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dcc reverse loop


DAVE1562

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Hi all... i am thinking of adding a removable 3ft x 3ft board on one end  with a  reverse loop to my GWR Exe Valley N gauge layout  ..... any advice on a suitable module to reverse polarity (make, fit etc) would be welcome :scratchhead: ... track power is dcc using a powercab, points are on a seperate 12v-16v dc bus via cdu(seep pm1) to switch frog polarity.

 

Dave

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Hi dutch- master...  i have searched a good deal on types of modules but just asking advice on peoples preference etc .. as a recent newbie convert to dcc i am confused about a suitable module for n gauge and its required  ampage suited to powercab 

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A simple solution I've used but maybe not the cheapest is a Tam Valley Depot dual frog juicer. Just have an isolated section on the loop and connect an output from the juicer to each rail.

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Hi all... i am thinking of adding a removable 3ft x 3ft board on one end  with a  reverse loop to my GWR Exe Valley N gauge layout  ..... any advice on a suitable module to reverse polarity (make, fit etc) would be welcome :scratchhead: ... track power is dcc using a powercab, points are on a seperate 12v-16v dc bus via cdu(seep pm1) to switch frog polarity.

 

The simplest and lowest cost is to forget "auto-reversers". You don't need them in most cases, they are just an expensive solution to a simple problem. Instead, switch the polarity using relays or other switches associated with the movement of turnouts. 

 

In the simplest reverse loop (one turnout entry/exit to loop), connect a relay to the turnout movement control, and use that relay to switch both the crossing (frog) and the outer running rail polarity for the loop. You may need some DC power to operate the relay, ideally that is a separate power feed, but it can be done by rectifying the DCC track supply (four diodes to make a bridge rectifier).

 

 

If you have an auto-reverser, but don't change the turnout automatically as the train approaches it from the rear, the train derails.  So, in most cases, the auto-reverser doesn't actually protect against operator error. ( automating the turnout change can be done, but I've rarely seen it implemented ).

 

 

- Nigel

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'Auto Reversers' are probably best reserved for those times that there is no directly associated  mechanical route setting - or where perhaps a variety of routes passes over a diamond crossing or other common set of trackwork.

Most work by detecting a short-circuit occuring in the first metal wheel (on either rail) to bridge the start-of-section insulating gap.   Some designs therefore have a tweak to set the expected level of current for normal use, so as to identify the larger current of a short circuit:  these can be a problem if a wide range of locos might pass over the gap.   'Older' designs also tended to use relays, rather than electronic solid state switching, and with some DCC Controllers, the time-to-operate has been long enough for the DCC Controller to trip in its short-circuit protection.

 

In the larger gauges (eg G) the level of short-circuit current can be very high! - and so Massoth have introduced an alternative design, in which 'sensor' sections are used in-advance of the actual-switched-section: this 'pre-detection' is used to pre-set the auto-reverse polarity ahead of the (loco) entering the section, so that no short actually occurs.

IN smaller scales, it might simply be difficult to differentiate between different makes of loco.

 

it is this latter idea which links in with Nigel's idea of linking switching (an associated point if there is one), or simply the polarity-control relays:  As the train approaches the section, your chosen type of detector (optical, magnetic or current, as you prefer - a simple beam-break kit will do) is used to trigger the point and polarity change: ideally changing associated signals as well, to give a GREEN to continuing on into the section......    Then, again, towards the end of the section, a 2nd detector is used to repeat the process, but setting the polairty and route, and EXIT signal appropriately.

So 2 detectors would allow a ONE_WAY reverse loop to be automated - with associated signals, route and polarity. 

For operation in 'either direction' around the loop, then 2 more detectors will be needed, so that the APPROACH to each isolating break is covered in each direction.

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There have also been compatibility problems where some boosters will cut out quicker than the auto-reverser. I seem to recall the Dynamis was notorious for this. So, if you do choose to use an auto-reverser, find someone with the same system as you and a working auto-reverser, and follow what works for them.

 

Andrew

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Dave,

 

Regarding Crosland's point about compatibility, I have three Hornby reverse loop modules and one Gaugemaster unit in use with Powercab/Procab and have had no problems in five years.  I changed one Hornby to the Gaugemaster early on because I thought the Hornby one was faulty but, in the end, discovered that the problem was a defective electrical connection in my trackwork within the reverse loop.

 

Harold.

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Hi Dave and other,

 

Digitrax Auto Reverse Controller AR1

Lenz produces a module but I heard that some users experienced sensibility issue.

I do not the Hornby one.

 

The Digitrax is I think the most sensible choice. It is compact and you can adjust the sensibility (current) manually.

 

 

Good luck

 

Luc 

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Dave,

DCC Specialities PSX-AR would be your best bet  (particularly if you are using  a Powercab trip current can be set from 1.27-19.2 amps also they have a booster function for low current systems),

These will also allow for automated turnout control on the reverse loop (PSX-AR for stall motor, PSX-ARSC for solenoid).

 

I my opinion it is best to use electronic auto reverse units as they are much faster than relay types such as Digitrax ar1 or the gaugemaster dcc40 as well as the Hornby unit.

 

Tam Valley Dual or Hex frog juicers work well on 5 amp systems, not sure (have not tried) on lower current systems such as the Powercab .

 

Anyway, just my 2 cents worth.

 

Regards,

 

Don

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The  simplest  way  to  do  it  is,  to  use  a  dedicated  digital  reverse  loop  module,  there  are  quite  a  few  brands  available,  Bachmann,  Hornby,  gaugemaster,  massoth  etc.

 

Coinnection  is  simple   2 connections  from  the   track  whch  is  not  part  of  the  R Loop to  the  Module,  and  2  connections from the  module  to  the  R loop itself

 

Naturally  the    R loop itself  has  to  be  electrically  isolated  from  the  rest of  the  system, by insulating  rail joiners.

 

The  attached  pics  may help to  explain!

 

The  R loop  module  is  a  Gaugemaster  one.

post-10539-0-92968900-1401804407.jpg

post-10539-0-10059900-1401804418.jpg

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I am using two autoreversers with my NCE Powercab. My n- gauge layout Radcliffe North Junction, is based on a junction on the old ELR railway, Bury to Manchester( now used for part of the m/cr metro tram way), it consists of two crossover junctions,one left and one to the right plus several sidings including two slips. For a bit more operating fun on my layout I decided to connect these together, they join together and run across on a high level, effectivly making a figure eight. I was going to wire it with switches but decided on the reverse units for simplicity. I am using a Dcc specialities Ongar for one track and a Hex juicer for the other,this allows me to run two trains across the section at the same time, its brilliant no stopping, you just run the trains and forget about it being a reverse loop. But I would reccomend using the psx-ar unit, the ongar requires 5 amps to work, ok for me I am also using a SB5 booster  along with psx4 circuit breakers.Definately use one of the electronic units they are far superior to the old relay units, if you decide to use a reverse unit.

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