Baffled as to why h/l bulb worked but LED will not.

[on30gn15]

While we've been talking LED headlights on a couple other threads; 

Have a DCC ready with 8 pin socket 2-10-2 by IHC: while working on the Bachmann 0-6-0 for me, and John's old AHM RS-2, and another LED h/l job for Kathy, cut off the 2-10-2's apparently 12v rated "dim bulb" incandescent headlight bulb and after 20 minutes of playing with LED and resistors there was no "let there be light" moment.

Even hooked an un-resisted LED to the wires and nope, nothing, no light, no blowout.

Am baffled as to why a 12v light bulb works on the circuit but a 1.5V LED stays dark no matter which pole is attached to which side of the headlight bulb wires.

It wasn't a bad LED, it is the one now in the 0-6-0.

Y'all have any ideas?

thanks again
Forrest

[richg]

Reverse the wires. As I told you before, LED's are polarity conscious. I have put in LED's before with the needed resistor with no issues.
Making sure you have the light selected by the controller as that happened to me before. I got out my voltmeter and checked the light coonection at the decoder and zero volts. I had inadvertently hit the light button and then off the function. Stuff happens.

Link below is about light bulbs and LED's used with DCC.

http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm

Rich

[on30gn15]

1.5V LED stays dark no matter which pole is attached to which side of the headlight bulb wires.

<-- I did

[richg]

1.5V LED stays dark no matter which pole is attached to which side of the headlight bulb wires.

<-- I did

Then that tells me the LED is burnt out. A sure check is to get a nine volt battery and a 1k resistor. With the proper polarity, the LED will light if it is good. LED's can burn out without a noticeable pop.


Rich

[on30gn15]

Then that tells me the LED is burnt out.

It wasn't a bad LED, it is the one now in the 0-6-0.

Y'all have any ideas?

thanks again
Forrest

[richg]

This getting really confusing. You say the LED is working.

Rich

[WoundedBear]

Nothing confusing about it......the LED won't work in one model, but he installed it in a different model and it works. So the LED was not the problem. Simple as pie. Slow down and read, Rich. You get in a huff and a rush too often.

Sid

[jward]

here's a shot in the dark (pun intended)......

did you measure the voltage across the buld when lit? just because it was a 12v bulb doesn't mean the circuit was designed to put 12v on the bulb. in fact, bulbs last longer at lower voltages.  my guess is that the bulb waas operating at a lower voltage, maybe 6v or so. having the resistors to operate the led off 12v may have put the current down to the point where the led wouldn't light. it's something to look at.....

[richg]

My bad. I was assuming he had used his voltmeter to check the decoder output. Most are about 12 vdc for the lights. The decoder instructions clearly tell you what the specs are.

Rich

[richg]

on30gn15

Get a couple of the below meters if you want to work at the component level. They will be a big help in trouble shooting.

I have had three of these for quite some time. My meters read about 13.6 VAC on the track when checking my NCE Power Cab DCC controller.

http://www.harborfreight.com/7-function-multimeter-98025.html

For model railroading.

http://www.trainelectronics.com/Meter_Workshop/index.htm

For reading current and voltage at the same time, two voltages or two different current measurements.

http://www.trainelectronics.com/Meter_HF/index.htm

Rich

[bapguy]

Since you installed LED's before, how did you check the 2-10-2? Loco on track with power to it, F0 button on, throttle set in forward setting? I agree with others: get a good multi meter and check votage out put for lights. Can you hook up the old bulb to a 9v battery to see how bright it is?   Joe

[electrical whiz kid]

Rich G; Wounded Bear; et al offer some excellent advice based upon their knowledge.  I am glad to see such on this site on a more or less regular basis.
Rich C.