R8239 DCC Booster input query

[Goathland]

I have read the DCC-Booster-English-Only pdf and as pointed out in the forum on a number of occassons it is more pictorial rather than textual and gives 4 different configurations on how to use the thing.

The major differences are whether to use an R8236 RJ12 cable from Elite to Booster (and daisy chain them thusly) or to use track level input either straight from the track output of the Elite or from the track itself into the "boost in" of the booster (and daisy chain from "boost out" to "boost in" of the next booster).

I have 2 questions on this:

1) On searching the forum there were a small number of posts that suggested using the RJ12 cable connection route was occassionally problematic. Is this down to the Elite, the cable, or the booster? The posts also go on to say the the track level connection is much more reliable. How big a problem is reliability of the RJ12 connection?

2) What happens if you plug signals from both an RJ12 cable AND a track level input into the booster at the same time (into the correct connections of course). Does one connection overrride the other, does it stop working, or does it permanently damage the booster? This type of configuration is not given as an option but it must happen inadvertently on a few occassions. I searched to see if this particular topic has come up before but could not find anything in the forum.

Any help on these 2 questions would be gratefully received.

[96RAF]

Let’s get the basics of power district boosting sorted then try to answer the questions.

The Hornby module is actually a power district supply and signal booster, in that it has its own 4-amp PSU that powers a second (or subsequent) totally isolated power district. It takes the DCC signal from the prime power district which is powered by and has the only DCC controller attached and passes that signal to the second (or subsequent) power district.

Q1. The RJ cable purports to use Xpressnet as the DCC signal transfer method when in fact it is not true Xpressnet, just basic low power DCC signal data flow. The unreliability comes from the fact that the Boost and Prog outputs of the Elite are both low power signals from a common circuit switch twixt one another by a change over relay, hence if programming whilst talking to a second power district the signal is interrupted. How important is reliable comms twixt power districts - very important if you want to maintain control from one to the other.

Q2. The connection options are either/or not either/and. Using both is akin to having two DCC controllers connected to the one track system. Damage could occur as a design fault in the Elite PCB motherboard puts the Boost and Prog outputs anti-phase. How do I know - I connected a 4-channel oscilloscope to all the Elite outputs and killed the Elite Prog/Boost circuit. In general use this would not be noticeable to a user as the Hornby ‘booster’ module also acts as a reverse loop module, thus the phasing would be switched to match, and a Programming track would never connect to any power district track, but do you risk it. The simplest and most reliable connection twixt power districts is using the direct track connection shown in Figure 4 of the booster manual.

I trust this clarifies things.

[Goathland]

Thank you for the quick response.

The unreliability of the RJ12 connection I can live with as it seems limited in its scope and I don't tend to program CVs whilst also running trains around my layout.

I would rather have liked the booster to "fail safe" if both the "boost in" and RJ12 connections were connected just to be on the safe side and my understanding is that the "boost in" is electrically isolated so this should be easy to accomplish. It is not something I intend to do and I just wanted to know the full facts as I rarely pick up a new piece of kit to use before I know it functioning inside-out. Thank you.

[Fishmanoz]

Goathland, while I can see that Rob has given you some context on the reason track to boost in is the preferred connection method, I am surprised that you are choosing to ignore it.

If I can provide some further context - this is not a recent conclusion that Rob has reached, this exact same advice has been coming for some years now from Rob and from the now departed Chris Saf to many forum members seeking to optimise their power district arrangements. I can’t remember anyone coming back to say the arrangement is unsuccessful.

Can I also ask that you stop inserting more than one carriage return between paras as the forum software adds the second.

[96RAF]

I repeat my caution not to connect both at once.

[Goathland]

No intention of ignoring Rob's advice, sorry if I gave this impression. When I said that I could live with the unreliability I meant that it did not make the product useless if used in this way with circumspection. As you say this advice has been repeated many times - I was just enquiring as to the reasons behind that advice.

[96RAF]

I just remembered about my tear down report…

This is an extract from it:

Most faults are likely to have been user induced by incorrect connections to the layout. Reference to the user’s manual as stated earlier will show that you can connect this unit to the main power district in several ways. For various reasons it has been found that the most reliable way to power and control a second or subsequent power district is using the method shown in Figure 4 in the manual. You should not attempt to connect the unit by any more than a single method at a time, else damage will occur.