Voltage drop question

I ran my layout for the first time in a couple of months yesterday before I had some friends come over to look at it. It ran flawlessly for the two hours before they came over. I cleaned all the tracks with my CMX.

Once they got here and I started running it, it ran ok for ten minutes or so, and then a couple of sections of track on the opposite ends of the layout seem to have either voltage drops in them or the track gets really dirty in these same spots very quickly.

So after they leave, I run the CMX over the whole layout again, and the problem goes away for a while, then it comes back in these same spots again. Why?

I have a Digitrax DCC system with feeders installed every three to four feet. I have insulating joiners about every 8 feet, but within six inches of every insulating joiner I have a feeder. On one of the hesitation spots, there are literally three feeders in this 6 foot section of track.

Why would certain sections of track get very dirty very quickly, and others be fine, even when the area has plenty of feeders.

And why can I run my layout flawlessly when no one but me is watching, but then have dead spots and derailments that have never happened before when people come over to see it run?

 

Well, to answer "why" when there are spectators, and not when you are alone is simple. murphy's law.. lol..

Seriosly, phycologicaly, when there are spectaitors, one tends to be more anxious to impress, therefore tends to make more hasty, and not as careful fluid movements resulting in mishaps. Just a theroy.

As far as trouble spots, assuming you have checked voltage, andit is consistant, which it should be as long as you have feeders as you mentioned, and good electrical connection. If the track is getting dirtier in spots causing it, I would assume the surounding area is at fault? Do you have more dust, loose ballast, vegitation, glues in that particular area? If there is alot more detail, and terrain, or scenery in that area, I would say that the train is picking up dust and debri from that, or near it, and depositing it there. Maybe a low spot in the track even?

Thinking aloud..

 

I have been trying to help my brother in law with this same problem on his DCC layout (his is HO). Here are my obsevations:
1. DCC is more sensitive to dirt/oxidation. This becomes more critical during more humid weather.
2. Use of plastic wheels - all metal wheel use doesn't seem to cause trouble - but throw on some plastic wheel rolling stock and the track quickly gets "dirty".
3. Areas where plastic wheels and dirt are problems are for the most part on curved sections of track and turnouts. The sharper the curve, the quicker the dirt build up happens.
Just some random observations.

 

One of the areas is in a curve, and one is in a curve to straight transition. The curve that's the worst is about an 18 inch radius, and my tighter curves in my tunnels don't have this problem

First off, how do I measure DCC voltage without the DCC tool? I don't have a voltmeter, and the reason I don't have one is
that I thought I couldn't measure DCC voltage with it.

Secondly, how do you clean plastic wheels and keep them clean?

 

A regular volt meter should be fine. All the track does is supply voltage to the DCC decoder in the locomotive. The only difference is it is a fixed voltage in lue of a variable voltage used in DC.

 

Well, a test with a volt meter will tell us what is exactly happening (or give a good idea). But some questions first...

1, How big of a layout? How long is your main? Lot's of sidings?

2, Which Digitrax system? Are you using just a command station, a booster, PM42, BDL16?

3, What size main buss wire are you using.

Set your volt meter for AC voltage, then check the voltage on the track nearest to the DCC system. Then measure on you problem spots. You should not have more than a .5 volt drop between them.

If you get a good sized drop, you need a bigger buss. If there's no drop, then there's another issue here.

Kel

 

Not sure of the best way to clean plastic wheels - some of the cleaners that work on metal wheels, such as electrical contact cleaners in aerosol cans that I use tend to breakdown plastic. I am currently preparing to convert to all metal wheels.
Do you know what size wire your bus wire is? I would go with no. 14 or 16 wire for the bus - and then use no. 20 or smaller to connect from the bus to the track. Too small of a diameter of wire can add resistance over long distances and can reduce voltage/current.

 

Every section of track should have a pair of feeders dropped to common bus lines. You won't have any voltage drops on your layout if you do this.

If you're using DCC, clean your track with 91% iso-propyl alcohol.

Stay cool and run steam.....

 

I just happened to think of another thing to check for - a loose rail joiner. I know a couple people that solder every rail joint.

 

For my own information:

Wouldn't a cold solder joint cause lower voltage across it?

Would a cold solder joint still show normal resistance?

Thanks.

 

Sometimes, but not necisarily. Voltage shouldnt be confused for "amperage". You can have a cold solder joint, and even though it isn't the best electrical connection to pull a load, it may still be making electrical contact, and voltage will be the same as a good solder joint. But, as soon as you put a load on that joint, the voltage will drop substancially do to the resisitance though the bad solder joint. You can't really do a good voltage check without the load on it. You will however possibly see resistance through it doing a resistance check on the dead line, but be sure it isn't connected on the other ends so that you will not get a false reading (feedback resistance)


The make the point about the voltage: You can take a standed wire and run a voltage though it. You should see no voltage drop. If you cut all the strands, except one, and check the voltage, you should still see the same voltage. But, there is not enough conductor there to light a lamp, due to the limit of load that one strand will carry. Not sure if that will make sense or not, but that is an example.

 

I checked votlage twice yesterday. The first time was after track power had been applied for an hour or so, and I came up with 12.8, everywhere it was checked. I turned off everything by unplugging my Digitrax.

The second time I checked it, I had just turned everything on, and just plugged my Digitrax in. This time, I got 13.3 volts, and again, it is 13.3 everywhere, even with a train in the parts of the track where I'm having problems.

So at least the voltages are consistent, although I am curious as to why when I first turn it on I have higher voltage than after its been on for a while.

14 AWG for the bus, and 22 AWG for the feeders. Feeders are placed every three to four feet, and I'm using Atlas flex track.

 

.5 volts difference between times checked isn't that bad. Many things could cause that. As long as it is consistant at any given time all over the track. The different times may have been difference in humidity, temperature, or things like that. All those things can cause slight differences between time frames it is checked. Point being, cold copper, conducts electricity slighty different than warm copper.. It's a molecular thing. But should not be enough to cause problems unless it is widly differnce, like sub zero vs. 120 degrees.. I doubt that was the case? hahhah.. The difference you are seeing is about 4 percent, and isn't very much fluctuation. Can you check along the different zones when the train is on that zone running? Check with no train, and check with train running, and see what kind of voltage drop you get between those two variables.

 

Ran it last night for a little bit, had ALMOST zero problems. Haven't cleaned the track at all since this problem started, so nothing should have changed. Voltage was at 13.2 in the problem areas, and 13.2 everywhere else, with and without trains in the area.

I'm going to throw another little wrench into this problem. For some reason, this problem seems to magnify itself when the loco is pulling a train. I was running one train(new Kato SD40) with five front runners, a Kato Maxi 4, and a Walthers husky stack(all of these but the Husky stack have metal wheels), and running a Kato C4400W with no cars. The C 4400 seems to stall a bit more than the SD40, and my SD70MAC(Kato) is about the same as the C4400. The SD40 doesn't seem to have the hesitation as often, but it does get it.

The C4400, running light, had ZERO hesitations that I noted in the original post, even though I haven't cleaned the track or changed anything. It was pulling the same train as the SD40 listed above. The area is level, so grade has nothing to do with it.

I'm at a loss. Good voltage everywhere, excellent running engines, and hesitation gremlins.

I'm going to work on my project car for a while. This is driving me nuts

 

It would make complete sense that it would be more problematic with cars in tow. The more cars ya pull, the more load on the motor, meaning the higher amprage draw from the rails, resulting in more of a voltage drop. The more questionable the electrical contact is, the more voltage drop you will see under a load.

To make it easier than checking running trains, make yourself what I have always called a "load light". When I was an aircraft electrician, this was an "unofficial" hand made tools all of us electricians made ourselves, and the most used, and valuable troubleshooting tool. Get yourself a couple wires (color coded), what works best is a set of meter leads. Take 3 or so small light sockets, and wire them all in parallel, and connect them in parallel to the leads. Tape them up pretty good to make a neat clean tool that you can hold onto while you use the test leads. It works good if you have leads that you can also connect alligator clips too for ease of use. Add lamps (bulbs) to the sockets. The more you add, the more load you will put on the circuit. I would start out with one lamp, see if it lights. Then add another, and so on, and so on, until you see where the lights will no longer light (this will be the maxium load the track will carry). Be sure to know the load rating of each lamp, so you can add them up for total load being used. Know how many lamps a known good circuit will light. Then use that for your benchmark. You can clip this new little troublshooting tool to your rails, and apply power and see if they light. If they don't, you have a connection problem, or high resistance somewhere not letting them light. You can check with a meter, and see if there is voltage, and then check with the light to check for load capacity. Youc an narrow down a bad connection by zone using the load light in stratigic locations.

 

Ryan,

When it stops/stutters, does the headlight remain on and steady or flickers? I ran into something similar tonight on my layout. Atlas Dash-8 with TCS AMD1 decoder. The thing ran flawlessly in the pass.

While running, it would stop for 2 seconds and then continue on in random areas. Headlight was on and steady at all stops. I discovered that if I unplug my DT400 and then plug it back in, the instant it was re-plugged there was that 2 second stop.

It turned out that my loconet cable to another jack was loose and my DT400 throttle was having intermittent contact with my Zephyr command station. Unplug/plug back the loconet cable and all was fine.

 

Do not worry about plastic wheels. all my wheel sets are mt. My bus wire is 12 guage though. Have you tried adding a few more feeder wires into that spot. Voltage is good but it may be amperage and amperage can be affected by track distance. Try adding some more feeders. i run feeders to every track and have found some trouble spots. Most were bad solders but some just needed more voltage available to handle the amperage. I run 3 locos in front of 20 to 40 cars. The coal trains are all 35 to 40 cars and that is where I notice the problems. Run 12 autoracks over the same spot and no problems. I ended up with some more feeders (2 per track section) in 4 spots and problem solved. Not bad in 400 feet of track to double up on 4 lengths.