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Reducing Light Flicker

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  • Member since
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  • From: Visalia, California
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Reducing Light Flicker
Posted by dcfixer on Thursday, April 3, 2008 7:34 PM

My latest project has been to reduce the flicker and  "brown outs" of my interior lighting.  The biggest improvement came when I converted all my lit cars to the Walthers trucks with 8 wheel electrical pick up.

 To take it a step further, I went on a quest for a capacitor and/or a battery that would take care of any remaining dropouts.  There's no rechargeable battery small enough or light enough that will work for me.  The rechargeable cell/button batteries that I could find cannot delivery 20 ma continuously (average draw per car with 6-8 LEDS).  The best I found could do 0.5 ma.   Any rechargeable battery that can deliver that current is way too big and heavy for my interiors.   I'm not interested in any battery that needs replacement after 10 hours of use either.  I want to minimize handling and "popping open" my cars.  Inevitably, something happens that I have to fix.  So, that left capacitors.

I found a small, lightweight SMD capacitor that is 1500uF at 4volts dc. With the 8 wheel pick up, 3volt light rails and 20ma draw, it looks like a set of 3 of these caps in parallel, with 10 ohms in series with the set appears to be doing the trick.  The caps easily fit in the roof area of my cars, in between the light rails.  I could easily put a dozen of these caps in the roof area.  The caps are small enough to put in lockers or dark rooms with the shades pulled, etc.  The voltage on these caps has a limit of 4v dc.  My regulators are 3v (gives the caps a little room to work).   I AM STRONGLY AGAINST using even one of these high capacity caps across the output of a regulator without a series resistor.  The cap will initially look like a dead short to the regulator when it is charging, and damage to the regulator may occur.  Even regulators with over current protection may become compromised with the repeated charging and discharging of the caps.

 3 volts and 10 ohms means my regulator will see a maximum peak of 300 ma, which is well below its 1 amp maximum.  The regulator will only see that load when the cap charges, and for a relative short time.  That maximum load time depends on how much total capacitance and series resistance there is. 

300ma x 3v = 0.9 watts that the series 10 ohm resistor will see, but it is for a short time, so a 1 watt resistor is not necessary.  I'm using 1/4 watt resistors on my cap circuits, and I feel no heat what so ever on the resistor after repeatedly charging and discharging.  Now, if I was going to use 6-10 caps, I would go to a ½ watt resistor (longer maximum load time), or divide the caps up into more than one set.  If more than one set of caps is going to be installed (so the caps can be distributed and hidden around the inside of the car) there has to be a resistor in series with each set of caps.  For 2 sets, the series resistor for each set would be 2x10 = 20 ohms; 3 sets would be 3x10 = 30 ohms on each set, and so on.  An option is to stay with 10 ohms per set, but the number of sets would then be limited by the equivalent parallel resistance of the 10 ohm resistors and the current capability of the regulator.  In my case with a 1 amp max regulator, that would be 3 sets, i.e. (3) 10 ohm resistors in parallel = 3.33 ohms, and 3v / 3.33 ohms is under 1 amp, barely.  One can have as many caps in a set as wanted, but the series resistor for each set must be determined so that the total current draw when all the caps are acting like shorts does not exceed the current capability of the regulator, and the resistors will not over heat.  If this seems confusing, I'm sorry, but I'm trying to avoid technical impedance calculations involving AC theory, which would be even worse.  If anyone needs help, please feel free to contact me.

The more LEDS and the brighter the LEDS, the more the current demand, and more caps will be needed to get the same filtering.  My dome obs lounge will need at least 6 caps, because it has 17 LEDS, drawing about 40 ma.  Also, for those cars with 4 wheel electrical pick up (wipers, all metal trucks) more caps will be needed to achieve the same effect has I did.  This will require some experimentation by those users to determine how many caps are needed, cause I no longer have any cars with wipers or all metal trucks.  A dc incandescent circuit will require a lot more caps cause of the large current demands, but remember, NOT OVER 4 volts dc on these caps and don't over heat the resistors.  Any amount of caps will help reduce the duration of the dropouts.  I say "do what you can".  These caps cannot be used in AC circuits, cause the caps are polarized (plus and minus terminals).

Yep, there's a big down side.  Shock [:O]These caps are pricey; $6.50 at mouser.com, but the price goes down quickly with quantity.  I got 25 for $4.25/ea; 100 was listed for $2.60/ea.  A group of people could go in together and buy bulk, thus reducing the cost to each person.  If anyone can find them cheaper, please let us know.  The part number is 597D158X9004R2T.  The data sheet is available at Mouser.

I got to say, modelers, that it has been a sweet experience lately to finally sit back and watch my train go around all lit up and see my interiors with no distracting dropouts.  It's really cool to be creeping along at 5-10 mph, and no flicker.  It's been worth every penny and minute of work.  Still have to clean track and wheels once and awhile, but a lot less than before, and I have a small, reliable, low power, hands-off interior lighting system.  Smile [:)]

DC   http://uphonation.com

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Posted by tomikawaTT on Thursday, April 3, 2008 9:28 PM

A big THANK YOU!!!

You've provided the answer for a question that I have been planning to address.  With a large passenger roster, a number of brake vans and full cabooses of various types and plans to operate night trains in a darkened room, I was looking forward to a period of experimentation.  You've probably saved me a good many hours of time, not to mention silencing a lot of uncouth language.

Considering the total size of my roster, I may have to take Mouser up on the 100 capacitor deal.

Chuck (modeling Cental Japan in September, 1964)

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Posted by SteamFreak on Friday, April 4, 2008 12:28 AM

Amazing work there, DC! Cool [8D]Thumbs Up [tup] You really live up to your name.

Those surface mount caps sure save space. What sort of power interruption interval can the capacitors span? Do the LED's fade out when power is removed? And where did you get that flex braid?

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Posted by dcfixer on Friday, April 4, 2008 9:57 AM

Chuck, you are most certainly welcome.  The only thing I ask in return is that you post a lot of pics here so we can all enjoy.

Good luck on your project.

DC 

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Posted by lvanhen on Friday, April 4, 2008 10:11 AM
Good solution, although a little pricey.  I think the Rapido Easy Peasy, at about $15 list, is an easier solution.  They use the LEDs, but with 2 small batteries.  I have 4 of the Rapido cars, and have started equiping my Walthers that do not have their lighting units with the Rapido's.  I have a small fleet of Bachmann Spectrum heavyweights, and they are the worst as far as flickering, and darned near impossible to remove the roof and put it back on with the lights still working!!  As soon as all my cars are lit, the Bachmanns will be next!
Lou V H Photo by John
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Posted by dcfixer on Friday, April 4, 2008 12:59 PM
 SteamFreak wrote:

Amazing work there, DC! Cool [8D]Thumbs Up [tup] You really live up to your name.

Those surface mount caps sure save space. What sort of power interruption interval can the capacitors span? Do the LED's fade out when power is removed? And where did you get that flex braid?

I knew it!  I knew it! Someone was going to ask me for numbers. Banged Head [banghead]

LOL 

Seriously, though, thanks for the kind words.  My AC theory is pretty rusty, and my calculus is all but faded away, but I will rough out some numbers for you.  Give me a little time to do some crunching, and I'll get back to ya.

Yes, the LEDs fade out.  They always will with an RC circuit.

I got the flexible wire from junk bins at work, and don't know any part numbers. I stripped the insulation off to make it more flexible.  It's about a 22g, multi-stranded (at least 100 strands, maybe 200), twisted pair computer/printer wire from a ribbon cable. I would think Mouser, Digikey, Newark, etc. would have something like it.  That's all I know.

P.S.  Had a little scare there when I came back and couldn't find my thread. 

 DC

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Posted by SteamFreak on Friday, April 4, 2008 2:27 PM
Don't worry about exact numbers, because if it fades slowly then it can keep the lights on across a significant gap. I only meant a really rough estimate, based on the LED to cap ratio you're using. Smile,Wink, & Grin [swg]
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Posted by larak on Friday, April 4, 2008 2:52 PM

Just curious - has anyone tried the newer computer CMOS caps that have values in the 1 Farad range?

  link

They probably have a high ESR, but with low current draws that should not be a problem.

Karl 

The mind is like a parachute. It works better when it's open.  www.stremy.net

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Posted by dcfixer on Friday, April 4, 2008 2:56 PM

 SteamFreak wrote:
Don't worry about exact numbers, because if it fades slowly then it can keep the lights on across a significant gap. I only meant a really rough estimate, based on the LED to cap ratio you're using. Smile,Wink, & Grin [swg]

No problem. This is for my Walthers set up with 6 LEDs, 3V, 4500uf, 10 ohms. The perception of brightness/illumination in relation to the impedance at any given time is a little tricky, but here goes: about 100ms-200ms to the start of noticeable fade, and around 600ms-800ms to complete fade out.  

Hope that helps. 

DC 

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Posted by dcfixer on Friday, April 4, 2008 4:20 PM
 larak wrote:

Just curious - has anyone tried the newer computer CMOS caps that have values in the 1 Farad range?

  link

They probably have a high ESR, but with low current draws that should not be a problem.

Karl 

Thanks, Karl for your interest. Smile [:)] It might be a viable option; I'm not sure.

At 20mmx5mm, it's a little large for my application. It might be a better solution for someone else. 

Also,  these are designed for memory backup, which is typically in the hundreds of microamps today.  I wonder how long they will last, or even if they can deliver 20 - 40 ma. Can they take the duty cycle?   The large change in capacitance and internal resistance over time concerned me, also.  The price/capacitance is a real plus - just not sure of its performance in my application.

DC

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Posted by dcfixer on Saturday, April 5, 2008 2:10 PM

I hope that I haven't given the impression that this is my final solution.  As far as I am concerned, the "flickering" issue is still open.  I will continue to look for smaller, lighter, and cheaper devices and solutions.  I think it won't be too long before we will see a small, rechargeable battery that can deliver.  I hope ideas, suggestions and other solutions for improvement continue to appear here.   I have already bought all the capacitors I need, and I am going with this for now.

If someone was going to start from scratch (trucks, LEDs, regs, caps, resistors, etc.), this would be a pricey deal, indeed.  It wasn't so bad for me.  I needed to upgrade/correct my Soho and Rivarossi trucks anyway.  I got resistors, FW bridges and hook-up wire from liquidators and Ebay for dirt cheap.  8 LEDs, regulator and 3 caps average $25 per car.

In the short term, there are cheaper, easier solutions out there.  How many batteries am I going to have to buy, store, and properly dispose of in the next 10 years?  How many times am I going to handle my cars to change batteries?  I don't want every car lit end to end, ceiling to floor.  I want to light specific areas.  I want different degrees of illumination, and effects.  I can slip an LED in a shrink tube and make a spotlight.  How much time will I spend bashing a commercial light kit?  In the long term, and with the present technology, batteries are not the easiest solution for me, but it's nice to have viable options.

I spent some time last night installing caps in my cars, and decided to experiment on one car.  I tried a 30 ohm series resistor on a 4500uf, 6 LED car.  The total fade out time went to a least a second.  It was noticeable.  This means, though, that the time to the-start-of-noticeable fading would be shortened.  Increasing the capacitance now would increase that time again along with the fade out time.  There's going to be a ratio of capacitance to resistance that will make the most effective gap filler at the same RC time constant (0.66 x resistance x capacitance).  Some experimentation will be necessary to achieve individual satisfaction.  Having a selection of 10, 30 (+-2), 50(+-3) and 100 (+-10) ohm resistors, I can get the illumination, lighting effect and filtering I want on my 3vdc LED system.

If I still had 4 wheel pickup wipers on my Rivarossi,  I would see if a 6 cap, 30 ohm filter would reduce the flicker enough for now.  Later on, if needed and when I could afford it, I would add more caps.  "Do what you can".Smile [:)]

DC

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Posted by dcfixer on Friday, April 11, 2008 9:05 AM

It has come to my attention that the application of large capacitance could be a problem for DCC restarts due to the inrush current.  I don't know yet how much is too much, but having just a bridge and regulator (<$2) should make a lighting system compatible with DCC - just won't do anything for the flicker.  Also, DCC may require using a high speed Si or Shottky bridge (still about a buck).  I have been looking for a DCC system that I can test my cars on, and, also test an RCC system that I'm going to install in my locos.  I'm hoping to make the RCC system operable with 13-16v AC, DC or pulse-width modulated power.  I plan to start a new thread on the RCC when I have more.

DC 

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Posted by Arjay1969 on Friday, April 11, 2008 9:22 AM
 dcfixer wrote:

It has come to my attention that the application of large capacitance could be a problem for DCC restarts due to the inrush current.  I don't know yet how much is too much, but having just a bridge and regulator (<$2) should make a lighting system compatible with DCC - just won't do anything for the flicker.

That's what I've settled on for mine.  The local club uses DCC, and that's where I run my equipment (lacking a home layout at this point).  Yes, there is flicker, but it's not terrible at road speed, using Hippie Pickups (and thanks again for the name! Big Smile [:D]). 

Also, DCC may require using a high speed Si or Shottky bridge (still about a buck).  I have been looking for a DCC system that I can test my cars on, and, also test an RCC system that I'm going to install in my locos.

I've been using just the standard cheapo bridge rectifiers from Radio $hack with no problems so far.  We'll see what happens a little further down the line, though. 

I'm hoping to make the RCC system operable with 13-16v AC, DC or pulse-width modulated power.  I plan to start a new thread on the RCC when I have more.

I've seen that system advertised for quite a while.  I thought about picking one up back when the local club was still using the Aristo Craft wireless throttles.  The transmitter for both systems is the same, I believe.  I look forward to seeing what you come up with there! 

Robert Beaty

The Laughing Hippie

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The CF-7...a waste of a perfectly good F-unit!

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Then it comes to be that the soothing light at the

end of your tunnel, Was just a freight train coming

your way.          -Metallica, No Leaf Clover

-----------------------------------------------------------------

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Posted by dcfixer on Friday, April 11, 2008 10:02 AM
 Arjay1969 wrote:
 dcfixer wrote:

It has come to my attention that the application of large capacitance could be a problem for DCC restarts due to the inrush current.  I don't know yet how much is too much, but having just a bridge and regulator (<$2) should make a lighting system compatible with DCC - just won't do anything for the flicker.

That's what I've settled on for mine.  The local club uses DCC, and that's where I run my equipment (lacking a home layout at this point).  Yes, there is flicker, but it's not terrible at road speed, using Hippie Pickups (and thanks again for the name! Big Smile [:D]). 

Also, DCC may require using a high speed Si or Shottky bridge (still about a buck).  I have been looking for a DCC system that I can test my cars on, and, also test an RCC system that I'm going to install in my locos.

I've been using just the standard cheapo bridge rectifiers from Radio $hack with no problems so far.  We'll see what happens a little further down the line, though. 

I'm hoping to make the RCC system operable with 13-16v AC, DC or pulse-width modulated power.  I plan to start a new thread on the RCC when I have more.

I've seen that system advertised for quite a while.  I thought about picking one up back when the local club was still using the Aristo Craft wireless throttles.  The transmitter for both systems is the same, I believe.  I look forward to seeing what you come up with there! 

Thanks for sharing that experience, Robert.  I was NOT looking forward to replacing all my bridges.  You have saved me some time. Big Smile [:D]Thumbs Up [tup] I still might have to remove the large RC filters, if I want to run on a DCC system.  We will see.  If your bridges work now, they will continue to work.  At an average of 7kHz, it was the diode recovery time that I was concerned about, but it seems you have answered that.

Yep, the Train Engineer.  I do believe it is the same transmitter.  That's nice, huh?  I got the CRE55000 and one extra receiver for the B unit for $115 + shipping.  As I stated in another forum, my wife and son sometimes run the train when I'm not around, and I wanted remote control, as simple, reliable and affordable as possible. DCC seemed a little too "iffy" for my family, not to mention that it would cost more. The Basic Train Engineer was a little too simple since I plan on modeling a couple of more trains in the future.

DC 

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Posted by richg1998 on Friday, April 11, 2008 2:57 PM

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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Posted by dcfixer on Monday, April 14, 2008 12:48 PM
 richg1998 wrote:

Here is a little more info that might help (complicate matters).

http://www.awrr.com/lighting.html

http://www.dccwiki.com/LED_Lighting_and_Resistors

http://www.dccwiki.com/Installing_LEDs_with_DCC_Decoders

http://www.dccsupplies.com/shop/product_info.php?products_id=765

http://cgi.ebay.com/LED-Lighting-Strip-10cm-SMD-for-9v-18v_W0QQitemZ250220654268QQihZ015QQcategoryZ19138QQcmdZViewItem

http://www.members.optusnet.com.au/nswmn/dcc_articles.htm

Store these in your Favorites folder for future reference or for answering someones lighting questions.

Rich 

Thanks for the links.  Smile [:)]I think these will be helpful for everyone.  I especially found the last link helpful, cause sound is next on my wishlist.

DC

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