DCC Power Districts

[CDRC]

Hi,

I have search through the forum for a definitive answer but have been unable to find one. My layout has been divided into 4 separate power districts with four stand alone buses all isolated from each other. A mainline, a goods/ storage and maintenance section with turntable and two accessory buses. The 2 accessory buses provide power to the point motors (Cobalt IP Digital) and signals that manage the mainline and yard and are standalone.

I would like to isolate the mainline from the yard so if a short occurs in one it does not effect the locos running on other and would help to identify the origin of the short.  I am not overly concerned with the accessory buses as shorts in these areas, from what I've read, will be rare. I'm using an Elite and have a spare Select that I use as a slave to the Elite when it's connected. I plan to use Railmaster when the layout is complete.  My research suggests the use of a PSX-2 which at £75 is a hefty amount to pay when from what I understand (correct me if I'm wrong) will only protect a power booster if fitted and does not offer protection to decoders. I further understand the Elite has an adequate level short protection built in.

My question revolves around the connection of the power from the Elite to the 4 buses. I plan on connecting the  Elite to a 15 amp terminal block and by using loops at each input, wire power out to the buses. If I do wire the buses in this manner logic would say that a short on one bus would automatically short out the whole of the layout via the Elite. Is this correct? If so is there anyway I can build in a circuit breaker or separate the 2 track buses. I thought of using thermal curcuit breakers but these were not advised for DCC. I researched the use of the  'Tail light' option but the majority of web advice was this option was not advisable for DCC either. Is there an alternative or do I have to live with the fact that shorts are an inevitabe part of the hobby? Or more importantly am I over complicating the issue?

Thanks

Charles

[RDS]

If I have read your post correctly, it seems to me that as soon as you connect all 4 separate districts together, then as you say, they will all see the same short.

[ColinB]

Why don't you do what we used to do with analogue systems have separate lengths of track separated by nylon fishplates then enable each section with a switch connected to the DCC supply. That is how my system is wired up. Then if you think you have a short on that section just turn it off. I cannot see why you cannot use circuit breakers on DCC if they trip at the right value, the only issue you will probably have, is that the controller will probably trip before the circuit breakers do. Switches is the easiest.

[96RAF]

At first reading I thought you had four separate track power districts, which would in normal terms have the first district powered by the controller and the second and subsequent districts powered by their own power supply via a signal booster module echoing the control.er commands.

 

Not so though. All you have is two isolated track buses using the same power supply and two isolated point/signal buses again using the same power supply.

 

You can provide each bus with a circuit breaker but as Colin points out these each have to trip before the controller or you still lose all districts.

 

You need to think about if you want to go to the expense of circuit breakers or regular power and signal boosters or as Colin says if just for fault diagnosis purposes simply use toggle switches to isolate the various buses.

[Chrissaf]

CDRC,

Although DCC Circuit breakers are cheaper than Boosters, I cannot in all honesty recommend using circuit breakers with Hornby DCC control solutions.

 

One would need to be very careful to select a DCC Circuit Breaker based upon its electrical specification. Many have fixed current trigger levels.

 

For example, lets say you are using Hornby's 4 amp power supply for your layout and that under normal layout operating mode the nominal background current being drawn from the controller by your layout is 2 amps.

 

Now let's assume that the four circuit breakers you install are fixed at a 3 amp trigger current level.

 

Now if a short occurs on a Circuit Breaker [CB] protected circuit, the short needs to draw 3 amps before the CB will trigger. But if you add this trigger current to the nominal current that is still being drawn by the other three protected sections, then the 4 amps of the Hornby system will be exceeded, thus the Hornby controller will still trip anyway.

 

You have to remember that these specific DCC CB products are primarily USA based in origin where they use Boosters that are capable of providing far in excess of 4 amps, some I have seen listed and specified up to 10 amps. In a 10 amp based layout, DCC CBs would be a critical addition to add.

 

These DCC CB products in my opinion really don't suit the Hornby controller configurations in the UK where the booster function is incorporated into the Hornby controller.

 

I have seen posts raised previously on the forum where USA branded DCC CB products have been added to a layout and the scenario I have outlined above regarding switching currents and Hornby controllers still shutting down have been reported issues. For a DCC CB solution to work, you would need to have DCC CB products with very low trigger currents, typically not more than 1 amp. Such low trigger current products may or may not be available [i haven't undertaken any research personally to find out].

 

In a Hornby controller environment. The only viable all electronic automatic solution [in my opinion] would be to use 'Boosters' instead of DCC CBs. Each booster has its own dedicated power supply, thus the nominal current being drawn by the other protected sections across the layout is completely immaterial. And as the Hornby controller is effectively isolated from the layout power distribution [the track power coming from the booster power supplies rather than the Hornby controller power supply] and therefore the Hornby controller is very unlikely to be affected separately by any shorts. It is the individual 'Boosters' that are performing the 'short circuit' current trip management.

 

In the Hornby portfolio, the Hornby booster was the R8239 and this came with its own dedicated 4 amp power supply. However, Hornby in their wisdom have discontinued the R8239 and made it obsolete.

 

Just purely as an overview example. The page below lists a number of Booster products available in the UK. They start at £70 [and the £70 one doesn't include the power supply] and only go up in price. So four of these are going to cost in excess of £300 [cheaper versions may be available elsewhere with further research, but it is still going to be a potentially expensive solution for four units].

 

https://www.coastaldcc.co.uk/products/boosters/

 

Your choice, but personally for the cost involved I think your last statement in your post may be valid.

 

Or more importantly am I over complicating the issue?

 

EDIT: Others posted whilst I was still writing my long reply.

 

[Rog RJ]

How about the NCE CP6 circuit protection? https://ncedcc.zendesk.com/hc/en-us/articles/201045719-CP6

 

It can be used with other systems, not just NCE.and it's pretty cheap.

[CDRC]

Hi thanks very much for your responses.

Rog (RJ) I considered the CP6 and classed that in the 'Tail Light' option and came to the same conclusion that it was not advisable on a DCC/Elite system.

Chrissaf. You confirmed my own research but expressed it in a more understandable way. I don't fancy shelling out £300 for what is basically a short prevention/ identifying process and your right, overthinking it..........

Colin B. The switch idea is one I'll persue  as it contains the key word 'easiest' also the price of a couple of switches is negligible in the scheme of things.  A thought echoed by RAF96.

Thanks to all.

Charles