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Can two LEDs share a resistor?

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Posted by Overmod on Friday, May 5, 2023 8:32 PM

None of the epoxies I'm familiar with do anything to resistors.  In fact the most common 'potting' materials to make circuits shock- and weatherproof are epoxies.

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Posted by CSX Robert on Friday, May 5, 2023 8:49 PM

crossthedog
I was wondering the same thing, cuz it sure looks like they've wrapped a tiny resistor in there, but this package of LEDs I bought specifically because I wanted some withOUT built-in resistors. So I think that's just the soldered joint under there.

crossthedog
The only "specs" I have for the LEDs is that the package is labeled Warm White and 9.0 to 12.0 volts.

A white LED will typically have a voltage drop of 3-3.5 volts, If they are labeled 9 to 12 volts, then they do have resistors so you shouldn't have to add any unless they are too bright.  

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Posted by crossthedog on Friday, May 5, 2023 9:19 PM

CSX Robert
A white LED will typically have a voltage drop of 3-3.5 volts, If they are labeled 9 to 12 volts, then they do have resistors so you shouldn't have to add any unless they are too bright.

Well that's what Ed (or was it Dave?) thought, too, just looking at my photo. But I was pretty sure that I intentionally bought LEDs that did NOT have resistors. But I've bought a lot of lights lately, trying different things. Since I have a whole pack of these I suppose I could spare one for a test. I'll hook it up without a resistor and see what happens. If it doesn't blow up, I guess that means it has one built in. And if that is the case it might explain why I thought the cafe looked a little dim when I lit it up for a test. I'll report back later. It's pizza night at our house, my wife's homemade pizza dough.

-Matt

Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.

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Posted by gmpullman on Friday, May 5, 2023 10:04 PM

I can see the profile of the resistor under that heat shrink. It looks like a snake that swallowed a dumbell. I have dozens of that style, too. They're perfect for a direct replacement of the old Life-Like bulbs in their locomotives.

Good Luck, Ed

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Posted by crossthedog on Friday, May 5, 2023 11:56 PM

gmpullman
I can see the profile of the resistor under that heat shrink. It looks like a snake that swallowed a dumbell.

Speaking of dumbells, color me embarassed. It turns out there ARE resistors in there. Here's a test hookup with no (additional) resistors.

I feel sheepish having run everyone "all around Robinhood's barn" all day trying to figure out how to get resistors into the wiring.

It's actually not that much brighter than the test with resistors, but the fact that the bulbs didn't blow up proves that they are protected by embedded resistors. I think I was sold something I did not order, or else there was "order incompetence" on my part.

You can see that greenish cast to the light in the cafe. It's worse in person. I may paint the inside of the lower floor white -- and the ceiling -- to see if I can make it more like a busy diner in there. I may also put up a false wall in front of those wires coming down the inside. Or paint them, as someone suggested. And I'm hoping that painting the exterior of the building will take care of the light leak that's showing right through the outer wall above the upper windows.

The upper floor light I like a lot, although I may have gone a bit heavy on the red paint on the bulb, because it almost looks like firelight, and I was aiming more for a reading lamp vibe.

Anyhoo, this parTICKular job will be much easier than I'd anticipated. But thank you all. I will save this thread and refer to it because I'll only be doing more and more structures in the months to come. I have a five or six story hotel to do, and I may wire it up with Brent's copper tape method before I even assemble the walls.

-Matt

Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.

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Posted by hon30critter on Saturday, May 6, 2023 1:24 AM

crossthedog
I have a five or six story hotel to do, and I may wire it up with Brent's copper tape method before I even assemble the walls.

Hi Matt,

I think that learning how to plan ahead for details like lighting and wiring is one of the more challenging aspects of building a structure. In the past I have been a bit like a bull in a china shop. I always wanted to charge ahead with putting the major parts together when I should have spent much more time planning for the interior details. My bad!

Good luck with your lighting project!

Cheers!!

Dave

I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!

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Posted by Overmod on Saturday, May 6, 2023 6:08 AM

That slightly greenish color is how I remember the ceiling in Hopper's Nighthawks.  I thought of it then as being light reflected from pale celadon green interior paint.  I think if you put further resistance in the line to those particular resistors you could re-create that 'look'.

(I went back to check if I remembered this right and there are all sorts of 'corrected' tonal ranges in commercial prints of the painting...)

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Posted by crossthedog on Saturday, May 6, 2023 9:00 AM

Overmod
That slightly greenish color is how I remember the ceiling in Hopper's Nighthawks.

Overmod, great catch! Nighthawks is one of my favorite paintings of one of my favorite painters. And one of my favorite bands of the '80s/'90s made a video that riffed on it.

I also see that you can buy the whole Nighthawks neighborhood in HO scale.

-Matt

 

Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.

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Posted by MisterBeasley on Saturday, May 6, 2023 11:34 AM

Be careful if you are using different LEDs in the structure.  They may have significantly different resistance values so using parallel wiring may "steal" the power from one LED to light the other.  I wired a signal bridge using red, yellow and green LEDs, and my parallel wiring didn't work and I had to re-do the circuit for series wiring.

It takes an iron man to play with a toy iron horse. 

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Posted by BATMAN on Saturday, May 6, 2023 11:52 AM

Brent

"All of the world's problems are the result of the difference between how we think and how the world works."

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Posted by BigDaddy on Sunday, May 7, 2023 7:01 AM

lots of useful info here  https://electronicsclub.info/leds.htm

I used an orange translucent paint (Tamiya?) to warm up a bright white led.  That might take the green out of the lower floor.  I wouldn't use too much though, or else it will look close to the top floor.

 

 

Henry

COB Potomac & Northern

Shenandoah Valley

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Posted by crossthedog on Sunday, May 7, 2023 3:55 PM

Henry, that's the exact look I'm aiming for. Wow, that bookstore or library is amazing, complete with a print of The Flying Cloud on the wall!

-Matt

Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.

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