diode is across the LED to protect it when the polarity is reversed. That diode could also be an LED. With DCC, each LED would be on only half the time, but on alternate polarities.

So instead of have one of these circuits for each LED, you could have a single circuit with two LEDs and avoid the need for the simple diodes.

In fact, since DCC is over 12V, for applications like passenger cars where more than two LEDs may be desired, you can replace the single LED/diode in each path in the circuit with multiple LEDs.


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## ED-RRR (Jun 4, 2015)

*Update*



Mark R. said:


> I see a number of errors in addition to what was already pointed out. White LEDs require 3.2 to 3.4 volts to operate, not 2.0 volts. 2.0 volts would be for colored LEDs such as yellow, green or red.
> Mark.


Sorry: (But I Posted)..
.."MOST".. small LED's operate between 1.8/2.0 V-DC..
Also looking at "small" 3.mm LED's
There must be over a (x400) different LED's..
Each different LED will require different V-DC & mA..



Mark R. said:


> The term "clear" is rather misleading. Clear refers to the epoxy casing and is ofter referred to as water clear, as opposed to opaque casings. "Color" refers to the color of light emitted and there are usually three classes of white. You will find white, pure white and warm white. White usually has a slight blue cast to it - much like a flourescent light - which can be useful if you are wanting to represent that. Pure white is just that - a solid white with no blue over-tones. Warm white is a yellowish white much like that produced by an incandescent bulb.
> Mark.


You have done a lot of excellent "color" descriptions..:smilie_daumenpos:
-BUT-
Go to Ebay searching for LED 3mm = over 7,000 (Business & Industrial)
- the cheapest place to purchase LED's (China) 
- 98% only show LED picture color (No Detail Color Information)
- 75% do not show mA requirements
- that is why I have over (x25) different LED's
- all of my "clear" LED's have a "blue" tint
- higher the V-DC = the brighter the blue tint
- that is why I purchase "warm white" LED's on Ebay..



Mark R. said:


> You "can" run LEDs off AC voltage, but it's not a "best practices" method. I use them (red and green) straight across my DCC track joints in a reversing section to indicate "polarity" in the reversing section, and DCC is a like form of AC. If possible, it would be recommended to use a bridge rectifier to convert the AC to DC to run your LEDs.
> Mark.


I totally agree using a "bridge rectifier" converting AC to DC 
- BUT -
A "bridge rectifier" can get very hot requiring air cooling
and if installed "inside" a plastic rolling stock
may/could melt the plastic unit..
......


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## wvgca (Jan 21, 2013)

ED-RRR said:


> 1A, 50V, Signal Diode, DO-41
> At 12.V there was only -.5V drop
> ......


voltage drop across a silicon diode like the 1n4000 series is dependant to some extent on forward current, at 10ma its around 0.7v rising to 0.9v at 1 amp ...for small leds a 1n914 rated for 500mw is much smaller physically, and works well, you could also use a germanium or schottky diode with less than half the voltage drop of silicon, in my case i use whatever is handy as i do have a varied selection ...the differences are minor in most cases and the cost is negligible for any of the above style diodes ..
in any case the voltage drop and subsequent calculation of final resistor value is pretty forgiving of small errors or mis-calculations ..especially if a larger value resistor is used rather than running the led at maximum design brightness .. it's only a couple of pennies for the parts, but a pain having to take the shell off again , lol .. just out of curiosity i took a 20mA rated led [70 degree view angle] and ran it up to 42mA before it turned into a flashcube..it lit up a section close to eight feet in front very brightly, but not very long, lol


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## T-Man (May 16, 2008)

If any calculation doesn't burn out the LED, IT"S GOOD!. A lot of good comments. My favorite for AC is two LEDs back to back with no diode or bridge and one resistor. It works.

A thread back in 2010










I remember back in 2008 I couldn't verify how to use a diode with an LED The first breakthrough was the article in CTT .

It is a pleasure to see a thread with this information because I had to answer so many questions and there are many answers.


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