The MTH DCS User's Manual, page 17, "Recommended Wiring Method - Older Transformers" if using an older transformer without a "solid state" circuit breaker (like the good old ZW) that you should add a "AG3C" fast-blow 15 amp fuse between the Transformer and the TIU.
Page 13, "Connecting The Transformer To The TIU" --- Plugging transformer wires to the "Fixed Input" and the track to "Fixed Output" gives you DCS Control. Plugging the transformer into the "Variable Input" and the track to the "Variable Output" gives you Conventional Control.
Don U. TCA 73-5735
Good info! The ZW, although a work horse, is glacially slow when it comes to the circuit breaker. By the time it fires off, your state of the art pieces could be fried. Also it's recommended that you always have an incandescent light running off each power circuit. This helps surpress transient noise ie; sparks and spikes from normal train operation. I have looked at the "noise" on a toy train layout during operation and it's pretty active stuff. The older stuff, Pre-Post War doesn't care about this stuff to a point, lets just say that they are a lot less sensitive to operational noise than the new stuff. It's just another "insurance" against a dead engine or accessories. The PW transformer is a big "sink" for trainsients also but as I said it will have a tendency to cook newer hi tech stuff.
Sounds like you need to have a couple of TVS(transiant voltage suppressors) devices in the system for the older transformers. You can order them from Mouser Electronics, Bob Nelson put me wise to using the TVS units. Not that much investment for a whole lot of protection.
Lee F.
Yes, its completely possible. I have my layout set up this way. I use a z4000 to power the pike, so I bought a 4 pole double throw center off switch. The z4000's two track outputs are wired to one side of the switch and to the TIU's fixed inputs. The outputs of the TIU are wired to the other side of the switch. The center posts are then wired to the two distribution terminal blocks(one for each main power district). This setup allows me to switch from conventional to command any time i want, and the center off position prevents any backfeed .
I got the switch from All electronics-- website www.allelectronics.com scroll down to switches,toggle, then look for the 4PDT switch. cost is $4.85. shipping/handeling is $7.00---
HTH--
A Day Without Trains is a Day Wasted
Thanks for all the suggestions, everyone. I'm sort of resurrecting this thread, as I have some updates on the situation (and some new questions, of course!)
OK, so we scrapped the idea of using the ZW to run our layout in conventional at times, so just went with 4 Lionel 180W power bricks to power the TIU, and have all DCS, all the time. This simplified things a whole bunch. So now, my question is about protection. :) First off, the CB in the power bricks--does anyone know what the amp rating is on those? Reason I ask is: we actually had one of the automotive mini fuses inside the TIU (20 amp) blow during an operating session. We're pretty sure it was due to operator error, but it got me to thinking: #1-should we have another CB, maybe 10 amp, resettable, in between the power bricks and the TIU's inputs, and #2-should we also have TVSs wired in there somewhere? I'm thinking that the resettable CBs should go in line between the bricks (on each brick's "hot" lead) and each TIU input (4 total,) and the TVS should be wired right across each of the TIU's black and red input terminals (again, 4 total.) Does this sound right? Because the TVSs do not really "conduct" electricity under normal conditions, they're not going to cause a "short" and really shouldn't have any effect on the DCS signal, especially if they're wired in on the input side, before the DCS signal is generated, (right?)
Thanks in advance!
The CB's in the Lionel bricks should be a 10 amp. Here's a mostly unknown fact: "standard" breakers and fast blow fuses will trip(or blow) in just about the same amount of time. Even though the fuses in the TIU are 20 amps, 10 amps should be the limit for each channel. I'd use 10 amp breakers or fuses.
The only CB's that are reliable and have a set trip level are the "magnetic hydraulic" type. They are the modern equivalent of the old lionel 91 breaker. They are more expensive than the standard thermal breakers.
As to the TVS, the TIU has them in the unit. It wouldn't hurt to have additional TVS's installed on the layout, as I subsribe to the notion that it doesn't hurt, and will help, especially if they are installed at various places on the layout---not just at the TIU.
As for circuit protection, even a 10 amp circuit breaker is a little high, maybe something around 7 amp breaker would work better for circuit protection. If you have a long passenger train and two motorized engines then maybe 8 amp breaker would do.
The TVS units should work right after the transformer output and not interfere with the DCS unit.
A word of caution with command control voltage, make sure your lighted caboose or lighted passenger cars don't short out at the center rail pick-up because of getting a constant 18 to 21 volts applied to the track. I had a Lionel caboose short out on me # 17605, until I took the caboose off I didn't know what happened, thought my MTH engine was shot!
Thanks, everyone, for all the suggestions. As time and $ permit, we'll be implementing these suggestions.
My next question is: since the TIU has 4 outputs (2 fixed, 2 variable,) we have our layout (24'X55') broken into 4 blocks--3 blocks of mainline, and 1 block for the yard. We wired each block so that not only was the center rail in each block isolated from the others, but the grounds were isolated as well, ie, ground does not travel between blocks. Now, we're wondering if this is such a good thing. So, what the consensus on ground--should the grounds of all three blocks be isolated from each other, or should the grounds all be tied together (as in, not isolated at the junction between each block) and only have the "hots" isolated from each other? What will give us better DCS signal, as we have some areas where locomotive response is less than stellar. Thoughts??? Thanks!
Taran, normal practice is to break the center rail only. DCS sends commands out on the center rail, and listens for replys on the outside rails. connect the outside rails(grounds) together. I'm assuming that you have each TIU output going to a "central" spot, and then to the tracks . In your DCS manual, there is a section that tells how to run signal tests. Run an engine around your entire layout taking readings as you go. As lomg as the signal strength is above 5 or 6, you should not have problems controlling the engines. If it's less than 5, try putting an 18V lamp across the power feed at the terminal block for that section.
The reason for doing this lies in the fact that the wiring acts as a transmission line in regards to the DCS signal, and if it isn't properly terminated, the signal reflects back on itself, and the result is a weakened signal. Hope this helps----
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