Reality Reduced Blog

Kato P42 MRC Sound Decoder Installation

Sat, 21 Aug 2010 08:28:48 -0500

My box is done, I have found a solution to my capacitance problem. I am testing a few last details, and then need to shoot some final video so I can show you the finished product.

In the mean time, I thought I would share a decoder install. The box does no good on its own, you must also have DCC locomotives, switches, signals and other items to get the full benefit. I thought what better way to show off what DCC can do than to show a sound decoder, which is exactly what I do in this episode.

My Amtrak train is my only passenger train, and it’s pulled by a single Kato P42 locomotive. I figured this was a good place to get my feet wet with sound, there are near drop in decoders for this locomotive and it’s a nice simple train everyone likes to see. After reading some of the forums I decided on an MRC sound decoder; there is still a lot of new development in the sound decoder space and I expect it to heat up in the near future for a number of reasons. I think we may even seen factory sound from major manufacturers soon.

Anyway, watch the YouTube video to see the decoder go in, it’s really quite simple. At the end of the video is a treat, the decoder in action. Listen for yourself and decide if sound in N scale is worth the cost and trouble. This does demonstrate some of the things you can do with a DCC system that just can’t be easily done with DC though, perhaps some of these features will make you take the plunge.

Too Much Capacitance

Tue, 6 Jul 2010 16:31:36 -0500

As documented in my last blog post I have a problem. It turns out I have an incompatibility between my RIGrunner 4010S and my Digitrax DB200+.

Let me first lay out all the documenation:

• RIGrunner: Product Page / Documentation
• Digitrax DB200+: Product Page / Documentation
• International Rectifier IPS0551T Data Sheet

The RIGrunner uses the International Rectifier IPS0551T as a switch. This product was designed to be used in this way, and is not a plain MOSFET but rather has integrated logic to make it ready to use as a switch. One of these bits of integrated logic is an over-current detection circuit which is being tripped in my application.

After describing this configuration to the guys at Digitrax they replied that there was about 12,000 μF of capacitance in each DB200+ booster. I took the cover off of my booster and in fact find a pair of 8200 μF capacitors, so I think the actual amount may be closer to 16,400 μF! I can’t be 100% sure, it the power input side appears to be a fairly simple arrangement. Power goes into a bridge rectifier, and then is buffered by the two capacitors to provide a steady output.

What I believe is happening is that when first powered on the capacitors draw a large inrush of current in an attempt to charge. This may in fact exceed 100A for a few microseconds, or it may just be a high enough inrush that it is fooling the current sensor in the IPS0551T. In any event, I can do this with a single booster, so there is no way I’m going to be able to power all of them on at once.

In an attempt to prove this was the problem and find a temporary work-around I used the automotive tail light in series trick. Visually this shows the inrush current, and it does provide a work around. It’s not a very elegant solution. So what are my options?

1. Replace the capacitors inside the DB200+’s. They are far larger than the need to be, no doubt designed to handle the wide range of inputs and potentially dirty power these boxes may see. My battery feed situation here though is about as clean as power can get, and thus the large filter capacitors are unnecessary. I’ve rejected this though as I don’t want to void the warranty, and want to be able to swap these in the field with factory units if they fail.
2. Install automotive tail light bulbs on each unit. A cheap work around, however they zap a lot of the power going in, and I’m not sure I can get one that will handle the 8A load into the booster. It’s a great solution for testing, but not a good one for production.
3. An inductor. This was my first idea, use an inductor to limit the inrush current. Unfortunately to be able to handle an 8A booster the inductor required is enormous and expensive. It’s just not practical at these amperages.
4. A thermister; or thermal resistor. This is a resistor that starts at a high resistance and as it heats up has a lower resistance. It would work, but has the “hot reset” problem. If a booster were to loose power the thermister would have to cool down before it would allow things to restart. Prematurely restarting would shut down the entire box.
5. Design a circuit to work around this problem.

I took a stab at #5.

Power comes in on the left, and leaves on the right. The bottom line is the negative connection and goes straight through. On the positive side current passes through a 15 Ohm resistor before leaving. This limits the inrush surge to under 10A, which is the fuse rating on the outputs I’m using.

However, you don’t want to keep running through the resistor and generating heat. A variable resistor, R2, controls how fast a small capacitor charges, C1. As it charges it ramps the voltage on a MOSFET, Q1, slowly allowing more and more current to pass via the MOSFET. Once the capacitor is fully charged, all current will take the lower resistance path through the MOSFET to the output.

My idea is to put this on a small circuit board with board mounted Power Pole connectors on the input and output. I’ll literally be able to plug one inline with each booster and adjust the variable resistor. I’ve created the following parts list (all part numbers from Mouser):

1 Q1 - STP16NF06 - 60V, 16A, TO-220
1 R1 - 280-CR15-15-RC - 15 Ohm 15W Wirewound
1 C1 - 140-50U5-104M-TB-RC, 0.1uF ceramic disc
1 R2 - 858-36PR100KLF - 100k-1,000k Ohm variable resistor
4 Powerpole 25 Amp Right Angle Contacts "G1"
2 Powerpole 15/30/45 Red Hoods
2 Powerpole 15/30/45 Black Hoods

However, I’m pushing the limit of my electronics knowledge. I attempted to calculate the right values for the resistors and capacitors and design a good circuit, but for all I know I’ve done a lousy job and this won’t work at all. That’s why I am posting the details here and soliciting input. I need your help to design a good circuit.

Feel free to toss my idea completely out and propose some other method. If you think I rejected one of the methods above when I should be considering it, let me know that as well.

I would like to point out this is probably part of (maybe all of) the reason Digitrax does not recommend powering multiple boosters with a single power supply. The inrush demands are large. Unfortunately this isn’t directly documented, so I had no real way to know in advance. This may also be of interest to folks using Digitrax products with “laptop” power supplies. These devices are FET based switching power supplies, and may not be designed to supply the huge inrush currents the boosters can demand.

I would like to thank the folks at West Mountain Radio, they took a bunch of their time to deal with someone using their product for a new application and helped me figure out the problem. They also were able to provide me the part number of the MOSFET inside so I could get the data sheet. I don’t think they had ever seen one shut down like this before, since the unit is rated only for 40A. The 100A limit was so much higher they had all but forgotten about it.

Digitrax tech support also gets an A+ for a fast reply with the capacitance issue once I reached their technical team.

I’m hoping the power of the Internet can help me solve this problem, if you can help, please post!

DCC in a Box #6 Complete!

Mon, 5 Jul 2010 17:45:04 -0500

At long last, the box is done. Well, done with two caveats. Eventually I will have to add two more DB200+ boosters and I will need to create some more remote circuit breaker pods and the cables to hook them up. Still, for the definitions of documenting this project it is complete!

I had to break the video into two parts. YouTube has a 10 minute limit, and I exceeded it. Normally I hate doing that because I think people just don’t sit through longer videos, but this time I just had to do it. I wanted a fairly detailed overview of everything that is in the box.

The features, at a high level:

• 35 Amp (27 continuous) power supply, Astron RS-35M.
• 40 Amp battery charge controller, Super PWRGate.
• 45 Amp-Hour AGM “Security System” Battery.
• RIGrunner 4010S DC power strip with electronic switch.
• DCS 100 Command Station
• Four DB200+ Boosters (2 installed).
• 4 RRAmpMeters
• 1 “Command Station” LNRP to protect the command station from the layout.
• 1 “Loop” LNRP to protect the backbone from the loop.
• UR91 Simplex Radio for Digitrax wireless throttles.
• UR92 Duplex Radio for Digitrax wireless throttles.
• UP5 Panel
• Two fans to control temperature, one powered directly from the power supply the other powered off the battery so that one is always on.
• “Power On” and “On Battery” indication lights.
• External LocoNet connections for the loop ThrottleNet, a PC, and the LocoNet backbone East and West.
• All plywood construction, stained and polyurethaned. Protective covers front and rear.
• Two fixed and two swivel castors to make moving easier.
• Four track outputs.
• One programming track output.
• One 5A white line output.

There are some accessories that go with it:

• White, Red, Yellow, Blue and Green “T” cables to connect to the layout.
• Three 30’ extension cords to connect it to the layout.
• One programming track.
• One PSX “four pack” of DCC circuit breakers, still in testing.

Eventually more circuit breakers, T cables, and perhaps more extensions will need to be built to travel with this beast.

I’ve produced a “one line” drawing: (Or, download DCC One Line.pdf)

A project like this is a bit on uncharted ground, and no matter how well you plan there are always some lessons learned in the process. Let me review a few of the things I learned:

• The cabinet should have been larger. It’s not tight inside, but it’s not quite as roomy as I would have liked. A few more inches would have made a big difference.
• Digitrax boosters have a large amount of capacitance on their input side which can cause a number of issues with your power supplies and equipment. Indeed, I will be doing a whole separate blog post about this issue as it is highly technical and I have not fully solved it yet.
• Each of the Digitrax small panels (LNRP, UP5, UR91, UR92) have a “Track Status” light. In my current configuration they are all off all the time. There’s really no reason to connect them, as with the RRAmpMeters we get a much better status output. I do wonder though if some folks will miss them, and have considered wiring them all up to the command station track output simply so they are on.

Now that it is done, I would love to hear your comments! What do you think? How could this be improved? How would you have done this differently?

I hope you found this project and the videos useful, and I hope if we end up in a layout together you find my box a reliable way to run the layout!

DCC in a Box #5 Assembly

Thu, 10 Jun 2010 20:33:30 -0500

The day has come to put it all together!

I am taking my time with final assembly, trying to make sure everything fits perfectly. Most of it is quite boring, but I tried to select some interesting video for you. I’m really trying to make this look pretty, both because I just want to take pride in what I did, but also because I will be using this at home and want it to look more like furniture than “train stuff”.

While I did hours of planning, there are always details that don’t come out until final assembly. For instance, the method I was going to use to secure the power supply ended up being way too close to the edge of the box. So I had to come up with a new method during assembly. Such is the case when building one of a kind, or initial prototype devices.

There are a LOT of connections in this box. That’s part of why I did this project, I didn’t want the connections to be set up and torn down at every show; but as I run all the connections it really hits home. I used 5 or 6 packages of cable clips to organize and hold down all the cables. However the inside is neat and tidy.

Anyway, I ran into an issue with the RIGrunner. In the video I thought it was bad, and sent it back. However, it tested fine for them when they got it back. We discussed several things that might be wrong with my setup, and I tested them all, no issues found. They are sending me a new one to try, and have been very helpful understanding how it works and what to look for as I test. It’s really a dead simple device, so it should just work. I either ran into one with a strange failure mode, or something about my application is interacting with it badly.

I’ve committed to get to the bottom of it though, and will install the replacement and do more testing as soon as it arrives. The guys at West Mountain Radio have also said they would help in any way they can. They have sold thousands of these with virtually no issues, so they are curious as well.

Anyway, I’ve been using the box with a RIGrunner 4005 I had laying around. I had to make a couple of Y Powerpole cables to get everything powered, but it’s working good. It’s allowed me to start on the next phase, installing and configuring decoders in all of my locomotives. I’ve already recorded two videos about installing decoders, so you have that to look forward to in the future.

The next episode will be the great unveiling, and I’ll show you all the features of this cool box!

DCC in a Box #4 LocoNet

Fri, 4 Jun 2010 15:13:33 -0500

LocoNet is the name Digitrax gives to their communications network. It is based on a 6 position cable that runs between the various components allowing them to communicate. It’s dead simple to configure in the simplest cases, just plug in and go.

Those little modular ends seem to intimidate a number of people, and I don’t know why. Nothing could be easier to put on than a modular end on flat cable. I do a demonstration in the video of just how easy it is to make your own cable. Running your cable neatly will keep it from being damaged, and the best way is to run your own.

A top of the line crimper can easily run over $100, but most big box stores now sell cable and modular ends and offer homeowner grade tools for under $50, and sometimes as low as $30. Check the same section you would go to buy a telephone or cable TV outlet.

For larger layouts, the LocoNet must be planned. Typically the first step is to separate the “ThrottleNet” (panels) from the “BoosterNet”. This is a natural outgrowth that the command station has two plugs on it and also of the threat model. People are much more likely to accidentally unplug a panel, or plug in a device that is not properly functioning taking down the ThrottleNet. By having the BoosterNet independent there is hope that an emergency shutdown on that side (e.g. via a computer interface) will stop all the trains.

Really though this proved to be a minor optimization. At the Derby City Express they tried out a new Digitrax product, the LNRP. An LNRP, or LocoNet Repeater, breaks the LocoNet into a T-shape. If a leg of the T has problems it is electronically disconnected from the rest of the network. In an NTrak design there is typically one per loop so that any problems inside the loop are isolated from the rest of the layout. That loop will still go down, but not take the rest of the layout with it.

They also used one at the command station to protect it from the layout. Basically the PC is directly connected to the command station, and then an LNRP is used as a gateway to the rest of the network. This protects the PC to command station interface for monitoring, and the central LNRP provides an instant indication of a layout wide problem.

As a side note, the document I referenced in my first DCC in a Box post has been updated to be non-specific to the Derby City Express and reposted. See “Digital Command Control for NTrak Layouts Design & Operational Considerations”. If you’re building larger layouts that require LNRP’s you will need to read this document.

In my box I will be using all of these best practices. An LNRP to protect the command station, and an LNRP for the “loop” which is contained entirely in this box. Off of the loop LNRP I will run a separate ThrottleNet and BoosterNet.

The box will not be able to handle all LocoNet duties though. UP5’s will need to be placed at strategic locations, and additional UR91 and UR92 radio panels may be needed for coverage. If the box is ever at the heart of a multi-loop setup we also need the loop to loop connections. All of these will leave the box via a telephone jack panel making it easy to connect and disconnect without having to disassemble the box.

This concludes the back story and planning. The next episode will be some clips from final assembly. You can then look forward to the big reveal, where I show off the entire box, completed.

DCC in a Box #3 RRampMeter

Tue, 25 May 2010 12:52:24 -0500

Monitoring DCC power isn’t as easy as connecting a volt meter. Yes, you can measure using the AC settings on your volt meter but due to differences in the way it averages you have to do some math to get the true voltage.

The RRampMeter by Tony’s Train Exchange is your answer! Accurately measure volts and current, as well as the presence or absence of an AC signal. I really believe if you run DCC this is a must have item.

For my box though I wanted to panel mount them, and that presented a challenge. You can get the bare board and dimensions for panel mounting, but really that only works if you have a sheet metal or other precision cut, thin wall material for mounting. My plywood construction makes this not work so well, as I found in my first attempt to mount one.

After studying the available parts I decided to make a front mount version. It’s far easier to tell you to watch the video than describe it, so that’s what I am going to do. However there is one detail I can’t easily put in the video, and that’s the plan for the bezel. If you want to make your own, here is an EPS (Bezel for RRampMeter.eps) of the cut out. I provided this file to my laser cutter and they were able to do the rest.

Also, by using for of these in my box I ended up with extra banana plug leads. I keep one RRampMeter version 3 for walk around troubleshooting, so I modified some of the sets of leads to cover the various situations I might encounter. From top to bottom, AARL (and white line) power pole arrangement, NTrak power pole arrangement (for tracks between modules), Cinch-Jones connectors for legacy modules, and lastly the standard clip leads. This way if I want to measure current at any location on the layout I can drop my portable unit in place and take some measurements.

DCC in a Box #2 Command Station and Boosters

Sun, 23 May 2010 11:40:26 -0500

Command stations and boosters, the heart of a DCC system. The command station is the brain of the system, controlling all of the other parts. The boosters take ordinary power and turn it into DCC power with a DCC signal superimposed on top of it. As one of the most expensive components of a DCC system, you want to get the right units, and the right number of units the first time.

Let’s start with the command station. I’m going to head right to North Raleigh’s Rules for DCC Design and Operation of NTRAK Layouts document and quote “Rule 8 Only One Command Station Can Command”. Because there is only one command station, and without it the entire layout is useless the recommendations are quite conservative for a large NTrak layout. That is, they recommend using the command station as a command station only. Not as a booster, not as a programming controller, just as a command station.

For this role the DCS 100 is the perfect choice. It is the cheapest “full blown” command station Digitrax sells, and since we won’t be using it as a booster there is no worry about the booster capacity. If you’re building a smaller home layout and wish to use the booster output of your command station I recommend the DCS 200, the same thing but with an 8A booster capacity.

For the boosters, you could use DB 150 (I misspoke in the video and called this a DCS 150, there is no such thing) which is a 5 amp booster that also has the ability to be a limited command station. However I’ve found that for an average of about $15 more you can purchase a DB 200+ which is an 8A booster only device. Given we don’t need the command station functionality of the DB 150 (and indeed, misconfiguring it can cause issues) and that we can get more power so cheaply the DB 200+ is the way to go in my opinion.

Please keep in mind here I’m talking about larger layouts, generally club or NTrak layouts. My general rule would be if you need 3 or more boosters you should be following the recommendations for large NTrak layouts. If you have something smaller, use the booster output on your command station, or scale down to a Zephyr to meet your needs.

I will complain about the physical design of these boxes. While quite well engineered to be robust, reliable and cheap they are not easy to panel mount. I thought about many options, including partial disassembly. In the end I settled for the solution most people use which you’ll see in the final assembly article coming up. To make that work though I had to find the 7 position “euro style” terminal blocks they use in a configuration where the wires came out down. I show these in my video and there’s a picture in this article, but I could only find them in green. I would love to have some grey ones to better match the Digitrax equipment but I just could not find them. If you want to get them, look for part number ED1764-ND at Digikey. They are a little over $6 each, so it’s not a cheap upgrade just for better cable routing but they are a huge improvement in my opinion.

How many boosters you need is a bit of a black art, particularly for an NTrak layout which is always a different size and shape. I spent a good bit of time pondering different configurations of how I might use the box, and came up with two likely scenarios.

Scenario #1 - Very small layout, like I might use at home. Potentially there are four tracks involved, red, yellow, blue and green. I’m a big mountain line fan so I always include green. While it’s overkill from a capacity perspective, wouldn’t it be easy if I had four boosters, one for each track?

Scenario #2 - Large layout, capacity is an issue. First I had to define a large loop. I decided that a 100’ x 50’ layout was what I considered the largest likely single loop. I made this doodle:

If I put my box at the center of a 100’ x 50’ layout and divided into three, 100’ segments I could reach them all with 50’ extension cables as shown. I liked this a lot, for one a maximum segment length of 100’ has been a rule of thumb for many of the digital designs I’ve seen. Secondly, 50’ extension cables are quite workable, I used a voltage drop calculator (available here) to calculate the drop over 50’ of 10ga (the largest wire I can use with 45 amp power pole shells) and got a .9 volt drop at a full 8A of power. I then added 50’ of 12ga wire (the wire under the modules), but this time with a 4A load (figuring the two trains would not be right next to each other) and got .7 volt drop. So my worst case drop around the layout would be about 1.6 volts. Given the DCC boosters output about 11.5 volts in “N Scale” mode, that’s around 10 volts at the lowest point under full load. That meets my criteria of a good design.

Let me point out the loss is load dependent. If I redo the calculations with a booster feeding a much more likely 4A, and use 2A through the module feeders I get a drop of only .8 volts, taking my 11.5 volt output and turning it into 10.7 volts at the lowest point.

My ace in the hole is a final detail. The Digitrax boosters have a switch on the front for N, HO, or O/G scale. The only difference in these settings is the output voltage! N scale is 12 volts, HO is 15 volts, and O/G is 20! There is also a small trimmer potentiometer inside the case allowing you to fine tune the voltage so all boosters match. For reference all of mine from the factory read 11.5 volts on my RRampMeter. If the voltage drop proves to be too much, I can simply move all the voltage selectors to the HO selection to up the voltage!

Three segments will get the job done with reasonable loss. I’ll note this is why many folks use distributed power, not wanting the .9 volt drop from the wires to the central box. I can understand that, but I think the benefits of having everything prewired in a central box outweigh the downside of a slight additional voltage drop. There are too many connections, too many details to assemble in a distributed fashion at every show, at least in my opinion.

But, and there is always a but, three segments might not get the job done. Why? Well, two reasons potentially. One is there may be a yard somewhere on this layout. Yards can get parked full of locomotives, but also full of lighted passenger cars. If there is a large yard on this layout I can see dedicating a 8A booster just to the yard. Alternatively, being a green line guy, I could see the green line run point to point around a part of this layout. In that case it would need a pair of auto-reversers and perhaps a regular segment or two in the middle. I could see a fourth booster serving that need.

Based on all of my usage cases I came up with four boosters being the right number. Since I’m designing for random layouts that are not yet built, I have to plan for the worst case. If you’re building a home layout you can probably be much more scientific about how many boosters you need and where they need to go.

Lastly, let’s talk a bit about power management. First, I misspoke in the video and said you could use a Digitrax DS54 (which has been replaced with a DS64) for power management. That is wrong, the DS54/64 is a stationary decoder, I simply got my part numbers mixed up. What I wanted to reference was a PM42, which is Digitrax’s power management and auto-reverser all in one.

I am not a fan of any of the power management devices. I believe they all have some shortcomings. For instance the PM42 uses mechanical relays and a funky card edge connector. The PSX which I ended up selecting is all solid state, but comes “some assembly required”. Tony’s Train Exchange has a nice summary of all the differences.

I’m not going to go into a lot of detail now about the PSX. I have my first one and I’m evaluating it right now. I think it is going to be a better answer than a PM42, but I’m not sure yet. In any event I will be doing a full review of the PSX as well as a summary of how I intended to use it. It’s not going in the box, so it can wait until my DCC in a Box is completed!

To summarize the booster situation, I will be using one DCS 100 command station and four DCS 200+ boosters. I only have two of the boosters now due to the cost, but I’m planning for the other two to be added later. I will be using PSX units to provide my power management, unless they don’t work out in which case I’ll use some PM42’s. Note how this feeds back into the Power article I’ve already written, since we now know the maximum draw of the boosters. While I’m writing these articles in linear fashion, things are intertwined in a complicated way.

Next up, monitoring your power output with an RRampMeter, plus a great way to modify them for panel mount!

DCC in a Box #1 Power

Fri, 21 May 2010 12:59:26 -0500

Any DCC system starts with a good power supply. Most of the major vendors sell high quality power supplies to match their various DCC components. Digitrax is no exception, marketing the PS-14 to power panels, and the PS315, PS515, and PS2012 as 3A, 5A, and 20A power supplies. These are all great options.

However, there is more to planning your power system than simply selecting a power supply. You need to consider the following questions:

• Where do I need power?
• What sort of power protection do I need?
• How much power do I need?
• How will I cool my power supply?

Where you need power is the easiest question. Consider all of your DCC components and where they will be placed. Components near each other can share a power supply, provided it is a large enough supply and you have fuses to protect the equipment. Components further apart are probably better with multiple power supplies rather than trying to run DC long distances.

Power protection is an important item many people forget. Your DCC equipment is computer equipment. You need to protect it the same way you would protect your computer equipment at home. At a bare minimum this means using a surge protector, usually built into a power strip. However I strongly recommend using a UPS (Uninterruptible Power Supply). I recommend these for all of your electronics, both for the superior surge protection but also to keep things working during momentary outages. For those of us doing public shows this is not an option, you don’t want the whole layout to be down for 5 minutes while you “reboot”.

How much power is both an easy and hard question. For small layouts with only a couple of components, add the maximum draw of all components and get a power supply that big. Just size for the worst case, it doesn’t cost that much more and you’ll never have a problem. For larger layouts that just doesn’t work, boosters are rarely run at full output and when you have 5, 10, or 20 boosters sizing for full load means grossly oversizing. However, I suspect if you’re on a layout that big you can handle the power sizing!

Cooling your power supply is important. Power supplies generate heat, and if you let them get hot they will have a much shorter life. Make sure your supply gets good airflow, or place a fan on it, or both.

Let’s talk about my specific design. I’m planning to have four 8A boosters. I’m also planning 5 Digitrax panels at approximately .3A each, four RRampMeters at about .1A each, a command station rated for 5A, and some lights and fans. All totaled, that’s about 39 amps of potential draw. However I also know it’s extremely unlikely all four boosters will be at 8A in N scale, and the command station won’t be powering any track at all. If I guess a maximum of 4A per booster, and 1A for the command station with no track and re-do my total I get a more realistic 19A maximum likely draw. I’d like to size somewhere in the middle.

Knowing how much power we need also allows us to size our power protection. Most folks would go down to the local Big Box Store and buy a UPS. This is the simple solution, and if you choose to go this way you made an excellent choice. However, I wanted to be a bit different, and found some really cool products.

A slight diversion. NTrak now recommends Andersen Powerpole connectors for all modules. These connectors have a huge following in the ham radio community. If you haven’t looked at sites like West Mountain Radio or Ham Radio Outlet then you are missing out. They have a ton of cool products that can be used for model railroading. If nothing else you should buy a PWRcrimp tool if you’re putting on Powerpole connectors, I did and there is no turning back!

One of the cool products you’ll find is the Super PWRgate PG40S. Basically this the the heart of a very simple UPS. You see, your consumer UPS is basically four components, an AC-DC converter which looks just like the power supply for your model trains; a battery charge controller which looks just like a PWRgate; a battery; and a DC-AC inverter to provide you 110V AC power back out. It just seems silly to me to buy a box that converts AC to DC, then converts the DC back to AC, just so we can plug back in a power supply to turn AC into DC!

So instead, we’re going to build our own UPS. We’ll use an AC to DC power supply, a Super PWRgate, and a battery. The Super PWRgate is rated for up to 40 amps, so that matches my load information quite nicely. All I need to do is select a power supply and battery. Note though that this also adds to our DC power load. We have to be able to recharge a battery. The Super PWRgate can charge at 1A, 3A, 7A or 10A depending on your battery. Without jumping ahead too much 7A is right for my battery, making my worst case now 26-46A!

For the power supply I looked at Astron. They are a well respected name in the Ham community with a reputation for rock solid power supplies. They seem to be over-engineered, capable of being run well past their specifications without damage. After reading their catalog and thinking about both how I would mount it and the power output I needed I decided on the RS-35M. This power supply is rated at 35A under a 50% duty cycle, and 26A continuous. That means it has the heft to supply my projected load, and still a lot of overhead in case my guess about the load is wrong. I also selected a unit with amp and volt meters so I could monitor the power supply.

Now for the battery. I could write pages and pages on batteries. The Ham sites have some good info, as well as off grid power sites. Basically what it comes down to is this: you need a lead-acid battery, similar to what goes in your car. However, standard batteries (like in your car) are “wet” cells. These can give off poisonous gas in some situations and thus should NEVER be used indoors. Batteries are also designed for “starting” (short, high amp draw) or deep cycle (long, low amp draw), using a car battery for a UPS will greatly shorten its life.

Fortunately there are both “Gel Cells” and “Absorbed Glass Mat” (AGM) batteries. These are lead-acid batteries where the acid is trapped in gel or a fiberglass mat which prevents the poisonous gas. There are many common models made for UPS applications, batteries to power security systems, and all sorts of other applications.

For reasons of cost and size, plus availability I settled on an AGM battery for my application. The only trick then was to size it, which is not quite as simple as it sounds. For instance, the battery I ended up selecting is a “40 amp hour” battery. However, you have to read the fine print, that is at a “10 hour rate”. So 4 amps an hour over 10 hours is 40 amp-hours. 4 amps is obviously not enough power, so what happens if we draw 8 amps from the battery? I know some of you are probably thinking you can draw 8 amps for 5 hours and also get 40 amp hours, but of course it doesn’t work like that!

As you draw more power from the battery it gets less efficient. At a 5 hour rate my battery is rated for approximately 7 amps per hour. A good battery manufacturer will provide some formulas, and there are also some generic ones out there on the web. Long story short after much research and calculating I decided my 40 amp-hour battery should supply 30 amps of power for approximately 15-20 minutes. More than long enough at full load to carry an outage we might have at a show, and also enough to count for the fact that the battery will degrade over time. At 5 years old it may have only 80% of its capacity.

I ended up choosing an MK “ES40-12”. One of the selling points is that this is designed for security systems, and is ok with having no input power for up to 6 months. Most batteries will suffer reduced life if not charged at least every 2-3 weeks, but I was worried that this one may sit from time to time without being charged. Also note why it is important to be careful with batteries, it is rated for a discharge current of 1600A for 5 seconds! Accidentally connect the two terminals and you can get a huge shock! For this reason I purchased a 40A fuse with Powerpole ends already attached and use it in line with the battery. If anything shorts out the fuses will blow and keep something really bad from happening.

There is one last component to the power system. Now that we have protected power we need to distribute it. Each major component should have its own fuse to protect it and the other components. Fortunately the Ham world saves us again, introducing the RIGrunner. The RIGrunner line is a set of power distribution blocks that use standard automotive fuses and have Powerpole connectors. Plug and play simplicity for 12v power distribution. After counting how many outlets I needed and thinking about how I was going to turn things on and off I selected a 4010S, a 1 in, 10 out power strip where one of the outlets can control the power to the rest. In a future article I’ll show you how I am going to use this feature.

Lastly, cooling. Since I am going to put all of this in a box I must have fans to move air and and out of the box. I also need to worry about cooling other components. I decided to have two fans, both for redundancy and for how I could wire them. The first fan is connected directly to the Astron. If the power supply is on, the fan is on. This provides cooling for the power supply, Super PWRgate and battery when just charging the battery. It will also stop if the power supply looses power. The second fan is connected to my master power switch. It is thus on when the box is “powered on”, and also runs off of the battery. This provides more cooling for the other items, and also gives a fan on battery if the power input fails for some reason.

So while my power system isn’t exactly typical, I think it will meet my needs quite well. Even with a 20A load (approximately 35-45 N scale locomotives) there is headroom to charge the battery, and even with a full 35A load of locomotives (70+!) I can still run off battery for a decent amount of time. This should handle even a large loop at an NTrak show and provide rock solid reliability. Best of all, the use of off the shelf components from the ham radio world made it really easy to put together, it just took a little research.

DCC and Portable Layouts

Thu, 13 May 2010 12:40:24 -0500

When setting up an NTRAK or other portable layout there are always electrical issues. Typically there are one or two electrically gifted individuals who are able to track them down fairly quickly; but from time to time you find a particularly vexing problem. DCC has brought a new level of complexity to this process, demanding better wiring but also introducing things like a DCC network that must also be troubleshot.

The NTRAK world has standardized around Digitrax equipment. The reasons why are long and complicated; steeped in good equipment, vendor support, timing, and a few large clubs who blazed the trail. I also can’t do a complete overview of how DCC works, or how Digitrax equipment is designed, not in a short blog post. I will however point to a number of extremely useful resources:

‣ NTRAK DCC RP
‣ North Raleigh NTRAK “Rules for DCC Design and Operation of NTRAK Layouts” (also available in PDF)
‣ Digitrax Manuals and Instructions
‣ Derby City Express “Digital Command Control Design and Operational Considerations” (Update, replaced with a non layout specific version)

The last document is of particular interest to me, as it covers an extremely large NTRAK layout and is one of the most recent documents.

What I have observed over the years is that there are three primary reasons why DCC systems are difficult to bring up on site:

* Too many components are assembled on-site.
* Too many people are involved in the assembly of those components.
* Different clubs use different “standards”.

When you show up at a layout and have to connect the booster, power supply, LocoNet and so on there are lots of opportunities to go wrong. In particular, there are lots of opportunities to cross the polarity of both the power and the LocoNet. You’ll also note I put standards in quotes, there is in fact in all cases only one standards. However for reasons of poor documentation and historical accident many clubs do not follow the one standard, but rather have everything in their club made to some different standard. LocoNet cables that all have the wrong polarity is a common case where this occurs.

Other than to push people to adhere to the standards there’s not much I can do about what other clubs are doing, so instead I’ve decided to take matters into my own hands. I’ve had bits and pieces of Digitrax equipment at home for years so I could run my DCC equipment at home. Now that I have a functional layout I realized that having the equipment just tossed on a shelf wasn’t good enough anymore. Also, now that I have a complete NTRAK layout of my own and there is no local NTRAK club I wanted the ability to “anchor” a show should the need arise.

The answer to me is DCC in a Box. I’m not the first, and I won’t be the last to try this solution. The idea is to build a portable box and pre-install substantially all of the DCC components in it. This way they can be tested at home and the entire box can be rolled into a layout. This should greatly reduce the troubleshooting on site, and should increase reliability since there are fewer components undergoing plug/unplug cycles.

I built a small version of this for NVNTrak several years ago, seen on the left. I know BANTRAK and the KSONS also have similar systems. For my system I’m drawing heavily on what I saw work at the Derby City Express and the great work in the DCC Design and Operational Considerations document produced by John M. Wallis. As with any project, we need to define requirements:

* Must be portable so it can easily be taken to a show.
* Must be easy to use, for a home or small show layout setup, startup, and shutdown should be able to be described on a single 8.5”x11” sheet of paper.
* Must be fully documented so if it does break during a show and I’m not around someone else can troubleshoot.
* Uses the best practices available.
* Must be able to run a single NTRAK loop of virtually any (practical) size independently.
* Must be able to form the anchor of a multi-loop NTRAK layout.
* Must look good, so it is not out of place in the train room at home.

I’ve been planning my Box for years, ever since I made my first one for NVNTrak. I’ve also been collecting Digitrax parts for years; although I still had to buy a few things to make the box a reality. In real life the project is about 80% complete as I write this, but I’ve already shot some video of the early stages and started to compose my thoughts for blog posts. I will be covering:

1. (Uninterruptible) power supplies and distribution.
2. Command Stations and Boosters.
3. LocoNet, including cabling, panels, and wireless.
4. Monitoring, RRampMeters and JMRI.
5. Operating procedures and documentation.

Expect to see the first installments very soon!

Nashville Great Train Expo

Sun, 18 Apr 2010 18:56:39 -0500

The Great Train Expo came to Nashville April 10th and 11th 2010, and the Nashville NTrak guys organized a layout. Participating were folks from the KSONS from Louisville Kentucky, and from CINTRAK from Indianapolis Indiana. The Tennessee Valley Model Railroaders also had an NTrak layout at the show.

The Nashville NTRAK layout, was approximately 100’ x 60’ in size. Rather than have the usual rectangular layout the availability of three inside corners allowed for one end of the layout to feature some additional curves. Getting away from the standard rectangle does a lot to add visual interest to a modular layout. My four 45 degree “Broad Corners” were used to make a 180 degree inside corner to help make this possible.

The KSONS brought two yards and Nashville NTRAK brought one yard allowing ample train assembly, tear down, and parking space. The Nashville yard is notable in that all the turnouts are DCC controlled with routes. Dialing up a single number on your Digitrax throttle aligns all the turnouts necessary to enter or leave the yard.

The one down side to the entire weekend was the low attendance. The previous year a World’s Greatest Hobby show at the Convention Center greatly exceeded everyone’s expectations and was wall to wall packed. This year a move to the Municipal Auditorium and what might have been the most perfect weekend weather since last summer conspired to keep most people outdoors. It honestly might be one of the poorest attended train shows I have ever seen.

There was also an unusual perk. Many of the Nashville NTRAK folks moonlight on the L.A. & Salt Lake H.O. layout in Nolensville, Tennessee. This is a private layout of the Southern Pacific railroad covering over 3,500 square feet! The entire layout is DCC, with full signaling and many sound equipped locomotives. Much of the NTRAK crew spent Saturday evening doing an operating session at this amazing layout.

With no club in Memphis I am an exiled member of NVNTrak. NVNTrak often has 30+ shows a year to and now I’m in an area that doesn’t even have a proper NTRAK club! Fortunately with layouts like this nearby I don’t have to go through too much withdraw. The crew that showed up in Nashville was able to provide a great NTRAK fix. I look forward to showing up in Nashville or Louisville for the next train show to see everyone again!