Accessory addressing using Hornby select

[Trackandfield]

Good Morning All

I would like some advice on how to wire up a point using an R406 yellow switch to a Hornby Select Controller under DCC conditions. My (new) layout (which was constructed for me) is on an 8' x 4' folding board and uses 12 points numbered #61 through to #72 with respective R8243 point motors and 3 x R8247 Digital decoders. As I have one spare point from my old layout I purchased an additional Point Motor but with no Digital decoders spare I thought I would try and use an R406 connected to the Aux Output on the Hornby Select, but try as I might, cannot get it to operate under any circumstances. Is anyone able to produce a wiring combination that would work, or is what I'm trying to attempt totally flawed.

Many thanks

Paul

[Chrissaf]

Is anyone able to produce a wiring combination that would work, or is what I'm trying to attempt totally flawed.

.

Yes flawed, but more to do in the way you are trying to do it. Not necessarily the concept. But do read the Postscript first, at the end of this reply.

.

First thing first. The Yellow Hornby switch must never be used for operating point motors. Firstly it is a R046 switch not a R406 [OK just a typo on your part, but worth mentioning it to you and future readers]. Secondly, the R046 Yellow switch is a 'permanent contact' change-over switch. If you use this with a power supply capable of providing more than 0.5 Amp then the coils of the point motor will start to swell up and smoke and if left connected to power will burn out.

.

The correct Hornby switch for operating Solenoid points is the R044 Black switch. The R044 is called a 'Passing Contact' switch and only gives a brief momentary connection as it is operated in each direction. Whereas, the electrical contact connection with the Yellow switch is permanent in nature and not momentary.

.

What has probably saved your point motor from damage is the inadequate current output capability of the Select Aux output which incidently is only 15 volts DC (more of which later in this reply).

.

The coil resistance of a Hornby point motor is in the region of 5 to 8 Ohms. For all intent and purpose this is as near as damn it a 'short circuit'. This combined with the incorrect use of the R046 Yellow switch is very likely to drain every available milliamp of current from the Select power supply and cause the DCC function of the Select to be affected sufficiently to prevent efficient operation of DCC locos.

.

At the instantaneous switching on of a Solenoid point motor (before the effect of inductance takes effect) the motor will try to draw about 3 Amps from the Select. The standard Select power supply is only rated at 1 Amp max. But because you have used the incorrect Yellow switch, the Select will be permanently trying to provide this high current request that it is incapable of providing. It is no wonder you cannot get it to work.

.

The 15 VDC Aux output of the Select DCC controller just does not have the current or voltage available to robustly operate a directly attached point motor. It is not designed to.

.

Personally, I would always use a separate dedicated supply to operate points using DC analogue technology as you are planning to do for this additional point. You need a power supply that is preferably 16 volts AC rather than DC and capable of supplying a minimum 2 Amps.

.

Although I would still use a separate power supply, even if using a CDU. But you may still be able to resolve your issue by inserting a CDU between the 15 VDC output of the Select and the point operating circuitry. A CDU (Capacitor Discharge Unit) takes the low current 15 VDC output of the Select and stores a charge in the capacitors. This charge can then produce (when required) a very high current kick of several Amps to robustly fire the Solenoid point motors. It is the CDU that is providing the high current that the Solenoids require and once a point is operated, the CDU recharges at a more sedate rate from the Select power supply. Thus the CDU prevents the attached Select 1 Amp power supply from being overwhelmed.

.

IMPORTANT NOTE:

If it is accepted that you need a CDU to resolve your issue. Note that the internal design of the Hornby R044 'Passing Contact' switch is not 100% compatible with a CDU and the R044 is not recommended for CDU use. Instead use either a PECO PL-26 switch (which requires an additional housing) or a standard electrical momentary changeover action toggle switch. This previous post gives more details on switch types.

.

https://www.hornby.com/uk-en/forum/point-motor-switches-newbie-sorry

.

Note that the R8247 Accessory Decoders that you are using for the other points already have a CDU integrated inside them.

.

CDUs also offer additional benefits. The way they work protects the Solenoid coil from over-heating and burning out. They also provide enough power to operate multiple Solenoid point motors in parallel. Loop cross-over or passing loops for example. They also eliminate the noisy buzzing you get when using an AC voltage supply directly on Solenoids.

.

CDU's are cheap......very cheap......Hornby do not make or sell stand-alone CDU's. They are very simple to install. A CDU is a 'shared resource' you do not need a separate CDU per additional point.

.

An example CDU.

.

POST SCRIPT: Alternative Solution that might be doable.

.

Subject to the way that you are using your current installed R8247 Accessory Decoders you might be able to modify your point wiring to generate a spare port for your new point.

.

If your layout has cross-over points that create a route between two ovals for example. Then those two points must always operate together (else the route is not made). Now if you have wired each of those two point motors to their own dedicated R8247 Accessory Decoder ports, then you could modify the point wiring so that both the point motors share the same Accessory Decoder port wired in parallel. This will free up a R8247 port that can then be re-assigned with a new address for the new point.

.

TIP: I write long posts. If you intend to write a reply, it would be appreciated if you didn't use the 'White Arrow in Blue Box' button. This is not a 'Reply to this post button. It is best to write any reply you want to make in the 'Reply Text Box' at the very bottom of the page and click the Green 'Reply' button.

.

[Trackandfield]

Hi Chris. . .Many thanks for the detailed reply, much of which has left me baffled, but the basics have been absorbed. In between your first and last post I ordered a 044 switch, thus negating the need to modify existing point wiring. As the point I'm trying to wire up is off a siding I just want it to be operated independently and PROVIDED I get the wiring correct (I'm assuming the wiring diagram in the pack will suffice) then all will be OK in the end. Any other tips will be appreciated.

[Chrissaf]

Since you have jumped the gun and purchased a R044 switch. Then that kinda makes the recommended addition of a CDU something that isn't going to happen due to the incompatibility of a CDU with a R044 switch. In my opinion, you will still be better off using a separate power supply of at least 2 Amps to operate your point with the R044 switch. The separate power supply should ideally be either 16 VAC or 19 volts DC to obtain power equivalence. I can prove this AC to DC power comparison with maths, but that would probably baffle you as well.

.

Point wiring diagrams can be viewed here:

.

https://www.brian-lambert.co.uk/Electrical_Page_2.html#Bookmark4

.

[Trackandfield]

Thanks for the updated information. I'm not sure if it's relevant but my layout builder has provided a P9300 15v 4amp transformer.

[Rog RJ]

The 15Volt power supply will be perfectly ok for powering your point motors.  I operate my points with the 4Amp 15Volt power supply that came with my Elite controller, even operates 2 points at the same time very easily.

[Chrissaf]

Yes as Rog says, the 4 Amp Power Supply substituting the standard Select 1 Amp power supply makes all the difference.