My son runs a DCC system using Hornby's Select unit. He has three ovals of track on an 8' x 4' surface. He's been having reliability problems so I have removed the inner oval to reduce the overall size of the track run.
Is there a 'rule of thumb', guideline or rule that dictates the maximum run of track for a given size of controller ?
The length of track is irrelevant to the amperage of power supply. What does matter is the way the electricity gets to the locomotive. Rail joiners are definitely imperfect electrical connectors, so you need feed rails at regular intervals. The further the feeder track from the power supply the thicker the wire connections need to be. A given wire has a specific resistance per foot/metre so a long feed wire will lose voltage - the train runs slower. A second feed section on an oval will effectively halve the resistance between power supply and loco because the electricity then has two paths, both of which get utilzed in inverse proportion to their resistance. I take this system to it's logical conclusion and fit a feed wire to every length of rail - trains run at constant speed anywhere on the layout.
There's nothing difficult about extra wiring :-) Especially compared to trying to work out why a loco runs fast o one piece of track and then slow on the next. Crimped fishplates may well solve such problems instantly, but the solution is likely to be temporary, particularly if you balast your track. Sure, wiring can be tedious, but I long ago concluded that the effort is worthwhile. A part of that would be that I like to run my branchline steam locos at scale speeds.
It's been a looong time since (40 years..) I used set track, but on my Mk.1 cellar layout (Hornby Super 4!!) mixed with Peco (about 20' x
16) I just used to nip joiners up with a pair of pliers when laying the track to get a good interference fit. This removed all problems permenantly and needed only one feed from each controller - it took a coupe of attempts sometimes but was much easier that extra wiring.
All I can say is my method worked just fine, with ballast, flooded with plaster of paris and any other scenic endeavours! Having been a Wireman at one stage, I'd still go down the joiners route - for better or for worse I'm a believer in fixing the cause rather than hiding the symptoms, but each unto their own and all that.
the 'cause' is incomplete contact. Rail joints move because baseboards twist, because wood and metal expand and contract at different rates, and because we're running mechanical weights over the joins. To some degree the movement should cause mechanical cleaning, but in my experience it doesn't. It does provide a space for oxidation and dirt to accumulate. Any three items joined only by mechanical tension under such conditions are not 'fixed'. Also, a rail joiner has a smaller cross-section than the rails it joins and so becomes an additional resistance.
Soldering of course is less than perfect, but it works for me, particularly long term.
On the 'original' three oval layout I wired in two additional track feeds on the far side but these were 'piggy backed' off the original which could be my problem !
I think I will keep his layout to two ovals as his Select has only a limited power output but rewire the second track feed direct from the Select. It will also give him more room for his goods yard and also for me to put in an access hole.
Thanks for the advise folks, it's what I expected, but it's good to know other people with greater experience than me in these matters back up my thoughts.