I have a 55 sf folded dogbone walkin-U layout with a mainline of about 50 ft. It has two power districts gapped with plastic rail joiners. I ran a 14 AWG stranded bus underneath the main and at the end, each bus feeds two sets of feeders (18 AWG single strand) just “before” the gap. Never had any problems.
There’s a lot of half right info in here, but most of it isn’t harmful, so it’s ok.
A larger gauge bus allows for less voltage drop through the wires before the power/signal reach the locomotive. Enough voltage drop and the decoder can stop working (part of the power down the rails powers the logic in the decoder), or can prevent the decoder from delivering the required/desired power to the motor.
The quarter test allows for a rough check of voltage drop, if a short (quarter) across the rails is not sensed by the control station, then there was so much drop in the trip to the point of the short that the short circuit current wasn’t required to drop all of the output voltage.
I will almost disagree with Betamax’s comment on gapping the end of the loop, except that he did say “under certain circumstances”. Those circumstances would be a very, very long loop. DCC signals are “slow” in electronic terms, and colliding with each other at the end of a loop isn’t really an issue, generally. On the other hand, not gapping the loops means that there is twice the wire, or half the resistance, and therefore voltage drop through the bus. Unless I saw a problem, I don’t think I’d break the bus. But, if everything has been done right, it really shouldn’t matter, one way or the other.
Thanks bearman. You bring up the next question on my steep DCC learning curve … “power districts”. As an old model railroader, I had tons of blocks, but with individual operating engines, what is the point of having power districts?
Breaks up your layout into sections that a single booster can power.
“Power district” can be a confusing term. Some, like Dan, use it to describe the section of track powered by a single booster. Some call that a “booster district”. Others refer to the section of track protected by a circuit breaker as a “power district”. Some call that a breaker or protection district.
A layout is divided into booster districts when a single booster doesn’t supply enough current to run the whole layout.
Booster districts are divided into breaker or protection districts so that a short in one area doesn’t shut down the whole layout (or booster district). Breaker districts also have a side benefit of making a short easier to find.
Breaker districts, on layouts using signaling, are divided into detection blocks.
Even if one booster can power your entire layout (which is quite likely for most of us) power districts can allow for a short in one district not shutting the whole layout down until the short is cleared. That’s a good thing!
I intend to put switches (as in on off) on the tracks in my roundhouse and engine terminal. That way I can have all my sound engines that are not in use, powered off and I can’t accidentally switch to the wrong engine and send it into the pit.
I PLAN on doing one better – the TT alignment sensor (whatever that happens to be) will also drive an input to the selected track (incl the lead at the other end) so, all the tracks will be off unless the turnout’s aligned.
Will need to probably have some form of timer as well, so that it doesn’t power-cycle everything as the bridge sweeps past.
Well, the way I had it explained was that a “Power District” is the booster’s domain, which then (potentially) gets broken up into smaller sub-divisions by fuses / circuit breakers.
Guy who explained it to me came from the multi-cab-on-DC days, so perhaps his explanation was colored a bit (or a lot) by that experience.
If you’re doing the control yourslef, just code it such that while the turntable is in motion, no tracks ever get turned on. No need for time delays.
–Randy
No worries. I didn’t mean to imply that you were incorrect. I have heard “power district” used to describe boosters or breakers many times over the years. There doesn’t seem to be a standard usage of the term. I just wanted to help the OP understand the different reasons for segmenting the layout.
Guess i should’ve been clearer, Randy - I don’t plan on the tt to be motorized.
Not to worry about differences of opinion. I’m learning a bunch from this conversation. At least I now know the concept of applying the bus and what to consider. There are quite a few variables to consider, so I can understand why some would run the bus differently than others. Thanks for the discussion. It has really described the issues to think about before running a bus.
I’ve got 4 bars on my layout. There’s Lucky’s Bar, the bar in the Shamrock Hotel, Lady Buc’s Clam Bar, and the Brass Rat by the waterfront.
I don’t think he was looking for a new watering hole there, Mr. B.
Thanks carl425. That explains about everything I need to know about “districts” for now.