Reverse loop

Discussion in 'HO Scale Model Trains' started by cmn, Feb 2, 2004.

1. cmnNew Member

Hi;

I am building an HO scale layout that has a reverse loop in it.

I am looking for an automatic reversing curcuit any recommendations as to where and which one I should get? where is the best place to find one?

Thanks--

cmn--

3. cmnNew Member

Actually I do not have DCC so I need an automatic reversing circuit for DC only?

Thanks for the help---

cmn--
4. CN1Active Member

OK. Wiring reverse loops often confuses people because the track folds back on itself, and in the process can create a short circuit.

OPERATION - Reversing Loops

PART 1

In the running of trains, eventually there is a need to reverse the direction of travel. The desire is to send a powered unit into a loop and have it continue on its course in a forward direction, but come out of the loop going in the opposite direction.

To do this, somewhere in the process the power polarity has to be changed in order to change direction. This requires continuity disconnects and reconnects with a different polarity. In doing these things there is always the potential for conflicts in the flow of electrons and a sizeable voltage and or current differential can develop.

The Reversing Loops on our layout are intended to create a neutral area that is not Controller dependent so that polarity can be changed within a limited section of track.

The entry and exit points are the potential source of relatively large surges and so the operation must be undertaken in a way that minimizes the potential of having those surges run through the powered units and the electronic components that accompany them. When you consider that the voltage can be +15 volts on one side of the gap and –15 volts on the other side of the gap, you could encounter a 30 volt differential, enough to cause pitting of the wheels and/or damage to electronic components in the powered unit.

The following definitions are used in establishing the best methods for Reversing Loop switching:

1.The ENTRANCE BLOCK is the block just before the Reversing Loop and is controlled for both power and direction by the hand controller.

2. The REVERSING LOOP BLOCK is the area separated from the rest of the track by gaps in both tracks, so that polarity changes can take place. It is controlled for power by the hand controller, but direction is controlled by panel switches. The direction control on the hand controllers have NO effect in the reversing loop.

3. The EXIT BLOCK is the block just after the Reversing Loop and is controlled for both power and direction by the hand controller.

The most hazardous points for surges occur at the gaps between the Entrance Block and the Reversing Loop, and the Reversing Loop and the Exit Block. The power color and direction in both the Entrance Block and the Exit Block need to match the Reversing loop as the powered unit crosses the gap.
5. CN1Active Member

Part 2

There are two ways to do this :

1. Hand Controller Method:

Set the Entrance Block, the Reversing Loop Block , and the Exit Block power color all the same.
Use the same color hand controller, (matching the power color), for Entrance Block, Exit Block and Reversing Loop Block power and direction control.
While the powered unit is in the Reversing Loop Block, change the direction switch on the hand controller before the powered unit crosses the gap to the Exit Block.
2. Reverse Loop Method:

Set the Entrance Block and the Reversing Loop Block to the same power color, and the same direction.
Set the Exit Block power color to a different color and the direction switch to the opposite direction of the Entrance Block.
While the powered unit is in the Reversing Loop Block, change the power color for the Reversing Loop Block (on the control panel) to match the Exit Block power color, before the powered unit crosses the gap into the Exit Block.

--------------------------------------------------------------------------------

Reversing Loop physical boundary identifications (Mainline operation) – all proceding counter-clockwise

CODE B - Garcia (West Loop) – from before the bridge to just before the tunnel entrance.

CODE C - Tijuana (South Loop) – from just before the entrance to the tunnel by the window to just before the exit from the tunnel in front of the bridge.

CODE D - El Centro (East Loop) - from the farm house by the wall to the switch past the silos.

CODE E - Rose Canyon (North Loop) from the beginning of the draw-bridge crossing to the exit of the draw-bridge crossing going in the opposite direction.

NOTE: All power and direction switching must be done while the powered unit is in the Reversing Loop before it crosses the gap exiting the Reversing Loop for either method.

BE SURE TO RESET SWITCHES AFTER EXITING FOR THE NEXT TRAIN COMING IN.

SAN DIEGO MODEL RAILROAD CLUB Mainline Reverse Loop Configurations. Each Configuration shows 4 Block Gaps numbered 1,2,3, &4. Blocks are 1 to 2 (Entrance), 2 to 3 (Rev Loop), & 3 to 4 (Exit).

Note: ALL power and direction switching must be done while the Powered Units are in the Reversing Loop, before it crosses the gap exiting the Reversing Loop Block for either method.

6. cmnNew Member

Form the circuit you send I understand its manual right? is there
an automatic curcuit avaibale like the DCC one that I can use
and control the reverse loop?

cmn--
7. 60103Pooh Bah

As far as I know, there is no automatic control. The problem comes down to the fact that you have to reverse the whole rest of the layout for it to work. If you just had two reverse loops and a bit of track, you could wire the joining track up through contacts on the switch machines. If your reverse loop is part of a layout with multi tracks and other trains running, I think you're sunk.
The DCC black box works because the track power is AC and it doesn't matter to the loco if you change the power supply. We found that running a DC loco through the DCC reverse loop (loco #0) caused the loco to reverse itself when it hit the exit to the reverse loop.
8. CN1Active Member

E-x-a-c-t-l-y.........hu....did I spell this right
9. Fred_MGuest

QUOTE: The entry and exit points are the potential source of relatively large surges and so the operation must be undertaken in a way that minimizes the potential of having those surges run through the powered units and the electronic components that accompany them. When you consider that the voltage can be +15 volts on one side of the gap and –15 volts on the other side of the gap, you could encounter a 30 volt differential, enough to cause pitting of the wheels and/or damage to electronic components in the powered unit.

Sorry to disagree, but with a standard DC power pack this isn't so. The greatest difference can only be 15 volts. If you want to look at the output of a standard DC powerpack as + and - the 0 would be in the center, so at 15 volt output the negative would be -7.5 and the positive would be +7.5 for 15 volts. As science says, you can't create energy. A 15 volt powerpack can't generate more than a 15 volt potential no matter how you hook it to the rails. FRED
10. Mike RMember

If DC layout operators were willing to just provide means/ need for their train to just STOP in the ''reversing section", the control, and therefore the wiring, becomes very very simple.

No changes to cabs, no doubled-up reversing switches, nothing....just one only DPDT switch that routes power to the reversing section from either the cabs, or from the adjacent non-reverse section tracks themselves.

It is quite common for 2-rail layout overseas to simplify reversing loops in this manner, and when one considers it, how 'necessary" is it for a train to have to run through a reversing section without stopping ?
Just a thought.
Reversing loops have always been very simple for me because of this "let them stop" philosophy.
regards
Mike
11. jon-mononActive Member

The "exception" for lack of better terms, would be if you have two seperate supplies (or a dual supply), they could have a potential of producing 30 VDC. This is common practice with a dual +/- 15 VDC bench power supply when you need more than 15 VDC. You tie + on one supply to - on the other, then you get the sum of the voltages between the untied + and -, regardless of if/where it is earthed, as long as there is no more than one earth point. Our train transformers outouts are generally not earthed.
12. papasmurf37Member

Go to www.ttxdcc.com.
This is website of Tony's Train Exchange, a really knowledgable dealer in all things DCC. On website, look up the in-depth testing which was done by a third party. I believe 3 brands of reverser modules were tested. ALL of them produce some sparking when the first wheelset activates the electronic switchover in reverser units. Tony's own brand operates at lowest current and thereby produced the LEAST sparking, thus, less pitting of rail/ wheels. For this reason, we purchased their unit for our HO layout's reverse loop. TTFN.....Tom in NH
13. Fred_MGuest

But if you are running two cabs off of one power supply the max is still 15 Volts. It's only with more than 1 power pack (transformer) that 30v can be had. We also use to hook lights up to each end of a reversing loop so we would know which way the switch was set. I also think with todays electronics a DC auto reverse switch could be rigged up using overload detection and a flip flop circuit, but not by me. I don't know enough. FRED
14. LightbenderMember

Hello Cmn,

If you can't handle Mike's idea of stopping your train in the loop to throw your reversing switch and just have to highball through the loop there is an analog solution if your loop turnout points have a motor.

Get 2 Atlas snap relays and wire them in parallel with the turnout motor. One relay has the input connected to your cab and the 2 pairs of outputs are crossed to provide relay operated reversing to your control panel and ultimately the track blocks.

The other relay has the inputs connected to the track power and the 2 pairs of outputs are once again crossed to provide relay operated reversing to your isolated loop. An additional wire taken from the output can be used to power your frog if needed.

If you want to have signals you will have to add an additional snap relay. You may also want to consider a capacitor discharge unit if your power supply has problems throwing 4 motors at a time.

To use this set up you open throttle and run through the turnout onto the loop. After the train has cleared the turnout and before it reaches it again you push the button to throw the turnout switch.
That's it.
Nothing to remember.
Around \$10.00.

If you don't understand I will draw you a picture showing how to wire this setup. Just ask.
15. jmarksberyActive Member

Tony, you can draw it for me, i am stuPid on this stuff. Thanks
16. LightbenderMember

Hello jmarksbery,

The cab relay is just another reversing switch so it doesn't matter if you get the wires backwards. If the train is going the wrong way just throw your cab reverse.

The loop relay wiring is important, so test it as you go. Power and throw the turnout points which will also set the relays. Power down and get your Ohm meter or continuity probe.

Check that you have continuity through the frog and onto the isolated track. If you don't get a reading or light, touch the pick up lead to the other rail. If the tester now lights up you need to switch the pickup wires.

Test again to make sure and then manually throw the motors and check that the continuity is now correct to leave the loop.

Don't use a DC meter with powered track as reverse current will whack your d'arseneval (and we all know how painful that can be) setting it to 100 volts or more will ease the pain if you have to try to see the throw.

Hope this is clear.
17. LightbenderMember

Woops almost forgot. If you have more than one reversing loop or wye you will need to add a cab relay for every one of them. Just stack them in series. You cannot simply add to the actuating wires of the existing cab relay as this will cause all of the relays to fire...BAD.
18. Mike RMember

Tony:
Although I will stay with my own "stop in the reverse block" method, partly due to my hand-thrown Peco turnouts, ( and partly due to my track plan and control locations ), your method and schematic look very good.

Well done! :thumb:

I'll bet your brother in Toronto couldn't have come up with that !
regards,
Mike
19. LightbenderMember

Hello Mike.

Thanks, as you say it looks good but unforunately there is a rather big flaw. This is a One Cab deal. For multiple cabs the whole system fails.

I have come up with a solution in the Tech Forum under the "reversing section" thread that suggests rotary switch preselection.

Please don't think that ground throws excludes you from the 'stringing metres of wire' club. The hand throw is quite capable of actuating switches using rods and elbows. It would be a lot cheaper than using relays but a lot more work to get the mechanics lined up and working smoothly. The wiring would be the same as the relay version except for the substitution of DPDT's for the relays.

Sadly along with all this helpful advice I have omitted to mention that I too use toggles to go through the loops and I have stations and water towers in useful looking positions to stop a train for discrete electricity manipulation.

The really sad part is that there are other Hairy Otter operators (easy for me to say) that frequent this forum both lurking and visible and I have been asked "Why don't we have that?" Oh well for the price of a bag of relays I'll get to give up trying to teach the control panel switching. Serves me right for preaching without practising.