Thanks for the responses everyone. The obvious solution would be to replace all the resistors with higher values, but that's going to be a PITA and I was hoping there might be a quick fix.
Mel's post encourages me to try the single resistor trick to see how it affects brightness in different lighting configurations (e.g. when the ditch lights are flashing). If it's not too noticeable, I might just go with that solution. Otherwise, I'll just bite the bullet and replace all the resistors, but I'll most likely just live with it for a while until I don't have any better hobby projects to work on.
I also like the suggestion of building a LED test rig with a potentiometer, so I'll definitely look into that. Thanks for the suggestion!
Dan Stokes
My other car is a tunnel motor
One resistor for all of them on the blue wire will result in varying brightness depending on how many lights are on at the same time.
If you make a test rig with a potentiometer, I'd suggest 2 things: 1, use a 5K pot not a 2.5K, since with SMD LEDs you can eaisly use 4.7K of resistance to get the desired brightness, and 2, put a 1K resistor in series with the pot. Since the LEDs are fine with 1K, if you accidently turn the pot all the way to 0, you'd still have 1K in the circuit and not blow up the LED. It's rare to ever need less than 1K, I haven't seen anyone say 1K is too dim and use less. Same calculation, just add 1K to the measured value.
Or build a resistor substitution box, with a rotary switch and standard value resistors, starting at 1K. S common 12 position rotary switch would handle the entire E12 (10% tolerance) range, from 1K to 8.2K And if you label the knob you know exactly which resistor to use. No multimeter needed. You'd have 1K, 1.2K, 1.5K, 1.8K, 2.2K, 2.7K, 3.3K, 3.9K, 4.7K, 5.6K, 6.8K, and 8.2K. Just dial the best option for brightness.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
richg1998 At one time I had sets of flea clips and a 2.5k pot. Connect pot in series and adjust for proper brightness. Measure resistance of pot. Choose closest standard resistor from the junk box. I don't like working with math so I went the easy way. Rich
At one time I had sets of flea clips and a 2.5k pot. Connect pot in series and adjust for proper brightness. Measure resistance of pot.
Choose closest standard resistor from the junk box.
I don't like working with math so I went the easy way.
Rich
That's how I do it, too.
Dave
Lackawanna Route of the Phoebe Snow
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Trial and Error. Do it on the bench, try 2k ohm or maybe 3k ohm until you get what you want. LION has some LED sighals that are too bright, Him conqured that problem by putting hoods over the signals. Now looks purrfect they do.
Speaking of Trials, LION has been called for Jury Duty. I wonder if they even let LIONS into the courtroom? Findout we will.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
I don't know if adding a single resistor to the blue wire will do the trick, but I will say that the SMD LEDs are very, very bright. I wound up using a much higher value resistor than 1K ohms to reduce the brightness.
Alton Junction
voltage drop across a resistor is depenent on current flow E=IxR, with the single resistor the more lights you have on would mean more voltage drop , don't know though with LED's low current draw if it would be noticable.
I have a Blue Box loco that I upgraded with a DCC decoder and SMD LEDs. There are six total LEDs (dual headlight, dual rear light, two ditch lights), and each one has its own 1k ohm resistor. Everything works fine, but the LEDs seem a bit too bright for my taste. I could replace all the resistors with higher values, but was wondering if this could also be fixed by placing a single resistor in the blue wire from the decoder? If so, would the overall brightness be noticeably affected depending on how many lights are on at once (e.g. when the ditch lights flash, or when both headlight and rear light are on)?