08-01-2010, 10:01 PM
(08-01-2010, 09:50 PM)Archie Wrote: Many thanks for the quick reply, sorry I don't quite understand the question, maybe I have got it wrong, but if I increase the resistance, which will lower the voltage, and increase the drop shunt, or is this nothing to do with what you are asking me.
The latter half of your thought process is correct, but the first part is not.
It is true that if you have lower rail volts, you can have a higher value of drop shunt resistor to drop the relay. However, remember that the ballast resistance is in parallel with the rails so an increase in the ballast resistance will result in less leakage and hence a higher rail voltage meaning that to drop the relay you will need a LOWER value of drop shunt. An easy way to remember this to sense check any answer is that if you set up a track in wet conditions (low ballast resistance) and then it dries out, the track will be moving towards wrong side failure.
Your appear to be adopting a logical stepwise approach to thinking about the effects of a change, just make sure you are starting off in the right direction!