I've been away from model railroading for about 30 years and I'm building a new HO layout. The finished project will be about 4' X 20'. I going to use EZ Command, but I was wondering if I should divide the layout into power districts (or blocks as some call it). The DVD and manual that came with the EZ Command doesn't really say much about it - only a quick little blurb about turning all power districts on before turning the unit on. Any suggestions? Thank, Jerry
Hi Jerry,
I run only DC/Analog with 'block control'. There are some great DCC experts on this forum that can answer your question in detail, but I believe one of the very nice things about DCC is that you don't need to worry about 'block control' like us DC/Analogers use.
Blocks with DPDT switches, etc. in DCC, as I understand it, are a 'thing of the past'.
welcome back to model rring.
lanny nicolet
Power districts for DCC are more like channels for your home surround sound system, than traditional blocks.
Each district is powered by a dedicated booster power supply with any needed special componets for that district( auto-reverser, detection...),
and each district is fed DCC info from the command station.
the avantage is that each district operates independently from the others, one may need only 2 amps, say a branch line, while that big yard and loco facility may need 5 amps or more( satalite tweeters vs sub woofer).
The district also offer short protection for each section, so if you forget and run a loco across a closed tunout, the derailment will only shut down that district, not the entire layout, so everything doesn't come to a screeching halt, and makes troubleshooting easier, you know the general area of the problem.
with standard blocks, you are selecting between different cab controls for specific "blocks" of track, cab A or B, positive, negitive, or off power.
Jerry,
A layout using DCC can be just one power district.
The need for power districts is not based on the size of a layout but on
• controlling how much of your layout is shutdown when a short circuit occurs
• providing sufficient power to a section of the layout based on maximum power draw in that section
The following PDF link may help you understand the concept of using power districts and how it differs from the old way of DC Cab Control using multiple DC power packs and wired blocks of track.
http://www.tonystrains.com/download/MRR-PowerDist.pdf (http://www.tonystrains.com/download/MRR-PowerDist.pdf)
If you are running your trains by yourself, one power district is usually enough. A typical 5 amp booster can run 3 powered locomotives with sound, each consisted with a second powered locomotive, all at one time. Or about 10 non-sound locomotives. Or many other combinations, most of which are difficulat for one person to keep track of and still enjoy the layout.
If you are running trains with a group, then multiple power districts can be desireable for two different reasons. One is to provide enough power to run all the locomotives, lighted cars, and DCC controlled animation that the group wants to run at one time. The second is to isolate operation in various parts of the layout from what is happening in other parts of the layout. The most obvious is preventing shorts in one part of the layout from shutting down the whole layout. More power means either more boosters or larger boosters. More districts for better isolation can often be done more cheaply with proper power management, using hardware such as Digitrax power managers or Tony's power shields.
i would think that you would Block on any layout of any size even if you are the only operator. It makes it easier to find shorts.
Quote from: RAM on April 11, 2007, 10:39:57 PM
i would think that you would Block on any layout of any size even if you are the only operator. It makes it easier to find shorts.
By all means. But do not confuse multiple blocks with multiple power districts. As an sole operator, you might divide your layout into a dozen blocks for fault finding but still have only one power district.
Let me see if I understand this.
When my layout is complete, I figure I could have a switcher, a through passenger train, a manifest freight, a way freight, and a coal shifter operating at the same time. This would be the maximum number. They would all be either single steam engines with sound or maybe a two diesel lashup without sound.
So I can divide the layout into power districts but get away with just the command station and perhaps a power shield for each distict?
Gene
Gene et al,
I will have a similar setup near year's end. I understand that one power district would suffice.
Is it practical or advised to use one 5 amp booster for two power districts, or do you need two boosters? Lionel Strang shows how to do two power districts with one booster and some sort of electronics, of which I forget, probably something from Tony's.
Best, Jack
Having sat at the feet of my ftf guru today, I will buy a Digitrax PM-42, which allows me to run a buss wire to four power districts. I believe there is also one for only two. Only the command station is needed.
Gene
Dear Gene,
Muchos Garcias! That is just the ticket for me.
Best, Jack
Jack,
Doe tashe musta!
Gene
Quote from: SteamGene on April 12, 2007, 03:40:00 PM
Having sat at the feet of my ftf guru today, I will buy a Digitrax PM-42, which allows me to run a buss wire to four power districts. I believe there is also one for only two. Only the command station is needed.
Gene,
You seem to be confused (maybe it is with terminology). The Digitrax PM-42 will allow you to create 4 power
sub-districts within a power district; not 4 power districts.
Also, you can only have one DCC command station (unless using the new ECoS digital command station). Are you confusing
command station for a
power station? Lenz refers to their DCC power booster as a power station.
A power manager like a Digitrax PM42 can be a good choice. One of its neater tricks is allowing the full five amps of a five amp booster to be available to each and every subdistrict, but still not shut down the booster even if three of the four subdistricts is shorted. At first, this seems impossible - three shorted sub districts each drawing 5 amps and a forth district still in operation with five amps available to it would appear to be 20 amps total. And if you were using current limiting to each sub district, for example, by using incandescent lamps, it would be impossible. A 5 amp booster cannot produce 20 amps. It cannot produce even 10 amps, at least not continuously. But it can produce 10 amps for a small fraction of a second. And herein lies the secret.
When a sub district is shorted, the PM42 shuts off that district until the short is cleared. How does it know if the short is cleared? It applies power to that sub district for a very short time, just long enough to see if the short still exists. If it does, it cuts the power to that sub district and tries again a little later. If more than one sub district is shorted, then the PM42 shuts off all the shorted sub districts. Every once in a while, it test the shorted sub districts to see if any of the shorts have cleared. But it does not test them all at once. It tests them one after another, so that there is never a moment in time that the booster is asked to deliver more than 10 amps. And this 10 amps is never drawn for longer than a small fraction of a second.
So why doesn't the 5 amp booster shut down when asked to produce 10 amps? It is all a matter of timing. The PM42 must be faster than the booster. It must shut down its sub districts before the booster can shut down. This is why a PM42 will not work with, for example, an MRC Power Station 8. The PS8 shuts down quicker than the PM42, so the PM42 cannot test a shorted sub district without shutting down the PS8. If you plan to use a PM42 with other than a Digitrax booster, I strongly suggest finding out from the booster manufacturer either how fast his booster shuts down or whether it has ever been shown to work with a PM42.
I will leave the discussion of Tony's Power Shields to someone who has actually used them. I have no idea how these devices test for shorts or the speeds that may be involved.
Quote from: Jim Banner on April 13, 2007, 01:18:41 AM
...
I will leave the discussion of Tony's Power Shields to someone who has actually used them. I have no idea how these devices test for shorts or the speeds that may be involved.
Over-current Trip Time Adjustment uses manual jumpers to set 40, 60, 100 or 190 milliseconds.
More information is far beyond my usual reply word count. ;D
So for more details start with
http://www.tonystrains.com/technews/powershield_icb.htm (http://www.tonystrains.com/technews/powershield_icb.htm)
Probably terminology. It seems to me that DCC is trying to be very PC since one of the original claims was "You don't have to divide your layout into blocks anymore!" So instead its power districts and sub-districts.
I will grant you that terminology can be very important, but it seems the only difference between a district and a sub-district is that one is powered directly by a booster and the other goes through a power manager.
Gene
Jim,
Thanks for the very good timely reply.
Just as in the experiment that shows why a 50# bag of sand will not be knocked off a plank by a 180 gr .30-06 bullet with 2500 ft-lb of kinetic energy, but easily pushed off by a small child, the answer is time.
Hunt,
As usual, a very precise answer.
Thanks all for very good info. Looks like my layout will be served with a PM-42 and sub-districts.
However, Hunt, is it wise to use this Digitraxx component with CVP or other mfr's components, or is that not an issue?
Best Wishes, Jack
Quote from: SteamGene on April 13, 2007, 07:19:11 AM
... it seems the only difference between a district and a sub-district is that one is powered directly by a booster and the other goes through a power manager.
Gene
Close, maybe half a cigar for this one. A district is all the trackage that is powered by a booster. A sub district is one of several divisions of a district. Each sub district has its own power management. It is unnecessary to divide a district into one sub district as each booster has its own power management built in. So no, they are not equivalent except for a power manager.
The reasons behind districts and sub districts are quite different than the reasons for blocks on a dc railroad. With DCC, the concern is providing enough power for all the trains without providing enough power at any one point to weld the locomotives to the rails in case of a problem. Independent control of locomotives is inherent in the system. With dc, the concern is keeping all the locomotives powered separately so that you can control them independently. Power distribution is inherent in the blocking. From an operational strand point, the major difference is where speed and directional control take place. Imagine 10 men operating a DCC layout. Each controls the power in his own locomotive (and only in his own locomotive) using speed and direction controls. Imagine the same 10 men operating a dc layout. Each controls the power in his own locomotive (and only in his own locomotive) by disconnecting the block of track on which his locomotive is running from all the other blocks of track and connecting that block of track to his own power pack (and only his own power pack.) In the DCC case, all he has to worry about is speed and direction. In the dc case, he has to worry about speed, direction, which block of track he is on, which block of track he will be on next, and whether someone else is already using his next bock. Thus the expression - DCC is controlling your trains. dc is controlling your tracks.
Question - a blind man walks into the middle of a model railroad operating session. Without asking anyone, how can he tell in the first 30 seconds whether the layout is operated by DCC or by dc??
Answer - He just listens. If he hears "look out, we're going to crash" he knows it is DCC. But if he hears "who's got my block??" he knows its dc.
Quote from: jsmvmd on April 13, 2007, 10:51:04 AM
Hunt,
As usual, a very precise answer.
Thanks all for very good info. Looks like my layout will be served with a PM-42 and sub-districts.
However, Hunt, is it wise to use this Digitraxx component with CVP or other mfr's components, or is that not an issue?
Best Wishes, Jack
Jack,
The compatibility of different manufacturer’s DCC components depends on the components, how you are going to using them and when they were made. So I suggest you ask each of the component manufacturers if there are any caveats to using one of their components with another’s. Some manufacturers will not give you an answer.
I am not aware of a significant issue to using Digitrax’s latest power manager with CVP’s command station or power booster (stay within the ratings).
With the exception of selecting a decoder, I suggest one use the same brand components as the command station until one has a very good understanding of the electronics involved.
Gene,
"Close, maybe half a cigar for this one," wrote Jim Banner.
With a careful reading of the first paragraph of Jim’s reply you may realize when comes to electronics, especially some DCC components, that sometimes, what appears to be the condition because it seems so commonsense obvious is in actual fact not the case. Some do find on the front leg of their DCC learning curve(s) having to deal with the drawbacks of assume. As you may now understand, it is not just the terminology. :)
Hunt,
Roger that. Will check specs and install as instructed by the mfr.
Best Wishes, Jack