Electronics and DCC

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?

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:

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.

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.

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

Okay, Joe, now I gotcha. I can split the inner loop from the outer loops with no problems, which is consistant with usage and should ONLY TAKE ABOUT A DAY to do.

But then again this layout is my learning layout so I'll do it.

Selector:

You got it! Should work just as you describe.

All:

I hope to post the wiring installment tonight ... that should help more of you get an "ahah!" from all this light bulb discusssion.

TOPIC THIS POST: Wiring details for 1156 bulb train blocks

Here's a typical DCC layout with three power districts, each powered by their own booster.


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Let's zoom in on the wiring for a single power district and then see how we “upgrade” it to add the 1156 bulb short management.


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Here we are zoomed in on our power district. Let's go through the steps to add the 1156 bulb short management protection.


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To add the 1156 bulb short protection to the power district, you first need to cut gaps in both rails to break the track up into train length blocks. Here we can see this gives us 8 train blocks.


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Next, we need to run a third bus wire for each train block thereby creating an 1156 protected bus feed for each train block. For each block we add a feed from the main bus to the third bus, through a SPST toggle switch and an 1156 bulb. If you wire a SPST toggle into each train block bus feed, you can kill the power to the block for debugging purposes, like when looking for mystery shorts. This is what I have done on the Siskiyou Line and it has come in handy more than once.


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You can now add the toggle and 1156 bus feed to each train block bus, and run track feeders to each rail section for a given train block from its associated third bus and the block will be protected from shorts by the 1156 bulb.


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Once you add all the toggles, bulbs, and track feeders for your power district, here's what you get. This is the complete wiring to add 1156 bulb short management to your layout.


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HOW THE WIRING ACTUALLY LOOKS ON THE LAYOUT
Here's how I wire in the bulbs. I solder wires to the terminals on the bulb, add crimp spade connectors so I can wire the bulb into a terminal strip. I mount the bulb using a plastic 3/4” cable clamp and a drywall screw.


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And here's how it all looks under the benchwork at a train block location on my Siskiyou Line.


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TOPIC NEXT POST: All about DCC friendly turnouts

All very clear, and clearly a lot of work!!![:O] I can see that you get great benefits from all that work, but....whew..that must have taken many days to do, Joe. I'm glad that my 'salvation' will be done in about two hours.

Selector:

It took one other guy and me 3 eight hour days to rewire the Siskiyou Line to be set up this way. That was back in the summer of 2000 and it was the best thing I've ever done wiring-wise to the Siskiyou Line. It was time *very well* spent.

Before we leave the 1156 light bulb short management, have we answered everyone's questions? Do the two posts make it clear why and how?

Yup, makes things clear. Thanks a lot. Any thought to perhaps creating a little more "standoff" for the bulb to reduce fire risk from "microscopic" to "infantesimal"?

You certainly could - just use scraps of dimensional lumber fromt he benchwork to make 'stands' to lift the bulbs out of direct contact. Or you could (at great expense) buy actual sockets for the bulbs which would put the base of the bulb near the benchwork and the globe well above it.
Keep in mind in their intended application, these bulbs are inside a tightly closed plastic space - and I don't hear very many reports of the taillights in cars catching fire. Given that a 12v short in a car is far worse than even a 10 amp booster shrting out, I don't think there's much issue there.

--Randy

QUOTE: Originally posted by jfugate Before we leave the 1156 light bulb short management, have we answered everyone's questions? Do the two posts make it clear why and how?

i think so Joe , even i understand how the bulb works now [:D]
now we just need someone to test the block detector issue to see if they will work