power supplies

[pdlethbridge]

When you have more than a few (3 or 4) decoders, you should have another power supply? right
?  I have 4 engines and 3 stationary decoders. I have 2 decoders that operate the switch machines, with the possibility of adding a 3rd later on. Each has its own wall wort. The other stationary decoder is for the turntable and roundhouse lights. 3 locos can be in the roundhouse and their  track can be turned off so that I'm only running at most 2 decoders and the turntable decoder can be turned off as well.. The only other electrical device is the auto reverser, is that considered a decoder too? With the NCE power cab, I should have enough juice for all this. Any thoughts or suggestions would be highly welcome.
Paul

[Yampa Bob]

Paul
You might want to download the "Combined Document" (1.58 mb).  This PDF has a lot of information about DCC voltage losses, even if you don't buy the meter.

Don Fiehmann, author of "The DCC Guide" and Mike Polsgrove, author of "DCC Projects and Applications", both recommend the RRAmpmeter. I bought both books this week at Caboose Hobbies, very informative stuff.

http://www.tonystrains.com/technews/rrampmeter.htm

I'm considering ordering the RRAmpmeter, if anyone has it please review and advise.

[Nathan]

I have two RRAmpmeters I use with both DCC and DC.  I put one on the output of the booster or power pack and use the other to check the voltages at various places around the layout.

If you find that you are using 75% or more of the boostes rated output then you should use an additional booster.  Make sure you choose a logical brake point so that the load is shared between the boosters.  This can be done by setting some temporary blocks on the layout and using the two meeters ot see if the load is about even.

[pdlethbridge]

now I'm really confused. Bob, didn't you say the other day you liked the ez command because it was so simple to use yet here your flying way, way over my head with this. 

[Yampa Bob]

Yes, I do like the simplicity of the EZCommand for my small layout.  But I also like to keep up with the technology, not only for my own benefit, but also so I can help others.

With DC, you can use two VOMs, one to check voltage, the other to check current. But since DCC is not a 60hz sinusoidal waveform, only a true and properly calibrated RMS (Root Mean Square) meter can accurately measure DCC power. Page 3 of the PDF has a diagram to show the difference in waveform and frequency.

We generally refer to DCC as "AC", as the voltage does alternate from plus to minus, but the similarity ends there. Note the frequency is 118 times as fast as ordinary household AC. (7100 hertz, average)

The Global Positioning System (GPS) uses a similar waveform, but it takes 4 different sattelites to accurately determine position, and the "packet" contains much more information.  

The questions you asked could be answered by a lot of calculations if the current requirement of the devices are known, but they wouldn't take into account all the various voltage losses around the circuit.  The easiest and quickest way to determine if your power supplies are adequate is to measure voltage and current at the device.

The information wasn't intended to confuse you, but a more sophisticated system also requires a greater knowledge of how that system works. If you will slowly read through the PDF several times, it really isn't that complicated if you have a basic understanding of voltage and current.

Having said all that, it's really as simple as buying the RRAmpmeter and doing the tests.  For a little more than the price of two digital meters, the RRAmpmeter does it all with only 2 simple connections.

Nathan,
I assume your comments to be a favorable review of the RRAmpmeter.  I will probably order one at some point.

Thanks 

[pdlethbridge]

I think I got another brain cramp. Bob, I love your explanation, but it is still too far over my head. I still have to think about which way to turn a bulb to screw it in. I'm more a mechanic than a electrician. I did read the article and saved it to my computer but it was over my head as well and really crossed my wires. Oh, I hate being SHORT. (pun intended)

[Yampa Bob]

As mentioned repeatedly on all sources, including this forum, the first step is proper wire sizing for buss and feeder wires, not just for the present, but also for anticipated added devices.  If there is any doubt always use the larger AWG wire size to be safe. For HO scale buss, this generally means a minimum of 12 or 14 gauge. This is referred to as the "ampacity" of the wire for acceptable voltage drops.

The sizes listed in the PDF table is for 1/2 volt voltage drop. Distances are usually indicated as "round trip" lengths. "Volts" only provides the potential for work, "Current" does the work, and moving electrons produce heat.

The number of strands in the wire is also very important. My buss wires are on the order of 52 strands.  If wire sizing is correct, then usually the worst to happen is a tripped breaker in the power supply if you exceed its current limits. Using wire that is too small not only increases voltage drop in the run, but also produces excess heat to the point of melting something or causing a fire.

I continue to "harp" on the matter, but a VOM is an absolute essential tool for model railroaders.  Without one, you're just shooting in the dark.  As noted in the PDF, there are all sorts of voltage losses, including the track and joiners.

Jim Banner has graciously volunteered to write up a tutorial on using VOMs, and is probably drafting it "as we speak", so I won't elaborate on the subject here except to answer specific questions. However I want to mention that taking voltage and current measurements is only half the procedure.  The other half is interpreting the measurements as applies to the circut.  For this you need a basic understanding of "Ohm's" law and to a lesser degree "Kirchhoff's" laws.  I'm sure Jim will address these laws in his tutorial.   

[pdlethbridge]

Don't forget Paul's law If it ain't broke, don't fix it!

[Yampa Bob]

Ok, then I can give you a "shoot in the dark" answer.  IF you are confident that your wire sizes are adequate; IF all your devices are operating normally; IF the power supply overloads aren't tripping, then it probably isn't "broken", so don't worry about it and have fun. 

However, if devices are sluggish, breakers tripping, locos running too slow, etc, then it needs "fixin".

I have been following your progress on installing all this stuff, and I don't think your brain is as cramped as you might think. Actually, I'm quite impressed with your fortitude and perserverance.  Tell you what, you just hold the light bulb and I'll turn the ladder for you. 

[CG04]

Hey Bob,

I'm not sure we can handle many more of your three day trips to Denver.

Clif

[Yampa Bob]

Hey Clif,
If you think it's bad where you are, you should see my office. It's building up faster than I can shovel it out the door.  LOL.  Actually you can blame Paul, he asked the question.  Right now he's thinking "Why did I ask?"

There is a definite connection with my trips to Denver.  Caboose Hobbies has just about every book published on model railroading electrical and DCC.  So far I've perused about 1/4 of their library, and only found 2 books worth the price.  Not surprising, they are both Kalmbach publications. But don't worry, I'm going back next week for more reading.

I learned electronics many years ago, and have studied (and used) GPS for about 6 years.  DCC is not a new "rocket science", it's merely a new application for an existing technology.  I'm attempting to impress on readers to not be afraid of the technology, broken down it's just "nuts and bolts" stuff.  We are more used to mechanical applications, where we can actually see parts moving.  Electricity is really no different, there are parts (electrons) that move, we just can't see the action, only the result. (the loco moves). 

In a previous post I mentioned "RMS" voltage, but didn't elaborate as I didn't want to bore you to tears.  So here is a site that has the simplest explanation.

http://www.ee.unb.ca/tervo/ee2791/vrms.htm

Ok, I'll sit down now and let someone else contribute. 

[pdlethbridge]

I'll even make it easy for you, Bob, I'll put wheels on the ladder. I just got my second ds-64 installed and I have 3 switches wired in. That will complete the wiring until I get the other half of the table built. The ds-64's have their own power,  a.k.a. wall wort, My problem now is how to program it so I can operate the turnouts its wired to. I followed the instructions to the letter, but maybe I was supposed to go to a different letter???

[fieromike]

Your PowerCab has a built-in ammeter. you can use it to determine total amperage used on the track.
Go to "Cab Parameters" by pressing
PROG/ESC button, I think 6 times and the first item is "Ammeter". Select it
"ON" and see what the Power Cab shows for the actual current to the track.

[Yampa Bob]

Paul, I believe the book "The DCC Guide", may have the answers you need.  There is a brief section on "Accessory Decoder Programming."  I'll send the information email.

[pdlethbridge]

After doing a lot of research, I found that you have to have a loconet connection working to program the second stationary decoder (DS-64) I also found out that you shouldn't have 2 power sources for the DS-64, Wall wart and track. I also found out that this has made me very sleepy and I'm about to solve that problem