Model Railroading > Electronics Question

I`m doing signaling using 12 volt DC 4PDT relays. I`m using separate 12 volt DC power supplies for the relay coils and for the relay contacts. My detection system and signal system are completely independent of my DCC system and track power. All of my detectors work perfect. I`m running into a few spots where voltage is present across sets of contacts even though they are open and show no continuity with a meter. This is occuring even with the coils not energized and only the 12 volt supply turned on for the 4PDT contacts. It is also occuring when the coil supply is on and coils are energized. The voltage that is getting thru is fluctuating in value and sometimes there is no leakage. It is not always on every set of contacts on a single relay. Some of my panel indications and signals are lighting dimly or changing in intensity even when my circuitry says they shouldn`t be lit at all. I do have alot of parallel wires bundled together going to various locations. I also have places where as many as 4 sets of coils are wired in parallel and energized thru one input. All coils have one side wired in common. My coil power supply is rated at 15amps and there is no way I`m reaching that even the maximum number of coils energized. This provides me with 16 sets of contacts. On a color postion signal head red LED`s are lit correctly when my circuitry says they should be but there is also green lit very dimmly and I can measure that small voltage back at my circuit board. My question is, what could be causing this and is there anything I should be putting across the coils to prevent them from interferring with the contact voltage. I know this is basic electronics but I`m seeing things happen that I can`t figure out. I have checked all my wiring and that is solid.

Any help is greatly appeciated,

Tom

I'm no exopert on electrickery, but it sounds to me as though somewhere in there you are picking up AC which is why you are getting the false green on LEDs. It may being picked up as 60cycle hum from somewhere. Is your mains wiring screened? or properly earthed?

Is your Signal wiring close tor your Main track Bus? That can cause a problem if that's the case or does it do the same thing with the track power off.

This is happening with no DCC or track power turned on. When I disconnect the connection to the LED it goes dark so voltage is getting there thru the wiring. I have a positive 12 volt common and when I disconnect negative 12 volts from the circuitry for that LED it still shines dim or is flickering

Tom

mgwsy1978 Wrote:
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> Is your Signal wiring close tor your Main track
> Bus? That can cause a problem if that's the case
> or does it do the same thing with the track power
> off.

Does this happen to just the green LED on one signal or all signals?

Is it just te Green Led or Yellow and Red also?

the problem has gone away in a few heads and has not come back. The main one now is a tower board indication. I`m also having a few problems in two heads that use the 4 sets of contacts on one relay. I used liquid flux to make the solder joints on the relay socket contacts. I`m really starting to believe that some of it may have splattered and is now bridging the contacts inside some sockets. I found out this can happen when I used it to make solder connections on the printed circuit board of a decoder one time. I saw arcing when I tested it out and found out that some flux was on the board between connections. I`ll try some fresh sockets and relays in the trouble spots and see what happens. What I`m seeing just doesn`t make any sense so I`ll look for this.

Tom










mgwsy1978 Wrote:
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> Does this happen to just the green LED on one
> signal or all signals?
>
> Is it just te Green Led or Yellow and Red also?

Sounds like either a ground loop or high resistance in wiring or contacts somewhere. Do you have connectors or screw terminals? Prototype signals NEVER used a common return to avoid just this kind of problems. They always have a complete separate loop for each circuit all the way back to the power supply.

Barry Draper