My implementation & DCC "electronics stack"

My DCC implementation is based on my usage. Since I want to:

• MU diesels
• doublehead steam
• use helpers
• have a number of locos on the rails at all times

I needed to be sure my system could do what I wanted.

Current: (amps)

I need a lot of amperage, that's the first thing people think about.

I measured the current draw on USAT F3 units, and I'm using about 1.7 amps per USAT F3 unit under load on a grade. I need to be able to handle a maximum of 5 or 6 units, so this is a challenge.

Voltage: (volts on the rails): 

Many people do not realize that voltage can also be very important in G scale.

I did some testing, and found that I lost 3 volts in the booster, i.e. 24 volts DC into the booster yielded 21 to the track, under no load conditions.

The DCC decoders can also lose about 2-3 volts between the track input and the motor.

What does that mean to you? I experimented with the effect of voltage on the maximum speed on the locos. Many power supplies for DCC are a simple AC transformer, or DC supply, unregulated.

I was also seeing a situation that a "24 volt" transformer would yield 20 volts out under load.

So there were real situations where the locomotive motors only "got" between 15 and 18 volts. 

First thing to realize about DC motors: There is NOT a linear relationship between motor voltage and motor speed. Virtually all the "top speed" in a motor comes from the last few volts applied.

So the difference between 15, 18, and 20 volts to a loco made a BIG difference in the top speed.

Now, the real example: I found that my USAT F3 locos would only run 62-65 mph at 20 volts on the rails, but would hit close to 90 with 23 on the rails. Absorb this information. This means you need to pay attention to your power system if you need anything near 70 miles per hour from a loco. The USAT locos run fast too, most Aristo locos run more slowly. My E8's would just crawl.

What to do:

OK, so I know (now) I need a high amperage booster, and also to get as close to 20 volts into the motors.

I purchased the 10 amp NCE system.

Originally I bought a big 10 amp transformer from Tony's Train Exchange. I found a perfect box to put it in, from LMB, a #142, 4x6x5" high. But I found the voltage sagged quite a lot under load. Also, since I'm running passenger train also, I needed all the voltage I can get. (A transformer alone is always going to have it's output voltage sag under load).

The voltage to the rails often sagged to 17 volts. No wonder that people say their locos run slow!

How to make it better:

The NCE booster has a settable output, but normally it maxes out at about 20.1 volts. I have a calibrated speedometer car, and my USAT F units only went about 67 mph at this track voltage. I checked with NCE since they said the unit could go to 24 volts. I sent it in, they modified it to give me the max voltage. So adding 3 volts, I needed 27 volts in.

So, now I have a regulated 11 amp, 27 volt supply, it's on the bottom of the picture below. The passenger train can now hit 92 scale miles per hour. There are more reasons for having this top speed, it allows you to speed match all your locos (you usually match to the lowest tops speed loco). It is a Meanwell S-320-27, about $70 on up. Several companies carry them, Jameco Electronics www.jameco.com has the best price recently.

My "power stack":

The Meanwell power supply is on the bottom of the "stack".

The power supply feeds the booster on top of the "stack" via the red and yellow wires.

The booster combines the input power with the DCC signal from the command station, which is the middle box in the "stack". The output to the track is via the red and white wires. The booster provides power to the command station by the green and yellow wires.

I wired each track feeder to a stackable dual banana plug. They are cheap and can handle lots of amps. You can see the white and red wires feeding the stack of plugs at the bottom right, which are all the track feeds. You can get them from electronics supply houses or Radio Shack. This also makes it easy to reconfigure power, or hook in DC to some tracks.

The command station, in the middle of the stack, gets the hand controller(s) connected to it, the wireless base station(s), and also has the output for the programming track. You can also see the serial port which connects to the computer in the house that allows computer control and decoder programming (it's the large white plug with the screw slots in the "knobs").

Finally, on top is the 110v on/off switch, and the silver box is the RS-232 extender that allows a remote computer to control the command station using JMRI or other software.

The enclosure is a 12" x 12" irrigation "catch basin", but inverted. So, normally you would have a drain grate on top, but now the drain grate is the base. Underneath, I have added some finer screen mesh to keep critters out.

The top is the "catch basin" "box". It usually sits in the ground and connects drain pipes together. You glue the plugs in both sides. Put a handle on it and it makes a perfect waterproof cover:

Here's the stack with a DCC Specialties autoreverser added, just use the banana jacks to add it into the circuit, easy, fast. This autoreverser will eventually be placed right at the wye that is the entry to the switchyard.

http://www.heller-modellbahn.de/Dietz.htm