Am I correct that the brand name for the Atlas DPDT switch is the Selector? Also, would one of those work to switch between a DCC system and a DC system on the same layout and using the same (common) power buss?
Purchase of a new DCC system is eminent, and the only thing slowing me down is my reluctance to give up dual type operation IF I decide on a DCC system that does not support DC as well.
The Atlas Selector is actually 4 SPDT slide switches ganged together in a single box. The Atlas scheme is set up to use common rail wiring, which only requires single pole switches for the block switches.
The common method to move into DCC is to substitute the DCC unit for one of the DC power packs in the dual cab control system. Common rail wiring is OK in this instance provided the DCC unit and DC power pack do not share the same power supply (highly unlikely).
Operation with split DC and DCC may require more discipline than you are used to to prevent the DC powered blocks from accidentally being bridged to the DCC powered blocks. Your DCC system is not going to like being connected to the DC power supply through bridging of the block gaps or insulated rail joiners, and the DCC decoders may object by letting the magic smoke out. The safest way is iron-clad adherence to the following rules:
Finally, even if a DCC system can support DC operations through zero stretching, that is only one DC locomotive in addition to your DCC locomotives.
hope this helps
Fred Wright
Thanks, Fred. That does help. As it turns out, I was thinking about the Atlas Twin, not the Selector. The Twin is a pair of DPDT swithches, and seems to me capable of being wired so as to make it impossible for both systems to operate at the same time. That may still be a bit risky, so I'm not sure what I'll do.
Mike
I don't see any gain by using the Twin instead of the Selector, unless you are going to use the second pole for indicator lights of some kind. The Selector has a center off position, which can be useful. By the way, toggle switches are cheaper than a Twin and can be had cheaper than a Selector. And toggle switches can be mounted in a track diagram, unlike the Atlas components.
As I said in the earlier post, common rail is fine for a DC power pack and a DCC system provided they plug into the wall separately. Plugging into the wall separately means their independent power supllies provide sufficient isolation so that a shared portion of the circuit won't bother anything.
What causes problems is if the one block is powered by DC, and the adjacent block is powered by DCC and a car or locomotive with metal wheels spans the gap(s) or insulated rail joiner(s) used to electrically separate the blocks. When that happens, both wires of the DCC output are effectively directly connected to both wires of the DC output. And that does mean trouble. Which is why the strong suggestion to have all blocks set to DC or DCC, but never a mix. Note that this bridging can happen with both rails gapped or just one rail gapped (common rail). So there is no real advantage in this situation to the Twin.
Where common rail can (doesn't always) become a problem with DCC is when you are using more than one booster to separately power 2 or more power districts. But you are not likely to use more than 1 booster on a layout small enough to use Atlas wiring components (which effectively limit you to 2 throttles). When you are operating a DC-blocked layout with DCC, all blocks are set to the DCC system position. This blocking can be useful for trouble-shooting. Problems can be quickly isolated to the block-level by turning off blocks one at a time until the problem goes away.
Fred W
As an add-on to my last post:
A good use of the Twin or DPDT toggle is to use it select the 2nd power pack or the DCC unit. This scheme allows you to operate in DC mode with both power packs. The output of the DPDT toggle feeds the block selectors instead of one of the power packs. The inputs are one of the power packs track feed and the DCC system track feed.
When in DCC mode, you still need to set all block power to the DCC system (or center off), and none to the DC.
yours in wiring
The safest way to switch between Analog and DCC is to use a plug. Install one plug on the analog power supply and another of the same plug on the DCC power supply. Install one socket on the layout and just plug in the power that you desire. This is referred to as an "air switch". No way to have both supplies connected at bthe same time. You can't even bump it by mistake. Well, you can but the most that will happen is it will be unplugged.
We use an expanded version of this on our club layouts.
Martin Myers
Thanks for the responses. All I really want to do is establish what might be called an A-B switch. One switch when in A position routes control through the common buss wiring from the DCC controler and when in B position from the DC source. I'm pretty sure this ain't rocket science. I asked about the Atlas Selector (actually Twin) because I had an unused one (Twin) in my parts drawer. Is there any possibility to keep this simple?