R8247 Accessory Decoder Output Question

[Ed_Cairns]

I am fairly new to DCC but have had basically no problem connecting the R8247 to point motors such as R8243. However, at certain areas of my layout I employ two points to move from an inside to an outside loop of track. These two points always need to switch together. My question is this: 

Can a single output on a R8247 decoder drive two point motors so that only one DCC address applies to two point motors? Could this damage the output of a R8247 or would it simply not work? If it was electrically okay to drive two point motors in parallel would I need to adjust the CV's?

Or am I stuck using one R8247 output per point motor?

Thanks in advance!

[Chrissaf]

Ed, welcome to the forum with your 1st post.

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In principal you can do either. Many users here wire two solenoid point motors in parallel to a single R8247 port output without issue. In rare situations (subject to the point motors used and the quality of their installation - alignment etc) the output of the R8247 might not have enough oomph (if you have this issue then look at my alternative suggestion below). There is no requirement to alter any additional R8247 CVs, not that there are many to adjust anyway.

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I have three R8247 (12 ports) serving 17 points. Seven ports for individual point motors and five ports for twin point motors - giving the total of 17 points.

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Alternatively to having an individual port address for every individual point motor, you can give TWO different R8247s the SAME DCC port addresses, say purely for example port addresses 17-20 then when you tell port 17 to switch, BOTH R8247s will respond and switch their 1st port, then similarly with ports 18, 19 & 20. This way you can achieve the result of getting one port address to switch two points together, but with the advantage that each point solenoid gets the full available R8247 firing current.

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If two points are wired in parallel and one of the points switch the wrong way, then just reverse the two (non-common) wires on the R8247 output + & - port terminals relating the the point that is not synchronised correctly.

 

[Ed_Cairns]

Chrissaf, thanks for the information. On the same topic I assume the R8247 uses a capacitor type discharge to fire the point motor. If that is how the R8247 works? - does the R8247 have a serious impact on the current available from the DCC bus? Does Hornby for example suggest a limit to the number of R8247's on a single system?

Again, much appreciate the information!

[Chrissaf]

You are correct, the R8247 does include a CDU function internally. The nature of a CDU means that the current drawn from your DCC connection is minimal. At rest in idle the R8247 draws about 10-20 mA. Once a solenoid point is fired, the idle current rises briefly (and I truly mean briefly) to about 150mA - 220mA to recharge the internal capacitors. A solenoid point not fired via a CDU would need to draw several Amps from the DCC power.

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In general as a rule of thumb, points distributed across a layout will be operated sequentially and not all together. Therefore the recharge of one R8247 will usually complete well before you ask the same or another R8247 to fire. Thus, in principle there is no limit to how many R8247 you may connect to your DCC supply as you are using the stored energy within the internal CDU to fire the points. Of course there will be a finite limit in practice, but that will be well beyond the size and capacity of the average or even larger home layout.

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There are R8247 addressing limits (that is to say how many R8247s your controller can logically operate) but that is a variable defined by what DCC controller you are using. Don't know the figures off the top of my head, but a Select controller can only support a limited number of R8247 decoder ports compared to the likes of eLink & Elite. The figures will be in the controller instructions. Thus, these limitations are a logical addressing constraint and not based upon currents and power, and will define the actual practicable limitation of how many R8247s may be attached to the DCC supply.

[Nick_]

Ed, further to Chrissaf's comments I have found that using a R8247 I can reliably switch two hornby points using a single port and then need to wait two/three seconds before trying to switch another point connected to another port on the same R8247. A point connected to a port on another R8247 can be switched immediatly.

I have also found that, probably because of the stronger spring, I cannot reliably switch a pair of p*co points connected to the same port.

[96RAF]

I have 13 points on 4 accessory decoders of which 4 points are paired up as 2 double wired sets on single ports.

i have purposely numbered these sequentially (1-13) across my 4 acc decoders and when RM sets them on startup they fire bang, bang, bang no problem.

[Fishmanoz]

So the short answers to all of Ed's questions would be: yes you can drive 2 point motors from one port; no, there is no problem firing to motors in parallel; and, yes, you can have many 8247s on a layout as they draw little continuous current?

[Nick_]

So long as we are talking about Hornby points, yes.

In my case I have found I can only connect one peco point per output for 100% reliable switching.

[Fishmanoz]

Try removing the spring then Nick, that should fix it.

[Fozzy Bear]

I too have 2 point motors connected to 1 port and as an experiment, I also connected some auto relays (making a circuit for signal switching) to a port with 2 motors and it could fire all 3 with ease.

As I read down this thread I realised a solution to a problem I have had with the set points option. Upon start up, RM would click away madly but the 2nd,3rd and 4th points wouldn't change (not enough time for the CDU to recharge). I now see if I redo the plan layout so that 1 point from decoder 1 fires first, then 1 from decoder 2, then 1 from decoder 3 and so forth, by the time I get back to decoder 1, it will have recharged.

Can someone just verify for me, that the firing order is the order that the points were added to the layout plan?

 

Bryan

[Nick_]

Bryan, if you have RailMaster Pro then you can select the order of firing on startup, there is an extra box in the configuration dialog of each point for this. If you have standard RailMaster then they fire in point number order on startup

[Nick_]

Fishy, I'm using surface mounted point motors and they don't latch so if I removed the springs from the points they wouldn't stay switched over. Anyway it's not a problem for me as I have enough ports to have one port per Peco point in the places I've used Peco points and solenoid motors. I have a mixture of Hornby and Peco points

[Fozzy Bear]

Bryan, if you have RailMaster Pro then you can select the order of firing on startup, there is an extra box in the configuration dialog of each point for this. If you have standard RailMaster then they fire in point number order on startup

Ahh, but thats still an easy fix. I just renumber the points. I should have thought of this earlier, must be senility

[St1ngr4y]

Bryan, if you have RailMaster Pro then you can select the order of firing on startup, there is an extra box in the configuration dialog of each point for this. If you have standard RailMaster then they fire in point number order on startup

Ahh, but thats still an easy fix. I just renumber the points. I should have thought of this earlier, must be senility

.... but if you use R8247's, you are stuck with 4 consecutive addresses on each decoder, so your ONLY option is Railmaster Pro.

Ray

[Chrissaf]

post deleted

[96RAF]

The simplest way to set your desired firing order if not using PRO is to delete each point and replace it on the plan in the order you want as RM-AMpack fires at startup in the order of original planting on the plan.

 

Merely renumbering your points may not give the derisred result.

 

You could of course just shell out 30 quid and reap the other zillions of PRO benefits as well.  

[St1ngr4y]

....... RM-AMpack fires at startup in the order of original planting on the plan.....

  

Are you sure about that, Rob, as that conflicts with what Nick said at the top of this page.

Ray

[Fishmanoz]

I'm with Rob on this one Ray, they fire in the order you put them on your layout in Design mode.  When Nick posted his, I thought he was in error but hadn't checked to be able to say any different.  Of course, if you add them in point number order the two are the same.  That is the AmPack method, ProPack you can put the order you want in.

 

One thing you can do to minimise delay in startup firing and increase reliability is to rotate your point firing through your decoders by have port 1 on each decoder set in turn, then port 2 etc.

[Nick_]

Sorry, got that wrong then. Thought that's how I remembered it before I installed the Pro pack and was then able to choose any order I wanted. Apologies for any confusion caused.

[Fozzy Bear]

Ahh, I thought it was the order that they were placed on the design. I recall a fair while ago when adding point motors to the design as I added them to the layout, they were firing in an odd order. Then I wiped the plan, remade it and just added them again in number order. Thats when the misfiring started.

Again an easy fix, just delete them and add them , 1 from each decoder at a time.Thanks guys

 

Bryan

[Fishmanoz]

Or you can increase the delay between point firings in your ini file.