Bus wiring vs. star wiring and location of toggles

[lionelsoni]

I took that 455 kilohertz frequency from TMCC. I couldn't find what frequency DCS uses. If you know, we could verify the capacitor size.

[wrmcclellan]

Good input Bob. We will have to try that and see how the DCS reacts.

[lionelsoni]

If we're talking about terminating an rf transmission line, 100 nanofarads (.1 microfarad) has an impedance of only 3.5 ohms at 455 kilohertz but more than 26 kilohms at 60 hertz. You could put the capacitor in series with the resistor to vastly reduce the power that it would have to dissipate, and reduce the load on the transformer by 3.24 watts at the same time.

[Anonymous]

You might try the Xicon 25 watt cement power resistors. 25 watts should be plenty without the need to combine parts in series/parallel. The Mouser part number is 280-CR25-100 and they are only $0.99 each in quantities of 10.

[spankybird]

Hi Dave,

Having DCS, and even before having it, I used a Star patteren, but the legs of the Stars are far from being equal length. DCS single is 10's

[FJ and G]

thanks Bob, ROy, I'm gonna keep your suggestions handy.

Roy, the sketch you drew looks like my trackplan! Don't know if you knew that when you drew it.

[wrmcclellan]

Hi Bob,

1. We settled on the 40 watt as they were very cheap at the surplus store and ran cooler. I suspect 3 watts on a 10 watt resistor alone will get very hot although there would be no damage to the resistor, the issue being absolute safety under the layout. The 40 watt units get warm.

2. We did try some other combinations and values and the single resistor worked best for DCS signal level (10's). RF reflections on the transmission line is the issue.

Interestingly not all light bulbs do the job either. This is the reason we changed to the resistor. We could not always find the bulbs we needed.

Regards,
Roy

[lionelsoni]

Roy, Dave could put 4 100-ohm 10-watt resistors in series-parallel for much less money. Radio Shack sells 2 for $1.79 (271-135) and Mouser sells them for $.55 each (280-CR10-100). However, I suspect that a single 10-watt resistor would do the job, since 18 volts across 100 ohms is only 3.24 watts.

[wrmcclellan]

Dave,

I put a few thoughts on paper. See what you think.

http://home.comcast.net/~roy.mcclellan/Photos/Electrical_thoughts_for_FJ_and_G.doc

BTW - the wirewound ceramic power resistor is available from www.mouser.com, Mouser P/N 588-F40J100 (Ohmite brand). But in the catalog it is a $13 item. We get them at the local electronics surplus store for about $1-2 each.

Regards,
Roy

[wrmcclellan]

Dave,

From our club layout experience:

1. Star wiring (hub and spoke) is best. Make sure common and power (hot) leads are kept together. DCS is a radio signal - so recall the old 300 ohm twin lead TV antenna wires - and needs a transmission line to make the trip effectively. If you get the two wires in common insulation (such as that sold on the OGR website and in Home Depot) that is ideal.

2. Unless you are big into central control panels - we found that having the controls near the track geometry they control is best. This also keeps wire runs down and is best for the DCS signal.

3. Common to both outside rails is best. Also good for Lionel TMCC. If you decide to use an outside rail for control (as we have), just isolate the rail section and its wire and you already have the wire below for hooking up the rail section to the trigger of whatever you are controlling (e.g. signals).

4. For best DCS - cut all the rails for isolation between power districts. This eliminates "loops" for the DCS signal and improves it's reception by the trains.

5. To avoid soldering upside down, we used wire nuts to attach the track pigtails to the main feeder underneath the layout. Makes it easy for troubleshooting and additions.

6. DCS likes a termination. An 18 volt light bulb has been recommended. We got tired of changing the bulbs and calculated that a 100 ohm, 40 watt ceramic wirewound power resistor has essentially the same characteristics and this has worked great for several years. Put the resistors at the end of long wire runs or at the hub of a set of spokes feeding the layout.

7. Switches - ideally DCS should be controlled with a DPDT or DPST switch where both hot and common are switched. I have noticed on the OGR forums that this has not been necessary and that a SPDT or SPST switch works fine. Just make sure you route the common wire along with the hot wire to the swtich (ie keep them together even when going by the swtich).

Regards,
Roy

[FJ and G]

Two questions (wiring and toggles)

1. Daisey chaining sounds like the way to go. I've tested DCS out and it seems to work for me, despite recommendations to contrary.

Getting ready soon to do all of the wiring.

Also, I soldered 2 wires onto each outside rail so there's a total of 3 wires per attachment, including the center. Do you think that might be overkill? I was thinking that later on, I might want to use one of the rails for controlling an accessory.

2. I'm going to route the wires to DPDT toggle (that is large enough for the amps). Haven't yet decided whether to group the toggles or to keep them near the power district they control, as my layout is 25 ft long and will involve lots of walking and switching.

Your ideas appreciated.