I have a larger layout, a double main around the basement, each about 128 ft in length. Because of the size, I've added a booster (DB150) to my command station, a DCS100. I've been operating in this fashion for about 2 yrs without any problems. Throttle is a DT400 which is tethered.
Today I was testing an engine that had just been repaired and had something happen that I can't figure out. On the side of the layout controlled by the DCS100, the engine runs fine but when I hit the gaped rails into track work handled by the booster, there is a noticeable speed increase. I've powered down the system a few times and this continues to happen. I then checked voltage to the rails using an older analog multimeter. On the section powered by the command station, it reads 15 volts. On the side covered by the DB150, it reads 16 volts or just a little less. As we know, output of this equipment should be 15 volts max.
I was wondering if too few track feeders might play into this? I tend to lay track but haven't kept up, so far, with feeders off the bus wires, especially on the side covered by the booster. I did just finish laying about 15 ft of track on the side handled by the booster.
I've also made sure that I haven't left anything on the rails that would cause a short.
I hope someone has a solution.
john
Anything changed? Different power supply? Check the track voltage switch on the DB150, make sure it's at the same setting as the DCS100 (15V suggests you have the DCS100 in the HO setting - if the DB150 got flipped to the O/G setting, it won;t reach all the way to 20V with a 15V power supply, but it will go over 15V). Likely this is all that happened, at some point you bumped the switch.
Too few feeders would result in reduced voltage, at least under load. Just checking the voltage on the track with nothing running won;t point out inadequate feeders, the load placed on the circuit by a meter is so small as to be negligable for our purposes, and even if you fed the layout through a pair of phone wires and nothing more, it would indicate proper voltage. Under load is when you get voltage drop cuased by wire resistence.
Another thing to do is try resetting the DB150, disconnect the Loconet cables, plug a throttle directly into it, and remove the config a to ground jumper that makes it a booster. Put the mode switch in OpSw mode, and select switch address 39, and close it. Power off, reset the mode switch to run, and reinstall the config a to ground jumper. But check the scale switch - it's probably just that.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy:
Thanks for you response.
I did check the settings on the DB150 before my first post. Nothing had changed, it was still set on the HO setting. Its ought of the way below bench work so it wouldn't be bumped. I'll have to try the other option you suggest.
Beyond that, would you know why this happened given that the scale switch was not the problem?
Anythign else change, like a new power supply for the DB150? Or the DCS100, for that matter, if the power supply is putting out slightly ledd voltage, maybe that one dropped rather than the DB150 going up.
Also check track voltage the way mentioned in the Digitrax Tech SUpport Depot - rail to to ground, and rail b to ground. They shoudl be eual or VERY close. If the are way off, Address 00 may be selected somewhere and at non-zero speed.
You do have a failry heavy (bus size) wire between the ground on the DCS100 and ground on the DB150, right?
All else fails, the DCS100 and all recent production DB150's have an adjustment potentiometer inside to fine tune the track voltage so you cna set them to be identical. It's expected they be a little different, every component from the power supply down has a tolerance, but for smooth operation they difference should be less than half a volt. any more and you get the noticeable speed change you are seeing.
First, I did the reset of the DB150 as you suggested and that has solved the "speedup" problem. Ran several engines across the gap between the two segments and no more speed change.
I then checked track voltage with my multimeter and it's still the same, 15 V from the DCS100 and about 16 from the DB150 side. I use 14 gauge wire for the grounds and overall as buss wire.
And no, I hadn't changed power supplies for either unit, but I did forget to mention something that may have caused the problem. Just yesterday I was adding feeders to the new trackage just added to the DB150 side. In doing this I attached the first feeders to the wrong buss wire which of course caused an immediate short. That has now been fixed.
I will look into the better way to check track voltage as suggested by Digitrax.
Thanks again,
The best tool for checking track voltage is the RRAMP meter from DCC Specialties. It can be hand held or mounted in a panel. Checks voltage by touching it to the rails and also Current when wired in series with the track buss.
I still say it's a neat gadget that is mostly just a waste of money. If you want better voltage accurary, which isn;t really critical, a couple of dollars worth of resistors and capacitors will build a proper filter for DCC. I recall seeing somewhere someone did a comparison with a cheap DVM and the difference was less than a volt actual.
They key thing here is the difference between sections. Reading 15V on one and 16V on the other. OK, so the RRampmeter might show it to be 14.5V and 15.V volt - it's still going to be a 1V difference regardless of the absolutes. It's just not that critical. The RRampmeter is a nifty gadget, but a $3 Harbod Freight meter does a plenty good enough job for our purposes. In fact, my $3 HF meter is more accurate than my very expensive (glad I didn;t pay for it) Fluke desktop meter - because the Fluke is calibrated for 60Hz sine wave RMS measurement and the cheap HF meter has no such fancy enahancements.
Guess that's why I'm an engineer not a scientist - I worry about absolutel accuracy only when it really matters.
http://www.wiringfordcc.com/track.htm Scroll down just past halfway to the section on Measuring DCC track voltage and current to see the circuits I mentioned.
rrinker I still say it's a neat gadget that is mostly just a waste of money.
I still say it's a neat gadget that is mostly just a waste of money.
LOL
You are referring to the RRampMeter. Yes, it is a really neat gadget, so in that sense, it is not a waste of money. I have placed mine in-line on a small control panel next to the spot where I keep my DCC command station. Sure, there are cheaper ways to accomplish the same thing. BUT, it is a really neat gadget.
RIch
Alton Junction
I'd check the decoder's settings, and disable DC. It's usually a CV setting, sometimes part of CV29. The engine might momentarily lose contact going over the gap, and when it comes back online it might not pick up the DCC signal right away, and revert to DC mode.
Thanks to everyone who have offered suggestions. I think I've found out why this one engine (Athearn Genesis 4-8-4) was speeding up as it crossed the gap between the command station-booster section of the layout.
The gap at this location is at the end of an Atlas # 8 turnout. I had yet to add any turnout control plus wiring to power the frog. On this turnout, this engine was experiencing a momentary stall as wheels passed over the frog. I was running it just fast enough to stall and then hit the rails on the booster side of the gap. If the booster is putting out a little too much voltage, then when the engine hit those rails, the increased voltage caused it to speed up. Stopping the engine, turning the track power off and then on would bring the engine back to normal operation.
I had just installed a Tsunami decoder to replace the original MRC. I haven't checked the Tsunami instructions regarding disabling the DC mode but will do that. None of my non-sound engines have experienced this problem at this location. Anyway, I added temporary wiring to power this frog and the speedup problem was gone.
To turn off DC operation, subtract 4 from the value that is in CV 29, regardless of the brand of decoder. CV 29 is the same for every brand of decoder because it is required by the NMRA DCC Standard.
The 'usual' value that should be in CV 29 is 34, which tells the decoder to use a long address; no custom speed table; no DC sensing; 28/128 speed steps; and normal direction.