The DCC system at Fillmore is by Digitrax. At the time, it was packaged as the Empire Builder Duplex Radio starter set (5 Amp) and I later added a second 5 Amp Booster. It has served me very well. The Command Station is Power District 1, the Booster is Power District 2, and they are labelled as shown below.
To manage the track power requirements, due to the high density of DCC sound-equipped locomotives, I took some time to consider how I would divide the two power districts that the command station and booster naturally provide. Here is the result:
Power District 1 (PD1) includes the roundhouse stall tracks, garden tracks, turntable, the coach yard, the staging fiddle yard and staging elevator. This seems like a relatively large area: in DCC, it’s not how big a given area is, it is how many locomotives will be running in a given area:
Stall tracks – these tracks are normally not powered for safety reasons. An operator needs to hold down a switch to power the track for the stall he wishes to use. If he gets confused or goes in the wrong direction – it happens to all of us – all he needs to do is let go of the switch and the track goes dead. The intent is to help prevent a locomotive from crashing through a roundhouse backwall. Therefore, any locomotives inside the roundhouse (up to 14) do not draw any current.
Garden tracks – the two of the three garden tracks are always powered (the third one is not at all – too short to be of use), but locomotives are not usually parked here. If one is, it’s not a big draw. Normally a box car or the snow plow is spotted here.
Turntable track – is always powered. Only one locomotive can use it at a time, so this is not a big draw either.
Coach yard tracks – are always powered, but usually only one switcher is working. Even with two running, this is a limited draw. Locomotives from the engine terminal do not run here.
Staging fiddle yard tracks – the four are always powered, however only rolling stock is staged here with the coach yard switcher entering as needed.
Staging elevator tracks – the upper level locomotive staging has SPDT switches on each of the five tracks to turn on/off the track power. The lower service trains level has one SPDT switch for all track power. A level that is not aligned to the layout is switched off, for safety, so there is no power draw. The locomotive level can have as many as 11 engines running, but this can be managed by switching individual tracks on/off.
So, Power District 1 can see as many as 28 locomotives, a maximum of 14-15 of them normally powered (remember, the stall tracks are normally dead). By managing the staging track power, fewer would be running. However, existing operations have only about 7-8 powered engines at once.
About individual locomotive current draw…
I measured the locomotive draw, for each type of locomotive, on stationary rollers with an RRamp meter. An RRamp Meter properly measures the current and voltage output from the DCC system at the tracks.
It can be connected in series (the cables were included) between the command station and, in my case, programming/test track. My test setup is shown below.
As a standard, I have the command station and booster tuned to output 15V (as recommended by Digitrax). This is done inside each box by turning an adjustment screw.
Each model type was run at a higher speed (35% throttle setting – normal speed at Fillmore is no more than 6%), headlight on, and sound on. Since locomotives run light here, I did not have to consider the load when pulling a string of cars. Below, NYC H6a Mikado is at speed.
Here are the results of the testing:
- Class Des-7 HH600 Switcher (Atlas) – .30 Amp (with Tsunami 2)
- Class B-62 0-6-0 Switcher (Walthers) – .26 Amp (older, former QSI, now Tsunami 1)
- Class U3a 0-8-0 Switcher (Walthers) – .11 Amp (factory-equipped with Tsunami 1)
- Class H6a 2-8-2 Mikado (BLI) – .18 Amp (former Paragon 2, now Tsunami 1)
- Class J1d/e 4-6-4 Hudson (BLI) – .19 Amp (former Paragon 2, now Tsunami 1)
- Class J3a 4-6-4 Hudson (MTH) – .16 Amp (former Proto 3.0, now Tsunami 1)
- Class L3a 4-8-2 Mohawk (MTH) – .18 Amp (former Proto 3.0, now Tsunami 1)
The actual numbers aren’t important (although the little HH600 is a surprise), the take away is that “modern” DCC/sound equipped locomotives don’t draw a whole lot of power. With an average draw of .20 Amperes, therefore, a power district at 5 Amps each has more than enough power to run lots of locomotives – and actually more than can be physically accommodated on the tracks.
The issue is if a short happens (like running a switch in the coach yard) – the locomotives will power-off and will all start at once as soon as the short is cleared. The start-up in-rush current is much higher (for an instant): if there are enough locomotives trying to start at the same time, there is likely not enough power from the 5 Amps available. I could not measure the in-rush current – it must be practically instantaneous, however experience has showed that any more than about 7 locomotives in the power district will cause problems on restart. As I related already, locomotive staging alone can have up to 11 engines.
The solution is simple. As noted above in the “staging elevator tracks” section, the majority of the locomotives in PD1 will be on the staging elevator. Upon a short (which rarely happens in practice), the Staging Master will turn off all track power to the staging elevator. Then he will turn on each track one at a time. This can be done as quickly as every 1-2 seconds. This is enough time to power-up the locomotives gracefully and eliminates the need for a more sophisticated control module, which I believe is available.
If a short happens in PD1, it will not affect locomotives running in Power District 2 (PD2). The opposite is also true.
PD2 includes the double-tracked roundhouse inbound leads, the double-tracked ready tracks, the single outbound track, the steam plant spur, and the service track to the coaling tower. The potential for having lots of locomotives here is great, even though the area is much smaller than PD1. In theory, there could be as many as 10 locomotives running here, but the schedule does not allow this.
Normally, a maximum of five engines are in this district at one time. I believe that this is also prototypical – a normal engine terminal servicing capacity would be anticipated to avoid traffic jams. Like on any part of a railroad, the movements are spaced for efficiency and safety resulting in a steady flow. No doubt there were intensely busy periods too, as found in my era. While not typical, we could handle up to the 10 noted locomotives. If a short were to happen, then we would have to tilt a few locomotives off one rail until most have restarted. Discounting shorts, there is plenty of power at 5 Amps to run this number of locomotives.
As noted above, I have the turntable in the same power district as the coach yard (PD1). My Walthers turntable handles correcting the DCC track polarity mechanically – there is a dead spot in rotation every 180 degrees where a running locomotive will power off. It will then restart as rotation moves away from the dead zone. Early on in testing, when a locomotive on the turntable powered off, any other engines in the coach yard would too! Very annoying…especially if someone was operating a switcher there. I installed a Digitrax PM 42 Power Manager that allows for separating a power district into up to four sub-districts. I isolated the turntable into its own sub-district and the rest of PD1 into another. The problem of yard engines shutting down went away.
A large, busy engine terminal needs some careful planning to manage the track power. Alternatively, one could always add more boosters in smaller power districts if unsure of power demands. In my view, this starts to get expensive and complicated. To run sound-equipped locomotives, we don’t need that much power, but a strategy for restarting them after a short is a good thing to have. I think this would be best planned ahead of time. In fact, not knowing how this would play out, I designed PD2 so it can be split into two and another booster added to create PD3. I hope I don’t need to do this.