Droppers and decoder

[kiltedscot]

Hi 

just stripped 8x4. DCC layout running several era3 trains moved house so new layout on the cards 14x5. Issue I have is how far apart would the dropper wires need to be,where I’ve read some say every rail others say 3ft apart.

 

having been given era3 dc loco which run very good on DC. So fitted DCC hornby decoder now runs like a bag of nails. So my question is anyone recommend a chip that can cope with the current draw of the ringfield motot.

cheers Dave

[Fishmanoz]

Which decoder did you fit?

Always best to do a stall current test so you can be certain about the current requirement for your decoder.

[LesXRN]

I put DCC decoders in half a dozen tender drive Ringfield loco's just last weekend. I used Lais 860021 in all of them and they run well.

 

[Rog RJ]

38 minutes ago, kiltedscot said:

Hi 

just stripped 8x4. DCC layout running several era3 trains moved house so new layout on the cards 14x5. Issue I have is how far apart would the dropper wires need to be,where I’ve read some say every rail others say 3ft apart.

 

having been given era3 dc loco which run very good on DC. So fitted DCC hornby decoder now runs like a bag of nails. So my question is anyone recommend a chip that can cope with the current draw of the ringfield motot.

cheers Dave

Have hou removed the capacitor from the motor, it isn't needed for DCC and can badly affect running.

[What About The Bee]

28 minutes ago, Rog RJ said:

Have you removed the capacitor from the motor, it isn't needed for DCC and can badly affect running.

Okay, I admit to being confused right now.

It is my understanding that RF noise is created from the electric arc of the brush to the commmutator.  The discrete component RC network is added to a DC locomotive to suppress the arc, and thus the noise.  

From the advice given above, which I respect, it appears that the RC network is onboard the decoder.

Is that correct?

If the discrete component RC network from DC is not removed, interaction between the now TWO noise suppression RC networks can be expected.

Bee

[Rog RJ]

The problem is that the motor capacitor distorts the back emf from the motor causing the decoder to be unable to control the motor correctly.

Some models and some decoders are more or less affected and sometimes a particular combination of motor and decoder results in poor performance.

[ntpntpntp]

With regard to the frequency of fitting droppers:     personally I feel that fitting droppers to every discrete section of rail is overkill, you'd have to be carrying out very poor track laying if your rail joiner connectivity is so bad you get noticeable voltage drop or DCC signal corruption 🙂   Remember DCC train sets come with one pair of wires and they work fine 🙂  That said, there is of course some benefit to fitting a pair of droppers every so often.   As I now build modular layouts with a typical board length of about 3' this does mean my track feeds (to work with DC or DCC) are naturally at that sort of spacing, plus any additional feeds for DC section switching. 

[Fishmanoz]

Suppression components across the motor (includes capacitors in parallel and inductors in series) causing back EMF distortion?  Hadn’t heard that one before Rog, could you please expand?

However, I do agree such components are unnecessary for DCC as the suppression components are part of the decoder design and a reliability risk if these components fail (capacitors going short circuit, inductors open circuit).

Still need to know which decoder was fitted for further advice.

[ColinB]

21 hours ago, kiltedscot said:

Hi 

just stripped 8x4. DCC layout running several era3 trains moved house so new layout on the cards 14x5. Issue I have is how far apart would the dropper wires need to be,where I’ve read some say every rail others say 3ft apart.

 

having been given era3 dc loco which run very good on DC. So fitted DCC hornby decoder now runs like a bag of nails. So my question is anyone recommend a chip that can cope with the current draw of the ringfield motot.

cheers Dave

When I was fitting decoders to my locos with Ringfield motors I use Zimo MX600R decoders they are rated at 0.8 amps. I tried several different makes and these worked the best and didn't self ignite when the loco stalled at some points (some did although their current rating was the same). 

[Rog RJ]

15 hours ago, Fishmanoz said:

 Rog, could you please expand?

 

It's basically knowledge gained over the years from reading other online posts, I think it was one of the DCC experts such as Mark Gurries (RIP) or Alan Gartner (maybe) that first explained it.

Of course I could be mistaken, my memory isn't as good as it was.

Edited May 20 by Rog RJ

[ColinB]

I think it is not that big a capacitor, it will probably round off the edges of the square wave PWM, so a lot depends on what frequency your PWM runs at. I doubt it would make that much difference, the biggest issue is they can go short circuit, which does cause a lot of issues. I suppose it depends where the micro tries to read the back emf but I must admit I would be surprised if it made that much difference. 

[Bulleidboy]

I would fit droppers to each individual piece of track - I did, and have had no problems whatsoever.

Edited May 20 by Bulleidboy

[Brew Man]

I tend to agree given the unreliability of fish plates.

[SteveM6]

While fishplates alone may be ok when the track is new and clean, they will get dirty and potentially fail in time. Soldering droppers to every piece of tack effectively future proofs the track against possible issues going forward as it's easier to add droppers during the build rather than retrofitting them after the event.

[ntpntpntp]

The oldest parts of my N gauge exhibition layout were built 28 years ago.  It's been to many dozens of shows and spent most of the rest of its life stored in a garage or set up and run in a conservatory, so it's lived in environments with significant temperature variation.  I'm happy to say there have been no issues with rail joiner conductivity degradation in all that time other than a couple of joints either side of a bridge which I had deliberately left as removable with sliding fishplates.    If after some time you're getting problems with the fishplates/joiner conductivity which then require all these power feeds then I think not enough care is being taken when laying the track.  Giving the joiner a squeeze with pliers immediately after laying has worked for me for decades 🙂 

[Pendragon Sailing]

To avoid connectivity issues with fishplates, I sometimes drop a small blob of solder on both ends of the fishplate (on outside of rail) at the time of installation. That way, the electrical connection is clean and it also avoids the joints moving in the future. That said, it of course makes the join more ‘permanent’, which is not ideal if/when you want to dismantle the  layout !

 

[96RAF]

1 minute ago, Pendragon Sailing said:

To avoid connectivity issues with fishplates, I sometimes drop a small blob of solder on both ends of the fishplate (on outside of rail) at the time of installation. That way, the electrical connection is clean and it also avoids the joints moving in the future. That said, it of course makes the join more ‘permanent’, which is not ideal if/when you want to dismantle the layout !

 

Not ideal as it also prevents expansion and contraction.

[Pendragon Sailing]

True, Rob….that too……but nothing is foolproof in this hobby, it seems ! 😳

[ntpntpntp]

Got to agree with @96RAF there, I avoid soldering rail joints unless absolutely necessary for a structural reason eg. strain on tight curves, but even then I'll try and use a single length of flexi instead of having joints. 

[ModelerXYZ]

I soldered a particularlly problem joint on a curve coming off a point. The train now can go over it, but its the exception rather than the rule. I don't solder joints usually. I also have few problems with fishplates. Squash them with pliers. I have more trouble with dirty tracks and rail wear than i do with fishplates.

XYZ