Friday, June 29, 2012

A warning - Please read

While reading the Aus_Model_Rail Yahoo Group tonight I noted a discussion on the use of DCC high amp boosters (10amp), short circuits and the way to handle them with circuit breakers, etc. The discussion has prompted this post and I pass on a warning for those using PCB sleepers with copper on both sides.
Recently I was at the first running night on a friend's new layout, now this layout had handbuilt points using the Fast Tracks method. My friend had been having mysterious short circuits that very day and said that the layout was out of action due to the short. On turning the system on so that we could check for the short he found that it was now working so the running night proceeded.
All was good for a while then as I was shunting his branchline terminus I saw a small approximately 8mm ball of flame erupt from one of the sleepers on a point. I quickly called for the layout to be turned off as the cause was immediately apparent.
There was a short caused by the track pins/spikes passing through the sleeper which had the usual piece of copper removed between the rails, however the copper layer on the bottom was still there and both pins/spikes were touching the copper at the top and the bottom of the sleeper hence a short circuit.
The scary thing here is that this is relatively standard practice in point building and as we often leave the power on the layout when we leave the room a fire could result.
The solution is simple, do not put a track pin on both ends of a PCB sleeper if it is double sided.
I checked my handbuilt points and sure enough I have the same situation on my Cassilis branch terminus but luckily mine aren't shorting.
I am going to remove one track pin/spike from one side of each PCB sleeper.
The interesting thing with this situation is that the booster didn't trip it just kept putting out the amps. I should also point out that the DCC booster was only rated at 5 amps, a very normal booster.
So beware, you have been warned.


Nemesis said...

A good piece of advice too! That would explain why I experienced 'unexplained' shorts which I could never locate!

Thanks Ray, will remember next time I get another layout going.

sparksey4869 said...

Another issue that people could over look is the use of real blue metal. It is also conductive and can create a load or a short circuit.

Ray P said...

I suppose it could add a load but I haven't seen anyone using it have a short circuit. Each piece of aggregate would like be insulated from the next by the glue holding together. Dampness in the glue could be an issue until dried.