LED Headlights for a Dummy Diesel - Odd Behavior

I think you're getting bit by the LCRU oddity with the light outputs.  If my memory serves, that's one that actually doesn't necessarily maintain the same polarity of output for the lights.  The only fix I figured out was a bridge rectifier to make sure the polarity was correct all the time for the lights.  Also, you can use a .01uf 50v capacitor across the light output instead of the resistor, it doesn't dissipate any power and does the same job.

Definitely appreciate the reply...  Polarity is something interesting that I noted early on as I began to tinker with this.  Prior to the odd behavior I described today, the lights worked with their positive connected to ground, and the negative lead(s) connected to the light outputs on the board - the opposite of what I initially tried.  That the polarity isn't necessarily always the same coming off of these boards is definitely something I missed in my previous searches.  I realize I also forgot to mention in my original post that I am operating in a command control environment, not conventional in case that makes any difference.

I'm pretty much a noob at attempting to create electronics such as this - so forgive me...  Does it make a difference where the bridge rectified would be placed, as in between the board and the LED's, or between the LED's and the common ground?  Is there a particular bridge rectifier part number I should seek out for this application?  

Thanks!

It does make a difference, the control of the triacs in the older board design was such that they triggered on any quadrant, hence the polarity in command mode would change at random.  They should actually work in conventional mode as they pass full-wave power.

The bridge would be after the .01uf cap (or your resistor) and before the LED and dropping resistor.

John - just thought I'd let you know that your advice did indeed do the trick!  I had to order the bridge rectifiers and .01uf caps, but after getting them installed and soldered in place my headlights work just like I wanted and no more odd behavior.  

Thanks!

I love a happy ending.  I also found that out the hard way a long time ago.

What is the Digi Key p/n for the .01uf 50v capacitor?

bruce

As usual  the OGR gurus fix the problem.  Best example of the forum's power.  

Almost like Jedi warriors.

I find myself in the situation of having to bump my thread, since after the initial success I had with this issue I've noticed something else that I'm curious about.

First off though, Bruce - sorry I didn't reply to you with the Digi-key part number for the capacitors I got...  I actually ended up ordering them off of Amazon under this description: Uxcell a11102000ux0341 50x DIP Low Voltage Ceramic Disc Capacitors, 10000pF, 5OV  It looks like these are still available on Amazon today.

Anyway, on to the new issue...  When the engine moves across switches, the headlight that isn't lit briefly flashes on then back off and the headlight that is lit flickers slightly.  I'd almost describe as if the board "forgets" what the state of the lights should be if the supply voltage flickers when passing over a switch.  This doesn't happen 100% of the time on all switches, but does happen the majority of the time when passing over any given switch.  I've since performed the same dummy upgrade to a second engine, and it displays this behavior also - so what's going on wasn't just a one off occurrence.

What would be the best way to address this issue, if anyone else has had to address this also?  Would a capacitor across the hot and ground from the trucks work, and if so, what would be an appropriate specification for one?

Thanks!

The flickering of the unlit headlight is difficult to fix, the real fix is not to have momentary glitches in the power.  Truthfully, the most sure fix would probably be to add another roller or two to the dummy.  It's possible that you could add a slightly more involved circuit to "buffer" the power to the headlight and add a slight delay to it powering on.  I'm thinking along the lines of an electrolytic capacitor after the initial current limiting resistor and a resistor across the LED.  This would keep the capacitor discharged when that headlight is not on, and if a momentary power glitch came and a quick burst of power was applied, it would take a finite amount of time for the capacitor to charge enough to allow the LED to light.

John, appreciate the reply as always.  I'm beginning to speculate whether or not ditching the LCRX boards is something that I should consider?  I say this because I just finished converting an engine from an AC/DC Commander board to a Cruise Commander board - and as part of this I also wired in LED headlights.  Testing the engine this evening I noticed a couple things...  First, I didn't need to put the capacitors across the light outputs and the ground to make the outputs "fire", and running the engine I don't see the flickering behavior with the "off" headlights while running across the track and over switches.  This is on an engine that has a single pickup roller on each truck.  

I notice that 3rd Rail / Sunset Models has an ERR board called the Mini Commander EX, intended for dummy units.  Do you, or anyone else have experience with these to know whether they would be immune to the LED lighting challenges I've had with the LCRX boards so far?  

I actually use the RCDR for dummies, I like it better than the MC-EX.

The LCRX boards are ancient, so they'd be well down the list for me.  I once converted a Hot Box Reefer using one of those, thought I was clever saving money because I already had the board.  After screwing around with it for weeks, I realized that the flaky behavior was because the polarity kept reversing!