Power requirements

[UK78ALUM]

Planning ahead for my HO layout (table construction starts next week).   Looks like I have about 180 linear feet of track in two loops.  The layout is a 12 x 12 L shape, 4 feet wide.  There are two 4% grades, at least 12 powered switches (turnouts), and who knows how many lighted buildings, etc.   Furthermore, I want to have room (power wise) to grow.

I am also definitely going with DCC, even though it means retrofitting some locos.  I would think the most I would ever have operating at once is 4.   Soooooo...... given all that.....

1.  How do I compute power requirements?

2.  Is the DCC and power supply all one unit or are they bought separately?

3.  As always, any other thoughts?

EDIT 1:  Just to clarify (sorry - should have said this initially) I'm a fairly good weekend electrician.  In fact, that's the reason I mentioned the linear feet of track.  I'm used to calculating AC voltage drop across runs such as entry panel at the house to lighted gate posts, or determining wire size required based on required AC output at the termination point versus at the source, etc.

But it also occurred to me that the track is obviously a loop, so perhaps there is no "bleeding" of DC after all.  But either way, I'm comfortable discussing amps, load, whatever if that makes this question easier to answer.  Thanks guys!

EDIT 2:  Another omission on my part.  Even though the table is 48" wide, it is going to be a full walkaround and can be reached from all sides, including the hypoteneuse of the right triangle formed at the L, which obviously would be the longest outside to outside width.

Thanks!

[MisterBeasley]

DCC systems vary in their ability to support large numbers of engines, and the way they get their power.  The typical rating of a DCC system is in amps, or amperes.  That is a unit of current.  A typical system has from 2.5 to 8 amps available.  As a rule of thumb, I'd allow about a half an amp per engine.  Sound engines use a bit more, and realistically, an engine which is running down the tracks at a constant speed is using less than half an amp, but it's easy for computational purposes.  So, a 2.5 amp system should be good for running about 5 engines, all at the same time.

Some DCC systems plug right into the wall, and some require an external power supply.  If an external supply is needed, it should be at least as capable as the system it's driving.  So, I have a 5 amp supply for my 5 amp Lenz 100 system.  A larger power supply would do me no good, because the limit in my case is the DCC system itself.

You can, however, divide your layout into power districts and add additional booster units to it.  In this case, part of your layout will still run off the base DCC system, and part will run off the booster.  If done properly, engines won't notice the difference.  There will be no issues when you cross the track boundries, either.  Typical boosters are 5 to 8 amps per district.

I only run trains with my DCC system.  All lighted buildings are on a separate power supply, and my turnouts are powered separately as well.  I don't run my turnouts using DCC, preferring to use an old-style control panel.  That's your choice, but it's a question that comes up frequently, so I thought I'd mention it.

[larak]

UK78ALUM

How do I compute power requirements?

 

A quick Rule of Thumb: Add up the power draw at stall of all locos that you will run simultaneously. If you will be running accessories off of DCC add their combined draw. Personally, I would run switches, lights, etc off of a separate DC supply. This provides isolation, control and modularity.

Double the total for safety and expansion.

UK78ALUM

Is the DCC and power supply all one unit or are they bought separately?

I believe that they come either way depending on the brand.

 

You will likely receive many informative answers here. Good luck.

 

 

[dstarr]

 Firstly, the length of track doesn't effect your power requirements.  DCC systems are rated in terms of amperes of output current.  Old old locomotives with open frame motors and alnico magnets won't draw more than a ampere, worst case.  Modern locomotives with can motors and ceramic magnets won't draw much over 0.4 ampere.  So for locomotive power, I'd expect 4 amperes to be overkill and 1.6 amperes to be quite adequate for 4 locomotives running at once. Say an ABBA lashup of F units. . 

  Turnouts.  Will you go to the expense of using DCC control for your turnouts ?  This requires a decoder, perhaps one decoder for each turnout, which seems like an lot of money.  Will you go with stall motor switch machines (Tortoise)?  They take something like 20 mA (0.02 A) continuous and cost about $20 each. Cheaper ($7?) are the twin coil machines which will pull an amp or more for an instant.  Not sure if any DCC  supply could handle that sort of load. Or,  go with Peco turnouts, they have an over center spring and don't actually require a switch machine.  You throw the turnout with a finger, and the spring keeps it thrown.

   The traditional method of turnout power/control is to run a DC power bus around the layout to supply the switch machines and use SPDT toggle switches to control Tortoise machines or SPST momentary contact push buttons to control twin coil machines.  If you do it the traditional way, it doesn't draw any power from the DCC supply.  For a walkaround control layout, you mount the switch machine control on the fascia close to the turnout it controls. 

  I believe the DCC systems come with a reasonable amount of current capacity.  For higher current needs they sell booster amplifiers that connect to the basic DCC control box and offer outputs of 5 amps or more.   Check with a DCC supplier, but I believe you can start with the basic system and later buy an amplifier if you should need more juice. 

   You want to think about your 4 foot wide benchwork.  Most model railroaders limit the width of the benchwork to what they can easily reach, about 30 inches.  Also, you want to think real hard about 4% grades.  HO locomotives have a lot of trouble getting up 4% grades running light.  Best you can expect is to pull 3 or 4 cars up 4%.  Was it me, I'd keep my grades down to 2%. 

  If you are just starting to build a layout, you will like John Armstrong's  "Track Planning for Realistic Operation"

 

[jrbernier]

   DCC power requirements are usually based on the number of engines you will be operating at the same time.  If you figure about 1/2 amp for each active engine, you are pretty safe.  Most newer engines use a lot less power, but 'sound' engines can draw more.  Also, lighted passenger cars draw power off of the track.  In my case I have a 5 amp Command Station, and a 5 amp Booster.  10 amps may be a little 'rich', but I know I have lots of power if needed.  I have about 16 engines on the layout, and 8 of them are 'Sound' engines.

   The power supply for a DCC system may be integrated in the command station/booster or be a seperate unit.  My Digitrax system has a 'power brick' that plugs into the 120VAC house recepticle and has another 5' cord to the system unit.

   I would use that old DC power pack for powering bldg lights & switch machines.

Jim Bernier