DIY stayalive vs DccConcepts 3 wire connection

[777guru]

Does anyone have experience of using DccConcepts Zen Black decoders which have 'three wire' stayalive connections with DIY stayalive 'two wire' units?

I have made a DIY stayalive which is to the diagram attached with a modification of seven caps to take account of 18.66v track voltage (am I correct to do that?). It looks like the picture attached when installed (in the bunker of the Bachmann 3MT). On first trial, the caps get warm but there is no appreciable change in running - the engine (without its cosmetic body and thus weight) readily stutters over points. It seems that although I have not blown up the stayalive, decoder or dcc kit (haha) the stayalive is taking power but not being used.

So - I am wondering three things:

1/. Have I used a working wiring diagram attached - and has the sixth/seventh cap ruined the circuit?
2/. Does the third charge control wire need to be connected to someting or the setup otherwise altered - can a DccConcepts decoder be used like this?
3/. Does the components I am using match the spec on the wiring diagram?

The items used are as follows (all bought from RS (in the UK).

Capacitors: Nichicon 1F Supercapacitor ± 20% Tolerance, JUW 2.7V dc
Zenner Diode: Diode Zener Single 1.3W 13V DO-41
Diode: Rectifier Diode 1A 50V 1.1Vf 30uA DO-41
Resistor: Carbon Resistor, 0.5W ,5%, 100R

Would very much like to solve - not only is the price mark approx 1/3 of the cost of the stayalives when bought, tthey are also very easy to make into custom shapes and locations where a bought brick would not fit.