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Keep alive capacitor

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Keep alive capacitor
Posted by PRR_in_AZ on Friday, March 04, 2011 11:49 AM

I am installing a decoder in the tender of one of my brass engines and was wondering if I could use a capacitor to keep power flowing to the decoder over areas of the trackwork/switches where there might be a momentary loss of pickup.  Is this possible?  How does it get wired?  How large of a capacitor?  Anything available at Radio Shack?  BTW, this isn't for a sound equipped loco, just constant power for the motor.

Thanks.

Chris

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Posted by richg1998 on Friday, March 04, 2011 12:27 PM

Below is a link to the stay alive issue. From what I know, many do not use the cap for non sound decoders. Your mileage may vary.

http://www.members.optusnet.com.au/mainnorth/alive.htm

Rich

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Posted by DigitalGriffin on Friday, March 04, 2011 2:45 PM

I believe Lenz gold decoders are the only decoders that support this feature.  And the cap is quite costly as they are quite exotic in design.  Tonys trains sold them at one time.

Don - Specializing in layout DC->DCC conversions

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Posted by fwright on Friday, March 04, 2011 3:19 PM

There has been substantial research (see the link provided in a previous post) on where to hook a stay-alive capacitor to various decoders (It's not on the input).  So while the Lenz Gold directly supports a stay-alive capacitor, you can install one on other decoders - to keep the decoder alive, but not necessarily the motor.  It's quite difficult to find the space for a big enough capacitor to keep motor and decoder going for even one second.  And then current limiting circuitry is needed to prevent in-rush current (when the capacitor is charging) from tripping the DCC system circuit breaker.

My personal opinion is that a flywheel does the same thing mechanically for the motor as the stay-alive capacitor does for the decoder.  That is the route I would take.

Physical size vs stay-alive times are concerns when installing a stay-alive capacitor.  The other concern is limiting the in-rush current of multiple stay-alive capacitors during start up or after clearing a short.  If the total in-rush current is too high, some-to-many DCC systems will see the inrush current as a short circuit, and shut right back down.

my thoughts, your choices

Fred W

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Posted by PRR_in_AZ on Friday, March 04, 2011 3:41 PM

So you guys are saying this isn't practical unless:

1.  you use a sound decoder

2.  you have a non-sound decoder that has to support this

 

Chris

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Posted by DigitalGriffin on Friday, March 04, 2011 3:58 PM

PRR_in_AZ

So you guys are saying this isn't practical unless:

1.  you use a sound decoder

2.  you have a non-sound decoder that has to support this

 

Chris

I'm thinking it won't be easy for a home brew that wasn't designed for it in the first place.  You would need to find the input and ground pins on the main decoder chip and hook it to that along with a diode and a resistor.

That said, here's a video on the Lenz Gold with USP in action:

http://www.youtube.com/watch?v=2f2hmeNNCOs

 

Don - Specializing in layout DC->DCC conversions

Modeling C&O transition era and steel industries There's Nothing Like Big Steam!

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Posted by PRR_in_AZ on Friday, March 04, 2011 4:12 PM

Actually the capacitor, diode, and resistor combo are pretty straightforward.  The part I need is where to solder onto the decoder.  I'm using a DH163D wired decoder.  I know Joe Fugate uses these type of decoders and was looking for the answer as well.  I wonder if he ever figured it out?  A picture is worth a thousand words Big Smile

Chris

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Posted by richg1998 on Friday, March 04, 2011 4:57 PM

PRR_in_AZ

So you guys are saying this isn't practical unless:

1.  you use a sound decoder

2.  you have a non-sound decoder that has to support this

 

Chris

I have to assume you have not taken time to read the link I sent. Please do that now.

The main issue with a stay alive cap is the track/loco pickups. All have to be clean. Not look clean but have been cleaned. DCC is quite sensitive to poor or intermittent pickups. Flywheels will generally not solve this issue completely and in many cases, installing a flywheel is not an easy thing to do.

All decoders have four diodes that form a full wave bridge rectifier that feed an electrolytic capacitor. This cap will be the largest cap on the decoder and the diode/cap/resistor combo has to be put in parallel with the cap on the decoder. The values of the caps are on the top of the cap usually.

The link shows this very clearly. You need an Optivisor, for magnification, fine tip soldering iron and a steady hand.

If you are not experiencing any running issue, then don't worry about it.

Rich

 

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Posted by PRR_in_AZ on Friday, March 04, 2011 5:07 PM

richg1998

 PRR_in_AZ:

So you guys are saying this isn't practical unless:

1.  you use a sound decoder

2.  you have a non-sound decoder that has to support this

 

Chris

 

 

I have to assume you have not taken time to read the link I sent. Please do that now.

The main issue with a stay alive cap is the track/loco pickups. All have to be clean. Not look clean but have been cleaned. DCC is quite sensitive to poor or intermittent pickups. Flywheels will generally not solve this issue completely and in many cases, installing a flywheel is not an easy thing to do.

All decoders have four diodes that form a full wave bridge rectifier that feed an electrolytic capacitor. This cap will be the largest cap on the decoder and the diode/cap/resistor combo has to be put in parallel with the cap on the decoder. The values of the caps are on the top of the cap usually.

The link shows this very clearly. You need an Optivisor, for magnification, fine tip soldering iron and a steady hand.

If you are not experiencing any running issue, then don't worry about it.

Rich

 

Rich,

I did look at your link but am not an electronic hobbyist by choice so I didn't really get it.  If I take a photo of the decoder and post it, can you throw it in MS paint or something and circle the place where I'm supposed to solder?  I know about clean wheels and all, this is something I just want to try to see for myself if it works. 

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Posted by richg1998 on Friday, March 04, 2011 6:28 PM

A picture might work. Try to set your camera to Close Up.

Write down the decoder manufacturer number. Include a picture of the loco install. Run your loco on DCC for a while and watch the performance Sometimes, turnout frogs can be an issue for loco hesitation.

Also, it helps to have all wheel pickup on the tender and loco drivers or all wheel on the diesel. This can be an issue with brass steam loco tenders.

You did not mention, scale, steam or diesel.

Marcus has discussed this stay alive issue quite extensively in a Yahoo SoundTraxx Group. To my knowledge, I have not seen any discussions by users of non sound decoder.

Again are you seeing any running issues with your present system.

Please attempt to give people more info when you have a question. This can help in getting you an answer a lot quicker.

Removing the shrink on a decoder and soldering the combo will invalidate any warranties.

Rich


 


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Posted by fwright on Saturday, March 05, 2011 12:21 AM

PRR_in_AZ

 

I did look at your link but am not an electronic hobbyist by choice so I didn't really get it.  If I take a photo of the decoder and post it, can you throw it in MS paint or something and circle the place where I'm supposed to solder?  I know about clean wheels and all, this is something I just want to try to see for myself if it works. 

Newer non-sound decoders don't audibly or visibly reset themselves when the power drops out the way sound decoders do.  As a result, the need for a decoder stay-alive just isn't there for non-sound decoders.  Motor stay-alive to prevent stalling on power dropouts is a different issue - and stay-alive circuits are just one alternative.  The size of a stay-alive capacitor that can drive the typical HO motor in an untuned commercial drive quickly approaches the size of a small flywheel - and provides less weight for traction.  Multiple wheel pickups increase the number of parallel paths for power to get to the decoder, and decrease the odds of stall due to power dropout.

[ur]http://www.members.optusnet.com.au/mainnorth/alive.htm[/url]

At the end of the link are some brief explanations and photos of adding a stay-alive capacitor circuit to TCS and Lenz Silver decoders.  I would suggest reading and rereading the article, including the notes under the photos, so you do understand what you are doing.  I would be rather reluctant to simply say solder "here" knowing that any misunderstanding between us or subtle differences between photo and your actual installation will likely result in a non-functional decoder or worse.  I would much prefer you understand why I said solder "here" so that you can adapt to your circumstances.

The article explains the whys of a stay-alive capacitor, and the differences between a stay-alive for the decoder and for the decoder/motor combo.  The article goes on to state that in the decoders he has tried, wiring the capacitor/diode/resistor circuit to the negative side of the rectifier and the blue function output wire has worked.  Observing polarity with electrolytic capacitors is critical, as is getting the right voltage rating for the cap.  Too high a voltage rating and you sacrifice ufds in the same physical space that could be used to keep your motor going longer.  Too small a voltage rating on the cap, and it blows.  The photos show the size of the added wire compared to the decoder circuit board components.

Motor current and lighting load have a lot to do with how effective a stay-alive capacitor is going to be.  A circuit that works well for a 100ma, high efficiency motor and drive won't do much for a motor that needs 400ma to run the locomotive.

Personal opinion, but powering frogs and keeping the rail clean solves the power dropout problem for all decoders.  Adding flywheels, electrical pickup, and stay-alive circuits solves the problem for individual locomotives.

my thoughts, your choices

Fred W

 

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Posted by rrinker on Saturday, March 05, 2011 12:04 PM

 I think Fred summed it up pretty well. I don't think it is needed on reasonable quality HO and larger locos with just motor decoders. It's also not somethign to poke around with if you don't understand what is going on and WHY you would be soldering to a specific point and HOW you determine what that point is by looking at the decoder's components.

 I have one I will be adding a capacitor to, a SOundtraxx LC decoder I have in an F7 B unit dummy. While the Stewart dummies are fairly heavy and have good pickups, it does sometimes drop out where the headlights on powered units don't even flicker. And while it sounds (no pun intended) interesting, I just don't see a need for my motor only decoders, even with unpowered frogs I don't get any headlight flicker.

 I will say on N scale it can make a difference - if you can find a place for the capacitor. Myy friend has a loop of track through one of his city locations and runs sets of little 4-wheel Birney cars on it. He's doubled up most of them and used a Lenz decoder in the powered one with the Lenx USP module in the dummy. Still only the powered one has track pickups, so it's 4 small wheels on a short wheelbase and very light weight - without the USP they have to run pretty fast to kepe going but sometimes still get stuck. Witht he USP, they cruise completely reliably and stop and start automatically according to block occupancy, controlled with RR&Co software.

                           --Randy

 


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Posted by PRR_in_AZ on Saturday, March 05, 2011 6:09 PM

Guys,

Not to be ungrateful for your responses but I'm not really interested in what you "think is best for me".  I'm not going to hold you personally responsible for anything I do.  I fully intend to do this at least one time because the concept of keeping a motor alive is a really neat idea and if it works, what does it hurt.  If I post a close-up pic of the decoder and you are 99.9% sure you can help me locate the point I need to solder the wire(s), great!  If not I think you are wasting your time typing here.  I'm not trying to be rude, just honest, as I'm a big boy.Big Smile

Respectfully,

Chris

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Posted by richg1998 on Saturday, March 05, 2011 6:52 PM

Please post the photo. I have always liked experimenting with electronics, because I can. It may amount to something, maybe not.

If it bothers some here, just send it to me in a email and we can try to see what comes of it.

Rich

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 rrinker on Saturday, March 05, 2011 7:17 PM

 I'm sure we can tell from a picture - I just don;t have any Digitrax decoders to look at, other than one lone DH163L0 from a Proto2000. Those don;t even have shrink wrap, but they also are not laid out anything like the ones that do.

                    --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by PRR_in_AZ on Saturday, March 05, 2011 7:23 PM

OK, here is the decoder I want to experiment with.  So in reading, it looks like the capacitor /resistor/diode combo get wired to the blue (common?) wire and the bridge rectifier on the decoder (which wire?).  I'm  probably totally wrong but here are the photos.  They are large so you can click on them and zoom in to see the detail.

Chris

 

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Posted by cacole on Saturday, March 05, 2011 7:34 PM

The blue decoder wire is the voltage output to light functions.  Wiring a capacitor to this wire would have no effect at all on locomotive performance.

If you think you really, really need a keep alive capacitor, then purchase a Lenz Gold decoder instead of trying to cobble something together on a decoder that is not meant to be modified.  I think Litchfield Station may sell Lenz Gold decoders.

 

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Posted by rrinker on Saturday, March 05, 2011 7:55 PM

 At a GUESS from what I see there:

The track inputs come in from the second pin in from the top and bottom. This goes to the outer edge of the diode closest to the JST connector. The inner side of either one of those diodes should be the + side, and might even be directly connected to the blue wire terminal, although that's on the opposite side of the board and there's probably a pass-thru hole somewhare connecting it to the trace linking the two diodes. The - side should be the inside terminal of either of the two second diodes.

Cacole:the blue lead is often tied right to the plus side of the bridge rectifier, as shown on many example decoders on Marcus's site. Saves trying to solder TWO wires to the decoder.

                --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by fwright on Saturday, March 05, 2011 8:30 PM

rrinker

 At a GUESS from what I see there:

The track inputs come in from the second pin in from the top and bottom. This goes to the outer edge of the diode closest to the JST connector. The inner side of either one of those diodes should be the + side, and might even be directly connected to the blue wire terminal, although that's on the opposite side of the board and there's probably a pass-thru hole somewhare connecting it to the trace linking the two diodes. The - side should be the inside terminal of either of the two second diodes.

Cacole:the blue lead is often tied right to the plus side of the bridge rectifier, as shown on many example decoders on Marcus's site. Saves trying to solder TWO wires to the decoder.

                --Randy

Chris

I agree with Randy.  Hope it works for you.

Fred W

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Posted by PRR_in_AZ on Saturday, March 05, 2011 10:34 PM

Randy/Fred,

Thanks for having a look.  What I'm going to do is post some more pics tomorrow.  One of those is going to be the reverse side of the decoder to see if we can confirm if the blue wire is connected to + side of the first two diodes.  I'm going to post another pic where I circle in red the correct location to solder the wire for the - side.  Again thanks, and expect more pics tomorrow.

Chris

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Posted by WALTER SIMPSON on Thursday, October 10, 2019 7:47 AM

Hi Rich, Are Stay Alive capacitors suitable for DC locomotives?  Are instructions available anywhere?  Is there a product you would recommend?  Thanks!

Walter

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Posted by RR_Mel on Thursday, October 10, 2019 9:02 AM

WALTER SIMPSON

Hi Rich, Are Stay Alive capacitors suitable for DC locomotives?  Are instructions available anywhere?  Is there a product you would recommend?  Thanks!

Walter

 

I’m afraid the only keep alive for DC is clean track work.  What kind of problems are you experiencing?  
 
You know that this is a very old post, last response 2011.
 
 
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Posted by snjroy on Thursday, October 10, 2019 4:59 PM

Clean track and extra power pickups on the wheels. 

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Posted by rrinker on Thursday, October 10, 2019 5:15 PM

 Clean track and extra power pickups and you don't need keep alive for DCC either.

                         --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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