DCC Keep Alives, how they work and how to select components for your own (31)

[@CarminesRCTipsandTricks]

Extremely useful Larry!! I came close at one point about 7 years ago, of making a N Scale Keep-Alive! Close. I used SMD Capacitors and Diode. It worked well enough to pass any Frogs and small dead spots.... What I didn't take into account was the Bypass Circuit. Like I said, it worked, somewhat, and fit in 2 Atlas Hood Diesels, but there was only so much Capacitance I was going to achieve with that crude setup. Your Diagram might make it possible for me to try again! I don't know the availability of a SMD Zener Diode though. Thank you!! You're teaching this old Dog! 😊 Carmine ✈🚂🚙

[@tonyl259]

Excellent video.

[@georgeking3436]

Wow! Great Information. Thanks a lot!!!!

[@mikenugent6090]

You have referred to this video (31) in other videos for the “keep alive” parts list. I am having trouble sourcing the heat shrink tubes. Do you have a part number for that? I sourced the size mentioned in the video and I received a garden hose and not the nice, clean shrinking green one you used.

[@TheDCCGuy]

I Sorry but I bought it several years ago and have no idea who is selling it now, you’ll just have to search the eBay and Amazon listings like I did.

[@dltorres1610]

I liked a lot, very elucidate!! Thanks for sharing knowledgement!!

[@oregonwprrmodeler]

These are great videos. These in conjunction with your MRH articles just have tons of good information. My one beef is I wish you would have posted a part number for the Zener Diode. I just can’t seem to find these from the popular suppliers. I got some but they are little things with tiny little tabs on each end instead of the nice big wire on each end. The ones with wires always seem to be out of stock. What am I doing wrong searching for these things?

[@TheDCCGuy]

I did post the part numbers for 12, 13, and 15 volt Zeners in the description of the video. If Mouser is out if stock then check Digi-Key, Newark, All Electronics, and other electrical parts suppliers for them. There is nothing magical about the Mouser parts, any 1W Zener in the desired voltage will work. Just to prevent confusing folks, I write for Model Railroader not MRH (Model Railroad Hobbiest).

[@oregonwprrmodeler]

The DCC Guy Well shame on me! You just taught me something. I finally figured out how to see the description of the video! I never stop learning from you whether about DCC or KZbin! Thank you.

[@michaelwolak3098]

Hi Larry another great video have a question for you regarding the zener diode, i have some 2.7v 10 microfarad super caps at 2.7 v so if i wire 5 in series which will give me 13.5v total do i use a 14v zener or higher the track voltage would be 14 volts or do i increase the caps to 6 giving me a total of 16.2 v and use a 16.5 or 17 volt zener Your advise would be greatly appreciated Mike (England)

[@TheDCCGuy]

Mike-you need tp keep the voltage that the caps get equal to or less than their total volrage. So with 13.5 V you want a 12-13V Zener. Keep in mind that your actual voltage on the decoder will be less than the track voltage since it has to go through the bridge rectifier which could drop it as much as 1.4V.

[@michaelwolak3098]

The DCC Guy Hi Larry thanks for clearing that up up my problem will let you know how i get on Mike

[@wolfpack4694]

Hi Larry. Another informative video. I’m debating whether or not to use a keep alive with my steam loco dcc installs, and wonder why a keep alive is needed if the track pickups on both the loco and the tender are live. Wouldn’t those two sources suffice to get the pair across any dead zones?

[@TheDCCGuy]

The more wheels you have picking up power the less likely a stay alive will be necessary, especially if the tender wheels are part of the picture. In HO scale the real issue is with short wheelbase steam and diesel locos. Of course if you have ild brass locos with left/right side pickups its a different story.

[@wolfpack4694]

@@TheDCCGuy thank you for the insight. That makes sense. I’m doing an HO Hudson and a Niagara, so I think I’ll try them without a keep alive, and do a retrofit if needed. First task is to get the installs done successfully. Very much appreciate the response.

[@spencere3070]

Thank you Larry! I am adapting this design for G scale where I run 24 volts. Would you recommend connecting 8, 3V caps in series to get my 24 volt rating? I ordered some 10A 1000V Rectifier Diode to substitute for the 1N4001, do you see any problems with this? I am using a 2 watt 100 Ohm resistor. Do you recommend a higher resistance value since I am using 24 volts? The resister and diode remain the same values regardless of capacitance at 24 volts correct? Essentially, could I swap a 0.01F 25V capacitor with a 1F 25v capacitor and the only difference would be charge storage?

[@TheDCCGuy]

I suggest you take a look at this website, it has some suggestions for larger scales. I am not an EE so designing one for large scale is a bit over my pay grade😀 dccwiki.com/Energy_Storage

[@Nealeb1970]

G'day Larry, great videos on the Keep Alives. I have a question, is there a formula for working out how long your engine will run after power is lost? My problem is that some of our Aussie locos are very small, and while I try to keep my track clean, it's easy to miss a spot, so I only want a small KA to last for maybe 4 or 5 seconds which hopefully will make it a smaller unit. Could you use a single 3 or 4V super cap? Or would finding a Zener small enough be a problem?

[@TheDCCGuy]

The limiting factor is the electronics of deciders which require about 7V to operate plus you need a little overhead. The small commercial KAs use complex circuitry to boost voltage from fewer capacitors but those are too complex for home builds. Right noe the smallest I know of are the TCS KA1 and KA2.

[@Nealeb1970]

@@TheDCCGuy Thanks Larry, that helps a lot. I didn't know about the minimum voltage requirement. So I guess 10V would be the minimum, which still requires 4 3V Caps

[@edeptula2992]

RailPro seems to have a problem with Keep Alives burning out a component on their boards. Apparently when you shut down your layout the capacitors don’t drain completely. With that said, it is possible to cause problems with the decoder at 3 to 4 volt levels. Is there a component that we can add to prevent the voltage from dropping below 4 volts or possibly a component to assist with a complete drain of the capacitors when power is lost?

[@TheDCCGuy]

First I’ve heard of this. I’ll have to see what I can find out about this problem, but it sounds like a problem at their end. Is this happening with all types of stay alive devices? After a quick internet search I can only find discussions and questions about how to install stay alives with their decoders but nothing about this other issue. It is interesting that most other DCC decoders work with stay alives fine but theirs won’t. There must be something about this I am missing.

[@dalecherne5377]

So I have a locomotive where there just isn't enough room for much of a keep-alive. I have just enough room for a single capacitor of 16V 1000uf. Wont be a lot, but it'll be at least something. The Zimo sound decoder has solder pads made to be used with a keep-alive. However, since Im just using a single capacitor, do I still need to use a Diode, resistor, and a rectifier?

[@TheDCCGuy]

I’m not sure about that. I seem to remember you can install cap there but it would b best to dig out the instructions or contact tech support. Also youchoos.co.uk deals in Zimo and offers capacitors for them so give their website a look.

[@AlfK661]

Types of supercapacitor query: Hello I live in the UK and have been trying to locate a local source of 1F supercapacitors to try out your method of stay alive for one of my 00 gauge locos but but can only find some that say they are 3.3F capacity at 3Volts ( I have found some 1F ones from China, but they have a massive lead-time to ship to me).....could you advise if the local 3.3 F ones would be suitable please?..... Apologies if this is a 'stupid' question but my electronics knowledge is limited - however I think I am up to trying out DIY stay alives though (but just need some help getting right components ) P.S. excellent videos/content by the way - have spurred me on to have a go !

[@TheDCCGuy]

I think the bigger capacity ones are much larger diameter on the order of 12mm so I have not given them a try.

[@AlfK661]

@@TheDCCGuy The technical note for this particular 3.3F says 8x20mm. so not too big 🤔what do you think?

[@TheDCCGuy]

As I expected, that”s almost an inch in diameter and when you stack several to get a high enough voltage it will be at least an inch tall! Will that fit where you need it?

[@AlfK661]

@@TheDCCGuy At 8mm. diameter surely 3 side by side would only be 24 mm (1.4mm under 1" - 25.4mm?), so at 9V total would this be too low for my 14v track voltage & would the zener need to be 9v not 12v as per your example ?....sorry if this is nonsense, just trying to learn things.

[@TheDCCGuy]

So 3 high would be about 24mm and they would be 20mm wide so you have essentially a cylinder about 20x24mm or close to a cubic inch. But if that works for you then the numbers you mention should work.

[@2011Maynard]

Hi Larry - I have my components, my question is... Are there any polarity considerations for the Diodes and Resistor? It doesn’t look like it by the schematic you show, but I’m a novice at this, so better safe than sorry...

[@TheDCCGuy]

Yes, the diode and Zener are polarized but the resistor is not. On the diagram there is a black line at the tip of the triangles representing the Zener and the diode (the Zener is the one with the jagged line). This line corresponds to the white line across one end of the diode and the black line across one end of the Zener. You should be able to see this in the video where I show how to solder all this stuff together. After you put one together test it using an old mobile decoder before moving on to a more expensive decoder, just in case!

[@budgetwebsiteservice]

Hi Larry, just a bit of brain storming.. I model in 3 different scales/gauges, one of them being Z. Now the maximum voltage for most Z scale loco's is only 9v and this would obviously be running it at full speed, which in all honesty we modellers don't tend to do, so seeing as we're only looking at over coming a bit of dirty track or dead frogs (which are quite common in Z) do you think it's feasible to build one of these using only 2 capacitors for an output of 6v?? As in reality we're only looking for a burst of power to last 2-3 seconds at a time.. Please don't ask me how I'm going to make it fit of course, I haven't quite got that far! 😂

[@TheDCCGuy]

The problem is the decoder needs a minimum voltage to operate so you need to check that for those you plan to use then you could go about designing a circuit to meet those needs. I discussed these kinds of questions in my other videos on stay alives.

[@6axlepwr]

Thanks for this great explanation. I am a little confused though. Five years ago you put up a video on basically the same thing and you were building a 12v keep alive. This video is building a 15v keep a live. With DCC systems putting out 14v or so as you mention here, is it better to go with the 15v setup? Next question. I am starting to use the Soundtraxx Blunami decoder. Will this setup you show work well with them too? I am curios because I bought a Soundtraxx keep a live and it has a LOT more components on the board than just the few you talk about here. Any comments on these extra components would be greatly appreciates or possibly a follow up video explaining the additional components on the commercially available keep a lives vs your simplified keep a live. That would be great too.

[@TheDCCGuy]

The commercial stay alives are much more complex than these very basic ones but should work. The 12V versions I previously built were probably a bit too close to the break point since once track voltage exceeds the total capacitance they may pop although the zener diode should protect them as long as it is chosen correctly. I did this video to show folks how these devices work and provide guidance on how to select the right components if those I used are not available. I have not tested these with a Blunami so cannot advise on their use with them. If you blow a Blunami it may violate the warranty-just a warning.

[@tomcook5813]

Would it benefit using a cap with more Farads?

[@TheDCCGuy]

Yes, if you can find them and they aren‘t huge. So far I haven’t seen them. Right now it is hard enough for companies to get enough parts to keep their inventory stocked, just look at the number of DCC products on the NCE website that are listed as Out of Stock!

[@tomcook5813]

@@TheDCCGuy I believe I’ll stick to your parts list, most important please know that you are genuinely appreciated, have subscribed to you channel for some time. Pls Take care

[@tonydavey3741]

Hi Larry iv just got into N scale and was wondering if anyone makes a stay alive for N scale locos, im running modern diesel power mainly Kato as i like there product

[@TheDCCGuy]

Unfortunately I don’t know of any, the components are just a bit too big. I have installed a TCS KA1 in an N-scale tender along with a decoder and speaker but it was a big tender. Diesels are a bigger problem since most have barely enough room for a decoder.

[@DaleSchultz-mixmox]

Hi Larry, I don't understand the point of connecting capacitors in series. My understanding is that you will still only get maximum of 0.2 Farads out of 5x 1F caps in series. Is it just to get the total voltage higher? Why not use a 15V 1F cap?

[@TheDCCGuy]

Have you seen how big such a super capacitor is?

[@DaleSchultz-mixmox]

@@TheDCCGuy sounds like the real answer is: a series of lower voltage caps is more compact. Thanks.

[@DaleSchultz-mixmox]

what about slight variations between the components? See www.coilgun.info/theorycapacitors/capacitors2.htm where they say: if one capacitor is slightly leaky, it will gradually transfer its voltage to the others, possibly exceeding their voltage rating in turn. And if one of them punches through its dielectric barrier, it can then damage others in a cascading fashion. This is why series capacitors are generally avoided in power circuits.

[@TheDCCGuy]

Exactly, once you get above the 3 volt 1 F supercaps they get large fast. TCS has found a supplier of small caps for their KA1 and KA2 Keep Alives but I have not been able to find out their rating or source. I took the wrapper off to get a peek and they are plain bare metal with no markings at all! At any rate if the larger super cap will fit then that would be a better solution than daisy chaining 5 small ones.

[@2011Maynard]

Is the Mouser part number for the 100-Ohm / 1W resistor actually 71-PAC100001000FA100 ( versus ...100FA...)?

[@TheDCCGuy]

I just checked and the number is correct. I copied and pasted these nos. io get them correct. These are not for use in satellites so anytning rated at 100 ohms and 1/2 to 1 W should work.

[@2011Maynard]

@@TheDCCGuy thanks for the quick feedback, unfortunately the part that was provided comes back ....No Results... in Mouser's system...

[@TheDCCGuy]

I ran into that problem too and have no idea why it is doing that. I had to literally scan through the 100 ohm 1 W resistors to find the listing. However there is nothing magic about this resistor, and just about any 100 ohm 1/2 to 1 W resistor should work fine.

[@2011Maynard]

@@TheDCCGuy I did choose an alternate p/n, and my parts are ordered. Thanks for your help, and especially for your channel that educates and encourages others to make things they would not otherwise try... Best, JP

[@DennisFisherUK]

There is nothing in that circuit to stop any one of the capacitors being charged to a higher voltage than what they are specified to take. If one of them is a different capacity it will charge at a different rate to the others and may overvoltage.

[@TheDCCGuy]

The Zener will keep the maximum voltage to them at its operating voltage but the individual capacitors are not protected with resistors, etc. That is one difference between this circuit and the commercially available ones which usually have a surface mount resistor for each capacitor to regulate their charging voltage. However I have never had one blow on me.

[@allenbarnes7202]

Educate a dummy, what is a keep alive for?

[@TheDCCGuy]

It keeps the decoder powered and the locomotive running when it hits a dirty section of track, rough track, or an unpowered frog. Think of it as a little battery that gets you over the bad spots.

[@allenbarnes7202]

Ok thanks

[@404BOOMER]

If this is for dirty track or imperfections in the track why not do a better installation of the switches or track and clean the rails more often? Then the stay alive is not needed. Maybe there's something I'm missing.