I posted this on the Victron Facebook group but as Facebook is such a useless tool for searching and finding info.. i'm posting it on here too.. This should make mvader smile..
After making more settings changes, I thought I had it solved.. but alas.. the discharge came back.. it just took longer to manifest itself.. so there I sat today, on the boat, resigned to pulling out the BMV and returning it for testing.. talking to the reseller who was asking me questions, also at a loss. We did a full power down of the system with just the BMV running to confirm that the current was zero.. which it was... however accidentally i flicked to the voltage display and noted it had gone up.. and it now was exactly the same as the multimeter and BMS (the only 2 things left that had power) instead of the 0.15v difference.. when powered back up it the difference re-appeared.. it wasnt the fuse.. i checked that.. some more testing and more loads, the voltage dipped further and the BMV was showing 10a load.. my clamp meter was only showing around 5a.. not that i trust the clamp side of it (cheaper dc clamp type) but shouldnt have been that far out.. charger was off at this point
So that was it.. BMV had to be faulty.. so I told the reseller i'd bring it in and they could test it.. no problem.. so started by pulling the ve direct cable out.. and noted the voltage went up.. hmm.. wierd. plugged it back in.. and down it went by 0.15v.. took it out again.. back up again.. it now matched the Multimeter and the BMS.. i checked the current.. that was lower too and now matched the BMS (-4.9a) and almost the clamp meter (-5.1a) I had a spare Uart cable so quickly crimped a connector on (bloody fiddly) and plugged it in.. same issue apart from one of the crimps was a bit dodgy and when wiggling the cable the voltage would go up and down (as did the current) but it still send info to the venus device.. I pulled the ground cable out.. and it kept sending info.. but at the right voltage.. I pulled the +ve cable out of the connector too just leaving the TX & RX cables.. in place and it read correctly.. was programmable and transmitted to the venus.. great.. (see note below)
So 3 days wasted chasing my tail and even though my gut feel of the BMV being wrong was right.. it was the self-made VE.direct cable that was causing the pull down and I have NO idea why.. apart from its something to do with the USB power.. There is a reason the victron dont like home made cables.. and maybe this is why.. haha.. Its not the cost of the genuine cables (honest) its the challenge.. hahahaha..
Once again a note of appreciation to those that helped me on my journey of discovery!
As a side note - if you really have to make your own cable for the PI.. then leave the +ve out of the connector... as I can now easily find reference too via a google search.. but couldn't find when I was looking for how to make them!Steve