DCC Short Circuit Protection 101

[ATShinkansen]

Hello,

 

After a scary incident on my layout a few days ago, I want to learn more about how to go about implementing circuit protection on a layout.  This thread is for any and all DCC systems, but since I use Digitrax, I’ll start there.  I’m guessing I’d need a BXP88?  My layout’s broken up into enough segments to cover those 8 detection sections.

[inobu]

Do you have your NTSB report?  I'm kinda serious. You need to find out what happened and rectify the issue.

 

Helping you with completing your NTSB report. The Bogie melted because of the short.

The DCS51 should have tripped and shut the power off.

 

You may need to check your wiring.

 

There is a possibility that your wiring made the short look like a high impedance load instead of a short. This caused the power to remain on

and run current through the pickups that melted the bogie.

 

The BXP88 is your best bet as it gives to everything Detection, Power Management, Occupancy and  Transponding.

 

You still need to check your wiring again and perform the quarter test.

 

Always make sure the you put on your NTSB hat and find out what happened.

 

Inobu

 

[ATShinkansen]

I know the short was due to a derailment.  The last car was rear-ended by another train and pushed for some distance.  So I believe the short was through the derailed wheelsets.  Because my main line is entirely double-track, it may have even shorted between the two tracks, because it was after going through a curve that things got out of hand.  I don’t know if any of that is relevant or not.

 

If I get a short from, say, entering a turnout against the points, the system chirps like normal.

 

I just checked with the quarter test right now.  I noticed at the point where the incident occurred (at the far end of the layout), sometimes the command station tripped, and other times it didn’t.  The track is Kato Unitrack, and the wiring under the layout is entirely Kato cables, apart from a terminal block to switch to conventional wire to connect to the command station, and to take care of the auto-reverse unit at the turntable.  There are a couple of feeder sections right at that point on the layout.

Edited July 1, 2023 by ATShinkansen

[inobu]

As long as you know the cause of the derailment then you can address it.

 

Check the wiring and feeders. There has to be a poor connection or something.

 

This is why you should treat it like the NTSB. If you would have gotten a BXP88 and just wired it in.

It could have repeated itself. A poor connection is most likely the culprit.

 

Inobu

[ATShinkansen]

So I found something rather interesting.  I checked the cables directly with a pair of tweezers, and the command station trips as it’s supposed to.  The feeder sections are correctly oriented.  But I found something odd with the track between the feeders.  Below is a diagram of the part of the layout in question.  The blue bars are the feeders; the black ones at the turnouts are insulated joiners (both rails).  All the sections with the green check marks respond correctly to a short, while the red “x”s do not.  The blue arrow is the direction of travel for both trains involved, and the big “X” is where the car with the melted bogie stopped when I finally killed the power.

 

 

 

I’m not sure how to interpret this.  There’s no other wiring here except for the two turnouts, which aren’t even hooked up yet.  Trains otherwise still run fine through this section.

[ATShinkansen]

Alright, now the whole viaduct section (bottom of image) doesn’t respond now either, including the feeder section.  The cables, disconnected from the track, still respond as they should.  This updated image shows the entire affected area.  But even with no power to this district, the couple of sections of track on the adjacent district where the accident occurred still share the same problem.

 

[inobu]

You don't have enough feeders. 80% of your layout is reliant on your track for power.

 

You need to wire it something like this. The DCS51 in the middle of your layout.

Sections are in Black -----BXP88

Purple 4 Blocks

Green additional feeders.

The more you connect and disconnect Unitrack the weaker the jointers get.

 

Your layout is too big to rely on Kato wiring scheme.

 

Ideal would be to use 2 BXP88's and divide the layout into 2 halves and distribute the

BXP88 into a North and South area then distribute the 8 sections.

 

 

Inobu

Edited July 1, 2023 by inobu

[cteno4]

Kato feeders are also pretty whimpy 24g wire for higher amp dcc. Might think of running some 16 or 18g feeder wires instead of Kato and just cut a slot under the rails and solder directly to the bottom of the rail. This has let us do a lot more rack segments between feeders with our modular layouts and Ttrak.

 

cheers,
 

jeff

[ATShinkansen]

3 hours ago, inobu said:

You don't have enough feeders. 80% of your layout is reliant on your track for power.

 

You need to wire it something like this. The DCS51 in the middle of your layout.

Sections are in Black -----BXP88

Purple 4 Blocks

Green additional feeders.

The more you connect and disconnect Unitrack the weaker the jointers get.

 

Your layout is too big to rely on Kato wiring scheme.

 

Ideal would be to use 2 BXP88's and divide the layout into 2 halves and distribute the

BXP88 into a North and South area then distribute the 8 sections.

 

 

Ah, I was beginning to wonder if feeders were the issue as I was putting that last image together.  The station tracks at sections 3 and 4 already all have feeders, so that area is all set up.  I’ve also got the other end of the layout not pictured (where the main yard is) that I will need to apply this to as well.

 

The DCS51 is actually mounted on a mobile platform, as there really is no good permanent place to put it (the station tracks are where my TV is).  It currently connects under the engine facility, as the switch and turntable controls for that yard are on the same platform, and that’s the only level spot I can put the platform.  As I’m typing this, though, I’m thinking of how that can be simplified and reworked.  Wherever the DCS51 ends up, I just need to retain a spot for the programming track and my laptop for JMRI.

 

3 hours ago, cteno4 said:

Kato feeders are also pretty whimpy 24g wire for higher amp dcc. Might think of running some 16 or 18g feeder wires instead of Kato and just cut a slot under the rails and solder directly to the bottom of the rail. This has let us do a lot more rack segments between feeders with our modular layouts and Ttrak.

 

cheers,
 

jeff

 

What are rack segments?

[cteno4]

Sorry thumb Typing on the iPad. Track segments…

 

soldering to the track gives ver positive connection to the track. you can run all the feeders back to a screw terminal strip then for good positive contact. Kato track connectors, extensions, and splitters are good for smaller layouts on dc, but may be a bit wimpy for a higher amp dcc setup. I’m sure @inobu will have thoughts on this. Many dcc folks go way overboard on their wire gauges, but katos wiring system is really not designed for dcc from what I have gathered.

 

jeff

[ATShinkansen]

I guess I had never thought of the difference in amperage between DC and DCC.  I just simply thought the Kato wiring was easier to use.  I have a spool of 14-gauge speaker wire that was originally going to be for NTrak modules, I can probably use it here as well.

 

 I’m guessing the BXP88s should go one in each corner?

[ATShinkansen]

My first BXP88 arrived last week, and I need some verification on the wiring.  The diagram in the manual shows a common rail for all eight sections.  If this is the case, do I need to gap that rail into eight sections?  And how does this differ from “Whole Layout Common” wiring, which the manual states is not supported by the BXP88?