DCC and DC toggle switching arrangement

[paulbb]

I have a smallish (10'x8') continous/ roundy roundy  OO layout and I have wired it with insulfrog points . I can operate it in either DC mode using a very old HM Duette or as a  DCC operation using an NCE Powercab. The points are manually operated. Both work OK, but can members help with a neat way of quickly switching between the 2 as I have both DC and DCC engines, and I don't wish to bear the cost of converting  everything to DCC ,  or going DC and losing its features. In particular what type of switches can I use? I would also like to switch to a DCC program track as well , so a simple and easy type of 3 way switching is required. Has anyone out there done this?

[Dungrange]

1 hour ago, paulbb said:

a neat way of quickly switching between the 2 as I have both DC and DCC engines

 

The issue here is that you don't want DC locomotives sitting on the layout when you throw the switch.  Since changing from DC to DCC will involve removing your stock, the need to disconnect once control system and then connect the other shouldn't be a major issue.  It also means that there is no risk of you inadvertently connecting DC and DCC and thus risking damage to the DCC system.

 

However, if you really want a switch, then yes it can be done using a Double Pole Double Throw (DPDT) switch, providing it's the break before make type, so go for one with a centre off position.  There will be six terminals on the back of the switch.  The two centre ones go to the layout and the other terminals are connected to the the DC controller on one side and the DCC command station on the other.  The switch then connects either the DC controller or the DCC command station to the layout, but not both.  This is effectively how DC Cab control works and it's been used on thousands of layouts.

 

Brian Lambert's website has diagrams for setting up a programming track and you would effectively be taking the same approach but instead of both outputs coming from the DCC system (Main and Programming) you'd be using separate DC and DCC.  See about halfway down this page https://www.brian-lambert.co.uk/DCC-Page-1.html.

 

If you want DC, DCC Main and DCC programming, then you need to move to a rotary switch, which will typically have 12 contacts.  However, you really need to be confident that you understand what you are doing and there is no risk of DC and DCC shorting, otherwise you risk damaging the Powercab.  

[RAF96]

DPDT centre off switch

The switch flips DC to DCC by having the track wired to the centre pin pair and each controller wired to each outer pin pair.

DCC controller Prog output goes to your programming track and Track output goes as above, no need for a second switch, unless you want say a live siding to double up as a programming track. I have a rolling road as a dual use Prog/Run track.

[34theletterbetweenB&D]

14 hours ago, paulbb said:

...I can operate it in either DC mode using a very old HM Duette...

Something that hasn't been touched on, when running DC are you simultaneously using both controlled outputs to power two locos independently on tracks which are electrically isolated? Do you wish to retain this capability?

 

If so, the best course to retain both this DC capability and DCC operation by means of switching, is to section and rewire the layout for cab control, following the guidance on Brian Lambert's site. 

[Dagworth]

1 hour ago, 34theletterbetweenB&D said:

Something that hasn't been touched on, when running DC are you simultaneously using both controlled outputs to power two locos independently on tracks which are electrically isolated? Do you wish to retain this capability?

 

If so, the best course to retain both this DC capability and DCC operation by means of switching, is to section and rewire the layout for cab control, following the guidance on Brian Lambert's site. 

The risk with this idea is that with DC control and cab control switches, if you run a loco into a section that’s switched wrongly you cause a short and trip the DC controller. If you have DC on one section and DCC on another and run a loco across the join you feed DC into the DCC system which can quickly destroy the output stage of the DCC system. 
 

Better to keep them separate, I would suggest a simple jack socket input to the layout and jack outputs from the DCC system and the DC controller, Very quick and simple to unplug one and plug the other in. 
 

Andi

Edited July 29, 2023 by Dagworth

[Dungrange]

5 hours ago, 34theletterbetweenB&D said:

Something that hasn't been touched on, when running DC are you simultaneously using both controlled outputs to power two locos independently on tracks which are electrically isolated? Do you wish to retain this capability?

 

That's a good question, which I never thought of asking.  I was just assuming a single DC controller.

 

5 hours ago, 34theletterbetweenB&D said:

If so, the best course to retain both this DC capability and DCC operation by means of switching, is to section and rewire the layout for cab control, following the guidance on Brian Lambert's site. 

 

Like @Dagworth, I wouldn't recommend this.  Cab control is fine for a DC only layout.  If two adjacent sections are set to different Cabs, then a short will occur when a locomotive bridges the gap, but this will just be inconvenient rather than expensive.  All our club layouts use Cab control and forgetting to set a section to the correct Cab is a common enough occurrence.  As such, I'd consider the risk of inadvertently connecting DC and DCC to be far too high.

 

If we still want a switch solution, then the need is to step up to a Four Pole Double Throw (4PDT) switch.  Something like - https://uk.farnell.com/multicomp/1m41t6b11m1qe/switch-4pdt/dp/9473696.  Remember that you'll need a high current switch that is rated at more than the current output from your DCC Command Station.

 

The terminals on one side of the switch are connected to the two separate controlled outputs from the Duette.  The corresponding centre terminals are then connected to Cab Position 1 on each of the DC section switches (assuming these are DPDT) and the other centre terminals are then connected to Cab Position 2 on these same DC section switches.  The last line of terminals (opposite the ones that the Duette is attached to) is then connected to the DCC Command Station.  If you want Power Districts, then circuit breakers could be inserted between the 4PDT switch and the DCC Command Station.  If this were the case, then the DCC section switches would define which sections are in which power districts.  However, this wouldn't work if the DC layout has been wired using common return principles.

 

As @RAF96 has highlighted, it would be preferable if the programming track were separate from the layout, rather than a powered siding on the layout.

 

When thinking about the preferred solution, you need to think about the risk of inadvertently connecting DC and DCC, both when wiring and testing the layout and during operation.  That is, when wiring and testing, I would replace the DCC Command Station with a separate DC controller until I was certain that there were no crossed wires.

[Bigskybirds]

My layout is 10x8 and I have 4 loops, they are all switchable between DC and DCC and the third loop is 3 - rail which is also switchable between 2 and 3 rail plus DC and DCC. I use DPDT switches for each track and use isolated points for the sidings. I have had the layout since 2016 and never got mixed up or killed a Locomotive.

 

I also switch each loop separately between Gaugemaster DC controllers and Z21, Lenz and ECoS DCC controllers.

Edited July 31, 2023 by Bigskybirds
Removed link

[RonnieS]

Very interesting. I was going to switch between between DCC and DC by using an on off on switch 

 and just switch the Common return. However others seem to swear by a Double pole Double throw. So if the power units are not connected is this sufficient?

 

Edited October 2, 2023 by RonnieS
punctuation

[Dungrange]

3 hours ago, RonnieS said:

Very interesting. I was going to switch between between DCC and DC by using an on off on switch 

 and just switch the Common return. However others seem to swear by a Double pole Double throw. So if the power units are not connected is this sufficient?

 

I don't really understand your thinking.  You either don't need a switch at all (if the DC and DCC systems are NEVER connected to the layout at the same time), or you need a Double Pole Double Throw (DPDT) switch because your track has two rails.  You must switch both from DC to DCC.

[RAF96]

And if so you are advised to have a centre off DPDT switch so there is a definite ‘gap’ twixt the DC and DCC potentials.

[spamcan61]

8 minutes ago, RAF96 said:

And if so you are advised to have a centre off DPDT switch so there is a definite ‘gap’ twixt the DC and DCC potentials.

For sure make sure it's break before make.

[RAF96]

On 02/10/2023 at 19:54, spamcan61 said:

For sure make sure it's break before make.

That’s what a centre off does.

[RonnieS]

Thanks guys DPDT it will be