# LIGHT FLICKER



## Treeman (Jan 6, 2008)

I have been adding lights to all of my Cabooses. Running DCC, installed two axles for pick up, but still get a lot of flicker. I did three interior incandescent in series to get a softer glow, and Aristo lanterns that must have LED's. Does any one have a diagram and component ratings to add a capacitor for some power storage, I also understand a resistor to limit a surge when powering up. Thanks for some help.


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## Jerry Barnes (Jan 2, 2008)

Mike, 
I've been getting electronic stuff from David Bodnar, he just got through giving 3 classes at the east coast train show. He has some articles/cheap kits for just this problem. http://www.trainelectronics.com/ Nice guy to deal with and he takes paypal!


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## Dan Pierce (Jan 2, 2008)

For capacitor storage, you need a diode bridge, current limiting resistor for large capacitors, and bulbs/leds tied in series with a possible resistor to 'tune' the voltage. 

So, we need to know your track voltage, and ratings of your bulbs and Led's to give a proper/accurate answer. (Voltage and current ratings and how many of what in series). 

Light bulbs are easiest as 2 12 volt bulbs in series on 22-24 volt supplies will be OK. Leds at 3 volts each can have as many as 7 in series with a small current limiting resistor. Leds in series should all be the same type/mfg for all to be the same brightness, same for light bulbs.


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## dbodnar (Jan 2, 2008)

Mike - you may want to try the method that I used with my Mr. Rogers Trolley. The circuit uses "super caps" and will not only keep them from flickering, but can keep LEDs going for 5-15 minutes after the track power is removed. Here is the schematic:









and here is a link to the article that gives much more information on how it works and how to wire it up.

Article on Lighting

dave


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## Treeman (Jan 6, 2008)

I will gather more data and get back.


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## George Schreyer (Jan 16, 2009)

if you are using LED lighting, you can get away with just regular capacitors, 100 uF is enough to overcome most ordinary flickering with just the bridge and a capacitor 

see 

http://www.girr.org/girr/tips/tips2/hw_tips.html


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## Greg Elmassian (Jan 3, 2008)

Interesting Dave, no surge resistor to limit current to the super caps? Am I right in supposing that the overcurrent circuitry in the regulator is enough? 

Regards, Greg


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## dbodnar (Jan 2, 2008)

Greg - the circuit works like a charm with as shown - I have a small aluminum heat sink on the 7805 as it does get warm when first charging the caps as they draw a few amps for a very short time. The diode (D7) is important as the voltage from the regulator is just a bit too high for the caps. The diode drops it to a safe level. 

George - regular caps do work very well - the cool thing about the super caps is that they will keep a few white LEDs going for dozens of minutes before they are exhausted. This is particularly nice if you have a point-to-point like the one we are putting in at Children's Hospital. 

dave


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## Dan Pierce (Jan 2, 2008)

I would caution users to not use 2.3 volt super caps with only 2 in series for 5 volts. 
I am a firm believer in capacitors should have a 10 percent minimum margin of safety on voltage and 20 percent is much better, therefore I would use 2 of the 2.7 volt supercaps, or 3 of the 2.3 volt units. 
I know the diode can drop .3 or .7 volts depending on the type, but there is no guarantee that the end users here will know which diode does what. 
Also, a note for Greg, the LM7805 does have a current limit/clamp of 1 amp so the super cap charging will be regulated as far as a surge is concerned. I do not know the response time of the current limit of the LM7805. 
Also, the resistor seems large to me, 470 ohms at 10 ma gives a 4.7 volt drop, and the bright white leds would be on the dim side with this value. 

I am not picking on Dave, just trying to make sure if someone uses his circuit that they understand some variables that were not mentioned here and going to Dave's site would be better than trying to make the above circuit meet their expectations if the correct parts were not used. The site does need a note on the proper diode selection as Dave assumes .7 volts for the diode voltage drop and no mention of a particular type/part number to guarantee this.


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## dbodnar (Jan 2, 2008)

Dan - I agree that one would normally use a capacitor that has a voltage rating that is 20% to 50% above the expected voltage. I am not sure that this holds true for super caps as the circuits and documentation that I have seen indicates that no such precaution is in order. They note that the life of the caps will be reduced if the voltage is exceeded but nothing more.


The diode that I am using to drop the voltage is a 1N5408 which is rated for 3 amps. It does a reliable job of dropping the voltage by approximately 0.7 volts - I failed to put that number in the article and have added it.


Thanks for your help!

dave


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## Axel Tillmann (Jan 10, 2008)

I (pontentially) disagree that there is "no harm no foul". Not by sience but out of experience:

I accidently had several times in my electronic work used a too low voltage capacitor that just blew up in my face (boooom) after a few minutes. Now it could have been just coincidence that the low voltage rating had nothing to do with it. But I don't want to see that happening again.

Also as another precaution, I reccently experimented with the new transformer less 110 to 24 Volt power converters as used in halogen lighting, and after a few moments a capacitor in the rectifing electronic that I had connected to the 24V side of the power converter blew up. This begs the question are the capacitors also freqency rated? And if so what impact that it have when we use DCC output with frequency regulated voltage?


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## Treeman (Jan 6, 2008)

I now have more complete information on my project. I have 22.5 volts DCC to the rail. I have 3-12V Grain of Wheat bulbs in series, plus 2-LED Aristo Lanterns part #ART29500 in series with a 1K resistor. I don't need to keep anything going with track power off. Just want to reduce or eliminate flicker, while rolling. I do have 2 LGB electrical pick up axles. Track may not be real clean but Locos are runng well. I could go to 4 axle pick up, but hate to use more of these axles I have been holding on to.


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## Road Foreman (Jan 2, 2008)

Mike, 

I would go with George's responce.. Put in a bridge rectifier ( 50 volt ) & a capacitor ( 100 to 1000 uf @ 50 volts ).. This should stop the flicker.. 

BulletBob


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## George Schreyer (Jan 16, 2009)

if the goal is to stop flickering, the standard electrolytic capacitor is the most cost effective and easiest approach. The supercap treatment is good for long unpowered sections. 

The 7805 will go into current limiting in a few 10's of microseconds which prevents a spike from being long enough for anything else to notice. 

If a capacitor of any kind is used as a filter for a high frequency PWM converter, then it has to be able to handle rapid charge/discharge cycles. The ESR, Equivalent Series Resistance of that capacitor will determine how well it filters and how much heat it generates from repeated current surges. Lower ESR capacitors will filter better and heat less BUT they also can charge to higher spike currents and put extra stresses on other components from those current spikes. You pays your money and takes your chances....


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## Treeman (Jan 6, 2008)

George, is a rectifier required to charge the standard capicator. Also what is the 7805.


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## KVBarkley (Jan 9, 2009)

You need the rectifier since a standard electrolytic *must* be connected with the proper polarity. Our fixture assemblers occasionally reverse one (I am assuming that it is not done on purpose!) and the capacitors *explode* within a few seconds of reverse voltage application.

The 7805 is the LM7805, a three terminal voltage regulator - most popular in the TO-220 plastic package. Put 20 V on the input and 5 volts come out the output with (as stated) current limiting and over temperature protection. Pretty close to bullet proof.


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## George Schreyer (Jan 16, 2009)

you need the bridge rectifier to make constant polarity DC from whatever is on your track. 

It is also easier to dispense with the regulator entirely and just run your LEDs with current limiting resistors. You can run 3 or 4 on the same 20 mA. 

Figure each LED wants 3 volts. Multiply 3V by the number you are stacking in series to get the stack voltage, for example 12 volts for a stack of 4. Subtract that from your track voltage. Subtract 1.5 volts more for the drop of the rectifier. Then divide the result by 0.02 to get the proper resistor. 

The upside of stacking is that you draw less current. The downside is that it takes more track voltage to get a stack to light up. If you are using DCC or PWC, then this is not a problem. If you are using DC, then you don't want to stack them so that they will light at the lowest voltage.


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## Treeman (Jan 6, 2008)

Then in my case I see no need for the 7805. I just need to add a rectifer and a capicitor. Does that seem correct.


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## lownote (Jan 3, 2008)

I have 6 bachmann coaches running with LEDs, and in each coach I have a bridge rectifier and then a large value capacitor--the largest radial lead capacitor Radio shack stocks, I forget the exact values. Im pretty sure it's 50 volts and 100 uf

Becaue I run at a constant 20 volts, I just followed Dave Bodnar's site--just run track power to the rectifier, rectifier + and - to the cap, then a resistor in front of the leds, the value depending on the number of LEDS

I usually use this site to help with resistor values:


LED resistor calculator 


I bought a string of warm white christmas lights and have been cutting it up and using it in various places. I'm assuming that a warm white 5mm LED wants to see 3 volts and 25 ma. It's been working so far. The car below has four leds. I've been painting the christmas-string leds with polyscale reading yellow


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## KVBarkley (Jan 9, 2009)

Then in my case I see no need for the 7805. I just need to add a rectifer and a capicitor. Does that seem correct. 


As long as the voltage rating on the capacitor is greater than your track voltage, sure.


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## Trains West (Oct 4, 2008)

you will still get some flicker if you do not regulate it down to a lower voltage .. as the power switches from track to cap you get a voltage drop so the lights dim then as it goes back to track it gets bright again


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## George Schreyer (Jan 16, 2009)

yes, there is some intensity modulation, but it's not enough to notice


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## Treeman (Jan 6, 2008)

Got a chance to get by a nearby Raido Shack today. I found exactly the two items I needed. A full Wave Bridge Rectifier rated at 25 amps 50 volts. Also a Electrolytic Capacitor,rated 1000uf 50WVDC. Now looks like a easy job to install these two items, tomorrow. The only thing I did't understand was the W in the Cap rating. Iam not sure I'll try running it tomorrow, its very windy tonight, and snowing.


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## Dan Pierce (Jan 2, 2008)

From Google Working Volts Direct Current!!


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## Treeman (Jan 6, 2008)

Dan you get around early!! That is a new term to me.


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## Treeman (Jan 6, 2008)

WOW, Those two items installed, made a huge difference. Very little if no flicker. Now a quistion about the Super Caps, what are they, just a larger rating.


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## Greg Elmassian (Jan 3, 2008)

yes in a smaller space. 

Regards, Greg


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## SteveC (Jan 2, 2008)

Posted By Treeman on 04/01/2009 8:21 PM
{snip...}[/i] Now a quistion about the Super Caps, what are they, just a larger rating. 
Mike

Maybe the following will be of interest.

*Electric double-layer capacitor*
*(aka Supercapacitors)*


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## Dan Pierce (Jan 2, 2008)

Treeman, I was up early to go to Boston Children's Hospital for a 6:30AM setup to run the Inner City "G" train modules. Needed to miss traffic. 

The kids loved it, and some adults were fascinated. 

No pictures allowed!! 

We had a great time running trains.


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## Treeman (Jan 6, 2008)

Dan, sounds like you had a good day. You would be an hour ahead of us here in the Mid West.
Steve, I did find info on the Super Caps, but didn't find a good supplier.


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## dbodnar (Jan 2, 2008)

Mike - I got the supercaps that I have been using from Digikey - they are a bit over $3.00 each if you get 10 or more.
Here is a link:

Supercap link 


dave


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## Treeman (Jan 6, 2008)

Thanks Dave, would that charge from the same bridge rectifier that a smaller one would.


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## Treeman (Jan 6, 2008)

OH, I looked closer, it is only rated 2.3 volts?? I was applying around 20 volts.


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## Greg Elmassian (Jan 3, 2008)

you have to put them in series for higher voltages... 2 in series would handle 4.6 volts, etc... by the way, overvoltage makes for a spectacular bang in most cases. 

Regards, Greg


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## Treeman (Jan 6, 2008)

And I usually don't wear ear plugs when I work. I used to kid about putting on a welding helmet to throw a 480v disconect for the first time.


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## Dan Pierce (Jan 2, 2008)

The supercap 10 farad caps in series would most likely blow a fuse, or pop a circuit breaker if used in series for 20 volts. 

This is somewhat similiar to placing a wrench across a battery. 

The 7805 limits the charging current in Dave's diagram. The 7805 does get hot on the initial charging and I had to use a heat sink on the ones I used for replacing the LGB power storage unit and that was a 7808 regulator on a 20 volt track. 

I am cautious when using more than 470uf (.00047 farads) capacitors as the initial surge current can be very high.


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## Greg Elmassian (Jan 3, 2008)

I think it has always been recommended (at least by me) that ANY "cap bank" system have a resistor on the "charging" side to limit inrush when the caps are discharged. 

I think that's a question I asked earlier in this forum... 

Mike, you do not really want a 20 volt supply, right? Even setting up the circuitry right, it would only charge at 20v track voltage. 

The "trick" with constant lighting is to have lights that run at a very low voltage, so that the track voltage is usually higher and can "charge" your "energy storage system". 

Regards, Greg


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## Treeman (Jan 6, 2008)

Greg I see what you are saying.I probably went the wrong way on the first Caboose project. I had it set up to run straight off full track power, at first then added the rectifier and capacitor. It is working OK but want to go another route on the next one. I see using LED's or 5 V incandescent bulbs with the voltage regulator would be a better approach. I run old style trains so I need to find a glowing look from LED's or a socket for 5V push in bulbs and dim them down, and a source for the 7805 voltage regulator.


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## George Schreyer (Jan 16, 2009)

supercapacitors are a special technology that works only at low voltage, usually 2.3 volts. This is enough for keep alive for low power electronics but they are not practical for high voltage work unless you stack them. This gets into some real dollars and unless you REALLY need the super high capacity, the standard issue electrolytic will be much less expensive and cause you fewer problems. 

As a general rule in electronics, NEVER design in more capability than you really need. The extra stuff costs money AND usually comes with additional liabilities.


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## Treeman (Jan 6, 2008)

I don't see the need for the super caps either. I just think I should use lower voltage lights.


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