Power Supplies

Great article, Joe.

I do have one bone to pick. Contrary to Joe's drawings, most boosters do NOT connect directly to 110 VAC (or 220 VAC) power mains. They need a power supply - exactly what varies by booster - check out your manual.

Direct connection to the power mains will result in a spectacular fire works display and cause damage that will most likely NOT be covered under the manufacturer's warranty.

Picky Bones

Yes Joe did not specifically include power supplies in his diagrams, but he did include power supply information in the Comments section of the Universal DCC Boosters table and the following note under Table 1.

Bold added for emphasis. Of course real men actually read the manuals. They just do not admit it.

DCC bus wiring

Joe, what advantages or disadvantages to gaping every section of track that has its' own set of feeders?   thanx, J.B. 

Gapping

Some advantages:

Short Isolation; easy to find the short in larger layouts and less impact on the entire layout when one happens

More accurate blocking and location detection for automated operation, emergency crash detection/shutdown, automatic switch throwing or signaling

Easier to predict current draw in a single location, making breakers, power distribution, etc easier to judge.

Disads:

Biggest disad is that if a feeder fails (bad solder, gets snagged moving boxes around under the layout, gets chewed on by the cat, etc) then that section of track goes dead.  If it isn't isolated then you would probably not even know it failed.  I try to have at least two feeders between each gapped section to counter my lousy construction technique 

kevin

NIce work but. . .

Joe,

Your article is well written and follows what I would consider 'standard practices' in regard to DCC power distribution, but I was surprised not to find a DCC accessory bus in your diagrams. Maybe I missed it as I admittedly did not devour the article.  The low cost Tam Valley booster has been incorporated into my layout as a DCC accessory booster and has proven to be a good investment.  Furthermore, I use Tam Valley boosters to power my layout (3 in all) and they are all powered as is everything on my layout via the healthy Digitrax PS2012 power supply.  I look forward to getting time later in the day to read your article in 'comprehension' mode.   One of the benefits of using all Tam Valley with the boss PS2012 is that track voltage automatically is the same. I protect each booster using a Polyswitches which act as automatic citcuit breakers.

Thanks for the tutorial on booster standard practices! 

Joe Baldwin

Colorado

Polyswitches

I experimented with polyswitches while developing the power management system for my railroad. Could not find a suitable component that was faster than my power supply's internal shutdown circuitry. Your success lends me to believe the PS2012 must have a slower internal limit than my off-the-shelf switching supply.

Polyswitches are attractive due to simplicity and low cost. Wish I could have made them work.

Here is a nice guide for someone considering Polyswitches.

Focus is the key for an author

Don't be surprised, my focus was getting the power to the track and doing it well ... And that took 27 pages! Reverse section wiring and the accessory bus was NOT my focus. If I'd expanded the scope even more, then we would have had a 40 page article instead of 27 pages.

My original article had another 5 pages of tangent on DCC friendly turnouts that I cut out because it really wasn't about track bus wiring.

Another aspect of my writing is that I write from experience. Since I don't have reversing sections or an accessory bus on my Siskiyou Line, I'm not the best person to write about such topics. Joe, since you sound knowlegeable about the accessory bus, would you be interested in writing an article about it?

Scribbles

Joe,

I've got some scribbles on it and will see if I have enough coherent thoughts to make it worthy of your fine pub.  The accessory bus is allowing me to incorporate the work of Geoff Bunza's DCC Decoders (Arduino) along with my CTI-Electronics automation software. I share your thoughts on reversers. Don't have one on my Colorado & Santa Fe either.

Joe D.

Polyswitches

Alan,

I've found that a Polyswitch is somewhat like a regular fuse and I use them not to protect the trackage loads, but to protect the boosters and command station from the healthy 20 amp output of the PS2012.  I use the boosters and PSX circuit breakers to protect the track loads.  With four potentially healthy current loads on the 2012, it could easily fry something if I did something foolish, like I'm inclined to do on occastion.  I also find the polyswitches valuable to protect accessory circuits where the wire runs are off to some distant section of the pike.  I use .5a hold, 1a trip on accessories and probably should cut that in half.

I use 2.5a hold, 5a trip polyswitches to protect the boosters.  Hope I clarified the application.  They are so darn cheap, even cheaper than fuses, got to be useful somewhere!

Joe D.

I understand

Ah, that makes more sense to me. The spread between hold and trip (relative to time-to-trip) was the obstacle I could not overcome and why I ended up utilizing an LTC1153 based solution.

Defense

Alan,

I hardly ever mention multiple boosters on the PS2012 publicly else some one will flame me for connecting multiple unprotected loads to a healthy near arc welder  source. (LOL)  Then there is those who found where Digitrax mentions limiting your booster/command station to a single power supply. Of course they are talking about the 4-5a transformers that many people use as a power source.  

Joe D.

Where to mount the bulb

@ Joe,

Using an 1156 bulb to protect the power block from an operator caused short at the frog is an novel concept.  Where do you mount the bulb?  Can it be seen when illuminated?  Any other suggestions?

Building 31 handlaid turnouts, all with powered frogs, and this might just be the answer I've been looking for.  Thank you for suggesting it.

Dave

I've used a 1/2" cable clamp

I've used a 1/2" plastic cable clamp and a short drywall screw to mount the bulb on the benchwork near the fascia, but you could also mount it under the benchwork if you've not got a drop cloth or paneling covering the area under the layout.

Lamp Clamp -

Joe,

All I can say about your lamp clamp is duh, why didn't I think of that. Smart, really smart!

Joe D.

Consistent track voltage???

Thanks for the informative article Joe which did a good job bringing disparate information together, good diagrams too.

Technical question: A Digitrax Zephyr supplies a nomial 13.3v to the track (with their 13.8v power supply).

Do all boosters (e.g., Tam Valley) powering districts need to supply the same voltage? (TV recommends a 16v supply for 15v track).

Thanks
Alan

Great article.  The one item

Great article.  The one item I continually see is wire recommendations for feeders to the amount of feet they can run to be overly conservative.  The chart I post below is fairly common and can be found in various forms around the net. I am often amazed that some guys write that a #22 gauge wire should only run 6 inches at 5 amps.  I don't know where this idea came from, but its definitely over kill.  I'm guessing some guy wrote on the net, "in his opinion..... 6 inches" and after constant repetition it has become gospel.

Also using the popular #14 gauge, if memory serves me after reading your article (and it may not), you stated a maximum of 35 feet at 5 amps.  Most will read this and think if their layout is 70 feet long, they should use #12 wire.  But of course if you have two circuits (you will probably have more circuits than this) and your command station and power supply are in the middle, you can run 35 feet to your left and on the other circuit 35 feet to your right on #14 wire.

27 Pages of Gold

Agree with others Joe, a great article (in an edition with lots of great articles, worth the wait) on a topic that seems to baffle a lot of us.  Admittedly, I'm still a bit unclear on 'what' booster (or how) to choose and the power demand impact of accessories (Tortoise). From a cost perspective, despite starting DCC using an NCE power cab, I see a clear case for the Tam Valley booster option. What am I missing here?

Now I think I'm with Joe-Daddy, you need to put your head down prepare an additional 27 pages (forget this G scale, live steam thought bubble, its just distracting you) on the DCC friendly turnouts and accessory bus ++?? issues.

CBK    

The only problem with the Tam

The only problem with the Tam Valley booster is its power rating at 3 amps, but even that isn't that much of a big deal.  So if you have an area, lets say a yard where there are a number of decoded engines with sound, and multiple units have sound on and you are convinced you need 5 amps, you break that yard down into two power districts of 3 amps each using the Tam booster.

Actually I'm surprised they haven't come out with a 5 amp booster

5 amp Tam?

The tam valley booster would be 5 amps if Digitrax were selling it. There are two ways to rate these things-- continuous power and surge power. Tam quotes the continuous power in their ads includes the surge power in the fine print. Most of the others do it the other way (a merchandising ploy I first encountered in the 50s). There's a recent discussion  on this thread.

pqe

Complex

There is no one right answer, or rather the right answer is very complex to calculate, hence why recommendations are all over the board. Any wire of any gauge or length will create voltage drop. It becomes a question of how much voltage drop you are willing to accept.

The feeder wire question becomes more complicated because of parallel paths. The number of feeders used and the length of track supplied are additional variables. Multiple feeders, each carrying a percentage of the load, reduces the overall voltage drop.

Wiring choices are made during construction so it is often impractical for actual measurements to be made. Erring on the side of caution by using larger gauge wire is a practical means of minimizing voltage drop in the absence of empirical data for the particular situation.

The person claiming 22AWG should be limited to 6" at 5A probably came to the conclusion based on an arbitrary limit of allowable voltage drop. A single 6" feeder pair of 22AWG at 5A on a 14V system will have an end voltage of 13.9V or 0.5% loss. If the user specifies a voltage drop maximum of 0.5% then the recommendation is valid.

People love simple answers even to complex problems. Feeder size and length recommendations fall victim to this desire for simplicity. There is no one generic fits all answer.

Booster voltage

FPN Standards

5% is a good number to shoot for.  The US National Electric Code recommends no more than 5% loss through the branches all the way down the feeders to the driven item.

I've always wondered how many DCC "problems" are related to voltage loss and resistance under higher loads, caused by inadequate wiring that people thought were good enough....

kevin 

The basics of the

The basics of the calculations:

15 foot run single conductor 13.8 volts and 5 amp current.

The circuit is 15 ft out and 15 ft back = 30 ft.

Results

This calculation is based on

This calculation is based on full 5 amps thru a single conductor. If your feeder to track are spaced 6 ft apart then all feeders will share the 5 amps feed. To calculate that would mean to put the engine at a point on the track and calculate the resistance for all feeders to determine the amperage thru each feeder. Sort of like resistors in parallel. R1 divided by Rt  total number of resistors in parallel for each 22 AWG feeder.

Easy as pie...

Result

Voltage drop: 0.81
Voltage drop percentage: 5.87%
Voltage at the end: 12.99
 

Please note that the result is an estimation based on normal condition. The actual voltage drop can vary depend on the condition of the wire, the conduit being used, the temperature, the connector, the frequency etc. But, in most cases, it will be very close.

Basic Voltage Drop Law

V_drop = IR

where:
I : the current through the object, measured in amperes
R : the resistance of the wires, measured in ohms