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How To Find Electrical Track Problems

Posted by on Feb 11, 2015 in Miscellaneous, Tony's Tips |

by Don Fiehmann

It has been said that you don’t find trouble, it finds you! To go along with that, one of my favorite sayings is “Trouble is an opportunity to learn”. Here is some of my experience with troubleshooting. One other thing when troubleshooting is to always “Look for something simple”.

Types of Track Problems

Hint: When planning a layout remember that short length blocks make it easier to locate problems, shorts or opens.

RRampMeter

Open Circuit

An open circuit on the rails is not normally very hard to find. Most of the time an engine just stops caused by crud or dirt on the rails or wheels. If a push or thumping the layout does not get things running again, it’s time to get more serious.

Rail cleaning is best done with the CMX Clean Machine. For engine wheel cleaning, look for either the KADEE wheel cleaner or the Trix Wheel Cleaning Brush. Both of these wheel cleaners use opposed (R/L) brass brushes in contact with wheels. When the brushes are used in conjunction with an external power supply the brushes energize the loco through the brushes to spin and clean the wheels. If the problem is not poor rail-wheel contact it is most likely a bad connection, like a rail joiner. It is easy to run theĀ leads of a voltmeter along both rails until there is no voltage. This is a good job for the RRampmeter (see photo). Note that sometimes a high resistance open will pass enough current to fool the voltmeter, but not pass enough current to run a loco. If this happens, you can try using a 12 volt lamp on a couple of leads for testing as shown on the RRampmeter.

Short Circuits

Most of the time a short is caused by a derailment or a switch thrown against rail traffic. This is easy to find unless the short was caused by a cat knocking over a car in hidden trackage. One of the first things to check for is the last thing you worked on. If one of these isn’t the problem you need to get out the big guns!

Finding short circuits is not as easy as finding an open circuits. First your layout power supply normally shorts out and trips off. This makes it difficult to troubleshoot when there is no power on the rails to perform testing.

I developed a procedure to make this easier while working on a printed circuit board with a short between two lines. Sometime later I had a track short on my layout and used this same procedure to locate the short.

All Conductors Have Some Resistance

First you have to understand that there is resistance in all wires and rails. The phone company used to find shorts with a very accurate ohmmeter. The resistance of the wire per foot was known and it was just a matter of computing the distance to the short. Most ohmmeters don’t go low enough to measure rail shorts and simply read “0” Ohms.

Another way is to run a current through the conductor. Any current through the rails will cause a voltage drop. One advantage of nickel-silver rail is it is less conductive than copper and has more resistance per foot. The voltage drop may be very small, but it is still detectable with a digital voltmeter with a millivolt range.

To find a short you need a source of power and a digital voltmeter along with some jumpers. The power source needs to be able to put out a constant current. If you don’t have a constant current power supply, you can substitute one with a power pack and an automotive light bulb. (The constant current supply does not need the lamp.) The lamp, as shown below, acts like a load to prevent the power pack from shutting down and the current allows you to trace the short on the rails.

The Procedure

Since you are going to apply external power to the rails it is a good idea to disconnect the DCC system or power pack to the block and remove all rolling stock from the rails on the block with the short.

Next, connect the constant current source to the rails with the jumpers. Use the digital voltmeter to measure the voltage across the rails. The meter should be set to read millivolts. Then slowly “walk” the voltmeter leads down the track. The reading should be very low, in the millivolt range. The voltage should slowly decrease as you approach the short. Once the short is reached and you go beyond the short, the rate at which the voltage is decreasing will change. The reading may still decrease, but at a much slower rate. This gives you a place on the rails to start your investigation.

It could be in the switch machine contacts, or something dropped across the rails. I even found a place where dry lubrication on a set of contacts was the problem. Sometimes wire screen in the scenery can short out rails. Staples used in wiring to the rails can be a problem.

Happy Rails!