short detectiongreenspun.com : LUSENET : Wiring for DCC : One Thread
I have started to install DCC on an older DC layout that has a number of twin-coil switch machines (with polarity contacts). Removed all old track wire. New 12G bus and 20 G. feeders. I started wiring with Allan G.'s short detector (booster not connected and nothing on track). I inadvertently stopped using it for a short while - distracted making new control panels. My problem is: 1. a regular ohmmeter buzzer shows no short on either rail connected to main bus. 2. Allan's buzzer is quiet when leads are connected to each track, but sounds when leads are reversed. For example + lead connected to outside track and other lead to inside track = buzz (not very loud) but when these leads are reversed there is no sound. I don't understand why the buzzer would sound in one direction. I admit I'm a newbie and this has me confused. A DCC loco will run, but I'm concerned with shorts in the future. I've begun cutting lots of feeders and polarity connections to turnouts without any change. I'd appreciate any suggestions. Thanks, Ed W.
-- Ed Wozniak (firstname.lastname@example.org), November 12, 2004
It sounds like you have a very high resistance between your rails. If you cannot solve the problem, it is probably nothing to loose sleep over.
Still, I understand your desire to rid yourself of the problem if possible. Unfortunately, it is difficult to solve the problem over the Internet. It is particularly perplexing regarding the buzzer sounding in one direction and not the other. If you have done everything you say you have, you shouldn't have a problem. This means somewhere you have a mistake and you will just have to find it.
One common mistake is to wire both rails to the same bus. Usually, this results in a short that will sound the buzzer loudly. However, sometimes the mistake is made in such a way that power is flowing through rail joiners which are making poor contact. This results in a "high resistance short" like you are experiencing.
-- Allan Gartner (email@example.com), November 12, 2004.