Fireman_Ian Posted August 12, 2011 Share Posted August 12, 2011 I read with great interest the review in the latest Hornby Magazine (issue 51 Pg 81) of a DCC decoder with a 'stay alive' capacitor attached. This sounds like the answer to problems with locos stopping on Hornby points and/or not too clean track.My question is, is it possible to add a capacitor to any decoder to get this 'stay alive' feature or is the decoder in the review especially designed ?This is something for the electrickery experts on this forum to contimplate as I would love to be able to convert my locos to 'stay alive' over dodgy points.Ian. Link to comment Share on other sites More sharing options...
ace10086 Posted August 12, 2011 Share Posted August 12, 2011 it is something I have thought about, I'll have to take a look at the magazine. It should be possible however you will need to attach the capacitor after the diodes on the decoder which could make for some tricky soldering, depending on the decoder being used.If you were crawling over points you would need a pretty big capacitor to be able to maintain drive before the stored energy was used up.I had thought about fitting one further into the circuit to maintain power to the processor so it doesn't restart and slowly accelerate the loco back up to speed if you have accelaration delays set however I believe some decoders have this feature now anyway. Link to comment Share on other sites More sharing options...
ace10086 Posted August 21, 2011 Share Posted August 21, 2011 I've managed to fit a capacitor to a Hornby 8249 decoder. Like most decoders the blue wire is a common +ve feed which I used and connected the other end of the capacitor to the -ve part of the bridge rectifier.I used a 1000uF 25v capacitor and tested it on a 0-4-0 loco which has poor pickup and little weight so is a problem when crawling or going over points. With the capacitor it worked very well, only with the very first speed step wouldn't it make it over the points. I did have to disable DC running by adjusting CV29 otherwise the loco would leap about when it lost DCC signal and when into DC mode. This means that people with only a Select probably aren't advised to add a keep alive capacitor. Fitting a bigger capacitor would probably trip the controller when putting the loco on the track because of the inrush current charging the capacitor. In fact even with 1000uF if I converted a few locos I imagine there would be problems when first turning on the controller so the next step will be to add a resistor and diode.I've not trying programming the decoder with the capacitor in place. I can see this being a problem if using the programming track as the only time voltage is applied is during actual programming. I've noticed other people on the web using a small switch to overcome this problem however I always use Operate mode which means this shouldn't be an issue for me. Link to comment Share on other sites More sharing options...
poliss Posted August 21, 2011 Share Posted August 21, 2011 You need to add a resistor for reducing the charging Inrush current.See this website. http://www.members.optusnet.com.au/mainnorth/alive.htm Link to comment Share on other sites More sharing options...
mac_xpert Posted February 2, 2012 Share Posted February 2, 2012 ace10086 - can you post details of where you connected the wire for the -ve of the bridge rectifier for those that are unsure (me!)Thanks! Link to comment Share on other sites More sharing options...
mac_xpert Posted February 3, 2012 Share Posted February 3, 2012 mac_xpert said:ace10086 - can you post details of where you connected the wire for the -ve of the bridge rectifier for those that are unsure (me!)Thanks!Never mind i worked it out based on your posting!http://www.modelrailforum.com/forums/index.php?showtopic=21076 Link to comment Share on other sites More sharing options...
LesC Posted January 6, 2019 Share Posted January 6, 2019 Hi, I a looking at fitting stay alive to the x9659 decoder. The images in your posting ( http://www.modelrailforum.com/forums/index.php?showtopic=21076 ) have expired. Can you share them here? Thanks in advance, Les. Link to comment Share on other sites More sharing options...
2e0dtoeric Posted January 6, 2019 Share Posted January 6, 2019 Loads of threads on this forum about this, mostly by Chrissaf, so look up his articles, to find the info you require. Link to comment Share on other sites More sharing options...
Chrissaf Posted January 6, 2019 Share Posted January 6, 2019 As Eric advised....a couple of my previous postings on this topic are shown below. There are more than two threads on this topic if you use the forum search function. . Fitting a 'stay alive' to a Hornby R8249 or any decoder that is not designed for it. https://www.hornby.com/uk-en/forum/post/view/topic_id/13404/?p=2 . Same on a Hornby TTS sound decoder. https://www.hornby.com/uk-en/forum/stay-alive-install-for-tts-decoder/?p=1 Link to comment Share on other sites More sharing options...
96RAF Posted January 6, 2019 Share Posted January 6, 2019 Just for info the previous images expired because the forum died upon change of ownership and had to be reinstated and each member had to rejoin, etc, etc. Most folk call these add on capacitor circuits ‘stay alives‘ but its a bit like the generic terms Hoover and Fridge, these are registered trademarks by various kit manufacturers - e.g. stay alive, keep alive, and others. Rob Link to comment Share on other sites More sharing options...
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