LED mystery to me

The brightness of an LED is dependent on CURRENT, not voltage. There should be current-limiting resistors in this circuit somewhere.

• Are both LEDs connected to the same resistor? If so, then the problem is with one of the LEDs.
• If there are two resistors, are they the same value? If so, then the problem is with one of the LEDs.
• If there are two resistors and they are not the same value, that's the problem.

Thanks' Rich. Two resistors...I'll have to open up the shrink wrap to determine if the same value. But, you've given me an answer...either different resistor values or a 'dim' bulb....metaphor for me at times as well. 

@ToledoEd posted:

I understood when the same voltage is sent to like LEDs  they would burn with the same intensity.

Rich, you beat me to it.

Ed, Rich has pointed out that there's a fly in your ointment.  It isn't voltage that they follow, it's current.  This means that two LED's can be connected to the same voltage and have different intensities.

However in the case of your jet car it's even simpler than that.

Notice that your connections are covered in heat shrink tubing (see the yellow ovals above).  As has been pointed out if you pull this covering off of the leads you'll see that inside there are two resistors, one in each lead; one in each yellow oval.  My bet is that the values of those two resistors are quite different.  This explains the variation in brightness.

Resistors placed in series with LEDs in this way are used to set the current that these LEDs see (for a given applied voltage at the power source).  Different current means different intensity.  Different resistors mean different current.

If you want them to be same brightness you'll need to change one of the resistors to match the other.

Good luck.  Let us know what you decide.

Mike

You can also put the LED's in series and use a single dropping resistor, that will guarantee they get the same current.

@gunrunnerjohn posted:

You can also put the LED's in series and use a single dropping resistor, that will guarantee they get the same current.

Excellent point.  What I love about electronics is that there's always more then one way to deal with a challenge.

A good, and simplifying, suggestion.

Mike

Ed, your getting good suggestions here.  Personally, I like Johns approach, and that is how I also wire my LEDs'..

Try both methods, see which one you like best'...

Ted, I'll try both approaches...unless of course the first one I try solves the issue.   I'll get back to you.  Thanks again, Gents. This Forum is an amazing resource!

The resistors are the same...same color, blue and the rings are the same colors and in the same order. The plug supplies about 14v +-  I checked the resistance and the bright light resister read 987 and the other 994.   I guess the LED is tired. When I replace the LED I'll come back. Not sure I have a 3mm cool white in the inventory so it may be a few days.

Other than size (3mm) and color, cool white, does any other value matter?  If found this on Amazon.  More LEDs than I'll ever need.

Ed,

Interesting.

Thanks for the feedback, and the measurements.  As you're probably aware buy now they indicate that your two resistors are essentially identical so there should be no difference in intensity.  It's extremely rare nowadays for LEDs to exhibit this behavior, but it did happen from time to time in their early history, i.e., 1970's.

In the modern era most of the time they work, and all have the same intensity if using the same resistor; or they don't work at all, and they're dark.

Mike

Thanks Mike. Good info for me.  I guess I got 'lucky' with that LED. The engine was cataloged in 2011 if memory serves.

I found a white 5mm led from Evans in my 'pile'...I was able to stuff into the Jet engine nacelle and compared it to the original Lionel installed 3mm...I like the bright white 5mm. If replace the 3mm with 5mm, do I need to worry about heat from the 5mm LED?   

No difference in heat from a 3mm or 5mm standard LED, both are rated at 20ma.

thanks, John 

I decided to install 2 Evan Designs 3mm Cool White LEDs in the nacelles.  I can feel the heat when I fire them up!   Thanks for the help in solving this problem.

Cool.  I might have to get one of those ...

@Mellow Hudson Mike posted:

Cool.  I might have to get one of those ...

Thanks, you should. Control is conventional.  Not TMCC.. Sounds are really neat.

Okay Ed, I think it is time for a video, so we cab see this hot baby in action'..👀😁

@Quarter Gauger 48 posted:

Okay Ed, I think it is time for a video, so we cab see this hot baby in action'..👀😁

It’s in production. 😁

@Quarter Gauger 48 posted:

Okay Ed, I think it is time for a video, so we cab see this hot baby in action'..👀😁

Ted, here's a recording before one of the engine LEDs dimmed.  What I meant by "In production" is I'm editing a video that shows the three turbine powered trains in my inventory...two MTH and this Jet Car.  I plan to have it posted on YouTube later today...

That is a very cool Bud car'... I just watched a bunch of your videos I hadn't seen before'.. You sure have plenty of them... and WOW' I didn't know you had two Big Boys'.. in your extensive collection'... Very impressive'..👍

Ted, Thanks. I enjoy the hobby.  Correction.  one Big Boy, one Challenger