Pre-Wired 3mm LEDs

[Toolbelt]

Looking at some LEDs for a dcc conversion, and it seems most of the pre-wired ones for 12v use a 560 ohm resistor whereas I'd prefer to use 1000 ohm. Do most here just make their own using a bare led/resistor/wire/shrink tubing or is there a source for these? Amazon lists tons of cheap options for 3v or 12v use, but the few options that use 1000 ohm resistors the price jumps 400%.

Also, as I intend to use my loco for both DC and DCC, will a 1000 ohm LED even illuminate on a DC layout running at say 1/4 or 1/2 throttle where the track voltage is only say 4v-8v?

 

[Dub]

Look at voltage amperage and resistance. If the resistance is the same for both voltages the amperage will be lower at higher voltages.
You know it works at both voltages with 1000 ohms. Heck it will work with 1500 ohms!. So just add one more 560 ohm resistor and you should be good to go.

Going back to amperage I used .02ma for the calculation but that will give maximum brightness. So it is a game to stay within specs and have the Led work right. It is nice to calculate it out and then test it.

 

[ctclibby]

Looking at some LEDs for a dcc conversion, and it seems most of the pre-wired ones for 12v use a 560 ohm resistor whereas I'd prefer to use 1000 ohm. Do most here just make their own using a bare led/resistor/wire/shrink tubing or is there a source for these? Amazon lists tons of cheap options for 3v or 12v use, but the few options that use 1000 ohm resistors the price jumps 400%.

Also, as I intend to use my loco for both DC and DCC, will a 1000 ohm LED even illuminate on a DC layout running at say 1/4 or 1/2 throttle where the track voltage is only say 4v-8v?

If you can solder small stuff - roll your own. @Kusojiji ifn I remember uses SMT resistors and he does his own. As to the 1/4 or 1/2 throttle - assuming 16VDC is full throttle, 8V for Led would produce ( 8V - VLED) /1000 would be about 6.8mA assuming 1.2V VLED, probably pretty dim.

Look at voltage amperage and resistance. If the resistance is the same for both voltages the amperage will be lower at higher voltages.
You know it works at both voltages with 1000 ohms. Heck it will work with 1500 ohms!. So just add one more 560 ohm resistor and you should be good to go.

Going back to amperage I used .02ma for the calculation but that will give maximum brightness. So it is a game to stay within specs and have the Led work right. It is nice to calculate it out and then test it.

Um, what? Given current and resistance with an applied voltage - the current ( or power ) will never go down as the voltage goes up.

Assume you meant 20mA not 20uA? Usually 20mA is max for most of the smaller LED's. See their datasheet to be sure. Yes, you can pulse them at higher current but watch that duty cycle. Super Brights are a different animal - definitely check their datasheet.

L8r

 

[Dub]

If you can solder small stuff - roll your own. @Kusojiji ifn I remember uses SMT resistors and he does his own. As to the 1/4 or 1/2 throttle - assuming 16VDC is full throttle, 8V for Led would produce ( 8V - VLED) /1000 would be about 6.8mA assuming 1.2V VLED, probably pretty dim.


Um, what? Given current and resistance with an applied voltage - the current ( or power ) will never go down as the voltage goes up.

Assume you meant 20mA not 20uA? Usually 20mA is max for most of the smaller LED's. See their datasheet to be sure. Yes, you can pulse them at higher current but watch that duty cycle. Super Brights are a different animal - definitely check their datasheet.

L8r

Thank you for the correction, I would hate to confuse anybody.
If I do an Ohm's Law calculation I use .02A, the max value. What do you use for that number?

 

[ctclibby]

Thank you for the correction, I would hate to confuse anybody.
If I do an Ohm's Law calculation I use .02A, the max value. What do you use for that number?

Same same - .02A is 20mA. No clue as to the why part for me, guess that I have been in electronics tooooo long. I have seen some people miss that leading '.' which throws any design out the window. Whenever you 'do the math', that 20mA gets changed into Amps ( .02A ) either in your brain, or using calculator's EXP function ( 20E-3 ).

L8r

 

[Kusojiji]

I put the smt resistor on some double sided tape on a heat resistant surface to tin and connect the wire to it. The only thing shaking would be the soldering iron at that point.

 

[Toolbelt]

I put the smt resistor on some double sided tape on a heat resistant surface to tin and connect the wire to it. The only thing shaking would be the soldering iron at that point.

Resistance levels being equal, what's the benefit of using smt vs standard inline resistors, assuming you'd be using smt's as inline, rather than mounting them on a board? Are they half the size? My eyes can handle typical 1/4 watt inline resistors, but that's approaching my limits.

 

[Toolbelt]

If you can solder small stuff - roll your own. @Kusojiji ifn I remember uses SMT resistors and he does his own. As to the 1/4 or 1/2 throttle - assuming 16VDC is full throttle, 8V for Led would produce ( 8V - VLED) /1000 would be about 6.8mA assuming 1.2V VLED, probably pretty dim.


Um, what? Given current and resistance with an applied voltage - the current ( or power ) will never go down as the voltage goes up.

Assume you meant 20mA not 20uA? Usually 20mA is max for most of the smaller LED's. See their datasheet to be sure. Yes, you can pulse them at higher current but watch that duty cycle. Super Brights are a different animal - definitely check their datasheet.

L8r

Check my math, using 3.2v 20ma Warm white LEDs and 1000 ohm resistors, I would be feeding the LEDs 12ma at 12vdc?

 

[Kusojiji]

Resistance levels being equal, what's the benefit of using smt vs standard inline resistors, assuming you'd be using smt's as inline, rather than mounting them on a board? Are they half the size? My eyes can handle typical 1/4 watt inline resistors, but that's approaching my limits.

Size mainly. I use 1206 SMT. 1/4 watt, 3.2 x 1.1 mm. Common resistance values available. Yeah inline mostly. If I could make a board, I would. When I get back home I’ll post some pics.

I made a small thread on surface mount if a board is available. Using a heater like an IH stove makes it easy.

Thread 'SURFACE MOUNT SOLDERING'

Nov 5, 2025

I bought some boards that have an NPN IC circuit and resistor to change logic to power outputs from a DCC decoder. I'm going to need AUX 3 changed to power for one of my upcoming projects and didn't want to wire directly to an IC chip.

Unfortunately, I have to solder the microscoping IC chip and no-see-um resistors. I decided to give heatpad soldering a try, so I bought some low melt solder paste and used a cookie kit cast iron pan.

First step was to ensure the boards were cleaned with IPA. Then it was adding some solder paste to the solder pads. I...

• Kusojiji
• Replies: 6
• Forum: Wiring, Electronics and DCC

• 
• 

Sorry, I don’t know how to just post the link using an iPad.

 

[ctclibby]

Resistance levels being equal, what's the benefit of using smt vs standard inline resistors, assuming you'd be using smt's as inline, rather than mounting them on a board? Are they half the size? My eyes can handle typical 1/4 watt inline resistors, but that's approaching my limits.

I hear ya, SMT is smaller, but sometimes we try to put stuff in a spot that needs smaller; it was just a thought.

Check my math, using 3.2v 20ma Warm white LEDs and 1000 ohm resistors, I would be feeding the LEDs 12ma at 12vdc?

Assuming the LED's are not in series: looks like you forgot the led drop: ( 12V - 3.2V ) / 1000 ~ 8mA

L8r

 

[Toolbelt]

Assuming the LED's are not in series: looks like you forgot the led drop: ( 12V - 3.2V ) / 1000 ~ 8mA

You're right. Unfortunately, rather than doing the math, I just googled voltage, resistor and target milliamps and it spit out my original estimate. It never mentioned F voltage surprisingly. I think I'll stick to using resistor calculators where you fill in the values and click "calculate".

 

[Toolbelt]

O

Size mainly. I use 1206 SMT. 1/4 watt, 3.2 x 1.1 mm. Common resistance values available. Yeah inline mostly. If I could make a board, I would. When I get back home I’ll post some pics.

I made a small thread on surface mount if a board is available. Using a heater like an IH stove makes it easy.

Thread 'SURFACE MOUNT SOLDERING'

Nov 5, 2025

I bought some boards that have an NPN IC circuit and resistor to change logic to power outputs from a DCC decoder. I'm going to need AUX 3 changed to power for one of my upcoming projects and didn't want to wire directly to an IC chip.

Unfortunately, I have to solder the microscoping IC chip and no-see-um resistors. I decided to give heatpad soldering a try, so I bought some low melt solder paste and used a cookie kit cast iron pan.

First step was to ensure the boards were cleaned with IPA. Then it was adding some solder paste to the solder pads. I...

• Kusojiji
• Replies: 6
• Forum: Wiring, Electronics and DCC

• 
• 

Sorry, I don’t know how to just post the link using an iPad.

OMG those things are tiny. I would likely lose half an arm or at least a few fingers soldering those.

 

[Toolbelt]

Size mainly. I use 1206 SMT. 1/4 watt, 3.2 x 1.1 mm. Common resistance values available. Yeah inline mostly. If I could make a board, I would. When I get back home I’ll post some pics.

I made a small thread on surface mount if a board is available. Using a heater like an IH stove makes it easy.

Thread 'SURFACE MOUNT SOLDERING'

Nov 5, 2025

I bought some boards that have an NPN IC circuit and resistor to change logic to power outputs from a DCC decoder. I'm going to need AUX 3 changed to power for one of my upcoming projects and didn't want to wire directly to an IC chip.

Unfortunately, I have to solder the microscoping IC chip and no-see-um resistors. I decided to give heatpad soldering a try, so I bought some low melt solder paste and used a cookie kit cast iron pan.

First step was to ensure the boards were cleaned with IPA. Then it was adding some solder paste to the solder pads. I...

• Kusojiji
• Replies: 6
• Forum: Wiring, Electronics and DCC

• 
• 

Sorry, I don’t know how to just post the link using an iPad.

I always wondered why my local hobby store stocked frying pans. lol

 

[Kusojiji]

It came from one of those cookie kits. I forget who made it. I used to use it to make egg McMuffins.

 

[Toolbelt]

It came from one of those cookie kits. I forget who made it. I used to use it to make egg McMuffins.

Necessity is the mother of all inventions.

 

[Kusojiji]

I used it again today to solder an 805 size SMT resistor. Used double sided tape to hold the resistor, tinned it, then stuck the wires on.

I then cut the excess off and wrapped it in kapton.