Extending decoder wire

[Tomathee]

Hi guys, this question is partly to do with saving money as well as technical.

I'm trying to upgrade my son's Railroad Flying Scotsman with a TTS decoder. I'm a bit irked as the instructions for this specific model and video guides for similar models I found suggested there was a decoder socket in the tender and connection to the loco so that everything could be put in there. However that is not the case, the decoder socket is in the loco with screw holes for the speaker in the tender, and no existing electrical connection. I'm sure there's no space for the decoder in the loco, so I'll need to extend the 8 wires so that it can go in the tender. I don't mind doing this and think I can do it re. soldering etc. My question is around the type of wire needed. All I have is what I used for the bus wire on the layout (16/02). This obviously looks thicker than the wires on the decoder, I don't think I'll use it as there will be 8x of it between loco and tender which will add up to some size. I've looked and there is specific decoder wire, though measured differently to the bus wire numbers I have (a DCC concepts item said 32G, either single or twin wire, whatever the difference is), either way none of it means much, I just bought what other guides said. I think I'll buy some of this wire as part of a bigger order I'm putting together for stuff, but I wondered if there's any issue in using the bus wire I had for the decoder? For example if on another example there's room for the decoder in the loco and I only need to extend the two wires to the speaker in the tender. Also, is there anything to be done about making this connection non-permanent? Any sort of connection block I can think of would be too big for 8 wires, I thought about some kind of effort inside the tender with screw terminals but that also sounds on the large side. I looked at another loco I have which does feature an electrical connector between loco and tender and whilst it gives the idea and is small enough, I'm not sure I have the skill to solder within such a small space to keep the wires separate, if the parts are available. Thoughts appreciated, thanks for reading

[Free At Last]

You can buy pre wired 4 pin jst connectors like these.

For wire, I have stripped the cores from old computer cables, such as mouse, printer, keyboard etc.

[peterm1]

I have some of those wires/plugs/sockets that Pete mentioned, but I've used 32G wire because it's quite a bit more flexible. I've made various Zimo decoders fit into spaces either in the tender or loco or a combination of these along with speakers and stay alives. I haven't used any plugs and sockets but have soldered the connections either end so there's no chance of losing the juice. You'd probably be surprised how quickly you can get pretty adept at soldering if you get some decent kit.

[jamesed]

There are a few points here. First the simple answer, 7x0.1mm equipment wire will do the job, which is 30AWG but you could go down to 32AWG if you wish. 

 

Next, if there is a socket in the loco and the tender has been prepared to accept a speaker then it's designed to take a decoder. If the one you've got doesn't fit then you have the wrong decoder. The solution to this is buy a decoder which fits the space available.  In the long run that will be a far better option. 

 

Finally, it is concerning that you state you have used 16x0.2mm wire for your dcc bus. That's far too small by any standard and will cause you ongoing problems. With dcc it's not just about the current capacity (although 2A is still likely to be under rated especially if you are operating sound fitted locos). You need headroom to cope with the transient voltage peaks and troughs of the wave form to protect the integrity of the signal. The impedance of your small wire bus will be too high.  Most people use 2.5mm sq cable (13awg approx)  or on a small layout you may be fine with 1.5mm sq (15awg approx) . That will help ensure the bus impedence is low enough for the integrity of the dcc signal although other factors, like minimising any joins, soldering droppers etc. will also play a part in that.   Your 16x0.2mm wire will be ideal for the droppers between the track and the dcc bus.

Edited January 30, 2023 by jamesed

[WIMorrison]

What is 32g wire that DCC Concepts list? This is anew way of measuring wire that I havent heard of as it omits the length measurement that is needed when specifying the weight of something. I am used to seeing something like 5g/m (5 grams per meter), or 16/0.2 wire (16 cores at 0.2mm²), or even 24AWG (24 American Wire Gauge). 

 

32g leaves me confused as to what size the wire actually is 😒

[RobinofLoxley]

The problem is that you have the wrong decoder, and are going to bodge as a result. There are a significant number of posts here where decoders get fried and its usually either over-wiring or squeezing in.

 

Presumably you can see the decoder socket but otherwise check here

 

https://www.modelraildatabase.com/Hornby/locomotives/

 

This will tell you the right kind of decoder. Then you have to buy it, and put the wrong one on ebay. There could be some debate here as to what a TTS decoder is an update for, on another day. Its not a good time to be trying to buy decoders anyway.

[Tomathee]

11 hours ago, Free At Last said:

You can buy pre wired 4 pin jst connectors like these.

For wire, I have stripped the cores from old computer cables, such as mouse, printer, keyboard etc.

Thanks, I'll have a look at these, the decoder has 8 wires so presumably I'd need two. The other thing I'll try later is if the decoder fits in the loco and I only need two cables for the speaker to the tender, so I can get the 2 pin version of your suggestion.

 

2 hours ago, WIMorrison said:

What is 32g wire that DCC Concepts list? This is anew way of measuring wire that I havent heard of as it omits the length measurement that is needed when specifying the weight of something. I am used to seeing something like 5g/m (5 grams per meter), or 16/0.2 wire (16 cores at 0.2mm²), or even 24AWG (24 American Wire Gauge). 

 

32g leaves me confused as to what size the wire actually is 😒

This was what I looked at - 32G wire. Might mean AWG like you and the other guy mentioned, none of it means anything to me.

 

On the wrong decoder subject, the model ref is R3086 and I bought an A1/A3 TTS sound decoder, ref R8106. Further enlightenment appreciated.

 

[RedgateModels]

17 minutes ago, Tomathee said:

Thanks, I'll have a look at these, the decoder has 8 wires so presumably I'd need two. The other thing I'll try later is if the decoder fits in the loco and I only need two cables for the speaker to the tender, so I can get the 2 pin version of your suggestion.

 

Personally, if the TTS decoder will not fit in the loco then I'd rewire it to move the socket into the tender. You'd need a 4 wire connector, pickups from the loco and motor wires back from the decoder.

[Free At Last]

52 minutes ago, Tomathee said:

 the decoder has 8 wires so presumably I'd need two.

 

Unless the loco has lights you only need four wires.

If the decoder stays in the loco you would have two wires to the speaker and two for the pickups, if the tender has any.
If you move the decoder to the tender, which is what I would do, you still only need  four wires, two to the motor and two for the pickups.

[Tomathee]

10 hours ago, RedgateModels said:

 

Personally, if the TTS decoder will not fit in the loco then I'd rewire it to move the socket into the tender. You'd need a 4 wire connector, pickups from the loco and motor wires back from the decoder.

 

Thanks, I'll have a look at this when I get round to have a look at it next, would eliminate space issues.

 

9 hours ago, Free At Last said:

Unless the loco has lights you only need four wires.

If the decoder stays in the loco you would have two wires to the speaker and two for the pickups, if the tender has any.
If you move the decoder to the tender, which is what I would do, you still only need  four wires, two to the motor and two for the pickups.

 

Thanks, wasn't aware of the lights taking up four of the wires, guess it's a generic decoder with the sound file being the only variation. Will report back once I've gotten whichever parts and had a go at the work.

[Tomathee]

14 hours ago, jamesed said:

Finally, it is concerning that you state you have used 16x0.2mm wire for your dcc bus. That's far too small by any standard and will cause you ongoing problems. With dcc it's not just about the current capacity (although 2A is still likely to be under rated especially if you are operating sound fitted locos). You need headroom to cope with the transient voltage peaks and troughs of the wave form to protect the integrity of the signal. The impedance of your small wire bus will be too high.  Most people use 2.5mm sq cable (13awg approx)  or on a small layout you may be fine with 1.5mm sq (15awg approx) . That will help ensure the bus impedence is low enough for the integrity of the dcc signal although other factors, like minimising any joins, soldering droppers etc. will also play a part in that.   Your 16x0.2mm wire will be ideal for the droppers between the track and the dcc bus.

 

Thanks, I've been checking what I used. I started off with 1.5mm sq for most of it (bus and droppers, found the wrapper) which was some sort of electric cable from B&Q. At some point I saw the 16x0.2 by Peco at a model shop/show and started buying that instead, I'm sure I read somewhere it was ok but it seems not, or maybe for DC, doesn't really matter now as I'm close to switching to DCC so if it's no good for that I'll have to do something. It's mainly in sidings when I extended and part of the loop when I ran out of the original wire. Anyway, I'll swap it out in the areas I used it, but it's thrown up more questions. The layout is 4ft by approx 7ft, which falls into small or medium depending who you ask. I suppose what I'm getting at is should I just bring it into line with 1.5mm all round, or do I need to start from scratch with a completely new 2.5mm bus? As for specific products, on the 'railway specific' side, do I want something like this Rails 2.5mm, or an example from B&Q which is much cheaper, couldn't find the exact one I used originally. Cheers

[KingEdwardII]

6 hours ago, Tomathee said:

1.5mm sq for most of it

I use electrical FLEX cable for my bus cabling. 2.5mm2 and 1.0mm2 are readily available and relatively inexpensive. This works out cheaper than specialist model railway cabling.

 

For a small layout like yours, the smaller size will be adequate, since voltage drop will be negligible over the cable runs you are going to have.

 

Yours, Mike.

[WIMorrison]

Let’s be clear - there is no ‘specialist model railway wire’.

The wire used in model railways is exactly the same as wire from any other supplier and I would strongly advise you not to buy wire from a model railway outlet due to the exorbitantly high prices that are generally charged. 
 

You can buy wire from many outlets, B&Q, Wickes, etc or better Rapid Electronics.

[smokebox]

1.5²mm should be perfectly adequate for a layout of that size and 16/0.2 is good for droppers if kept as short as possible, no longer than about 12inches or 300mm is recommended.

[WIMorrison]

2 minutes ago, smokebox said:

1.5²mm should be perfectly adequate for a layout of that size and 16/0.2 is good for droppers if kept as short as possible, no longer than about 12inches or 300mm is recommended.

I think you are confusing 16/0.2 with 7/0.2. You can use 16/0.2 ‘droppers’ that ate several meters long without any voltage drop

[smokebox]

15 minutes ago, WIMorrison said:

I think you are confusing 16/0.2 with 7/0.2. You can use 16/0.2 ‘droppers’ that ate several meters long without any voltage drop

Fair enough

[jamesed]

A 4'x7' layout is fairly small so 1.5mm sq cable should be fine. As others have said, any standard copper electrical cable will do the job fine. If necessary strip off the outer insulation so you have two individual cables. Red/black, brown/blue doesn't matter; use whatever colours you wish; there is no "standard". Run the two lengths of cable fairly close to each other and then once you've soldered on all your 'droppers' (for which 16/0.2 is perfect) cable tie the two bus wires together. This will minimise any inductive field interference and is just as good as twisting the wires which is something you'll see often promoted (especially by one particular manufacturer that happens to sell twisted bus wire).  Avoid having spurs off your bus if you can, it's far better to keep your bus as a single continuous run.  There are good arguments for running it as a ring and bringing both ends back to the controller but despite being good with most controllers there are a couple of dcc controller manufacturers who state this method isn't suitable for their equipment so check first. If you have an open end to your bus wires it may be beneficial to terminate the ends with what is commonly referred to as a dcc 'snubber'.  These are readily available to buy cheaply online or you can make your own with just a few components.  

[RobinofLoxley]

It doesnt take a great deal of effort to introduce 3-4 twists per foot as you are doing it. Any problems later on someone will ask if your wires are twisted..

[Tomathee]

14 hours ago, KingEdwardII said:

I use electrical FLEX cable for my bus cabling. 2.5mm2 and 1.0mm2 are readily available and relatively inexpensive. This works out cheaper than specialist model railway cabling.

 

For a small layout like yours, the smaller size will be adequate, since voltage drop will be negligible over the cable runs you are going to have.

 

Yours, Mike.

 

Cheers, I've found something in B&Q to pick up next time I'm passing, £8 something for 10 metres, at least half the price of the Rails example I linked earlier.

 

12 hours ago, smokebox said:

1.5²mm should be perfectly adequate for a layout of that size and 16/0.2 is good for droppers if kept as short as possible, no longer than about 12inches or 300mm is recommended.

 

Thanks, I've found some 1.5mm that should be long enough to cover the bits I need to swap and any future extensions if they happen. The droppers are 6 inch max so I'm good there at least.

 

11 hours ago, jamesed said:

A 4'x7' layout is fairly small so 1.5mm sq cable should be fine. As others have said, any standard copper electrical cable will do the job fine. If necessary strip off the outer insulation so you have two individual cables. Red/black, brown/blue doesn't matter; use whatever colours you wish; there is no "standard". Run the two lengths of cable fairly close to each other and then once you've soldered on all your 'droppers' (for which 16/0.2 is perfect) cable tie the two bus wires together. This will minimise any inductive field interference and is just as good as twisting the wires which is something you'll see often promoted (especially by one particular manufacturer that happens to sell twisted bus wire).  Avoid having spurs off your bus if you can, it's far better to keep your bus as a single continuous run.  There are good arguments for running it as a ring and bringing both ends back to the controller but despite being good with most controllers there are a couple of dcc controller manufacturers who state this method isn't suitable for their equipment so check first. If you have an open end to your bus wires it may be beneficial to terminate the ends with what is commonly referred to as a dcc 'snubber'.  These are readily available to buy cheaply online or you can make your own with just a few components.  

 

Thanks, that's as I did before with stripping the outer cover so I was on the right path at one point but seem to have strayed. Twisting the wires isn't something I've come across before so I'll do that as I go. I did read somewhere about having a break in the loop so I did that on the first attempt and will keep to it. Also hadn't heard of a snubber so that's on my reading list. Think I have everything I need to go forward now, it's a bit off the original topic but that's waiting on wire and free time to do it now.

[RobinofLoxley]

45 minutes ago, Tomathee said:

Cheers, I've found something in B&Q to pick up next time I'm passing, £8 something for 10 metres, at least half the price of the Rails example I linked earlier.

 

Just be sure that its copper wire as it can be ferrous stuff which isnt as good, obviously.

[Ron Ron Ron]

22 hours ago, jamesed said:

……Avoid having spurs off your bus if you can, it's far better to keep your bus as a single continuous run.  There are good arguments for running it as a ring and bringing both ends back to the controller………

Why avoid having spurs?

If that was the case, then you should avoid having any track that isn’t a single continuous run either. No branches or sidings etc.

Your track is every bit a part of the DCC Power bus as the wires feeding it underneath.

 

A power bus can be linear, a loop, a series of branches, a tree or a mixture of all of those.

Just use the correct gauge of wire, as advised above.

So called “snubbers” are a useful addition.

 

 

 

.

[jamesed]

14 hours ago, RobinofLoxley said:

It doesnt take a great deal of effort to introduce 3-4 twists per foot as you are doing it. Any problems later on someone will ask if your wires are twisted..

 

The logic for twisting wires is to hold them close together to reduce inductive field interference.  Running the wires close parallel and then cable tieing them together achieves the same effect.  However, it's much easier to solder on droppers if they're not twisted and initially run parallel so that's a really good option. You can then cable tie them together once you've finished soldering all your droppers if you wish.  Ths whole twisted bus wire argument is perpetuated by DCC Concepts who have a vested interest in promoting it because they sell their own twisted wire.  Twisted wires can be helpful but it's not essential.  In fact, if you run your bus wires up to about 1cm apart it's quite likely that this will be fine as the inductance impact will be low. As you move further apart then it becomes more of an issue.  Decent dcc decoders can quite capably handle a low level of transients. 

[jamesed]

40 minutes ago, Ron Ron Ron said:

Why avoid having spurs?

If that was the case, then you should avoid having any track that isn’t a single continuous run either. No branches or sidings etc.

Your track is every bit a part of the DCC Power bus as the wires feeding it underneath.

 

A power bus can be linear, a loop, a series of branches, a tree or a mixture of all of those.

Just use the correct gauge of wire, as advised above.

So called “snubbers” are a useful addition.

.

 

I'm not suggesting that you should never have spurs. What we're all aiming for is to do as much as we can over a wide number of things to minimise the bus impedance and avoid transient voltages (often referred to as spikes).  If you add a spur to your bus the chances are that you're not going to be able to make an effective solder join on 2.5mm sq. cable so you are likely to use some sort of connector block.  Every time you break the bus and use a connector of some sort you are adding to the overall impedance. If you are using screw connectors (i.e. choc blocks) then as time goes by and the copper oxidises and flattens, which also results in the screw down becoming looser then the impedance in that joint will start to increase significantly.  If you have one such spur then it may not cause a problem but if you have a number of them it may have an impact over time.   If you can keep your bus as a continuous run without any breaks then that is a bonus which will contribute to keeping the impedance low.  If you are building a modular layout then joins in the bus will be inevitable between board sections. In this case if's worth looking at how joins are made.  Speakon connectors are a popular choice but there are other options.  

 

The reason we terminate the ends of bus cables is because the wave form of the signal can be reflected at the bare end and sometimes this can cause interference or phase cancellation.  The purpose of terminating with a 'snubber' is to supress this reflection. It doesn't eliminate it entirely but hopefully reduces it to a level which is less likely to cause a problem.  For this reason, the fewer bare ends we have on any dcc system the better but if you have two or three then that's unlikely to cause a problem.  It's just better, if you can, at the design stage, to plan your wiring routes to allow for a continuous bus without spurs.  All these little things can add up and compensate for where, perhaps, you have to make compromises in other areas.

 

 

 

 

 

Edited February 1, 2023 by jamesed

[WIMorrison]

11 minutes ago, jamesed said:

The reason we terminate the ends of bus cables is because the wave form of the signal can be reflected at the bare end and sometimes this can cause interference or phase cancellation.  The purpose of terminating with a 'snubber' is to supress this reflection

 

I fear you are confusing a coax terminator with a DCC filter. The coax terminator is indeed designed to quench reflections caused by the cable end, however in DCC they are designed to remove voltage spikes. A DCC R/C filter can also be placed anywhere on the bus, it doesn't need to be at the end of the wire, unlike a terminator which must be placed over the ends of the cable. The frequency of the signals on a data network and DCC wiring are completely different and devices and concepts used for computer networks are not valid on low frequency DCC wiring.

[jamesed]

7 hours ago, WIMorrison said:

 

I fear you are confusing a coax terminator with a DCC filter. The coax terminator is indeed designed to quench reflections caused by the cable end, however in DCC they are designed to remove voltage spikes. A DCC R/C filter can also be placed anywhere on the bus, it doesn't need to be at the end of the wire, unlike a terminator which must be placed over the ends of the cable. The frequency of the signals on a data network and DCC wiring are completely different and devices and concepts used for computer networks are not valid on low frequency DCC wiring.

 

That's interesting Iain. I'd like to explore that a bit if you don't mind as I know you're a very knowledgeable chap when it comes to anything dcc.

(Sorry to others if this is diversifying away from the original thread topic.)

 

My comments about using snubbers were made based upon my experience with DMX512 which is effectively RS485/RS422 and is used across the entertainment industry to control digital lighting.  It has some similarities with DCC in that it's a square wave signal and at 250kHz it works at a higher frequency than dcc but that's still a relatively low frequency compared with, say, standard ethernet at 100MHz.  Where it differs mainly is that it isn't carrying power and is just an 8 bit digital signal.  Now, with dmx512 the end of a data line (which is usually run along a microphone type cable) always needs to be terminated,  although this is achieved simply with a resistor. (I've seen the consequences of forgetting to terminate it!) A DCC snubber also has capacitors in circuit which I'd assumed was to cope with the higher power transient spikes.   So, my theory was that the snubber served two purposes, to terminate the dcc signal and minimise reflections but also to absorb (up to a point) any transient voltages.   

 

Now, maybe my theory is wrong so this is where I'd find your explanation helpful.  I appreciate that as the frequency reduces, wave form reflection becomes less of an issue. Are you saying that at 9kHz the effect is so minimal it can be ignored?  

 

Next, in terms of protection to suppress transient voltages, I can see that what you've said about putting the snubber anywhere on the layout makes sense but if we apply that logic then most decent dcc controllers have that circuitry built into the outputs anyway which would imply that deploying a snubber is pointless because the protection is already present.  My research on this seemed to imply that ideally you want your snubber to be as close as possible to the source of the transient spikes. Obviously we can't always predict where that will be so putting it at the end of the bus wires seems to make sense as we've then at least  halved the distance from the source to the closest suppression snubber for anything more than half way along.  Hence, on a bus wired as a ring circuit there's no need for snubbers at all because both ends are protected anyway by the dcc controller. 

 

So, my theory is that by fitting a snubber at the end of the bus pair we are achieving two things. We're providing a termination for the data signal to prevent reflections and we're providing transient voltage suppression at the optimum position.  If my logic on this is wrong I'm always keen to learn so please do explain where I'm going off piste.  

 

 

 

Edited February 1, 2023 by jamesed