LED's & AC POWER: Don't Be Afraid. They Are VERY Simple To Install

Of course, for long life on AC, you should also use a blocking diode.  The max reverse voltage specification of common LED's is between 5 and 7 volts.  This will be exceeded by any reasonable AC source.  The only thing protecting the diode is the current limiting, but they will have a much shorter life without the diode.

John,

     Of course we concur but we were putting it in the most basic terms so people will not be frightened to up grade their older E&T's or rolling stock.

Dave, LBR

I don't think most folks have an issue with wiring a single LED, IMO the issues arise when trying to install them in multiple buildings, lamps, passenger cars, etc.

How many LEDs to put on a single circuit, how do I run the wiring, what voltage power supply do I use, do I put them in parallel or series, do I use multiple power supplies, what kind of wire do I use, what size LED to use?  How do I replace a lamp (not knowing the voltage of the lamp) with a LED?

I expect a lot of folks have both AC and DC power supplies laying around, you have to consider all things when installing LEDs.

I don't know if I've ever blown a LED by wiring it up reversed polarity, usually it just doesn't work until I get the polarity right.

One thing I need to read up on is...what do I do when 1 LED in a string of LEDs goes out?  1 going out changes the voltage to the rest, depending on how it was wired (series or parallel) and could result in the entire string eventually burning out.

It's simple, but it's not THAT simple.

Bob, it's not a simple wiring in reverse, it's the cumulative pounding from the reverse voltage half of the AC cycle.  This is not unlike IC failures from repeated small ESD events, they don't fail the first time, but eventually they do fail.

I had several headlights die on TMCC installations for no apparent reason until I started using diodes to protect the LEDs.  Most people figure if they use an LED, they should never have to change the bulb again.  I'm just pointing out that without proper installation protection, this is likely a false assumption.

What is the problem installing 2 cent diode anyway?

Dale H

Dale, you have to know which end is "up", for one. I have a related question if it isn't stealing the topic. Why do I have three blown switch stand lights out of the sixteen Fastrack switches I have, if they are supposed to last forever? I haven't tried to change any, as it looks fairly complicated opposed to the new ones I got for 3-4 bucks. Which is easier in your and John's opinion; current limiting or resistors? I have used both, but I have only done a few conversions.

John

I need to know what they are and what voltage powers them. Track power? Both current limiting and fixed resistors work. Fixed resistors are less complicated. With fixed voltage input,I would just use a resistor. If voltage input varies,then LED intensity would vary. For an indicator light I dont think this is an issue. For passenger car lighting,it might be noticeable. I like CL2-N3 chips for current limiting. There is no one way to do things. Whatever works for you is the right way. John is a good egg and talented engineer. I am sure his circuit is well engineered and thought out.

As far as installing the diode. Put it in series to either lead. If it dont light it is backwards. Turn it around. Observe the markings and do them all that way. The simple way is not always the best way. Leaving this out of the LED circuit is like building a car and leaving the air filter off. The car will run without it, for a while anyway. But long term you will get the gas intake dirty and cause wear in the combustion chamber.  I dont know if I would want to buy a car from a company with that philosophy. Just my opinion.

Dale H

An easy way to protect LEDs on AC is to use two in parallel, with the +- connected together and then through the resistor. MTH uses this configuration on many of their products such as their aquarium cars.

Kevin, that's only useful if you have two LED's in close proximity that you want to run from a single circuit.

For the Fastrack switch, I'd assume you'd just need the resistor, I'm sure they power it with DC.  There is a problem with over-driving the LED's I've heard about that takes them out.

Right you are John, no argument here.  I was just making observations/comments

I had 7 or so buildings with LEDs, powered off a single wallwart.  1 LED went out, soon followed by a couple more, then they all stopped working.  I suspect it was the wallwart, can't recall what the output was other than it was DC, I think it was one of those with an adjustable voltage switch, from 1.5 to 12vdc.

The LEDs I've gotten from Evans Designs have worked well, just wish they'd use a bit bigger wire for the leads, that's got to be 30 gauge or smaller.  They have a resistor built into the circuit and have done what I wanted so I haven't looked anywhere else lately.  But if Dave's LEDs are anything like his decals they're bound to be good

All you need if you have DC power is the resistor.  If you put a 1K resistor in series with your LED and power it with 12 VDC, it'll be burning when you're pushing up daisies.

Bob,

     I suspect that all pre-wired LED's have a very small wire do to the size of the soldering lugs. We use 32AWG wire.

Dave, LBR

Bob,

     There is one other thing that all should know about our LED's that other retailers don't offer. We encase each LED in clear plastic (unless otherwise ordered). This is to insure that the solder joints on the LED themselves do not come loose.

Dave, LBR

Thanks Dave, I think you're right on the size of the wire having to do with the legs on the LED.  I did have 1 wire come off on 1 of my Evans LEDs, don't recall if I resoldered or just picked up another out of the pack.

I solder tons of LED's with #24 wire with no issues at all.  I don't see any issue soldering heavier wire to the LED legs, that contention really confuses me.

I use #26,works fine but you could use any gauge within reason. The issue is flexibility. Anyone have a source for flexible #26 wire?

Dale H

Here you go Dale, #26 Superflex in various colors: http://electronics.mcmelectron...wire&x=0&y=0

Are you soldering 1.08mm LED's?

It obviously depends on which LED you're soldering, most folks are soldering plain LED's.  You have to be specific.  For SMT chips, I do use #30 wire, but I only run it a short distance and after any resistors and/or diodes, I run #26 wire for strength.

SMT chips is just about all we have been soldering lately due to the new C-DOTS marker lamp product line.

Dave, LBR

I find wire thinner than #26 hard to strip and work with. Also,unless branch lines are fused (mine are) thin wire will burn up in a short. Thanks John for the link.

Dale H

I use the finer wire strictly for lighting, so unless something pinches the wire and shorts it, I don't worry about burning it up.

Dave, you are certainly correct that the small SMT chips require finer wire, no argument there.

AdaFruit carries some 26 and 30 AWG silicone covered wire:

https://www.adafruit.com/searc...lexible+wire&b=1

and a really nice solder sucker:

https://www.adafruit.com/products/1597