DCC Circuit Interrupters

Didn't take me long to get rid of the others and convert to the PSX-AR as the protection for every district on my RR.  Even for a four section model RR, the difference in cost is less than that of a new loco.  With all the features of the PSX-AR, why settle for the others?

Bulb section of article

Is the mag still in pre-release? If so...

Bruce, I understand what you mean when you say "Until the current being drawn through the bulb approaches the rated current for the bulb, the majority of the power is routed to the loco. More current draw (a second loco entering the protected section) will result in the bulb getting more of the power, perhaps glowing dimly." however the wording of the sentence may lead some to an incorrect understanding of current flow.

Current through a series circuit is the same at each component. There is no power routing going on. As you well know, the difference is power dissipation. Perhaps change the wording to reflect this better:

Until the current being drawn through the bulb and locomotive(s) approaches the rated current for the
bulb, the majority of the power is routed to consumed by the loco. More current draw (a second loco entering the protected section) will result in the bulb getting more of the power more power passing through the bulb, perhaps glowing dimly.

If you ever decide to do a DC circuit breaker article I have the hot ticket for you. 

Helpful Article

I hadn't fully understood the role of bulbs vs. circuit breakers until now. I especially did not understand the issue regarding the NCE PowerCab. I prefer the idea of full circuit breaker protection so a PSx is on my DCC wishlist!

More on using bulbs for short protection

For more on using 1156 bulbs for short management on your DCC layout, here's a web link with lots of insightful details ...

http://www.members.optusnet.com.au/nswmn/1156.htm#i1156test

One of the cooler things Marcus Ammann has done on this web page is do an in-depth study of amperage draw and the effect of the lights on voltage drop. Very cool and helpful.

Marcus has done his homework, too. An 1156 bulb will limit current to 2.1 amps, while a two-filament 1157 bulb (if the filaments are wired in parallel) will increase the current limit to 2.68 amps. Wiring two 1156 bulbs in parallel increases the current limit to a whopping 4.2 amps.

This means using something like:

1. Two 1152 bulbs in parallel (17 watts) would give you a 2.68 amp current limit
2. Two 1142 bulbs in parallel (18 watts) would give you a 2.88 amp current limit
3. One 1156 and one 1152 bulb in parallel would give a 3.44 amp current limit

Sounds to me like an 1156 and 1142 bulb in parallel would allow 3.44 amps to flow, which would not limit loco consists as much, yet keep the current low enough to not get bad damage from the short. Using two 1156 bulbs in parallel lets over 4 amps flow in the short, which is high enough it may cause the booster short protection to trip.

So working your way up the list you have:

1. One 1152 bulb - 1.34 amp limit
2. One 1142 bulb - 1.44 amp limit
3. One 1156 bulb - 2.10 amp limit
4. One 1157 bulb - 2.68 amp limit (if both filaments wired in parallel)
5. Two 1152 bulbs - 2.68 amp limit
6. Two 1142 bulbs - 2.88 amp limit
7. 1156+1152 bulb - 3.44 amp limit  ~ sweet spot?
8. Two 1156 bulbs - 4.20 amp limit
9. Two 1157 bulbs - 5.36 amp limit (if both filaments wired in parallel)

This allows you to tune your layout's amp draw and short flow limit to your liking. Going with ~3 amps seems about right, but going over 4 amps isn't a good idea since it would allow shorts to start doing more serious damage.

Charlie Comstock is using Power Shields, and he has them set at 3 amps, so the ~3 amp limit sounds like a good compromise. I'm currently using the 1156 bulbs on the Siskiyou Line but the 2.1 amp limit is too low when we've got a train with helpers (4-6 locos) on the train - the 1156 bulb filament starts to glow orange and rob power from the locos. I'm thinking of adding an 1152 in parallel and upping the limit to 3.44 amps.

For a few bucks you can do the bulbs in various combinations and see what you think. For the most universal protection, going with the power shield circuit boards is better, but it's going to cost a lot more.

Finally, the biggest problem these days with the auto tail light bulbs is they're being phased out and replaced by LED equivalents and LEDs don't behave the same as incandescents, so you won't get any short protection at all with LEDs.

Bulbs and breakers

In my view the biggest issue with relying on incandescent lamps to limit current is their inherently slow rise time.

In the event the short circuit causing connection is not tightly contacting then arcing is possible for an incredibly long time compared to the speed of electricity. The bulbs may prevent plastic side frames from melting but they are poor protection from arc induced pitting. Reduction of arcing was a primary objective in the design of my home brew circuit breakers. With a shutdown time of ≈20u seconds they have completely stopped the current flow long before a bulb even begins to glow when a short occurs.

Granted my breakers are not compatible with DCC. But for DC and RailPro layouts they vastly outperform tail light bulbs for roughly the same cost. 

Thanks for the suggestion, Alan.

However, it it too late for the change. That is one of the problems with proof-reading, especially your own work. You KNOW what you are tintending to say, so it is hard to understand what isn't working. I can't even blame the staff proofreader.

Anyway, it is clearer the way you rewrote it.

Thanks.

Bulbs vs, Breakers

As the readers can see from Joe's posting, this is one arena where we disagree a bit.

The good news is that Joe allows dissenting opinions in his magazine.

When folks discuss the WHY behind the WHAT, then we all learn and grow and can understand.

Joe's addendum on how to adjust the trip current is helpful for folks using bulbs. Thanks, Joe.

Improved the experience.

Our group decided the Digitrax DCS and DB units acted as their own short protection and set up with this understanding for years. The growth of the group and layout caused many pains as we went from 8 members and 20 modules to over 20 members and 70+ modules. We would set up at shows and running trains was like rolling dice. After the melting of many sideframes and the possible loss of a sound loco the group finally decided to look for a better mousetrap. We went from a command station with four DCS/DB districts with no additional short protection or Loconet support to a command station plus master LNRP with 5 DCS/DB plus two PSX/PM42 and LNRP's with each district. Also fresh batteries for throttles and DCS/DB units for every show.

The results were an experience that was much more enjoyable by all. No more reliance on one guy to set up and manage and problems are isolated making trouble shooting easier to track down and correct. The other benefits of the circuit protection were the errant operators only cause problems in a small area rather than an entire booster district.

Using the short circuit protection sure made running trains fun again.

Powercab Options

Very timely article - working on converting my DC layout to DCC.  Long way to go before I plug in my DCC system (Powercab).  It is a modest 40"x110" layout designed for one operator.  

As I read the article  I can use the NCE CP6 bulb system to offer some protection or go for the more expensive PCX or PowerShield X series.  Are these the only two options for Powercab users?  

Given I have a turn table on my layout I will also need an auto-reverser.  I read that the AR includes a circuit breaker.  Is there one unit that will provide short circuit protection for my layout and auto-reverse for the turn table?  

(Does it matter I'm using an vintage Arnie-Rapido ancient of days N scale turn table or is that irrelevant?). 

Maybe I'll just need to be patient and await the promised article on auto-reversing.  

We may be close than you think

We may be closer than you think, Bruce. My only contention with the bulbs is they are *a lot* cheaper and they do work after a fashion - perhaps good enough for some. I have used and still use the bulbs on the Siskiyou Line but they're not flawless and they do not work with some boosters like EasyDCC or Lenz.

As LEDs replace incandescents, the question may become moot - I'm guessing within another 5 years incandescent auto tailight bulbs will become as rare as hen's teeth. You will be able to get an 1156 "bulb" but it will be an LED equivalent that fits in the same socket - completely worthless for short protection.

So the whole bulb approach is going the way of the dinosaur and soon the short protection boards will be your only choice. And I won't disagree that as to how they perform, the boards are superior to the "poor man's" bulb option.

DCC Circuit Interrupters

Bruce, don't be too quick to dismiss the Digitrax PM42 because it has relays and is not fully solid state. It has one major advantage for modular layouts that are set up at train shows, and where the layout configuration is different with each show, e.g. NTRAK. The PM42 has a LocoNet connection. Using JMRI software this allows adjustment of both the trip current and the response time on the fly as necessary to keep the layout operating smoothly.

Our club has used 4 PM42s since they were introduced about 15 years ago, and have never had a problem with them.

John Wallis

North Raleigh Model Railroad Club

slow 1156 bulb issues

I found the slow response of an 1156 required me to use the long short recovery delay on my Digitrax boosters. Otherwise, the bulbs didn't light up fast enough to prevent over current and the boosters would deduce the short was still present.

I bit the bullet a few years ago and replaced all 1156 bulbs with PSX circuit breakers. Now the dreaded "beep beep beep" - short detected sound from the Digitrax units is never heard.

Charlie

David, re: Powercab Options

For one user and on such a small layout you have a few options:

Use the PowerCab's built in protection. It will trip nicely. However, when it does, it does a complete reboot, which can take the fun out of it, as you are down for several seconds (10 - 15) and when it comes back up, your loco speed is set to zero and the direction set to forward.

Adding one 1-amp bulb in series with the track feed will be much less expensive than the CP6 and will keep the PowerCab from shutting down and rebooting.

A PSx with a normally closed pushbutton switch between J7-1 and J7-2 with a jumper (J6-1 to J6-2) to select 1.27 amp trip current will be the most elegant and expensive (about $35 to $40) solution. The PowerCab should never reboot, but you will have to push the button to re-energize the layout after every short.

Charlie

Your layout runs very nicely now! Thanks for the Op Session last fall.

The addition of the audible

The addition of the audible alarm on the PSX is especially nice, but it mostly points to the same operators.

I didn't mention the alarm in the column.

I didn't think about it. You can add a Mallory Sonalert to eyelets on the board and it will squeal like a pig when the breaker trips and continue to squeal until it successfully resets. It will not stop when the breaker "tests" and discovers that a short persists.

Our club uses them and other layouts that I operate on regularly are split, some do and some don't.

Personally, I like the silence.

In the district that I'm scenicing on our club layout, I have installed a +5V and +12V power supply to power lights in (almost) all the buildings. The power from the power supply runs through a relay that is activated by the DCC in the district. Thus, if you short in the district, the town goes dark . . . and, since it is our club, the PSx squeals like a pig. Personally, I feel that having the district go dark is a strong clue by itself.

I refer you folks to my grandmother's statement, that I've quoted before: "It's a good thing different people like different things. Otherwise every woman would be in love with my husband."

Why a manual reset

What is the purpose or need for a manual reset button when using the PSx with a PowerCab?

PowerCab Reset Button

The button keeps the PSx from retesting the short.

Without it, the PSx will trip and then it will retry the short. This puts the short on the PowerCab twice in a small amount of time. The PowerCab will then shut down.

In other words, the PSx is useless on a PowerCab without the switch because the PowerCab will go down no matter what.

Hope that makes sense.

Thanks Bruce

It does make sense.

thanks

OK - some good options.  

I now need to find a good purpose for the six tailgate bulbs I bought for this purpose which are not going to help me.   I'm out $1.24 x 3  .... good thing they were cheap like borscht.  

I am going to be wiring a turntable which will need an AR - and as I understand it they also double as circuit protector?  Will have to wait for that article.  I'm some time away from re-starting trains on my layout - still working on wiring turn outs and building a control panel for turn out control, lights, turn table and other things.  

O scale Diesel sound Installation

Good Timing, I just installed that same decoder on my Atlas O Scale SW9. I am very impressed by the sound and all the capabilities that the decoder have. Excellent decoder. QSI did a mighty fine job. And just like the article mention it is a big decoder because it was really meant for G scale.

Thanks for sharing an interesting article

Bruce,

As someone who is embarking on a DC to DCC conversion I found your article "DCC Impulses - Short Protection" both timely and useful.

Locally different friends who are layout builders and owners have chosen and implemented different options, some all bulbs, and other different varieties of breakers. I really appreciate your analysis of these options and their issues. It is great to have this all available all in one place....

Thanks Again John Green - Modelling the CPR Kettle Valley Division - Coquihalla & Merritt Sub Divisions in HO Scale circa 1955.

Turntable wiring

David -

You can find my notes on turntables and auto reversers at the bottom of the Layout Wiring page on my web site: http://mrdccu.com/curriculum/wiring.htm

I'm always leary when the new

I'm always leary when the new is best and the model before is now not so good.  I was curious about PM42's versus electronic circuit breakers, is there really that big an issue.  And is it that big an issue in N scale, so I did a wee search of the net:

1. PM42's failing - "Our club in SW Florida installed 13 PM42's in 2004. Over the years we have seen half fail. Some due to electronics and others were relay contact problems. Our layout is large and relays over time will fail due to load and arching of contacts during short circuits.Today we are half way through converting to PSX and PSX-AR units. All the installed PSX and PSX-AR's are functioning great. We have added Sonalerts and Remote Status LEDs indicators.We especially enjoy being able to run 4-5 QSI engines on one power district. This was not possible before. They would not restart on the PM42 after a short.I've been an electrical engineer and involved in electronics for 50 years. The Command Stations/Boosters and circuit breakers/RL controllers are the base of the DCC infrastructure. Over time infrastructures must be upgraded or expanded. This is what I see in converting from the PM42 to the PSX and PSX-AR modules. The new modules are solid state and are designed for the higher current demands of today's DCC engines. Happy customer, "
- Lee D.

2. PM42 voltage spike: ""I have personally seen a number of decoders reset (sometimes partially, sometimes completely) following a short circuit. One explanation I have heard (but have yet to test personally) is that the scramble is often the result of a strong voltage spike when that energy is released. As a side note, I have only seen these spikes happen when using PM42s and not when we switched to PowerShields, and after that, not since upgrading to the PSX breakers."
- Doug B.

I am not defending PM42's even though I have two on my layout, but I will say the above two issues I haven't run into locally with Digitrax users here.  I don't have any PSX's on my layout but I do have two On Guard - Auto Reversers (they are electronic) which are the poor man's PSX-AR and I'm happy with those, will be installing a third soon.

With the PM42's I'm wondering if this issue is less in N scale, with less power demands and or should I say "consumers."