Terminating bus ends

[Antoine L.]

Hi

Yeah well, I've been following and reading all of Alan's blog and now I look at my layout and I feel like my standards have now grown up. I'm salvaging my current layout, and will start another, following most of what Alan shares on his blog which I think is a gold mine of good practices. (Thanks Alan you're awesome).

Now more on topic, here is what Alan says in one of his blog posts (http://www.lkorailroad.com/welcome-to-maryland/):  "To reduce the ringing it was suggested I add a dummy load of about 1 amp to each buss at the point furthest from the power supplies."
 (ironic that Railpro is from "ring")

Anyway, I am using Railpro Powersupply that comes with Railpro:  the PWR-56. I am fairly sure this powersupply offers the exact rail current needed and not a single volt extra for dampening purposes. My layout won't be bigger than 11x19 and will have continuous. (currently working on Givens and Druthers (again thanks Alan)and on a track plan with Xtrackcad). What is the best way to wire my layout with the Pwr-56 Psu?

What do you think?

Thanks!

Antoine

[Alan]

The only reason I had ringing in my supply lines was because of the massive quantity of wire in my power distribution system and the relatively long distance between power supply voltage regulation and load (loco). There is in excess of 2000 ft of 12 ga wire in the system. That much wire creates a lot of capacitance and inductance. The power supply regulator is challenged to keep the voltage maintained under these circumstances especially with fast current rise times (LM2 PWM). The ringing is a problem only when the power supply changes from an unloaded to a loaded state. The parasitic load keeps the power supply continuously loaded and thereby eliminates the ringing.

On an 11x19 layout you should not have this problem assuming your PWR56 is centrally located. Run your power bus in a star configuration out from the PWR56.

Thanks for the compliments BTW.

 

[Antoine L.]

Hey Alan, thanks for quick reply.

So star configuration implies that both my power bus and track do not connect at ends on the continuous track, basically no loop? Should I put insulated rail joiners at the ends and leave buses unterminated?

Thanks

Antoine

[Alan]

No insulated joiners needed. Bus may be connected, or not, at ends.

Think of your track loop as a clock. It is a continuous circle. The bus is also a continuous circle around the perimeter of the clock. Power supply sits in the middle. Legs from power supply go out in a star pattern and connect to the perimeter bus at the 12, 2, 4, 6, 8 ,10 o'clock positions. It doesn't matter if the perimeter bus is connected to itself at the 12 o'clock position.

[Antoine L.]

If the bus loops on itself just like the track does, That would basically mean I would have no bus ends right?

Antoine

[William Brillinger]

If the bus loops on itself just like the track does, That would basically mean I would have no bus ends right?

Correct!

[Alan]

The possible side effect is changing the inductance of the system. The connected track circle effectively becomes a giant air core inductor. If you connect the bus ends then the buss effectively becomes a second turn of the same inductor.

The coupling between the two is very weak and the air core is huge so it really doesn't matter in practical terms. More an FYI.

Parallel (un-twisted) bus wires are much more of an inductance/capacitance problem. Twist your bus wires a turn or two per foot. Twisting your track would also reduce inductance/capacitance but that tends to be bad on the train.   

[Antoine L.]

Thank you for your help. I will finish my track plan with XtrackCad and follow your advice.

Antoine