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Offline Chris6382chris  
#1 Posted : 02 March 2011 07:34:48(UTC)
Chris6382chris

United States   
Joined: 27/11/2009(UTC)
Posts: 1,218
Location: Middle of the US
I am installing a delta 66032 chip into an engine and wanted to replace the light bulb that came with the engine with an LED. What is the voltage coming out of the gray and yellow wires that feed the lights? I was thinking of going to Radio Shack and grabbing a couple LED's and was wondering what I should get. Also will I need to add a resistor as well, between the chip and the LED? If so what would be a good combination of LED and Resistor, looking for the lowest draw while still being somewhat bright.

Thanks,

Chris
Offline perz  
#2 Posted : 02 March 2011 08:35:41(UTC)
perz

Sweden   
Joined: 12/01/2002(UTC)
Posts: 2,578
Location: Sweden
I think this newer version of the Delta decoder has a steady 20 V lamp voltage (older versions had a voltage that varied with motor speed). You will always need a resistor in series with the LED. A LED typically draws 10 - 20 mA and the voltage over it is approximately 3 V (in case of a white LED). This would give 17 V over the resistor, and if you aim at 10 mA this means a 1.7 kOhm resistor. Nearest standard values are 1.5 kOhm and 1.8 kOhm. The power rating of the resistor can be calculated as U*U/R where U is the voltage and R is the resistance. Assume you have a 1.8 kOhm resistor: 17 V * 17 V / 1.8 kOhm gives 160 mW, so 160 mW is the minimum power rating for the resistor. Add some margin to that to be safe.

Offline H0  
#3 Posted : 02 March 2011 09:44:31(UTC)
H0


Joined: 16/02/2004(UTC)
Posts: 15,463
Location: DE-NW
Hi, Chris!
Originally Posted by: Chris6382chris Go to Quoted Post
Also will I need to add a resistor as well, between the chip and the LED?

You need something that limits the current through the LED - and a resistor is a simple way to achieve that.

You can have several LEDs (of the same type) in series. You'll need a smaller resistor and you'll get more light (and less heating) frome the same current.
Regards
Tom
---
"In all of the gauges, we particularly emphasize a high level of quality, the best possible fidelity to the prototype, and absolute precision. You will see that in all of our products." (from Märklin New Items Brochure 2015, page 1) ROFLBTCUTS
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Offline Chris6382chris  
#4 Posted : 02 March 2011 17:26:47(UTC)
Chris6382chris

United States   
Joined: 27/11/2009(UTC)
Posts: 1,218
Location: Middle of the US
Thanks to both of you for your answer. So I will look for a 160-170 mW rated resistor and wire it in series to my 3 volt LED.

Chris
Offline H0  
#5 Posted : 02 March 2011 17:38:25(UTC)
H0


Joined: 16/02/2004(UTC)
Posts: 15,463
Location: DE-NW
The standard type of resistors has 0.25 W (250 mW)
Regards
Tom
---
"In all of the gauges, we particularly emphasize a high level of quality, the best possible fidelity to the prototype, and absolute precision. You will see that in all of our products." (from Märklin New Items Brochure 2015, page 1) ROFLBTCUTS
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Offline frankie  
#6 Posted : 02 March 2011 17:53:29(UTC)
frankie


Joined: 27/10/2006(UTC)
Posts: 692
Location: Italy
I'm noy into electronics, but I have already used this solution, the resistor must be soldered on one of the pin of the LED, is there a way to figure out on which one? Because it works only on one of the two...
Alessandro
I have a CS1 Reloaded!
Offline perz  
#7 Posted : 02 March 2011 19:29:46(UTC)
perz

Sweden   
Joined: 12/01/2002(UTC)
Posts: 2,578
Location: Sweden
Originally Posted by: frankie Go to Quoted Post
I'm noy into electronics, but I have already used this solution, the resistor must be soldered on one of the pin of the LED, is there a way to figure out on which one? Because it works only on one of the two...


The resistor can be on either side of the LED, but the LED always needs to have the correct polarity. Probably when you only got it to work one way, you had the LED flipped as well.

Offline H0  
#8 Posted : 02 March 2011 21:53:32(UTC)
H0


Joined: 16/02/2004(UTC)
Posts: 15,463
Location: DE-NW
Originally Posted by: perz Go to Quoted Post
The resistor can be on either side of the LED, but the LED always needs to have the correct polarity.

Might be worth to mention that the decoder polarity is not what many expect: the common wire (orange with M* decoders, blue with NMRA standard (e. g. ESU)) is plus, decoder function outputs (yellow and grey with M* decoders) are minus.
Regards
Tom
---
"In all of the gauges, we particularly emphasize a high level of quality, the best possible fidelity to the prototype, and absolute precision. You will see that in all of our products." (from Märklin New Items Brochure 2015, page 1) ROFLBTCUTS
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Offline Dave Banks  
#9 Posted : 02 March 2011 22:57:26(UTC)
Dave Banks

Australia   
Joined: 08/03/2006(UTC)
Posts: 1,047
Location: Gold Coast, Australia.
Chris also you can modify this chip to have a function for your light. http://www.bogobit.de/decoder/66032.html
D.A.Banks
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