I have divided my layout into seperate blocks with a common rail for all of them. I want to put a DPDT switch to power each block. I have only one powerpack so the switch also needs to act as a reverse switch. I have no problem wiring the DPDT for a single block but can't figure out how to add another one to a seperate block. My wiring for the first one consists of attaching the two end poles to the powerpack and the two center poles to the (a) common rail & (b) block rail. Of course I have already wired diagonally across the opposite end poles as usual. the question is: How do I connect the next DPDT switch because the common rail wire in switch #1 already feeds that rail? Or is my idea impossible using just one power pack?
Thanks
The classic block wiring scheme assumes you have two power packs, call them cab A and cab B. The DPDT switch is wired to connect the track block to either cab A or cab b. Wire the track block (two wires, one for each rail) to the center poles of the switch, and wire cab A to one set of end poles, and cab B to the other end poles. Flip the switch one way, and the track block is driven by cab A, flip it the other way a the track block is driver by cab B. Install a switch for each and every track block. Wire each switch the same way. Which will result in the end poles of all the switches being jumpered together and fed to the power pack. Take care that all the switches are uniform, so that flipping the switch handle UP puts Cab A in charge, and UP selects Cab A on ALL track blocks. Having UP connect cab A on some blocks and cab B on other blocks is just too confusing for words. With luck, your DPDT switches are center OFF, so you can switch power off for a siding or a spur, so you can park a peddler freight and have it stay put while the hotshot freight takes the main.
You have common rail? no problem. You only really have to switch ONE rail to make things work. Common rail goes back to when SPDT switches were cheaper than DPDT switches. That was a while ago, pretty much all DPDT switches cost about the same now. So, you connect the negative power pack output on BOTH cab A AND cab B to the common rail. Permanent connection, no switching. Just switch the positive side of the cabs with one set of poles on the DPDT switches. Me, I don't do common rail, I switch both rails, just to make sure I turn the block off, even if I have a sneak path of some sort. That's probably just superstition on my part, but that's the way I do things.
You don't have a cab B right now? No problem, just wire up cab A. You may acquire a cab B sometime in the future, then you can wire it in. As a matter of fact, that's where I am today, just one cab. My layout is small, single track main, and I am the only operator. You need two operators before two cab make any sense.
David Starr www.newsnorthwoods.blogspot.com
Let's differentiate the DPDT and the DPDTCO.
The DPDT works great for a reversing switch. With DC, if you power pack doesn't reverse, you need one between it and the layout wiring in order to reverse the direction of all locos.
For block wiring, DPDT doesn't work as well. There is no center-off position to kill power to that section of track so a loco sitting there will stay. That's why you need DPDTCO swicthes for the blcok wiring.
Something else you need is a second DC power pack. With DC, you need to have as many powerpacks as locos you want to run. Since you're describing the wiring for a 2-cab DC system, or are very close to doing that, I'll assume that was your objective.
If so, the one side of the DPDTCO switch is wired to one DC pack and the other side to the other DC pack. Here, the CO position also interrupt power when switching from one to the other, preventing sparks and pitting of the contacts.
Plus, if you have 2 cabs or power packs, you'll need reversing switches on both power packs, so that the direction of each is independent.
Reverse loops are another story. Let's get this straight first.
Mike Lehman
Urbana, IL
have you read Model Railroad Wiring ?
DPDT switches are not necessary, as already mentioned, but won't hurt with a common rail. They are necessary for reversing sections.
greg - Philadelphia & Reading / Reading
When our club was built in the early 1980's, we used common rail, one reverse loop and fourteen blocks and four throttles.
We used rotary switches for selecting blocks. No reverse switches there.
Only one reverse switch was needed for the complete layout. Number 24 telephone wire was used.
Worked very well until we went to DCC.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
On all of my old DC blocked layouts over the years, I used only SPDT switches (common rail). I never had a reversing loop situation on any of my old layouts.
Thank goodness I am out of that mess with DCC.
Richard
If I can't fix it, I can fix it so it can't be fixed