That circuit diagram is confusing as hell, multiple fuses of different ratings on the same wire, two shunts, no apparent feed out to use what is in the batteries etc etc
Hmmm .... it's all there for a reason. Everything to the left of the dotted blue line is copied directly from the VW wiring harness diagrams from the ERWIN web site - specifically a 22MY California Ocean (My Van) - I've omitted the feeds to the vehicle fuse boxes where all the vehicle consumers are connected to keep it simpler - the diagram is for my solar install and nothing else so I needed to know how all the VW in-vehicle charging worked. I've connected my solar stuff to the isolation relay under the drivers seat, the fuse block attached to the first leisure battery and a couple of vehicle grounds - otherwise everything is VW original wiring.
The batteries are under the bonnet, under the seat and in the rear cupboard, they are all connected together with heavy gauge wires to enable charging from the alternator and the vehicle battery charger (In conjunction with the isolation relay controlled by the VW Special Vehicle Control Unit). As the batteries are connected with long heavy wires, they are fused at both ends (the fuse holders are all on the battery connectors). This is because a short in the middle can draw power from the battery connected at either end, so one fuse won't work.
In fact anything capable of supplying power needs a fuse as close to the +ve terminal as possible - both batteries and chargers.
There are also 3 shunts - the battery -ve connections are all grounded to the vehicle chassis near where the batteries are located, this results in one shunt on the negative terminal of each battery - all the shunts are connected to the central control unit which does the battery charge calculations. (wiring also not shown on the diagram).
The stuff I added is to the right of the blue dotted line - with exactly 4 connections to the original VW electrical system.
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Are all three batteries exactly the same? No DC/DC charger? Just the VW split charge relay? Do the leisure batteries ever get fully charged? Are the outputs at the blue dots 1 and 2 ever both active at the same time? What is the (Victron?) Blue box that is between the charge controller and the batteries?
Yes, all batteries are 75Ah AGM batteries, and yes they all stay fully charged.
To charge from the alternator, or the in-built VW charger, the VW isolation relay is closed by the VW special vehicle control unit. It has quite complex behaviour e.g. it is opened during stop/start to stop the leisure batteries being used to start the engine, and closed when hooked up to 220V. This means I needed a charging solution that did not bridge the isolation relay. It could have been done with a DC/DC charger but this setup doesn't need a DC/DC charger.
Yes, both outputs are active at the same time. The blue box (Argofet 100-2) is a battery isolator which takes an input voltage, usually provided by an alternator, but in this case the Victron MPPT, and provides it simultaneously on both outputs. The voltage drop across a FET is far less than the older diode versions so no voltage compensation is needed in the Victron MPPT.
Current then flows (up to the 30A total from the MPPT) to both of the outputs of the Argofet dependent on demand. The field effect transistors and the internal workings of the Argofet prevent current flowing back to the Victron MPPT or from the leisure batteries to starter battery and vice-versa - hence the reason it's called a battery isolator. These devices are normally used to charge two separate battery banks from a one-output alternator without actually connecting them together. Fortunately, as not all alternators are self-exciting and require a positive charge to get them charging, the Argofet has an "energize" connection which when supplied with 12v will supply 12v on the input - using this feature allows the Victron MPPT to function 24/7. It's a bit of a novel use for the component but it works and this usage is hinted at by Victron.
On my boat, I designed and built the charging and solar system to ensure the leisure batteries were properly balanced i.e. they all get exactly the same voltage using equal length cables etc. This was not possible in the bus because of the locations of the batteries and the need to use the VW wiring looms.
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And it's OK that the isolated outputs from the Argofet are defeated when the VW Isolation clicks in?
Yes, it is OK. They are not really defeated, just paralleled up, the VW logic creates one bank of 3 batteries, so all the MPPT current flows to this one bank through both Argofet outputs.
As I mentioned a bit earlier, this is not a properly balanced system due to the constraints of the battery locations and the VW design, but it works - the camper display shows all batteries full every evening and the MPPT has usually gone into float at some point in the day. There are also no errors reported by any VW components apart from one fault code which sees my tracker as a parasitic load that shouldn't be there - but I can't change that.
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