Do it right the first time, then you can forget about it. For a layout of that size, doing it right takes little more time and money than doing it any other way. There isn't much that is more frustrating than problems with electrical feed. And with a bit of planning you can easily wire so that a future switch to DCC takes only an hour or so.
If you want two cabs you should really get two throttles. The MRC unit you mention has only one transformer and supplies only .61 amps per throttle - less if you are using the AC output for accessories.
..... Bob
Beam me up, Scotty, there's no intelligent life down here. (Captain Kirk)
I reject your reality and substitute my own. (Adam Savage)
Resistance is not futile--it is voltage divided by current.
On the subject of the power pack - you were given some misinformation. The Tech 4 280 does have 2 transformers, and can be used for 2 independent throttles in either common rail configuration, or both rails gapped. All MRC dual power packs in the past 30 years have dual transformers to allow common rail block wiring.
The disadvantage of a dual power pack is that it is awkward to operate with another person. Conversely, if you are operating alone, and are display running one train while operating another, the dual power pack is convenient. In most cases, I would recommend separate power packs instead of a dual unit due to the increased flexibility. Any of the MRC power packs from Tech 2 onwards will do a nice job of controlling your N scale trains. If money is an issue, a good used Tech 2 power pack will work quite well.
More important is how you will want to operate in the future. Do you want to sit down at a control panel and watch and operate your train from there? Or do you want to walk around and follow your train as it goes places on your layout.? Do you want to throw turnouts at a central panel, or from standing beside your train or both? Do you intend to do switching operations? If so, how will you uncouple and couple cars and locomotives? How many people do you envision operating trains at once on your layout? How important is it to you to run trains in some manner before you complete the wiring? What I am trying to say is - let your preferred operations style drive your control decisions and the wiring.
As an example, my layout has to be quite high due to the need for an under-the-layout shelf computer work station and my modeling workbench. I prefer walkaround control, and have wired my DC layout accordingly. I have made my own walkaround throttle from a simple circuit, a Radio Shark project box, and a coiled telephone handset cable. Due to the height and preference for walkaround control, I have not made any provisions for a central control panel. Turnout controls are located in the fascia. I plan to use magnets to uncouple. Some magnets/electro-magnets will need controls in the fascia.
Splitting the layout into 2 sections is the most intuitive, and probably the worst way to use your 2 throttles. The problems occur when you cross the boundary between the 2 sections. Getting a precise match of speed between the 2 power packs is almost impossible. And when the metal wheels of your train bridge the boundary between the sections, the mismatch of voltage between the 2 power packs causes your train to jump, and creates a fault current between the 2 power packs. The fault current may or may not be protected against by the power pack circuit breaker.
What is the preferred DC method is to break your layout into electrical sections, commonly called blocks, so that one throttle (power pack) controls the same train anywhere it goes on your layout. Each block has an electric switch (often toggle switches) which selects which throttle powers that particular block. There are ways of automating this process, but it will take you getting familiar with the basics of block control first. I highly recommend a book on model railroad wiring - our hosts sell an excellent one at this link: http://www.kalmbachstore.com/12207.html. Older used books on model railroading will also work fine because the basics have not changed in the past 50 years.
In the beginning, you don't need feeders every 3 feet if you rail joiners are fresh and tight. Over the course of time is a very different story. As you use the track, put stuff on it, press on it, ballast it, etc., - at some point the rail joiners will cease to be reliable conductors of electricity. You will be chasing dead spots where the rail joiners no longer conduct. But if you press on the track near the joint, it will suddenly work. Don't ask me how I know this. Hence, the recommendation that every section of rail be connected directly to feeders or connected to feeders through soldered rail joints. Nothing is more frustrating than a layout with intermittent dead spots and/or derailments. Again, don't ask me how I know this.
On a DC layout, one set of feeders per block is usually sufficient in the beginning. You will want to add additional feeders (or jumpers at the unsoldered rail joints) as time goes on. DCC wiring needs to be more robust to avoid otherwise tolerable voltage drops and potentially carry more current.
Hope this gets you going in this wonderful hobby.
Fred W
If you are going to the work and expense of two cabs and block wiring I'd suggest starting with the DCC. Otherwise you'll sink a fair amount of money in power packs which you won't need with DCC, and their used value will be very low. Hence, a poor investment.
I don't know about feeders to every piece of track, but I wire so the electricity never has to go across more than one rail joiner. Should it go bad, there will still be no more than two joints to the next closest feeder. Also, I put a tiny amount of conductive grease at every joiner to seal the joint and make it less likely to corrode to the point it won't carry power. You can use the grease they sell for spark plugs or the waxy grease they sell for light bulb sockets. I'm sure you know what it can be like to remove a dead bulb after a few years of operation.
Good luck with your layout.
fwrightOn a DC layout, one set of feeders per block is usually sufficient in the beginning. You will want to add additional feeders (or jumpers at the unsoldered rail joints) as time goes on. DCC wiring needs to be more robust to avoid otherwise tolerable voltage drops and potentially carry more current.
To add to all of Fred's good advice and information, I have always soldered all rail joints within each block, making one feeder per block more than adequate. Some will warn against this for expansion/contraction reasons, I have never had any problem. Guess it dependson the environment of your train room.
Typically even the longest blocks on the largest DC layouts are not long enough for the resistance of the rail to be an issue. So with soldered rail joints or jumpers soldered around rail joints, one feeder per block is all you need.
Sheldon
Take it from one who has wired a dozen layouts over the years.......install "drops" on each and every section of track, and dont rely upon connectors at all. They may work well at first, but the will fail......at the most inopportune time, and you'll end up installling drops later.
There is no subsdtitued for "doing it right...the first time"!
Trainman
Of course the absolute most reliable electrical connection would be to run a feeder to each 3' section of flex track and solder it on. My "compromise" is to solder a feeder to the junction of every other piece of flex track.
Now I realize it is best to solder all the joints together also so you don't have to rely on the rail joiners to transmit electricity to the next piece of track. The down side is if you have a layout that is subject to signifiacant expansion and contraction like my garage layout was. The track will expand and contract to the point where solder joints break all over the place. I found in that situation, its good to leave joiners unsoldered so the track can breath without breaking solder joints. As long as you have frequent drops from the power bus, at least every other piece of flex track, or every joint if you want to be thorough, you will get good power flow.
Rio Grande. The Action Road - Focus 1977-1983
I have another question sort of related to this. With wiring for straight DC control, do you need to have feeder wires running to both rails, or just the one that is gapped in the case of isolated blocks?
Thge common rail is subject to the same problems as your gapped rails. Run feeders, you'll be glad you did. Also, make sure you frun a feeder after each turnout, one to each of the rails, if they are not gapped for another block which will have feeders for that new block. Don't trust the electrical connection of the switch points to conduct electricity to the far side of the turnout. Good luck and have fun.
Mill BayI have another question sort of related to this. With wiring for straight DC control, do you need to have feeder wires running to both rails, or just the one that is gapped in the case of isolated blocks?
I found the easiest way to ensure good power distribution with common rail was to run a common wire bus in a loop under the layout. I used 26 gauge magnet wire (or 22 gauge wire with O gauge) for feeders soldered to the common rail and to the bus under the layout. The bus was made of 16 gauge bare antenna wire. This worked very well with everything from HO hand laid track with no rail joiners at all, to Lionel O gauge.
As Sheldon pointed out, in DC the blocks are typically of a length that you can solder all the joints within a block, and use the gaps at the ends of blocks to handle rail and roadbed expansion and contraction. This makes for one set of feeders per block. If the rail joiners are new and kept tight during installation, I find that they will work as conductors for a couple of years before problems start showing up. That gives me time to not have to wire all the feeders in one shot.
Usually, I add the extra feeders when I'm laying the track (soldering feeders to rails is easier at the bench then on the the layout), and let them dangle under the layout until I have a chance to connect them up.
just my thoughts and experiences
Good wiring practice counts for DC as well as DCC. The electrons have to move no matter the source. For NTRAK we spec'd feeders every two feet. That's overkill but we do it anyway because every builder's abilities are different. Overdoing it helps reliability. Besides, the builder is only installing feeders one module at a time.
For a home layout, every 3 to 6 feet is probably sufficient. One set of feeders on the rail joiners soldered to adjoining tracks should do it. Put additional feeder on every piece of rail that's not soldered to an adjoining rail that has a feeder. Simply- don't trust an unsoldered rail joiner to conduct electricity.
Want to add some feeders later? Do it now while the rail is clean and the iron is hot. You will need additional feeders when that unsoldered rail joiner starts to corrode and it starts corroding as soon as it is exposed to atmosphere. Ever try to solder a joint on old, weathered, painted, and ballasted track? Do it while it's new and avoid that chore. There's a photo on another thread that looks like the result of soldering a joint on old rail. It ain't pretty.
Voltage drop is a factor of distance. It has never been a big issue with DC because as the voltage drops you simply turn the throttle up a little to maintain speed. Then turn it down when the engine speeds up in the next block. No problem but it is still voltage drop and if good wiring practices are followed, voltage drop can be minimized.
Martin Myers