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Led for lighting Passanger Cars

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Led for lighting Passanger Cars
Posted by cudaken on Wednesday, May 02, 2018 9:36 PM

 I bought some used PRR HO scale Bachmann Cars that had lights. Most of the lighting equiment had been removed and I am fine with that. I still have the light bar and think I know why the lights where turned off, they have light bulbs and not LED's from Bachmann.

 I am running DCC and know LED's need resistors. With the proper resistor can a LED work with out burning out with no decoder from straight DCC power? What OHM do I need? I all so think I will need 2 to 3 LED's depending on the car. Run in parrel or serices? I want the lowest power draw I can get.

 Thank You folks for the coming answer.s.

 Cuda Ken

I hate Rust

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Posted by RR_Mel on Wednesday, May 02, 2018 10:04 PM

I went with warm white wide angle LEDs for my passenger cars.  I use 5 to 8 LEDs in each car at very low current for max realism.  I use 4.7k to 10K resistors depending how much light is needed.
 
 
Mel
 
Modeling the early to mid 1950s SP in HO scale since 1951
  
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
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Posted by hobo9941 on Wednesday, May 02, 2018 10:53 PM

With the proper resistor, you should be able to use LEDs on DCC. They are after all, diodes. Resistor value will depend on the desired brightness.

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Posted by khier on Thursday, May 03, 2018 10:43 AM

A LED consumes typically 20 mA, and creates a voltage drop of 3 V. You should check the specs of the desired LED for the appropriate values. So, as a first step, you have to check if your decoder can provide the required amperage, No. of LEDs x 20 mA (or whatever rate). If not, you will need an external driver, be it a transistor or an ULN2003/ULN2803 (you will need a power source, I will come later to this point).

Now you know your decoder can handle the current needed to light the LEDs, you have still to "choke" the voltage to limit the current to the premissible value (20 mA for parallel connection, or No. of LEDs x 20 mA for series, which no one should do BTW). I assume your decoder supplies regulated 16V. Your LEDs create a voltage drop of 3V if connected in parallel (again, chec the value). So the remaining driving "force" will be 16-3=13V. The current "pushed" by these 13 V should never exceed the 20 mA. Therefore you need to choke them by 13/20 = 0.65 Ohm, right? No, wrong, 0.65 x 1000 = 650 Ohm connected in series with EACH LED. Add 10% safety factor and go to the next higher resistance and you should be somewhere close to 800 Ohm.

Of course you can add a single resistance of No. of LEDs x the 800 mentioned above connected in series with the LED tree (three LEDs connected in parallel), but you should check for the power dissipation and whether your resistance can handle it - Better not do it unless the space is limited.

What if your decoder cannot provide the required 60 mA and you need an externla "relay"? The decoder can easily be connected to the relay (ULN2003 for example) with now porblem, but who supplies the power? You do not have a battery in your little train, do you? The ideal solution is a rectifier bridge connected to the wheels. This will rectify the square wave of the DCC and produce a constant 16 V, or slightly less. BTW, this is the same way the decoder gets the power and provide it to the motor. Take the output of the rectifier bridge, hook it to your ULN2003, et voila, you have enough power to light the house.

 

Regards

 

Walid

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Posted by khier on Thursday, May 03, 2018 10:47 AM

It may be 100 times easier if the following guess is true: A decoder does not really supply current to the light pin, but connect it to the ground. If this is the case, you can add the resistor directly between the LED and the current pick up, and the other leg to the decoder. You will have effectively half of the brightness sind the LED will use a single half of the DCC wave. Probalby you should check with a voltmeter first what the decoder really does.

 

Regards

 

Walid

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Posted by BigDaddy on Thursday, May 03, 2018 10:56 AM

Interesting idea, but he said he wasn't using a decoder in his passenger cars. 

 

Henry

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By the Chesapeake Bay

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Posted by khier on Thursday, May 03, 2018 11:06 AM

BigDaddy

Interesting idea, but he said he wasn't using a decoder in his passenger cars. 

 

Oooops.... in that case forget about the text book I wrote above. Hook a resistor to the current pick up, connect the other side to on side of the LED, the other side of the LED to the other current pick up. The resistor value can be estimated as mentioned in the previous post.

 

If the light is too dim for your taste connect a bridge rectifier IC to the current pick up. Refer to the data sheet of the rectifier IC  as you may need a capacitor. Use the two pins of the rectifier marked (+) and (-) as a power source and connect the LEDs to it, but do not forget the resistor in between.

 

Regards

 

Walid

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Posted by garya on Thursday, May 03, 2018 12:11 PM

I replied to a similar thread a few months ago:

http://cs.trains.com/mrr/f/744/t/267418.aspx

I used a diode and two resistors with my LED strips.  Seems to work ok.

Gary
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Posted by gmpullman on Thursday, May 03, 2018 3:54 PM

garya
I replied to a similar thread a few months ago:

I'll try to make it clickable:

http://cs.trains.com/mrr/f/744/t/267418.aspx

Cheers, Ed

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Posted by garya on Thursday, May 03, 2018 4:43 PM

gmpullman

 

 
garya
I replied to a similar thread a few months ago:

 

I'll try to make it clickable:

http://cs.trains.com/mrr/f/744/t/267418.aspx

Cheers, Ed

 

I tried 3 times before I gave up...

 

Gary
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Posted by BigDaddy on Thursday, May 03, 2018 4:52 PM

Somedays they aren't clickable

http://cs.trains.com/mrr/f/744/t/267418.aspx

 

Henry

COB Potomac & Northern

By the Chesapeake Bay

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Posted by cudaken on Thursday, May 03, 2018 5:33 PM

 Hey thanks for all the answers folks!

 Walid Thank you for your answers. Honstley had no idea what you where typing about Whistling but thanks for the effort!

 I am going to check the other link.

 Thank You all Again, Ken

 

I hate Rust

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Posted by DigitalGriffin on Friday, May 04, 2018 11:58 AM

If it's rectified from 14.4Volts
Part 1: Voltage that reaches circuit
14.4V - 1.4V (rectifier drop)= 13.0 Volts

Part 2: Calculating required voltage drop with a single LED
13.0 V - Vforward led = V drop
13.0V - 3.2V = 9.8V WARNING: Some white LED's only have a Vf of 2.7V. So read the specs!

Part 3: Calculating the required resistor
V = IR 9.8 = .020 * R
9.8 / 0.020 = R

R = 490 Ohms MINIMUM

The closest standard resistor is 510 Ohms.

I would advocate for at least 20% safety zone. That .016 ma current (which is super bright still) That's a 612 Ohm resistor. The closest standard resistor is 620 Ohms.

Here is my personal parts list

https://www.amazon.com/gp/product/B00B889A7W/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1

https://www.amazon.com/220uF-8X12-Aluminum-Electrolytic-Capacitors/dp/B074RJ215G/ref=sr_1_13?ie=UTF8&qid=1523290331&sr=8-13&keywords=220uF+capacitor+25V

https://www.amazon.com/Projects-100EP5141K20-1-2k-Resistors-Pack/dp/B0778NVY3C/ref=sr_1_3?s=industrial&ie=UTF8&qid=1523290451&sr=1-3&keywords=1.2k+ohm+resistor

And here's the picture of it put together

 

https://drive.google.com/file/d/1fGxBuw34rfiOtjH_YHt_dFarRyoGSbVN/view?usp=sharing

 

 

Don - Specializing in layout DC->DCC conversions

Modeling C&O transition era and steel industries There's Nothing Like Big Steam!

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Posted by rrinker on Friday, May 04, 2018 3:11 PM

 (and I know we all do it) After running the calcs, the most likely go-to answer is - 1K resistor. STILL plenty bright, less than half the LED's current rating.

                            --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by DigitalGriffin on Friday, May 04, 2018 4:20 PM

rrinker

 (and I know we all do it) After running the calcs, the most likely go-to answer is - 1K resistor. STILL plenty bright, less than half the LED's current rating.

                            --Randy

 

 



lol.  Guilty

Don - Specializing in layout DC->DCC conversions

Modeling C&O transition era and steel industries There's Nothing Like Big Steam!

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