I have a new layout with MRC DCC and 8 amp booster. There are 3 power districts and each with its own circuit breaker. I can run locos fine within each district but things short out when I try to go between districts. All the wiring is relatively new. Any ideas on where to start? many thanks in advance.
Capt Wilb
Two things come to mind. one is that the DCC feed between the circuit breakers has had the polarity reversed, or the polarity of the track feeders has been reversed. I have hooked up PM42's and PXS circuit breakers (not together) and haven't had any problems moving between power districts. Did you double gap the districts (gaps in both rails)? What circuit breakers are you using? Did you adjust the current trip level and make it too low?
captwilbAny ideas on where to start?
Yes. It sounds like you have the power leads crossed between the districts and have a phase difference across the gaps.
Do you have a meter? Set the meter for the AC scale and read across the track gap for each rail. If the meter reads zero, then the rails are in phase. If you read a voltage across the gap, then the rails are not in phase. You will have to then switch, or reverse, the power to track connections for the problem district.
Once you do the swap, then you can check across the next set of gaps.
Not that it matters that I am 'thirding' the suspicion, but I can't think of anything else that would account for a simple district gap crossing to cause a short unless there were a polarity reversal between them. You'll have to triple check that you have the bus correctly oriented. I would think the feeders are okay if you can power that district and not have a short.
Crandell
As others have said,
Putting a volt meter across the gaps is the first step. Either AC or DC will do. If it shows above 0.1V then you have an issue with polarity reversal.
To add to the advice, make sure your feeders are not to far from the end of the power districts. A long distance from the last feeder to the end of the track block can cause a voltage drop. It may only be a volt or two, but because there is little resistence between districts, you could be cranking out very high amps, throwing the breaker.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
As you have three power districts and there can only be two states to the phasing of the AC current it should be possible to run between two of the districts. You'll need to experiment by attempting to run across each of the three districts. One out of the three crossings MUST work, otherwise your problem is more complicated than simply having a district out of phase.
The two crossings that don't work mark the two ends of the power district that is out of phase (wires crossed). You simply need to swap the wires in that district.
If you are handy with electronics then build yourself a simple LED circuit with an LED, a Schottky diode, and a resistor. I have one with two circuits - one red LED and one green. I run it over the rails with the green LED on and when it passes onto the next power district the LED should remain green. If it changes to red then I know I've got the wiring around the wrong way.
Hope this helps.
Cheers
The_Ghan
The_GhanIf you are handy with electronics then build yourself a simple LED circuit with an LED, a Schottky diode, and a resistor. I have one with two circuits - one red LED and one green. I run it over the rails with the green LED on and when it passes onto the next power district the LED should remain green. If it changes to red then I know I've got the wiring around the wrong way.
I'd be interested in seeing a schematic of that circuit.
Joe
JoeinPA I'd be interested in seeing a schematic of that circuit.
Joe,
You made me stop and think. I was wrong. That circuit is for DC only.
However, it is easy to check the wiring with a multimeter: simply clip one probe to "power district 1" Rail A and then contact the other probe to Rail B of each of the other power districts, including district 1. You should get the same reading for each district.
If a district appears dead when touching Rail B, touch Rail A instead. If it is "live" then it is wired incorrectly.
Thanks for checking me.
It's not too hard to make something that can handle DCC. An easy starting point would be a dummy diesel that has wheel pickups not grounded to the chassis - thinking Stweart F unit here. Or failing that you need 4 total contacts to rub ont he rails, 2 on each side, with a space big enough to span the gaps between districts.
For LED protection, easiest to use 2-lead bicolor LEDs. If your DCC system can do address 00 for analog this will also detect it in use. Total 4 LEDs, and 4 1K resistors.
Pair a resistor with each LED. Which side, does not matter. One pair across the 'front' two pickups. One pair across the rear two pickups. One pair diagonal left front to right rear. And the fourth pair diagonal right front to left rear.
On ordinary track, middle of a power district, you should get both the diagonal LEDs lit up if track power is on.The ones on the side - dark.
Span the gap between power districts, so the front pickups are in one, and the rear pickups are int he other. If it's wired correctly, again you should just have the diagonals lit. If the sides light up, the two power districts are out of phase. If one side lights up and the other doesn;t, you have a real wiring mess somewhere.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I use a 2 lead bi-color led with a 1k resistor soldered to one lead. Check across the rails in one district. Using the same orientation of the leads , check the next district. If LED lights up the same color, districts are in phase. Different colors, districts are out of phase.
This is actually quite easy with Digitrax boosters because they already have the bicolor led in the unit. Dial up address 00, turn speed all the way up and check the color of each booster track power light.
Checking for AC voltage across the gap with a meter is also very simple. No meter? Just jump the gap with a piece of metal. If the boosters short, phase is wrong.
Martin Myers
Agreed. But some people like gadgets. When I started my first DCC layout, I built a beeper box to hook to the feeders so I'd know before soldering if I had a feeder crossed.
I never used it.
Oh well, it was only about $5 in parts.
I built a decoder tester, too. Also never used beyond initial testing. After a few dozen installs, still haven't had a bad one, plus I always test on the program track first just in case.