Re: Gap width vs Scale

Flash Gordon

I just received a DCC Specialist On Guard circuit breaker and Auto Reverser OG-AR. While reading the instruction (yes I do read the instructions first) I found an interesting recommendation.  I am not an electrical engineer but I think the guys that make and sell these are, so I tend to follow the manufacturer’s recommendation for their product.  NOT all manufacturers recommend this.

Quote from DCC specialist helpful hints:

“For reverse sections, we recommended that the gaps be staggered about 1/8". Perfectly aligned gaps may reduce performance.”

As to gaps, on my layout the gaps for reverse sections are wide enough and filled so that one metal wheel will not trip the reverser, I have explained in past posts why I need this feature. It has to be the continuity of a powered truck that trips the reverser.  I.E. The leading axle and trailing axle are wired together by pick-up. When the leading axle is in one section the trailing axle is in the other and forces the reverser to trip.

Example in”What happens to a train when the power reverses in an automatic reversing section?”

Each layout and the needs of the user may vary and there is always more then one solution.

Ed S

At 12:44 AM 3/10/2014, you wrote:

<<Is there a rule of thumb as to how wide a gap should be. I'm modeling in 1:20.3 now referred to as F/Fn3 by NMRA.>>

Gap width is not related to scale.  Gaps serve four electrical purposes:

1)       To separate the track into blocks for purposes of detection (signaling, etc.),

2)       To isolate a reversing section from a non-reversing section,

3)       To break the railroad down into manageable sections for trouble shooting, and

4)       In the case of DCC, separate the railroad into booster power districts and circuit breaker districts.

In all of the above cases, the narrowest of gaps will suffice for purposes of separating one block from the next – a razor saw, an insulated rail joiner, or the thinnest cutting wheel in your Dremel is more than sufficient.  However, it may be better to use a slightly wider gap in order to place material in the gap to keep the rails from shifting and closing the gap.

Gaps need to be relatively small so that a wheel bridging that gap triggers your DCC reversing section (That’s how they work – they detect the short and reverse the phasing of the reversing section before your DCC Booster senses the short and shuts down).

There is no benefit is off setting your gaps for reversing section.  The first wheel to cross the gap triggers the reversing process – anything after that is irrelevant.  The circuitry doesn’t care if one or both wheels span the gap(s) at the same time – the sensing of the short triggers the reversal.

Best regards,

Steve Haas

Snoqualmie, WA

Join to automatically receive all group messages.