FORUM CLINIC: 12 years using DCC - SIGNIFICANT NEW INFO!

[tsasala]

Joe,

I've been researching DCC for a while now, and with my system on its way, I happy to see all this information in one place. Although I've been able to cobble together the same basic information by going to tons of web sites and reading a lot posts, it was a lot of work and very hard to put all the pieces together. This series really helps codify everything and provides a very nice "big picture" view. Where were you 6 months ago! ;) Kudos and thanks for all hard work!

-Tom

[selector]

Thanks for the quick response, Joe.

In a way, I am set up like Chip is; we have monolithic layouts with feeders to reduce voltage drop, and that is the limit to our sophistication. In my case (unsure of Chip's), I have no gaps. So, I could merely cut some gaps between each of my 3 sets of feeders, thus creating blocks (not 'districts', because each should have a booster). Then, wire a single bulb into each, in series, and since I only run a max of two trains (currently, each with sound), the single bulb per block will do the trick with ease as no more than two locos will ever be on any one block by chance. A loco fortunate enough to be on another block when the short appears will continue on its merry way because no resisting bulb is sucking that block's current up.

Sorry if I seem to be monopolizing the thread just now, but if you answer in the affirmative, I am on my way.

[jfugate]

Selector:

You got it right ... just think "loco consist" instead of a single loco. All locos in the one train block are affected by the short because the bulb will suddenly absorb about 2 amps and let almost no current get to the locos, so they will come to a stop.

Once the short is removed, all locos in that one train block will resume running and the booster will not think there ever was a short -- just a spike in current, as if you suddenly put a whole bunch of locos on the track at once.

[jfugate]

QUOTE: Originally posted by SpaceMouse

Yup, I like sound.

However, I must be missing a point here. I'm getting a Zephyr, which has a max output of 2.5 A. With the lightbulb, I'm limiting the output to 2A.

Why am I doing this?

Chip:

Yes, that's my point. Just putting a lightbulb on a single block feed to your entire layout will do just what you said -- limit your 2.5 amp output to 2 amps, for no real benefit.

If you don't use a lightbulb, you get the full 2.5 amps output to your layout, and the booster will "beep beep beep" when you get a short and then reset once you remove the short.

BUT -- and this is a big *but*, if you have from 2-4 (or more) QSI sound locos on the track and you get a short, once the short is removed, the QSI's have a high "inrush current" and the booster will think there is still a short on the track and won't reset until you start taking QSI locos off the track until the booster finally resets.

Now if you put a lightbulb in one of the two track feeds to your 4x8 layout, when a short occurs, the booster won't shut down at all, so things come right back after the short, even with 4+ QSI locos on the track.

However, you still have the 2.5 amp output but the 2 amp limit of the bulbs. If you bust your 4x8 in half, with 2 train blocks, *each* connected to a bulb, you get 2 amps per half. If you have 2 amps worth of locos on one half of your layout, you can have .5 amps worth on the other half and the bulbs will like that just fine.

In other words, by busting your layout up into train blocks (all still wired to the same booster), you are assuming you won't have more than 2 amps worth of locos in any one train block protected by the bulbs. You spread your full booster output across several 2 amp limited train blocks.

By making each sub-block the size of a train, you are assuming no one train on your layout will need more than 2 amps, which is a pretty safe assumption unless everything is QSI locos and you run more than 3 QSI locos per train.

Typical HO loco current draw:
non-sound = 0.2 amps
Soundtraxx = 0.4 amps
QSI = 0.6 amps

The other thing you can do, Chip, since you just have a 4x8 is to connect two 1156 bulbs in parallel on one of your track feeders, which will up the current limit to about 4 amps instead of the 2 amp limit of a single bulb.

Then you will be protected from shorts shutting down the layout when you run sound equipped locos, and you won't have to gap anything. However, a short will shut down all trains since you won't have any separate train blocks to isolate the effects of the short. But you will get the full 2.5 amp output of your system to the track with the two bulbs in parallel.

Yet the booster won't see the short so it will recover immediately even with lots of sound locos on the track. So you have options.

[selector]

I am a convert. [bow] Drive me to Wal-mart, Master.

Thanks, ever so much, Joe. I will have to spend some time getting this to solidify, but the the video is clear proof of concept.

So, if I understand, the more locos drawing current (volt-amps) in a given district, the more potentially lethal the short. The bulb offers a sink to the shorted power by glowing brightly and minimizing the detection of the short by the booster. Locos keep running and they stay cool. Only the one loco in that particular feeder block encounters the short.

Is that right?

[SpaceMouse]

Yup, I like sound.

However, I must be missing a point here. I'm getting a Zephyr, which has a max output of 2.5 A. With the lightbulb, I'm limiting the output to 2A.

Why am I doing this?

[jfugate]

QUOTE: Originally posted by SpaceMouse

Can I assume that if I'm running 3 trains on a 4x8 layout, that I need only one bulb to protect everything?

It depends on how many locos per train and if any of those locos have sound.

Assuming 1 loco per train and nothing with sound, the normal short protection of the booster should be good enough.

The bulb is best used to mask the short from the booster with multiple train blocks on your layout or with sound locos on the layout.

You only need to mask the short if you have sound locos or if you have a large enough layout that you want to run more than one train and let it keep running even if other trains get a short. On a 4x8, allowing another train to keep on running is of limited value on the main because the train causing the short may be in the way of the other train.

However, if you have a small yard or significant passing siding on your 4x8, you might want *two* train blocks with each protected by a bulb. That way, the guy working the yard can keep on running even if you short something on the main, and vice versa.

But one light bulb and one big train block on the layout is only of value if you have sound decoder locos. The reason is because sound decoders on the layout can prevent a booster from resetting after a short since they have higher current draw than regular non-sound locos. The high current tricks the booster into thinking there is still a short so it won't reset.

The bulb prevents the booster from ever seeing the short so the booster stays up, even with sound locos on the track.

Make sense?

[SpaceMouse]

Can I assume that if I'm running 3 trains on a 4x8 layout, that I need only one bulb to protect everything?

[n2mopac]

Thanks for the video Joe. It was helpful to see it work, and it came through smoothly evenon my dial-up connection.

I think my answers are slowly getting answered, and I'm sure the wiritn post will help immensely. I am an electrical dummy, but do I understand right that with this process I need larger powere districts only for each booster, and not with breakers for electrical protection? I am also unsure how the bus stricture works withing each larger district aas it feed each sub district or block, but this will probably be covered in the wiritn post.

Thanks again for all this great info.

Ron

[Anonymous]

The secret to the "bulb" trick to protect districts from shorts is that a tungsten filament bulb has about a 13/1 hot to cold resistance. Therefore the bulb acts like a short circuit when cold (no short) and as a current control device with a short and when the short is bad enough, the bulb will light limiting current to the bad section.

[Anonymous]

As far as a programming track, I use a section of my main track that is insulated and can be switched from normal DCC to the programming output of the controller. This works very good and I don't have to remove my locos from the track.

[ereimer]

happy birthday Joe !

i suggest everyone click on the link in joe's post . seems today is his birthday and he's giving all of us a present

thanks !

[jfugate]

Since my video volume 3 on all things DCC releases in a few weeks, the distributor has moved the video clip on short management to the top and has made a large broadband version available for those with a fast connection.

See: http://mymemoirs.net/preview.php

You'll need Flash Player 7 to watch it ... most people already have that plugin installed in their browser. If you don't there's a link on the page to download and install it.

[Bikerdad]

Thanks Joe, I look forward to it.

[jfugate]

Biker:

I solder wires to the end and side of the bulb, add crimp spade lugs, and connect them to a terminal strip. I hang the bulb under the benchwork with a 3/4" plastic cable clamp and a 3/4" drywall screw.

I'll explain all this in more detail, plus photos, in my next post.

[Bikerdad]

Very informative Joe. I'm thinking I'll probably go with a combination of the electronic devices for breaking the layout down into power districts, and then bust each district down into power blocks using the latbubs. In part, I like this approach because it addresses the matter of reversing loops, which undoubtedly is going to be a topic down the road in this clinic.

I'm still unclear though on how to mount / fixture the lightbulbs.

[jfugate]

QUOTE: Originally posted by Trainnut1250

Joe,

To see if I understand this correctly. The bulb is limiting the load to two amps or less per district or block. This will limit my locomotive loading to keep under the two amp "current limit". This means that I will have to have smaller districts than I might have if I were to be using 5 amp boosters as seperate power districts. My payoff is that the bulbs are quite a bit cheaper than boosters or breakers, will achieve the same effect and I can limit my shorting shutdown to very small areas. Roughly how many bulbs are on your layout and how are the laid out in terms of trackwork vs bulbs (ie. more for yards etc???)

Trainnut:

I have about 20 bulbs on my layout and the same number of train blocks. My mainline is 360 feet and I have about 1200 feet of track total.

A lot of this will probably become more clear once I do the wiring post.

You can have 5 amp power districts, just as you do today. You are assuming you won't draw any more than a total of 5 amps in that power district, so nothing changes there.

You then subdivide the power district up into 2 amp sub-blocks -- or 1.75 amp sub-blocks to give yourself a safety margin. This means you need about 3 sub-blocks in that power district, with the bus to each sub-block having an 1156 bulb in series on one of the feeds. You connect all the track feeders to the sub-bus, so that sub-block of rail is protected by the bulb.

If you have very many sound locos, you essentially need to double or triple your power districts to handle all that increased current. But per 5A power district, the process is the same - about 3 sub-blocks (gap both rails) protected by an 1156 bulb. That's an extra bus wire (12 guage wire) and $3 worth of 1156 bulbs to get this protection.

It took me and one other guy three 8 hour days to rewire the Siskiyou Line to have the bulbs. We had to cut more gaps, run a third bus wire around the layout, and wire in a bulb between one main bus wire and the local train block sub-bus wire.

I knew the bulbs helped prevent shorts from registering booster but I was amazed to see how trains in other sub-blocks on that same booster kept on running even when one of the sub-blocks to the booster was shorted.

[jwr_1986]

Joe, I retract my previous thought about the light bulbs. I just realized that because it was a high resistance load, neither would have protected the locomotive. I might just have to give this a try on our clubs layout. (The light bulbs not the melted locomotive) Thanks again for your clear and courteous responses.

Jesse

[Anonymous]

Joe,

To see if I understand this correctly. The bulb is limiting the load to two amps or less per district or block. This will limit my locomotive loading to keep under the two amp "current limit". This means that I will have to have smaller districts than I might have if I were to be using 5 amp boosters as seperate power districts. My payoff is that the bulbs are quite a bit cheaper than boosters or breakers, will achieve the same effect and I can limit my shorting shutdown to very small areas. Roughly how many bulbs are on your layout and how are the laid out in terms of trackwork vs bulbs (ie. more for yards etc???)

[jfugate]

QUOTE: Originally posted by ereimer

Joe , in your "DCC and Realistic Operations on the Siskiyou Line" DVD, one of the attendees raised the question of how does the 1156 bulb affect block occupancy using the current detection method . your answer was you hadn't gotten that far (in your detection / signalling project ) , but that the 1156 might cause a problem . any further info on that yet ?

ereimer:

Still no progress to report there. However, a lot of water's gone under the bridge since then around how the bulbs operate and do what they do, including some testing to determine what they do to the circuit when cold.

What I've seen so far leads me to believe the bulbs have virtually no effect on the circuit until the current reaches about 1.75 amps. Beyond that the bulb starts to limit the current flow, capping somewhere just under 2 amps. Between 1.75 amps and 2 amps the bulb starts to glow slightly .

If you have lots of locos in the train block and they make the 1156 bulb start to glow, you will start to notice the loco speed starts to flatten off. Cranking up the throttle doesn't translate into more current to the motor because the bulb is starting to limit the current.

With train length blocks and the typical current draw of a modern HO loco being around .2 amps or so, that means you can have somewhere around 8-10 locos on your train before you will start to notice this behavior.

Now with sound equipped locos, things start to get much more limiting. You will only be able to have about half the locos in the train block with Soundtraxx decoders, or about 1/3 as many QSI sound locos.

In other words, figure 4-5 Soundtraxx locos before the bulb starts to limit the loco speed, or 2-4 QSI locos. This is with train length blocks so we're talking per train.

The other option would be to wire two 1156 bulbs in parallel per train block, which should up the current limit to about 4 amps per train block.

[jfugate]

QUOTE: Originally posted by jwr_1986

I saw a highresistance load short on a bulb protected block and melt an engine once. While the breakers may be considerably more expensive they are the only safe way.
Jesse

Jesse:

Let me add that in 5 years of operating the Siskiyou Line about once a month with the bulbs for short protection, I've never seen any damage done to locos, rolling stock, or track from a short.

For every short protection device we might use, you will be able to find a case where it failed. There is a saying in legal circles that "deciding a case based on the exception is bad law."

You need to decide based on what's typical. And based on what's typical from several people's experiences, the light bulbs do the job for far less money than more expensive devices.

[ereimer]

Joe , in your "DCC and Realistic Operations on the Siskiyou Line" DVD from the clinic you gave at the 2004 NMRA convention , one of the attendees raised the question of how does the 1156 bulb affect block occupancy using the current detection method . your answer was you hadn't gotten that far (in your detection / signalling project ) , but that the 1156 might cause a problem . any further info on that yet ?

btw the dvd is great , i found it very helpful in explaining DCC , also it's a good intro to your other videos , which i'll be ordering when my paychecks catch up to my paypal account !

[jfugate]

QUOTE: Originally posted by jwr_1986

Joe, every item you've discussed makes good sense to me except this one. Circuit breakers are the solution to go for here because they stop all current flow not just some. I saw a highresistance load short on a bulb protected block and melt an engine once. While the breakers may be considerably more expensive they are the only safe way. My opinion of course. Thanks for the other good tips though.

Jesse

Like I said in the beginning of this FORUM CLINIC, you may not agree with me, and that's fine. We can continue to disagree and that's okay. If we all agreed on everything, life would be pretty booring!

In theory, Jesse, I agree with you. Stopping the current rather than limiting it would certainly be the perfect solution. In practice, there are several considerations that make the ideal not as perfect as it might at first appear.

1. Cost
It's hard to beat $1 per train block for short protection. At $30 each for a Tony's Power Shield, it will cost you a lot more per train block to get a layout that absorbs shorts and doesn't affect anyone except the guy who caused the short.

2. Simplicity
The non-bulb electronic circuitry solutions don't always work as you would hope in all situations, like on booster reset after a short. The humble light bulb does what it does without any fancy circuitry, so it's actually more predictable. You throw the load in the block to about 2 amps or more, and the bulb's going come on and limit the current - guaranteed. You can't get more simple than that.

3. Practicality
For all practical purposes, limiting the block current to a maximum of 2 amps no matter what is as good as dropping the block current to zero when you get a short. The net effect is the same: no short at the booster and instant resets once the short is removed. While the electrical result is very different, the practical result on your layout is the same, and that's what matters to the guys operating your layout.

Electronic gadgets are cool and to a purist they are not as "sloppy" or as "crude" as an 1156 bulb. But if you turned it all into a black box and never explained to those operating the layout what made it short proof, the result is the same. They just know they could run and didn't have to worry about shorts shutting things down.

Sometimes the low tech solution is actually more elegant and I think the humble 1156 bulb fits this characterization well. Also, I ask those who disagree to point to their example layout that "absorbs shorts" without incident the way the Siskiyou Line does and then we can discuss the pros and cons.

As it is, the 1156 bulbs have been field tested on large layouts (mine, Marcus's modular group [see previous post], and my friend Charlie Comstock's layout, to name a few) and work very well -- and they didn't break the bank doing it.

[jfugate]

BikerDad:

You ask about the power shield / circuit breaker devices ... they don't always seem to work like you hope. Here's a posting on the DCC4everyone Yahoo list made by Marcus Ammann from Australia. He was experiencing problems with DCC shorts and booster recycling with lots of sound decoder locos on the track in his modular group, and stumbled upon the light bulb option.

After trying it out, he's totally sold on the light bulb approach, and has been expounding it to everyone who will listen. Here's some of what he's said recently:

QUOTE: Comments by Marcus Ammann posted on the DCC4Everyone Yahoo list
Back in July last year while building a demonstration DCC module I came
across this problem, more than one Soundtraxx equipped loco in the same
power district and my NCE EB3 circuit breaker would not reset.

I looked on all the lists and found on the Digitrax list that some
modellers were having this problem. I posted on the NCE, Soundtraxx and
QSI list my test results and asked for some help.

I looked up Tony's site and under his auto reversers, that since has
been updated, a statement about Sound Considerations at:
http://www.tonystrains.com/technews/dcc_autoreversers.htm
and it said that the reverser had problems resetting with Soundtraxx
locos in the same power district.

Mark Gurries on the NCE group suggested I wire a 12 volt lamp in
parallel with my NCE EB3 and I tested with different wattage lamps and
was able to get the results I wanted with 5 - 10 watt lamps.

Tony's Power Shields, Digitrax's PM42s and PM4s as well as the NCE EB3
were having the problems along with some power boosters. I helped a
couple of U.S. modellers get their layouts running properly, but they
were happy to fit the "fix" if it meant be able to have normal trouble
free sound loco operation, One was a Digitrax user and the other was an
NCE user.

Many modellers with BLIs were very disappointed with the booster
inability to reset after a short. I have only Soundtraxx units and I
have the problem.

I had the same problem when I connected my EB3 directly to my Command
station/booster track outputs and only one piece of track on my work
bench, so in my case nothing to do with my layout and wiring.

About August and September last year, many modellers on the QSI group
voiced their frustration about this problem and I am sure that is all
DCC system are suffering the same problem.

...

My own layout is wired up using light globes as the short protection and
power division device. When wiring my layout for DCC, I like many others
had lots of questions and used the Internet and found Allan Gartner's
Wiring for DCC at HYPERLINK

http://www.wiringfordcc.com/track.htm"http://www.wiringfordcc.com/track.htm

invaluable with so many answers to the question I had. At Joe’s great layout web
site he also has a reference to light globes for short protection and
now a 3 minute video clip where Joe explains about light globes.

I did not want my layout to completely shut down when an operator
created a short at a turnout so I wired in light globes. Making the power
district as small as possible at approximately ‘one train length” as Joes
does removes the chance that two trains can be in the same power district
and with as many as 4 to 6 locos, some with sound, exceeding the light globe
maximum operating current before it has an adverse effect on loco
performance.

I have gone one step further than Joe shows in his video, I have mounted
the 1156 in a line side building, so that when the train stops, the building
lights up bright, not really very prototypical but a very good visual warning.

Wiring a layout for DCC now has become a little more than that “one
liner” about one of the advantages of DCC is “simple wiring, just 2
wires the track, that’s all there is”. But just like everything in life,
nothing is easy and for better operation (no complete shut downs of
layout with a short) come at a price, time effort and a few dollars.

The booster not being able to reset after a short circuit with a few
sound locos in the same zone does not happen when using light globes as
Joe also suggested, because the booster never shuts down if everything
is working correctly EXCEPT when you are operating near the booster’s
current limit, and now is the time to add a second or third booster.

Thanks a lot Joe.

Marcus Ammann
Model Railroading in Australia

[jfugate]

Simon:

Yes Rick and I were cracking jokes with the cameraman before the clip was shot. But we've also been told we look too deadpan in front of the camera so we've been working on trying to be more *alive* in our expressions and delivery. That's part of it too.

Glad you're finding the info useful.

[jwr_1986]

Joe, every item you've discussed makes good sense to me except this one. Circuit breakers are the solution to go for here because they stop all current flow not just some. I saw a highresistance load short on a bulb protected block and melt an engine once. While the breakers may be considerably more expensive they are the only safe way. My opinion of course. Thanks for the other good tips though.

Jesse

[IRONROOSTER]

QUOTE: Originally posted by jfugate

Not a lot of comments on this thread since the last post ... did it just stun everybody? Can you play the video clip, and does using the bulbs for short management make sense?

Any questions?

I haven't been commenting because I have don't have DCC. But I have been following along because I have been thinking about getting a DCC system. This has been very instructive and yes it is clear.
Thanks for sharing
Paul

[Bikerdad]

Joe,

Looks like a really good idea, although its unclear how the lightbulb is mounted/secured/electrically isolated (UL approved fixture, nah...). How does this compare in functionality and reliability with something like the Digitrax PM42?

[simon1966]

Hey Joe, were you telling jokes before the video? Rick looks like he is going to burst out laughing at any minute!

Actually, this is really clear. I will be getting some bulbs shortly!!

[jfugate]

Not a lot of comments on this thread since the last post ... did it just stun everybody? Can you play the video clip, and does using the bulbs for short management make sense?

Any questions?