#39 Part 1: How to make a Stay Alive Capacitor Unit (Hornby TTS Sound Decoder and Others)

This is Part 1 of an in-depth two-part series looking at home-made stay alive devices.
In this video, we look at making a stay alive/keep alive capacitor unit for use alongside a Hornby TTS sound decoder.
The principles and steps outlined in this video are, however, applicable for most other stay alive scenarios, including coach lighting, end of train (EOT) lamps and so on. The stay alive unit made could therefore be used in multiple situations, not just with a Hornby decoder.
As well as showing you how to make the stay alive unit itself and assemble all of the components, there's a brief explanation of the background to stay alive devices generally and the role that each of the components plays in the overall circuit.
+ Video Contents +
00:00 - Video introduction
01:08 - Intro to making a stay alive unit
02:18 - Overview of the components required
04:11 - Using resistors to manage in-rush
05:00 - The components in detail
06:26 - Circuit diagrams
08:40 - A quick word of capacitor sizes
10:58 - Putting it all together: soldering
15:40 - Adding hookup wires & heat shrink
17:22 - The finished article
+ Components +
You can buy items used in this video tutorial using the affiliate links below. Using these links helps to support the channel and is very much appreciated.
Hornby TTS decoders (Amazon): amzn.to/2PbRM9x
Hornby TTS sound decoders (eBay): ebay.to/2S1P4Ca
Capacitors (15,000 uF 25v): ebay.to/2AljFnF
Resistors (100 ohm 1/4w): amzn.to/2yzLtDx
Decoder wire (red & black): ebay.to/2NR9fj1
Decoder wire (Multipack): ebay.to/2PGEYoK
Diodes (1N4001 50v 1A): ebay.to/2CXBifB
Diodes (1N4001 50v 1A):: amzn.to/2ODFqYo
Heat Shrink (multipack): amzn.to/2PdO0N5
Heat Shrink (various sizes): ebay.to/2EvWI54
Kapton tape (10mm x 30m): amzn.to/2OBEpjB
Kapton tape (various sizes): ebay.to/2R2H2aU
Liquid Flux Topnik No Clean (Amazon): amzn.to/2Al6HpP
Liquid Flux Topnik No Clean (eBay): ebay.to/2CXy7EO
0.3mm Lead/Tin solder: amzn.to/2NT7pOy
0.3mm Lead/Tin solder: ebay.to/2S6Jpe0
Hakko Soldering Station: amzn.to/2CVLzca
Blue silicone electronics mat: amzn.to/2Pbv7ug
A2 green cutting mat: amzn.to/2P8aKy3
A1 green cutting matt: amzn.to/2P8aKy3
#StrathpefferJunction #HornbyTTS #StayAlive #KeepAlive
Thank you very much for watching.
Please comment, like, share and subscribe!
Visit us at: www.strathpefferjunction.com
+ Disclaimer +
This project does require a steady hand and competence with a soldering iron. Working with DCC decoders and tiny surface-mount components leaves little margin for error and it is very easy to permanently damage sensitive electronics if you are not very careful. If you choose to follow any of the steps or suggestions outlined in the video, you do so at your own risk and any damage or injury to yourself, your models, your equipment or others is your own responsibility.

[@GalgormHall]

Top work as usual David, you make it look so simple! Paul

[@StrathpefferJunction]

Many thanks, Paul.

[@alanmargalan5921]

Thanks for doing this David Having asked for your help you came up trumps again watching part 2 now Cheers

[@StrathpefferJunction]

Very glad it was of use, Alan!

[@SeanWalsh05]

Love it! Thanks for the tips! I like it how you are making a very low standard hornby railroad class 97 into an amzing standard!!

[@StrathpefferJunction]

Thanks, Sean. Really appreciate the feedback. I'm currently sorting our my spare room. Once it's cleared, I'll be able to set up my spray booth and hopefully get a wee bit of weathering done too. I've always preferred Bachmann and Heljan because of their detail and features, but if you spend a wee bit of time on these lower spec ones, you can get them looking a lot better. 🙂👍🏻

[@SeanWalsh05]

@@atticusuriel4580 nope, I personally do not care

[@UnfiedChamp]

Brilliant, everything I wanted to know. Now I have to watch the rest of your vids.

[@StrathpefferJunction]

Thanks for the feedback and support!

[@DaveHedgehog2006]

Great video David. One suggestion I have for anyone struggling to find room to fit a large capacitor is instead to look at using multiple smaller capacitors distributed around the loco. Connecting them in parallel will give a total capacitance equal to the sum of the individual capacitors but without having to find a single space big enough for one very large cap. For instance 3x 4700μF connected in parallel will give 14100 μF (very nearly as much as the 15000 μF used) but it may be easier to find 3 spaces for these physically smaller devices.

[@StrathpefferJunction]

Thanks, John. Yes, that's absolutely a good idea. You may be able to squirrel away some supercapacitors too and cram in a lot of capacitance. 🙂👍🏻

[@SimonLivertonCentral]

Very nice David, I suspect there will be a lot of people out there that will not be able to solder onto such small pads, but never the less excellent video...Simon

[@StrathpefferJunction]

Thanks, Simon. Yes. It definitely needs a steady hand and confidence with an iron, but I actually found it easier than soldering on ESU's Powerpack mini to their loksound 4 micro (now, those really are small pads!).

[@deltic5514]

Nice video very well explained will be giving a go so fingers crossed

[@StrathpefferJunction]

Excellent! I've done a few now and it works pretty well. Just need a steady hand!

[@irishsixtysixfanGbrf66739]

Should find this very useful

[@davidcurrie8564]

Hello there great work! what type is the capacitor and the resistor and diode please! I have a TTS Hornby valenta decoder in my HST that I have consistently cleaned the wheels and track and the problem was the wait for it ! point frogs .. the hornby valenta decoder is R7140 i am going to do the same as you. I used to work in an electronics factory back in the 80's (Burroughs computers) where i built the PCB boards for the Disc drives from scratch..

[@irishsixtysixfanGbrf66739]

It's up on KZbin

[@lairdpauljohnson8350]

It's very basic electronics and the components are available from any dedicated electronic component sellers and much more cheaply than the local model shop.

[@StrathpefferJunction]

Yes, absolutely. One of the reasons I wanted to do a video on this is because most people will be able to make them and they can save themselves a fair bit of money not buying pre-made units. For the price of just one of some of these branded units from the decoder manufactures, you could make a pile of your own. And like you say, components are much cheaper from specialist suppliers or even ebay. Packets of ten 1k resistors for £2 or whatever from model shops is not a cheap way to do it.

[@joshuahaworth987]

Do you produce the holder for the bottle of TK83 flux please? I've got these bottles and would be interested in one! Cheers

[@falken_gt4]

I assume you are like me and have tipped it out over the desk!

[@tomaswolf5882]

Hi thanks for the video. 1 question. how do I choose the right patametets of resistor and diode for given capacitor. u say use 100ohm and you ll be fine but why 100:-) thanks a lot

[@ztruckz]

hi, is it possible to use 2 o r3 capcitors inline, i have 2x 10v 6800uf capacitors, 100ohm resistors, and 1n4001 diodes,,,, excellant vids by the way,,

[@StrathpefferJunction]

Hi. If you hook them up in series, the charge across each capacitor will be the same irrespective of the capacitor rating, although you will have more storage capacity overall. Also, so long as they are in series, they will decide the voltage across them, so while you mustn't use 10v capacitor with DCC or even DC track voltage generally, you could probably get away with two or three in series, yes. But I would definitely test the circuit first before installing it in a model, just in case it runs hot or explodes. Capacitors can fail quite spectacularly!

[@billligon4005]

I should ask if this circuit would work in a Coach connected thru the trucks to the DCC rail? And those capacitors are not inexpensive.

[@jankochanowski3252]

Hello. If paralel to the capacitor Zener diode 15V, 0,5W will be added. In this case capacitor can be 16V and they are smaller than 25V. Can stay alive be done like this? best regards

[@stocktonjunction]

So what capacitors would u use for class 50s 47s 33s 20s etc if the larger one doesn't fit as I have a few heljan and hornsby locos that I want to do also if u change the capacitors to smaller ones do u still use the same resistor and diode sizes

[@StrathpefferJunction]

Yup. The for this sort of unit, the resistor and diode can remain the same. Re. the capacitor, in practice it really comes down to the biggest one you can fit in. Different manufacturers make them different sizes, but same capacitance value, so if you shop around, check the dimensions and you may be able to squeeze a reasonable amount in. Anything below about 4700uf, and I don't thi k you'll notice anything much different with a sound decoder.

[@MrHipwell1989]

brilliant video. just ordered some components. how would this be wired into a decoder which has got a 3 pin stay alive connection? what's the 3rd pin for?

[@StrathpefferJunction]

It really depends on the model of decoder. Some require three wires, with one being for logic. Others have three wires, but can be used without logic. The instructions with the decoder should explain what works with that decoder and also how to wire it up. These stay alive units are basic units with/which work well with many decoders, but they may not work with all decoders that require a logic level feedback from the stay alive unit.

[@railthefox1857]

can this be dun to a cd loco to heling get over crosing

[@StrathpefferJunction]

Yes. It should work fine, so long as the motor works OK with the decoder in the first place.

[@irishsixtysixfanGbrf66739]

Murphy models Wexford Street Dublin they do their own loksound v4 sound decoder for class 071 111 Northern Ireland class 141 and class 201 emd London ontario 1994 pre development of the class 66 the class 59s were developed from the class 201s for irish rail

[@robstrains8711]

Great video may I ask where did you get the topnix black stand from I could really do with one of those.

[@StrathpefferJunction]

Hi Rob. Many thanks for the comment. I actually designed the stand myself and printed it on my 3D printer. After knocking over a full bottle, I learned my lesson. I can make the 3D file available, if you'd like?

[@robstrains8711]

Hi I would be more than happy to buy one from you if that is possible, Like you I knocked a bottle over.

[@StrathpefferJunction]

@@robstrains8711 Drop me an email and I'll see what I can do... www.strathpefferjunction.com/contact-us/

[@johncollings9825]

Hi David , i have a Lima class 37 with a CD Motor fitted , i have also fitted a TTS Sound chip -- i then saw your video regarding fitting a stay alive . having purchased a DCC Concepts large capacitor and followed your video with great care. i fitted the unit . Since fitting the sound now is very low -- and the loco will not move it just sits there and clicks !!! If i turn sound off the loco moves , since removing the Capacitor and turning the sound on it clicks , WHAT DO YOU SUGGEST ------ I did ask if you could fit this for me but you said you were too busy --- is there any chance you could now you could look at it for me ---- im in no rush to get it done ,BUT i would like it sorted.

[@StrathpefferJunction]

Hi John. This isn't an issue I've come across, I'm afraid. I've done a few of these modifications now and they've all worked fine from the get go. What rating was the capacitor and did you also put the diode and resistor in the circuit? Are you sure you connected it up to the correct pins on the decoder? Did you manage to get the wires soldered quickly or is there a possibility that you applied too much heat to the pcb or disturbed any of the other components? If you're able to send me a photo of each side of the decoder, I'll certainly take a look and see if anything obvious jumps out, but it's possible that the decoder is now permanently damaged. They are really quite delicate bits of electronics and when they fail (particularly with tts chips) unfortunately there is often not a huge amount that can be done.

[@lorenzosdeadchannel]

Hi, i was wondering would this concept work on DC locos, it makes sense to me but just wanted to double check before i actually go ahead and buy the components, also if it does work would i still need to use the resistor and diode ?

[@StrathpefferJunction]

Hi Lorenzo. I think the issue you'll have is that dc uses the polarity of the track feed to set the directiob of the loco. Capacitors are also polarity dependant. You would need to devise a circuit that stored energy depending on the direction of the loco - probably with two seperate capacitors - and then gave back the energy correctly. It would be a more complicated circuit to the dcc stay alive circuit. The resistor and diode are there to protect the capacitor and guard against inrush current. You'd need something similar for anything where a capacitor is used.

[@philhimsworth]

You can sort of do it; the main difference is that you need an non-polarised capacitor which can supply the motor in either direction. Non-polarised capacitors are too small, but you can make one from two electrolytic caps back to back. I've been experimenting with an old Hornby smokey joe with 4 1F 3V supercapacitors in; it works, but it actually runs for too long once you kill the power, so I've been meaning to try smaller capacitors instead. You don't need the diode or resistor; it must be able to provide full power in either direction to run the motor. It will have a high startup current, but this doesn't really matter with DC as it will only be one loco at a time. You just need enough caps to accept the maximum voltage, paired back to back like +c- +c - -c+ -c+; nothing else is needed other than the wires. Give it a try. Probably not with your best loco, though :-)

[@johnm8342]

I used capacitors on direct current (DC) for filtering low frequency, I.e., speakers, and capacitors act differently for Alternating Current (AC, and in this case alternating square wave DC pulse)… I’m more f a programmer than engineer these days, so correct me if I’m wrong… anyway… great video that is still relevant over the years.

[@SofieBrink]

Hi David, i know this video is quite old but I’ve just installed some lights into a coach of mine but they keep cutting out at one specific point and turning back on about 40cm down the line. Oh and btw if i turn the function off and on on my controller after it cuts out the light comes back on. None of my other loco’s or coaches have any problems there

[@StrathpefferJunction]

That sounds very strange indeed! Normally, if it cuts out at the same point all the time my first guess would be the track, but if other models don't cut out there, it's less clear. I wonder if it's an overload issue? What lights are they? What decoder are you using? Are the ones that work long or short wheel base models, and what's the coach?

[@SofieBrink]

Strathpeffer Junction Hi first off Thanks for the quick reply, i’m not sure if it could be overload because all the other trains keep running even if the lights cut out. Or now i think of it do you mean a decoder overload? It has 3 lights 2 of which are red led’s for the taillights and one yellow ish lightbulb the coach came with. The white one is wired up to function 1 and the 2 red leds to function 2 and of course both positive wires connect at the common blue. Its using the Uhlenbrock 76900 function decoder. The coach with the problems is long wheelbase with left pickups at the front bogie and right pickups at the rear one. I don’t have any block detection so that can’t be related either. The other loco’s and coaches are mostly short wheel base. And its an old lima coach no real specifics.

[@SofieBrink]

Just to be clear the led’s have been bought from a model shop and they told me to “just attach the red to the blue and the black to the function pad on the decoder. No resistors or anything needed as far as i know this us one of the first times i’m doing this kind of stuff so i might just be stupid

[@irishsixtysixfanGbrf66739]

I clean my track regularly but Hornby express points has a couple of deadzone

[@StrathpefferJunction]

Yup. Absolutely agree. Insulfrog points can be a real headache...particularly for sound fitted models!

[@irishsixtysixfanGbrf66739]

Check out some Irish rail videos on KZbin class 201 and 071 diesels with loksound v4 with the wireless sound decoder and speaker

[@StrathpefferJunction]

I will do. I've just watched a couple of yours. I'm not all that familiar with the Irish stuff, but I really like the look of those diesels.

[@irishsixtysixfanGbrf66739]

Quite familiar with the English locomotives in diesels we run 071s on freight trains such as logs containers powder tanks ore trains most passenger services are 22000 drc two locomotive haul services are Dublin Belfast enterprise 201 class with mk4s with a dvt on end Dublin to cork

[@Finnertoncentralmodelrailway]

What is the purpose of the resistor? I would have thought it would have defeated the purpose of the diode? Creating your own stay alive capacitor is a good idea

[@StrathpefferJunction]

Hi Brian. It's to do with the direction of the diode. In this circuit, the capacitor charges through the resistor because the diode acts as a shut value when the current is flowing in that direction. When it's keeping the decoder alive, the capacitor discharges via the diode, which is open in that direction provides less resistance than the resistor. Does that makes sense? It's always easier to describe in a diagram rather than text!

[@Finnertoncentralmodelrailway]

Ah ok yes I get it mate thanks I am quite a novice when it comes to electronics

[@StrathpefferJunction]

No worries. We all start somewhere...I still have loads to learn about it all too! 🙂

[@Finnertoncentralmodelrailway]

Ok thanks look forward to part 2

[@StrathpefferJunction]

@@Finnertoncentralmodelrailway It's out now! 🙂

[@irishsixtysixfanGbrf66739]

Check out a programme on Irish railway history called ironing the land

[@StrathpefferJunction]

I'll have a Google and see what I can find. Many thanks!

[@irishsixtysixfanGbrf66739]

Then Again I don't run tts decoder in any of my locos I run esu decoders Murphy models sound decoder and dcc concepts

[@StrathpefferJunction]

Yeah. I don't think Hornby do any Irish sounds, do they? What would be the closest, if any, to some of the Irish diesels?

[@irishsixtysixfanGbrf66739]

Irish railway history is not to similar to UK railways history we have 32 counties here 26 are part of the Republic of Ireland and the 6 northern counties are belonging to the UK we had lots of companies who ran smaller branch lines and long distance lines all competitors against one and other then four main companies were set up great northern Great southern and western great Eastern railways then nationalisation was brought in 1954 at the withdrawal of steam locomotives a new transport company was set up to cover all areas of bus and train services including the buses that go to other counties called CIÉ which include bus Éireann(irish bus) Bus Átha Cliath) dublin bus and irish railways where as the northern counties were under the London midland and Scottish northern Ireland railway Committee same thing happened to them in 54 a new company was set up called NIR (NORTHERN IRELAND RAILWAY'S) around the 2000 a new company called translink took over northern Ireland and irish operate a cross border service called the enterprise hauled by a class 201 from Dublin Connolly to Belfast central

[@StrathpefferJunction]

Many thanks indeed for the brief history. Really interesting to see how it all developed. I've got cousins in Dublin, so I've used the buses and trains in and around that part of Ireland a wee bit, but I've never been to Northern Ireland.

[@irishsixtysixfanGbrf66739]

Most decoder with stay alive gives up to 10 seconds

[@StrathpefferJunction]

Thanks for the comment. In my experience, that's not the case. It depends hugely on the capacitor, the decoder type and whether you're using sound or not. If you turn off sound, for example, you can often double the amount of stay alive time. Some would also suggest that >=10 seconds is not recommended, as it's >=10 seconds that the loco will continue after hitting emergency stop, which is actually quite a long time if there's a head on collision or similar in the offing. With my models, I put in enough to cover points and the odd spot of dirty track, but each to their own. Rule #1 rules.

[@irishsixtysixfanGbrf66739]

Personally tts are really poorly made and not great had two replacement decoders for my Hornby class 66