DCC Power districts and more

DCC Power districts and more

Postby Juup » Sat Mar 01, 2014 11:23 am

Hi All,

I am in the early stages of wiring my layout (you may have seen the thread with discussion of my German DB loft layout). I have some questions, but first a description of where i am at - and my understanding so far.

I will be using DCC, and have bought the NCE PowerPro 5amp system; I couldn't find a bad review and like the different throttle options. I plan to put the power supply and the command station at the halfway point of the layout and from there to have a 'star bus' with 4 branches (4 sub-buses if you like). There will be a separate accessory bus so never mind that for now. Perhaps not right away, but eventually I'd like each branch of the Star (yes, I know I am mixing metaphors) to be a separate power district protected by a circuit breaker. So far I know that the circuit breaker (or breakers) will sit between the command station power supply and the 4 separate DCC buses. I also understand that each power district needs to be completely isolated (including track sections isolated from each other). I have all the wire I need - will use stranded 14AWG from the Command station to the circuit breaker(s) and since the four separate sub-buses are about 20-25 feet long each these will be 14AWG as well. Droppers will be 18AWG.

My questions:

The reviews of NCE's own circuit breakers are poor, so I am thinking of DCC Specialities which have good reviews. Any comments about that decision? Of course, I will double check the compatibility between NCE PowerPro and DCC Specialities also with the supplier when buying (Costal DCC in the UK). I am thinking about a single four-way circuit beaker.

Do circuit breakers 'distribute' power equally, or are they simply a means of detecting short circuits?

Alternatively, is the way they operate a 'de facto' limit on how many useable amps there for each power district because if you go above that then the circuit breaker cuts the power?

Does this also mean that if more current is consumed in one power district there is less available to other districts (despite the presence of the circuit breakers and subject of course to the limit set in the circuit breakers for each district)?

I have seen light bulb solutions for this, but they seem to operate like crude circuit breakers. Is that correct?

Do I need to worry about power being distributed equally across the power districts?

I assume in all of this that the NCE system's 5amp is plenty for running my trains (maximum 4-5 running at one time if more than one operator, and maybe 20 idling at different places on the layout ... and I think there is still current left to have some led lights in a few carriages). Yes of course, they are TT scale - mostly fairly new models. Am I right in my assumption? I guess I will discover the answer once everything is up and running ... if trains slow down etc.

Finally, how about a 'reverse module' (is that what it is called?) to switch polarity on the reverse loop track? Does that effectively mean a fifth power district? I think it does. But how is that wired alongside the above described Command Station and 4-way circuit breaker? Do I simply fork the supply from the Command Station power supply, with one side of the fork going to the reverse module and the other to the 4-way circuit breaker?

Okay, that was a lot of questions - a million thanks for reading :)

Juup
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Re: DCC Power districts and more

Postby Juup » Sat Mar 01, 2014 11:45 am

Perhaps I should have said 'sub-power districts' because each of these will be from the same power supply ... Hopefully my questions are clear even so.
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Re: DCC Power districts and more

Postby ctxmf74 » Sat Mar 01, 2014 7:31 pm

"Do I need to worry about power being distributed equally across the power districts? "

I don't think you need to worry. Those 5 amp NCE systems can run lots of HO trains so TT should be quite easy for them to handle. The DCC auto reversers can work off of track power in the district they reside in so don't need another power district. A good place to get DCC info is Tony's Train Exchange, they have been around for a long time,carry most brands and give unbiased advice..DaveB
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Re: DCC Power districts and more

Postby Juup » Sun Mar 02, 2014 8:06 am

Update … this is helpful for me to verbalise my thinking and understanding as I progress with my planning. I will try to be clearer with my terminology this time.

Blocks = electrically isolated parts of the layout fed by a single power supply.

Power district = an electrically isolated part of the layout fed by a separate power supply (e.g. a booster).

A power district may have more than one block.

To start with, I only have a single power supply (through the NCE command station) so only one power district. However, I will have four blocks each protected by a circuit breaker. There are two benefits with having these circuit breakers: a) to narrow down the location of a fault should there be one, and b) if there is a fault in one block then trains may still run in other blocks.
In order to future proof the layout (e.g. if I get a lot of long passenger trains with LED lighting in every coach) I will get two 2-way circuit breakers (e.g. two DCC Specialities PSX-2; price-wise not much different than a single 4-way PSX-4).

http://www.dccspecialties.com/products/ ... ield_x.htm

So initially, two times 2-way gives me 4 blocks each isolated and protected by a circuit breaker. In a future more power intensive scenario I can then feed each PSX-2 from a separate power supply (the standard command station plus adding a booster) and hence have two power districts.

The auto reversing module can, as DaveB has pointed out, can simply attach to the bus in one of the blocks at the appropriate location. It then becomes a kind of ‘sub-block’; the length of track protected by the auto reversing module needs to be long enough to accommodate the entire length of a (future) long passenger train with LED coach lighting.

Pheew …

Oh, Tony’s Train Exchange looks like a good supplier, except the small detail that I am in the UK :)

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