Reliable DCC and reversing loop POC (keep-alive, dual frog juicer, pfx brick)

[NilsvN]

Hi all, I've got something cool to share with you. I've been planning how to tackle my next 9v layout where I want to control multiple trains on a interconnected set of loops. On a regular 9v layout, you cannot do that. This is my solution:



It's a 9v motor with the motor taken out, feeding into a bridge rectifier (into the A/C connectors) so that the output polarity is always the same. Then from there it goes into a step-up converter set to 10v output (track power is ~12v, but a bit lower on the frog). From the step-up converter it's connected to both a TCS KA3 keep alive and a PFx Brick. The keep alive ensures that the PFx Brick stays powered (and keeps the motors running) if power suddenly cuts out very briefly. Let me explain why that is important:

For the reversing loop I'm using a TCS dual frog juicer. Basically, the "loop" part of the reversing loop is an isolated section of track, which we'll call the frog. You connect track power to the dual frog juicer input and connect the output to the frog. When the train drives from normal track onto the frog and the polarity of the frog is "the wrong way round", then it will automatically switch the polarity of the frog. This happens very fast, but it's enough of a delay when going into the bridge rectifier and then into the PFx Brick that the PFx Brick shuts off and turns on again, effectively stopping the train. That's where the keep alive comes in!

Demonstration: (watch the indicator LED change between red/green, this means polarity gets switched)

https://bricksafe.com/files/SystemTrains/lego-dcc-train-concept/video 1.mp4

https://bricksafe.com/files/SystemTrains/lego-dcc-train-concept/video 2.mp4

In the demonstration I used a PF remote. For my layout I'm going to be using Vincent Vergonjeanne's fantastic piece of software to control the PFx Brick with a Powered Up remote using bluetooth. That way I can control every train even when they are going through a tunnel for example. Here is the full post about the software: [link]

I hope you found this interesting :)

Thanks to Lazarus992 for the tutorial on how to open up and remove the 9v motor

[Toastie]

16 hours ago, NilsvN said:

I hope you found this interesting :)

No. I find it absolutely fascinating!!!

Although I am on my own route to reversing loops and so on, this is really nice work. Surely expandable - and the PFx soft/hardware is the best out there!!!

Good luck with your project - and keep posting here!

Very nice.

All the best,
Thorsten

[davidzq]

I did something similar. I added a PF cable to a 9v motor, separating the power pickup from the motor. With just this, the train can be controlled by any PF controller (Fx Brick, S-Brick, etc) running off track power. But I also added a battery box, connected through a diode (so train will run off 9v track power, and only switch to the 7.2v battery if track power is lost). It then runs through a Voltage regulator, keeping a constant 9v to the controller, so train doesn't slow down with track distance or battery drain. Best of both worlds.

[NilsvN]

7 hours ago, davidzq said:

I did something similar. I added a PF cable to a 9v motor, separating the power pickup from the motor. With just this, the train can be controlled by any PF controller (Fx Brick, S-Brick, etc) running off track power. But I also added a battery box, connected through a diode (so train will run off 9v track power, and only switch to the 7.2v battery if track power is lost). It then runs through a Voltage regulator, keeping a constant 9v to the controller, so train doesn't slow down with track distance or battery drain. Best of both worlds.

Ah, that's also a neat solution! I couldn't figure out how to make it so the battery acts as backup when there is power loss. Does it recharge the battery as well? I can imagine reversing loops are even easier to deal with in your case, just add 1 plastic RC track in the loop (granted you only have 1 pickup point).

The only downside that I can think of is that you are limited to the max current of the battery when track power is lost. With my solution, you can keep stacking motors until you hit the 3A limit of the PFx brick. Or is your battery some kind of RC car battery?

[davidzq]

On 5/25/2023 at 4:09 PM, NilsvN said:

Ah, that's also a neat solution! I couldn't figure out how to make it so the battery acts as backup when there is power loss. Does it recharge the battery as well? I can imagine reversing loops are even easier to deal with in your case, just add 1 plastic RC track in the loop (granted you only have 1 pickup point).

The only downside that I can think of is that you are limited to the max current of the battery when track power is lost. With my solution, you can keep stacking motors until you hit the 3A limit of the PFx brick. Or is your battery some kind of RC car battery?

Battery is not charged by track, I haven't had a need to incorporate that. I use the AA battery box with Eneloops, which provides a decent run time (~3 hours) on a heavy train with two 9v motors. I found that when running without battery that a single 9v motor could create connectivity issues with momentary power losses at weak track connections, but having a second 9v motor eliminated this issue. Current limitations have never been an issue for me, but I could see it being an issue with long slow freight trains.