I have a 5 by 8 layout that consist of three ovals. 1 inner mountain line, 1 middle mainline and an outer mainline. they are seperated by insulators. My ohmeter (a fluke) reads open on each individual line. when I connect the three segments together I read 80 meg of resistance that increases until the meter says open within a second or two. I have ballested most of the tracks but not all.
am I reading some resistance through the glue that holds my ballest down? If so why does it turn back into an open?
Hi Joe,
80 meg, or 80,000,000 ohms, is essentially open. I think what you are seeing is an electrical capacitance effect. If you connect a good quality ohmeter to a capacitor, it will lead a low resistance while current flows to charge the capacitor to the voltage level the meter uses to excite the load. As the capacitor voltage approaches the meter’s voltage, the current slows down, and the resistance reading goes up. Once the capacitor is fully charged, no current flows, which is the definition of open. I’m not sure exactly where the capacitance is physically, but probably there is some on each individual loop, but not enough for the meter to display. When you connect them together, you tie the capacitance for each loop in parallel, which sums the capacitance to a value the meter is sensative enough to read.
Thanks for the quick reply. I thought it might be something along those lines because the value changed to an open, where as resistance would stay resistance if it was actually there. Do you think that this capacitive action may affect a dcc system? or is this normal?
Jim is correct about the capacitance. There is a slight amount of capacitance between the parallel rails, as well as an equally miniscule amount of inductance along each rail. The high impedance Fluke meter takes a short but noticible time to charge this tuned circuit.
The amounts of reactance are so small that they will no have any measurable effect on DCC. With the right size layout you might be able to get shortwave radio from Berlin though. [:)]
