Going Nuts with DCC Wiring

Model Railroader Electronics and DCC
1

Setup: Digitrax Evolution Command Station, layout divided into five power districts four protected by a PSX circuit breaker and one PSX-AR for the wye. Each power district has a separate DCC bus. Turnouts operated by Tortoise Motors wired to a DPDT toggle switch on its own 12-volt DC bus.

I have used black and red wire for the DCC bus, but marked off the different power districts by using color coded zip ties. I checked the power districts and bus lines with the quarter test before adding drops and frog wires.

Problem: When I check continuity of the frogs of the turnouts everything has been fine until today. Now when I check the frog continuity with my meter, I get the correct ring tone for the points when they are switched. However, if I check the frog and the rail that is not touching a point, I get a buzzer from my meter and not the ring tone.

Also, I have noticed that the isolation gaps are no longer working. When I use the meter I get the continuity ring tone when I check the rails that should be isolated.

Lastly, when I turn off the DCC power and check the continuity between sections I only get the continuity ring on the black bus line, not the red bus line.

I am rather surprised that I am still able to run trains with this wire issue going on.

This only started when I added the last set of drops and turnouts.

Clearly, I must have tapped into the wrong bus wire, but I have so far been unable to detect where.

Solution: I plan on doing the following:

(1) Double check that no metal is laying across the tracks or between districts.

(2)I plan on testing again the end of the line for each of the power districts to make sure I can short them out.

(3)I will double check every drop and make sure that black is to the back, red is to the front, and I am connecting to the correct color-coded power district.

(4)I will double check all the turnout frog connections to the DCC bus.

(5)I will p

2

What meter do you have? I can’t say I have heard one with a buzzer in addition to the continuity beep.

However, perhaps you have it switched into a different mode - my better meters group the continuity with the resistence settings and use the range button to select a specific option.

Something that sounds curious - if you are testing from the frog to the OPEN point rail, that should have voltage, if the power is on. The buzz could be the meter warning of an incorrect setting (applying voltage to the resistence/continuity range). Which is nice if it does that instead of simply blowing up or frying something internally. Two of my meters detect certain goofs, like trying to measure voltage with the probe in the current jack, but it just gives off the same beep as the continuity test.

If the power is off - off the top of my head, I’m at a loss. You MIGHT get continuity across power district gaps on the same rail - two sides of a given gap, since the PSX only breaks one side of the circuit, and the other connects to all other PSXs through the circuit boards - if you have the feeds from the booster to each PSX wired the same way - Rail A to the same terminal of all PSXs, Rail B to the other.

Across the rail that is on the switched side, you may or may not get continuity, depends on the meter and the internal resistence of the PSX’s circuit.

Diagonally across gaps (left rail on one side, right rail ont he other) you should never get continuity, unless one of the PSX’s has its input or output reversed.

With the frog power wired throuth the Tortoise ocntacts, you should always get continuity from the closed point side and the frog, and never get continuioty from the open point side and the frog. Test both positions - the continuity (or lack thereof) should follow the point position.

You can also check voltage, it doesn;t have to be accurate, you jsut want to see a consistent result. When checking voltage,

3

Are you troubleshooting without a complaint? That is the pathway to the darkside.

If you are not having operational issues, what led to the diagnostics?

If you are using an ohm meter, or a continuity tester, on a circuit that is not completely isolated on at least one side from the rest of the layout, misleading results will happen.

-Kevin

4

Thanks Randy, I did not realize that the PSX only isolates one of the wires. Sure enough, I went back and tested from the PSXs and found that the black wires are not isolated even when the power is off.

This seems to indicate that my cross over between power districts must be on a red line of the buss. Too late to check tonight.

Once I figure this all out I will make sure I post the solution.

5

Much Ado About Nothing

This whole unnecessary nightmare started because I had accidentally wired two yard turnout frogs not to the yard power district, but to the main line power district. This was easily fixed once I realized it. Had I concentrated on solving that problem, these other issues I raised would have been revealed as inconsequential.
The buzzer that worried me is just my meter’s way of saying if you touch these two things together you will cause a short. Apparently, the warning is not enough to trigger the PSX circuit breakers. It would have been nice if the manual mentioned this feature.

As for the power districts not being isolated, they are. When I completely unplug my DCC system and PSX circuit breakers from my layout and test the isolation of my power districts they are indeed isolated.

Randy’s clue that the PSX circuit breakers only disconnect one power bus line was extremely helpful. Once I went back and tested from the PSX circuit breakers out I saw that as long as the PSXs were connected the black bus wire would be continuous between power districts with the track power off and that both the black and red bus wires would be continuous when the track power is on. When you think about this it makes sense. You want your tracks to provide continuous power when running trains. When I purposefully short out the tracks with a quarter the affected PSX kicks in and shuts down just the power district it is protecting.

My most important clue was that the trains were running just fine. I should have known that was a sign that the wiring was correct. I cannot believe that I could have laid down all of this tract and 60 turnouts, testing as I went, and never noticed before the behavior of my meter or how the PSXs work. I thought I have created a major wiring issue when I was just noticing how things are supposed to operate.

6

Maybe I’m just not seeing it, but other than Randy’s explanation, why did the buzzer buzz?

7

When you touch two opposing rails with my metter set to measure continuity, one line connected to the black buss and the other line to the red buss, the buzzer sounds. If I put a quarter on the same set of rails, then I get a short. The buzzer warns me that it is a short, but it is not enough to trigger the PSX circuit breaker.