More points trouble + a query

[ge_rik]

OK - the first proper running session of the season (work does tend to get in the way!). A short on the main circuit!! No idea where. I decided to narrow it down by isolating various sections (by sawing through the rail with a hacksaw - drastic but effective!). Narrowed it down to one particular station using a multimeter. Wiggled one of the R3 points and the short circuit disappeared. Now at least I know which point to wiggle if I get another short.

However - and here comes the query. My multimeter showed that there was a current flow with a resistance of about 2k ohms across the two rails in the other two sections. These sections were isolated from the controller (MTS Central Station) so it wasn't flowing through there. And yet, when I connected everything back together the 2k ohm leakage didn't seem to matter.

Any ideas where the leakage might be coming from - and why it doesn't seem sufficient to trip the Central Station?

Rik

 

[KeithT]

OK - the first proper running session of the season (work does tend to get in the way!). A short on the main circuit!! No idea where. I decided to narrow it down by isolating various sections (by sawing through the rail with a hacksaw - drastic but effective!). Narrowed it down to one particular station using a multimeter. Wiggled one of the R3 points and the short circuit disappeared. Now at least I know which point to wiggle if I get another short.

However - and here comes the query. My multimeter showed that there was a current flow with a resistance of about 2k ohms across the two rails in the other two sections. These sections were isolated from the controller (MTS Central Station) so it wasn't flowing through there. And yet, when I connected everything back together the 2k ohm leakage didn't seem to matter.

Any ideas where the leakage might be coming from - and why it doesn't seem sufficient to trip the Central Station?

Rik

Is there any vegetation under the track/ballast?
I had a 'runner' from a plant cause a short.

 

[stockers]

I agree, damp or vegatation.

 

[ntpntpntp]

... the 2k ohm leakage didn't seem to matter. ... why it doesn't seem sufficient to trip the Central Station?

basic electrical calculation: current = volts / resistance. Here's a little online calculator for folk to play with who may not be familiar with this stuff (just the first one I came across on google):

http://www.sengpielaudio.com/calculator-ohm.htm

To make it easy, assume your MTS outputs 20 volts, so 20 volts / 2000 ohms = 10 milliamps. Nowhere near enough to trigger the short protection, 'cos it's the same sort of load as an LED might draw. You wouldn't want your system to trip just 'cos there's a light on somewhere

I agree with the other guys, it'll be down to a little damp somewhere on the line, or maybe you have some gizzmos wired into your track (point decoders or lights?)

<edit>
Seeing as you mentioned it, thought I'd put my trusty multimeter across the track power feeds on my line (the dcc system is disconnected when not in use) just out of interest. Pleased to find it totally open circuit. The separate dcc power bus for my point decoders shows about 42k, which is fine.
</edit>

 

[ge_rik]

I agree, damp or vegatation.

Thanks chaps, hadn't thought of that. Yes, plenty of vegetation bridging the rails - tons of MYOB and also a few strands of ivy here and there - not to mention moss by the cartload.

Rik

 

[DoctorM]

Looks like you need to borrow one of these.....

http://www.tauntontrains.co.uk/ < Link To www.tauntontrains.co.uk