I have an interesting issue i found the other day on our club layout. I have been in the process of rewiring the whole layout. i have three power booster db150's and one dcs100 or 200 on three districts,(main line one, main line two and yard districts) . i have each district isolated. I noticed the other day that when you cross from one district to another i get a small short, i mean small. not enought to trip the booster. so i measured track power with AC setting on my volt meter and get 14.10 volts on the track. now if i measure the same rail, yes same rail at the gap seperating the districts, crossing from one booster to the other booster district i get 95 millvolts. Is this a ground issue?? i have no idea what this could be.
norcalmodeler now if i measure the same rail, yes same rail at the gap seperating the districts, crossing from one booster to the other booster district i get 95 millvolts. Is this a ground issue?? i have no idea what this could be.
Probably. Do you have a common going between all your DCS's and DB's (and PM42's if you use them)?
It's not actually a ground, even though Digitrax calls it that, and it shouldn't actually be connected to an earth ground.
But if you don't have that common between boosters, you could run into what you're seeing.
Could it possibly be a phase difference between the sections? Double check the wiring and make sure the wire color coding is the same on both sides of the gap, assuming you used color coded wiring.
With DC wiring, is would be called matching the polarity, but with DCC you're having to match the phase of the DCC command signal on both sides of the gap.
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Command station to booster is also one of the few cases where the polarity of the Loconet cable matters. Check that it is wired pin one to pin one. Someone may have slipped a six wire telephone cable in there someplace.
Dave
Lackawanna Route of the Phoebe Snow
thanks everyone, i am going to go down this afternoon and check things out.
Somebody I know had what sounds like a similar issue. A short would occur only when running into or out of the tracks powered by one particular booster. It apparently was out of phase with all the others. I think he reversed the track power leads coming out of the booster and that solved it. It was just odd since the layout had been in place for many years with its old CVP Products RailCommand system and there were no problems with shorting between power districts until the layout was converted to DCC, and then only one booster was affected.
Rob Spangler
norcalmodeler ...I noticed the other day that when you cross from one district to another i get a small short, i mean small. not enought to trip the booster...
...I noticed the other day that when you cross from one district to another i get a small short, i mean small. not enought to trip the booster...
So what was happening that caused you to suspect a short?
norcalmodeler...so i measured track power with AC setting on my volt meter and get 14.10 volts on the track. now if i measure the same rail, yes same rail at the gap seperating the districts, crossing from one booster to the other booster district i get 95 millvolts. Is this a ground issue?? i have no idea what this could be...
Probably just the difference in the voltage output of the two boosters. With a 14 volt output, 95 millivolts is less than 0.7% difference, well within the specifications of most power supplies and regulators. If the 95 millivolt difference bothers you, the track voltage on the DB150's and DCS100's can be fine tuned:
DB150 Track Voltage Adjustment
DCS100 Track Voltage Adjustment
However, with the varying loads as trains traverse the layout I highly doubt the boosters will maintain less than 1% difference.
95mv would NOT be a phase issue, it defiunitely sounds liek no or inadequate ground between boosters. You should run a wire at least as heavy as your track bus betwwen the ground terminals of all your boosters and the command station, also the ground terminal of any PM42s if you are using them. Othersise, the only ground reference between boosters is the thing Loconet cable, and over a long distance a 95mv mismatch is not out of the question.
Assumign you have all that in place, there IS a potentiometer inside the DB150 and DCS100 to adjust the track output voltage in finer adjustment than the scale switch on the front of the unit. Two units built even on the same day right after one another could easily be 95mv different from one anotherm so to get it to absolutely no mismatch you might have to fine tune this adjustment. Do this as a last resort, although in the tech support depot at the Digitrax site they do mention this adjustment. The common ground between boosters is the most important.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
cacoleCould it possibly be a phase difference between the sections?
I won't ever say never, but it's highly unlikely that this is a booster out of phase.
If it were out of phase, due to either a reversed booster or a reversed LocoNet cable, it would give him across the gap (roughly) the same 14v he measured from rail to rail within a section. But he measured 95 millivolts. That leads me to believe that his boosters lack a common point of reference.
My bet is still on a missing or ineffective ground/common between the boosters and if applicable, the PM42's.
Do these boosters have auto-reverse built into them? Or, is there a breaker or autoreverser between either booster and the track where you see the the short? Does this short occur only the first time you cross the gap after powering up, or every time?
Autoreversers will power up in one state and remain there until something out-of-phase crosses in. They actually detect a short, and that causes the reverser to flip and match phases. If you have an autoreverser in the circuit, this is the expected behavior.
It takes an iron man to play with a toy iron horse.
I tried to narrow it down yesterday and here is what i have going on. I connected a ground wire to the screws on the top of each db150 case and dcs100. I disconnected all the track wiring from the terminal strip and loconet, except between the booster. I also checked the loconet wires and they are correct. so here is what i have left.
dcs 100 - not connected to track power or loconet
db 150 booster #1 - rail a and b to terminal strip
db 150 booster #2 - rail a and b to terminal strip
db 150 booster #3 - rail a and b to terminal strip
14 volts + a little on average when i measure rail a to rail b. now if i connect b to b, i get the 95 mv. if i connect a to a i get 95 mv. there are no reversing sections set up yet. should i connect all with the ground where the jumper is on the boosters?
thanks for everyones help
Again, the 95 millivolts reading is probably caused by the difference in voltage output of the boosters. 95 millivolts would be caused by less than 1% difference in boosters. Unless you are having a problem, I would not worry about it. I'll ask again, what was happening that caused you to suspect a short?
I believe CSX Robert has answered your question already. What you are seeing is a miniscule voltage difference between two power districts. This is normal. As already pointed out, you could try to get an exact match (0 volts) by adjusting the pot inside the booster. I don't think it will be possible to keep it at that treading during normal operation as load changes. Best to just run trains and don't worry about it. I've seen this on numerous club and large convention layouts using more then one booster . It's never been an operating issue.
Martin Myers