Power districts?

[airjer]

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

[lanny]

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

[r0bert]

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.

[Hunt]

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

[Jim Banner]

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.

[RAM]

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.

[Jim Banner]

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.

[SteamGene]

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

[jsmvmd]

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

[SteamGene]

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

[jsmvmd]

Dear Gene,

Muchos Garcias!  That is just the ticket for me.

Best, Jack

[SteamGene]

Jack,

Doe tashe musta!
Gene

[Hunt]

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.

[Jim Banner]

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.   

[Hunt]

...
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. 

So for more details start with
http://www.tonystrains.com/technews/powershield_icb.htm