Tender wiring question

Model Railroader Electronics and DCC
1

This may apply to any tender with a LED/board wiring. The tender has no decoder, but only 2 wires that run to the light board. It has no resistors/capacitors on the board. I have a few questions.

  1. When using a multimeter, what setting do I use for a DCC equipped loco DC or AC to measure the voltage? I know that I must set it to the lowest reading initially. I burnt a DCC decoder once trying to read the voltage and I don’t want to repeat it with a DCC/Sound equipped loco.

  2. What are the usual classifications for LED’s…1.2V or 12V?

  3. How can I correctly test/troubleshoot a burnt LED…or does an LED look “burnt out” like a bulb? Thanks for any info.

2

  1. Actually it isn’t AC or DC but its more like AC on the track. But if you are measuring a light output from the decoder you want to use DC. I wouldn’t set my meter for the a reading a few times higher then the expected voltage. If you burnt out a decoder trying to read voltage you must have shorted the connections.

  2. Most LED’s used for MRR are usually 1.5 to 4 volts DC.

  3. LED’s don’t usually look any different when they are burnt out, I imagine if you really put a high voltage thru one it might look dark but I wouldn’t expect to tell by looking at one if its good. If this is an LED that once worked and now doesn’t, check to see if the leads are carrying any current by measuring the voltage, I would use a 10 or 20 volt DC scale. If you have something between 1.0 and 4.0 volts and the LED is not lit, I’d say its burnt out. If you have never seen the LED lit it could be installed backwards or have too high of a step down resistor and the LED could be good.

3

Thanks for the reply. I checked it at the bulb and got 9.2V, so I assume it to be a 12V LED? I have power all the way up to the bulb. The board is just that, it is a board with no resistors/capacitors and i could just as well bypass it as it reads the same voltage coming out of the loco.

4

You are confusing bulbs and LED. There are no 12 volt LEDs. There are 1.5 volt and 12 volt bulbs. If it is a LED, the resistor must be in the loco. When there is a 1.5 volt bulb, there will be a resistor. I have hit a LED with 12 volts accidently and the LED Popped. You can not test an LED with an ohm meter. You have to put the meter in series with one lead with the meter in say the 200ma current option. Be carfull or you can burn out the meter or at least pop the protective fuse.

If the headlight is a bulb, you will measure low resistance using the ohm meter.

How about telling us what the brand and type of loco you have? All the DCC steam locos I have are LED headlights but i know there are variations, i.e., bulbs.

This is a lot to consider if you do not understand electronics very well.

Here is a link to DCC for new people. There is a lot of electronics info for you.

http://www.members.optusnet.com.au/nswmn/index.htm

Rich

5

I replaced it with a 3.6V LED from Radio Snack and it works just fine. Thanks.