Adding LED lights to older Bachmann plus dc locomotives Issue

[jbrock27]

...the opposing LED  flicker will eventually blow the led and this has happened to me over time.

Has never happened to me.  
Over how long a period of time did this take to happen?

[richardl]

Typical ceramic bypass caps used in Bachmann DCC locos when I saw the circuit diagram.

The Mylar ones have little better specs as I recall.
I use to have lots of both from stripping old circuit boards for electronic experiments.

Rich

[electrical whiz kid]

There is a trick I like to tell my customers, especially with LED lighting; and that is for them to crack the dimmer back a bit.  This will provide a "cushion" for the voltage to bump up against.
I have 65 watt lamps in recessed cans in my house that have been there for (no kidding!!) some 28 years.  The dimmers are cracked back just a little.  You don't even notice the difference.  If you can do likewise-that is, drop voltage a tad- with LEDs in trains, the chances of burning an LED out is really diminished.  Don't forget; the lighting here is a resistive load, mostly because of the resistor; therefore, the load is directly proportional to your voltage.  The other thing is that LEDs are not a true light, but light is a product of the transconductance, which is why you need a resistor in the first place; otherwise, with no resistor, the LED will burn out as it will be operating under a 'short circuit' condition. utilize a threshold voltage; below that, the LEDs will not operate.

Rich C.   

[jbrock27]

Rich, JA is using a resistor w/his LED(s) and stated he is still managing to burn out the LEDs over time.

[electrical whiz kid]

Brock;
Jim, the only way I know of to surely burn out an LED is to push a straight voltage through it-with no dropping load between it and a complete circuit-in short, a short to completed; EG:  voltage going through the LED, and straight through to the other terminal of the source sans resistor.  If you have monkeyed around enough with these pups, you will see that if you start from zero volts, there will be no completed circuit via the load; this is because of the low voltage not being able to get through that resistor.  If you increase the voltage to where the 'light comes on', then the circuit will have achieved a threshold voltage and moved higher enough to complete the circuit via the whole load.
A decoder will (should) have the equivalent to a resistor between the LEDs and positive.  If you are able to check out that part of a decoder, I think what you will find is that there is a short somewhere across to the positive terminal of the source.   This, also may account for the "blink-blink" business.  I can't tell you that without playing around with that decoder.

OH...Amd justso you know, I am only a dumb old electrician-not an electronical engineer...

Rich C.

[Len]

The OP said he's running straight DC, no decoder involved. I'm wondering what power pack he's using? Tthe output on some isn't all that clean, and without the bypass capacitor the AC component may be hitting the LED with significant reverse current. Over time that could cause the LED to break down.

Len

[jbrock27]

Cormier;
Rich, reading is fundamental.
Also, hope you don't feel you need to remind me of your electrician background, since you know, that I am fully aware of that.

...without the bypass capacitor the AC component may be hitting the LED with significant reverse current. Over time that could cause the LED to break down.

Len

Len, would this not also show up though in a jack rabitt jump of speed by the motor?

[electrical whiz kid]

Jim; I know, I know.  I knew when I wrote it I would hear back.  Oye!  How you took that was not in the context in which I meant it to be taken.  There are other readers on this site besides you and me.  So don't worry, kid...
I hope I got my message over though.  As I said, I am no electronics techie-just a dumb old electrician.  I know very little about electronics; and the fact that is changing faster than I can keep up with it makes me happy I am retired-sort of.
HOWEVER...I still do know my electrical theory-and they still are the same, after all; so I guess that makes it all better, huh...?
On another note; I got some more Bachmann parts and will be "creating" this winter.  It is fun.  I am retired-and happy..(just so you got it the second time...ha ha)...

Rich C.

[electrical whiz kid]

Len, would this not also show up though in a jack rabitt jump of speed by the motor?

Jim;
This would not necessarily happen because of the variables involved here.  If there is a high-resistance short-or connection-then there could be some different things happening.  What puzzles me is that this is a DC circuit; so like Len said, if he is using a different xformer, then stuff like this could happen.

Rich C.

[Len]

Jim - More likely a motor running hotter than it should, rather than a jack rabbit start. Somewhere I've got some O-scope pictures I took of various power pack outputs 10 or 12 years ago. If I can ever find the box they're stashed in I'll have to scan them and make postable .jpg's. They're an eye opener regarding the so called "DC" output of a lot of low end power packs that generally used one or two small disc capactors for "filtering".

Everyone thinks of the output of a power pack as being a nice flat DC line. The reality is, without the better filtering of more expensive power packs, what you're actually getting is either the upper or lower half of a sine wave, depending on where the direction switch is set.

The nice neat drawings of half or full wave rectified AC you see in books show the AC neatly chopped off at the crossover point by the rectifier. The reality is, there's a certain amount of "overshoot" at the crossover point, which makes filtering even more critical when LEDs are used with low end power packs. It gets even worse with those "Pulse Power" packs which were made for a while to try and overcome starting issues with old style open frame motors.

Len

[richardl]

Cormier;
Rich, reading is fundamental.
Also, hope you don't feel you need to remind me of your electrician background, since you know, that I am fully aware of that.

Offensive material removed again. I will try to be more sensitive. lol

Rich

[jbrock27]

Offensive material removed again. I will try to be more sensitive. lol

Rich

lexxon/RichG/richardl, is your name Rich Cormier as well?   I was not even addressing you, LOL !!

[jbrock27]

There are other readers on this site besides you and me.  So don't worry, kid...
Rich C.

Rich(C), I know that and I am certain that many recall that factoid about you since you have wrote it enough times.  No worries.  It just appeared by the structure of your post you were addressing me.  I am glad we understand each other.

But speaking of understanding, while you have a great understanding of electrical properties, your first post did not reflect an understanding of what JA (the OP) had already said he was working with, so your first comments were really coming out of left field and of little to no value to assisting him with his problem, my friend.

Len I thank you and Rich (C) too for the expansion on what you meant by a possible power pack issue.  Gives more reason to delegate the "cheap" power sources to running lights or other accessories and save the good stuff by MRC for running DC locos

[Len]

Until I can find my O-scope pics, check out this page: http://sumidacrossing.org/LayoutElectricity/ModelTrainPower/PowerPackTesting/

Even some of the newer packs have a certain amount of "noise" and "over shoot" on their outputs. I have to admit to being a bit surprised by the output on a couple of them.

Len

[jbrock27]

Thanks for the info Len, I will check it out.