Accessory Decoder setup (R8247 MK2 modes)

[am549]

As part of my planning I’ve been reading about the accessory DCC controller (R8247). I’m a bit confused about its various operating modes and what they mean. Is there a good explanation of them available? I.e. if I wanted to wire up 8 sets of point motors could I use special mode 1 or would I need an additional standard controller?

I’m assuming there are no DCC point motors about? Should I also be thinking about a DCC bus or just taking power from the track for the accessories? I saw the diagram Chrissaf which was incredibly helpful on how to wire things in.

[Chrissaf]

I’m assuming there are no DCC point motors about?

 

 

If you cast your net further than Hornby, then other brands produce point motors with integrated DCC Decoders. For example DCC Concepts 'iP Digital' point motors.

If you go to the top of the RailMaster forum and open the 'RailMaster FAQ Index' sticky thread, DCC Concepts products when used with RM configuration methodology is described in FAQ 6. Contains useful info that can also be applied to the Elite controller without RM. FAQ 5 covers the original Hornby R8247 but doesn't go into the detail of the different operating modes of the MK2 decoder version.

96RAF will be able to give you "chapter & verse" regarding the MK2 modes when he sees your post.

[am549]

Thanks Chris for your rapid reply. I had come across the DCC Concepts ones and some made by Rails Connect.

I'll admit I didn't look at the Railmaster forum, thanks for the tip!

[96RAF]

It is presumed you are talking about R8247 Ver 2 when you speak about special modes.

The device has four output channels numbered 1 to 4 each with a pair of switched negative output ports oddly labelled + and -, which are used in conjunction with a common positive port labelled C. The + and - are not polarities but simply an indication of this way or that way.

Standard Mode is equivalent to a Ver 1 Acc Decoder in that it can send a variable pulse or steady output in turn to the pair of ports of the four channels e.g. point left and right or signal red or green. There is the additional functionality of being able to specify that one or more of the other channels fire when the target channel is fired i.e. in cascade.

Special Mode 1 allows eight ports to be configured to work independently i.e. both ports of all four channels. These can be set to pulse or steady. The rate of pulse and number of pulses can be set. The way this is done is by allocating double addresses to each channel i.e. channel 1 takes addresses 1-2, channel 2 takes 3-4, and so on, so you must take account of this double addressing when numbering points, etc.

To answer your question about do I need another controller - you mean accessory decoder - then you can see this double allocation method doesn’t really help with that and for points you are still better off with each channel controlling one point motor, so for eight points you need two acc decoders.

Special Mode 2 allows the four channels to be configured to pulse or steady output for both ports together. The rate of pulse and number of pulses can be set but both ports will be the same. I struggled to find a use for this setup.

These settings are controlled by CVs as detailed in the user manual.

[am549]

Thanks 96RAF.

I guess my next question is what would special mode 1 be used for?

How would I also know when purchasing if I've got a v1 or a v2? One would assume buying new now would be a v2 but I'd want to be sure.

[Chrissaf]

Having read Rob's reply. I do not see Special Mode 1 as being a mode that allows 8 standard point motors to be operated from a single R8247. Even in Mode 1, only four standard point motors can be controlled in both directions of travel. For 8 solenoid point motors you will still need two R8247 and I suggest that they are set to 'Standard Mode', which, by the way, is their factory default configuration.

EDIT: This reply was posted prior to Rob's edit of his reply.

[96RAF]

Note that I have amended my post to correct the Special Mode 1 8-way addressing.

I struggled to find a use for either of the special modes apart from the duration of pulse and number of pulses could be configured. For testing I had it flash lights, but as for a practical use . . . Open to suggestions.

Version 2 has this box with a big sticker on it. CV7 will read back as 135.

[am549]

Yes I suspect you're correct. Is it possible to connect 2 motors to one port, i.e. for 2 points that need to be changed at the same time?

[Chrissaf]

Mode 1 could be used to operate up to eight Dapol semaphore signals in pulse mode via relays for example (Dapol semaphores need a metallic loop to trigger them in a toggle operating mode, hence the relay to remove the voltage interface). In mode 1 constant output, then maybe individual control of LEDs or other motorised accessories, a powered conveyor belt for example.

I don't see Mode 1 as being designed for Solenoid point motors.

It's not clear in Hornby's documentation what was in the Hornby designers mind when developing the special modes. They just seem to be modes for the layout builder to utilise if they can devise a need through their ingenuity to adapt the product to their custom needs.

In answer to your supplementary question in your last post.

In principle you can connect two point motors in parallel to one Accessory Decoder port. This assumes that the two motors are the SAME point motor model. Mixing motor models or brands on the same port usually results with one of the pair working and the other not. This is because the coil windings of the different model / brands of point motor will have unmatched coil electrical specifications and the motor with the lowest Impedance will draw all the available switching current and deprive the other one from sufficient power to operate. If the coils are electrically matched then the power is split equally.

[am549]

Thanks for all your help and rapid replies Chris. I would definitely make sure that any motors which are paired up are identical.

Trying to decide between surface point motors (easiest) or standard and mounting under the baseboard (cleanest looking).

[96RAF]

Due to lack of flexibility on my part, all my point motors are mounted topside, both R8014 in their little huts and R8243 for tighter locations. There are some geometry situations where a motor just cannot fit line-side on the layout topside and has to be set remote from a point linked by a stiff wire.

Best situation is to have R8014 mounted direct to the points as reliability is usually much better along with the tidy visual element.

If you need additional switching for led indicators or frog polarity consider going for other make motors either solenoid or slo-mo stall motor types, some of which can have a decoder built in to save on accessory decoder cost on a DCC layout.

[Fishmanoz]

So Rob, it seems you are telling me that Hornby took an old technology and proving unreliable at the time product, upgraded it without changing to run/learn mode programming that most of the competition were already using but did add to it bells and whistles. But the bells have limited use (see Chris’s suggestion) and no known use has been found for the whistles?

We often see here suggestions that the marketers have failed to take account of the engineering. For this one, it looks more like engineering self-indulgence with the marketers playing catch-up, none too successfully.

Who are the losers here? The loyal Hornby fan base who buy Hornby because it is Hornby without researching the competition.

[96RAF]

To install run-learn would have required a hardware change Fishy and at the time of their moratorium if stuff could be ‘improved’ by a software change then that was the brief. It worked well for the Select but not so well for R8247. It all works fine as advertised but I am at a bit of a loss as to what to best use them for. A bit like some of the fancy degrees kids get these days, where no profession yet exists to employ them in their specific field.

[Fishmanoz]

A bachelor of bells and whistles I’m thinking?

PS. If I try to include an abbreviation for that degree, it breaches the banned words filter. Cannot think why.

[96RAF]

@Fishy

Bung it into any browser and you will see why. high_heel

[Fishmanoz]

Learn something new every day.