DCC Wiring the DCC power bus - short circuit protectors?

[Dog Star]

Whilst this question is driven by current work with 7mm track there is a fair chance that the question is relevant to other scales where the track is handbuilt / uses ABS fishplates.

Handbuilt track and turnouts in 7mm, using Exactoscale ABS fishplates, means that there are many "droppers" to be connected to the DCC power bus. In the past I have used the two insulated cables from "1mm twin and earth" for the power bus with the bus underneath the baseboard and following the route of the track - droppers from each section of rail are then soldered to the appropriate bus cable. Whislt this approach provides a workable solution I am not sure if a power bus under each line of track is the best way of doing things.

The current 7mm layout is roughly 3' wide, about 25' long, with four tracks across the board. The baseboards have full depth cross members every 15-18" with lightening holes in the cross-members.

For those of you who have wired a DCC layout, what are the options for routing of the power bus and connecting droppers to the bus(es)? How do you secure the power bus(es) to the baseboard?

regards, Graham

 

[Yorkshire Dave]

Graham

I mount my power buses (made from 3 or 5 amp mains wire) with screws (through loops twisted from the bus) at either end. One bus is towards one side of the and the other towards the opposite side of the layout keeping them parallel and as far apart as possible. I solder wires from the droppers to the bus after stripping the insulation on the bus where the join is to be made.

The other method of joining the dropper wire to the bus is to use Scotchlok connectors, which is common in the US. I'm sure others will have their own methods.

 

[Dog Star]

I mount my power buses ... with screws ... at either end. ... I solder wires from the droppers to the bus after stripping the insulation on the bus where the join is to be made.

This is what I have done with a previous layout. How have you removed the insulation from a bus wire that has been stretched between the screws?

regards, Graham

 

[Tim Humphreys ex Mudhen]

Graham
On Love lane we have installed 1 power bus, positive and negative, on each board with the droppers soldered to the bus. Stripping the insulation is carried out by either using wire strippers to cut through the insulation and then slicing off with a scalpel or alternatively using a scalpel for all the cutting, very easy with a sharp blade. The wiring is then fixed to the board with strips of 'gaffer' tape. Where two pieces of wire need to be joined we have cut small squares of brass sourced from the edge of etched frets and solder each wire to these, simple and inexpensive. To connect power between the boards we are thinking of connecting the wires to the hinges that are being used to join the boards, just need to ensure that the power flows OK. Sorry but no photos of this at the moment.
all the best
Tim

 

[BrushType4]

Tim, is it a split hinge with a rod (nail) holding them together? Just concerned that over time any flex in the joint will cause power problems.

 

[Ressaldar]

Hi Graham,

we have the one bus running under the layout and use male/female push together chocolate blocks as inter-board connectors/board terminals and the droppers are connected via Scotchblocks, the bus is 'self supporting' in as much as the droppers hold it in place (droppers attached to each individual piece of track so that there is no reliance on fishplates for current distribution.. This method is used on the permanent layout and will also be used on the portable one currently under construction.

cheers

Mike

 

[Dikitriki]

Hi Graham

We have tried to make Heyside bullet proof as far as possible.

There are 4 power districts (10 amp system by the way) - up main, down main, branch and yard - and short-circuit protectors on each power district. This means if there is a short somewhere 3 of the 4 circuits will run without interruption. Even with this level of protection, finding a short can be very time-consuming. I shudder to think of the consequences if there was only one power district.

Inter board connectors are mainly heavy duty 7 pin connectors (each pin 9 amp rated) except on the lifting section (which is only 2 wires) which used choc blocks as they are easier to engage.

There is indeed a dropper to every piece of rail, and yes, it is a pain. Droppers were 16/.2 wire and the main bus 32/.2 wire, stripped locally to make the connections. The wiring was tidied by screwed in tidies and plastic tags so that nothing hangs below the edge of the baseboard.

Regards

Richard

 

[Dog Star]

Thanks to all of you, details noted. Seems that the approach which I used on Scruft's Junction is similar to other layouts and I think that I shall modify that approach a tad after reading the post from Richard. In conversation with 4mm DCC users - and after reading one or two "specialist" books on the subject - I had been thinking of localising power buses to individual baseboards, however I think that Richard's approach of localising power buses to, for example, up/down/branch working is worth considering further.

Richard, how do you handle the transfer of an engine from one district to another at, for example, a crossover?

regards, Graham

 

[Dog Star]

Droppers were 16/.2 wire and the main bus 32/.2 wire, stripped locally to make the connections. The wiring was tidied by screwed in tidies and plastic tags so that nothing hangs below the edge of the baseboard.

Please post a photo of the under-board wiring to illustrate these points.

Removing the insulation from solid core cable in "mid-length" is bad enough... how do you strip the multicore stuff without removing some of the wires?

regards, Graham

 

[Yorkshire Dave]

Graham,
I just use side cutters to strip the insulation mid length. It's just from practice that I do not remove wire from multicore cable.

 

[Tim Humphreys ex Mudhen]

Tim, is it a split hinge with a rod (nail) holding them together? Just concerned that over time any flex in the joint will cause power problems.

Phil
Yes it is, good point to consider, I've been trying to identify potential issues with this method so perhaps connectors to link the boards will be better. Hope to catch-up soon
Tim

 

[Oliver Bulleid]

If you search the layouts section, there are some photos of the DCC installation on out 'not too small' layout. I do not submit as best practice, merely for illustrative purposes as pictures often help.

Please note that we are using DCC for both locos and turnout control.

Tim

 

[Dikitriki]

Richard, how do you handle the transfer of an engine from one district to another at, for example, a crossover?

regards, Graham

There's nothing to handle. Despite being broken into power districts, the whole layout is in effect only 1 big circuit. Remember that you are driving the loco, not the track. Providing the points are set the loco goes where it's pointed. The power districts only come into their own when there is a short circuit.

The logic behind having power districts to distinct operational cicuits, is that we would always be able to run 3 whole circuits, even if one was down. If you have them to individual boards, then every route across that board is out, in our case meaning no complete circuits operational.

Please post a photo of the under-board wiring to illustrate these points.

regards, Graham

OK, time for a laugh. Our wiring is not as neat as some (!) but it is colour coded and documented in a file.



This is the short-circuit protector. 4 districts with a repeater wire to the control panel so we have a visual indication up top. We can in addition switch any circuit in or out, or even switch between DC and DCC, though we have not added any DC controllers.



Top left is the pocket for the hand controller. Bottom left is the wiring loom to the fiddle yard. Bottom right is point/signal wiring connector.



Lifting section rail circuit choc block with 2 snubbers above right.



Typical board. The Tortoises are all wired identically to choc blocks. We keep 2 fully wired spares so changing them is a matter of minutes. More snubbers to close the circuits This is the other side of the lifting section, so we have the choc block rail connector, 3 sets of failsafes on the right hand edge of the board, so no power gets to the last yard of track unless the board is down and fully engaged. A signal servo and lead is also visible top right.

Hope this amuses you. I'm happy to answer any questions once you have finished spluttering.

Cheers

Richard

 

[Dog Star]

Thank you Richard.

There is much here to "digest", as to the original question... I think that I cannot spot a power bus in amongst the cables although I recognise that the snub-stubs are associated with that facility.

What is the wiring arrangement which is referred to as "fail safes"?

regards, Graham

 

[3 LINK]

There's nothing to handle. Despite being broken into power districts, the whole layout is in effect only 1 big circuit. Remember that you are driving the loco, not the track. Providing the points are set the loco goes where it's pointed. The power districts only come into their own when there is a short circuit.

The logic behind having power districts to distinct operational cicuits, is that we would always be able to run 3 whole circuits, even if one was down. If you have them to individual boards, then every route across that board is out, in our case meaning no complete circuits operational.

It's a pity Aberbeeg did not have a system like this at Telford the other year .

View attachment 17879

This is the short-circuit protector. 4 districts with a repeater wire to the control panel so we have a visual indication up top. We can in addition switch any circuit in or out, or even switch between DC and DCC, though we have not added any DC controllers.

Ahhh so maybe my 2-8-0 tank might get the chance to travel on the hallowed metals of Heyside , hopefully soon I will be going DCC .


Hope this amuses you. I'm happy to answer any questions once you have finished spluttering.

Cheers

Richard

P.S. Can you tell me what a " snubber " does ? Is that the electrical component that looks like a resistor and some other squiggly thingy that bridges the + and - ?

Regards,

Martyn.

 

[Dikitriki]

P.S. Can you tell me what a " snubber " does ? Is that the electrical component that looks like a resistor and some other squiggly thingy that bridges the + and - ?

Regards,

Martyn.

Hi Martyn

Yes, that's it. It's a filter designed to attack voltage spikes, and to remove unwanted frequency components from the signal. It cleans up the signal in other words, and is attached to the far extremities of the bus. That's about the limit of my knowledge. Any more, ask Steph

I put them in in response to the very occasional run away or instances where we lost control of the loco. The layout has performed impeccably since.

Yours

Richard

 

[Dikitriki]

Thank you Richard.

There is much here to "digest", as to the original question... I think that I cannot spot a power bus in amongst the cables although I recognise that the snub-stubs are associated with that facility.

What is the wiring arrangement which is referred to as "fail safes"?

regards, Graham

Hi Graham

If you look at the 3rd picture, the thicker wires going to/from the choc block are the buses, the 3 pairs of thinner wires going northwards are the droppers. Remember in all of this, DCC is only 2 wires....yeah, right.

This is a 100% grab from the 4th picture



All main buses going through the tidy, 2 droppers to one of the buses; snubber up top.

The failsafes are micro switches on each circuit, Contact is only made when the board is fully down. The contact allows power to the last length of track before the drop.

Richard

 

[Dog Star]

It's a filter designed to attack voltage spikes, and to remove unwanted frequency components from the signal. It cleans up the signal in other words, and is attached to the far extremities of the bus. That's about the limit of my knowledge. Any more, ask Steph

I shall ask the questions here... safe in the knowledge that Steph shall offer chapter and verse at some point.

* what is the design spec. for the snubbers?
* how is the snubber specification influenced by individual layouts?
* how is the placement of snub stubs determined by individual layouts?

Big hint... if the concept works / helps Heyside then that is good enough for me to want to tread the same path.

regards, Graham

 

[Dog Star]

Um, two whole weeks have gone by and no conribution from Steph as yet.

Richard,
Please tell me about the short circuit protectors... make, supplier, connectivity. How do you "manage" the change between 12V DC and 18V AC (for DCC)?

What are you using for the inter-board connectors for the power supply to the track?

regards, Graham

 

[Steph Dale]

Um, two whole weeks have gone by and no conribution from Steph as yet.

Graham,

Sorry, bit of a busy old time. To answer your questions:

1. Pass. I'll look it up - they're not tricky or even critical in their component selection.
2. They're not - the values for the resistor and capacitor are selected based upon their ability to 'clamp' the DCC signal and turn it into heat, rather than anything dependent upon the layout.
3. Again, it's not. If you think/plan every layout as an end-to end then the snubbers (if required) go on the ends of each/the bus.

In general there's no great difference between 'analogue' and DCC wiring. The issue is merely how well you do it. The main thing to remember is that under DCC there's the potential for some very high currents to be winging their way around your layout; using 5A rated cable is an absolute minimum. Even then Richard's using a 10A booster, so should be using something rated at least 20% over that (i.e. 12A rated). Same for any/all sockets and switches.

If you've got the points controlled through the DCC it's worth having them switched from the track supply (also switched). That way, should you end up with a short-circuit across a point (we've all driven into a 'closed' point haven't we?) you can switch out the track supply, change the point and restore the track supply with most people remaining completely unaware of what's happened.

One other quick thing to mention is that running all the buses as twisted pair is highly recommended. If you do this, there's a chance you won't need the snubbers as they'll do a great deal to reject any interference.

Steph