Hi all, I’m new to Victron kit and need to ask for some advice post install. Kit installed is Cerbo GX with 5" display, MPPT 75/15, PHOENIX Smart charger with 2 outs used on a 3 out 12v system. The PSC is supplying each battery directly. 1 battery shunt on the leisure battery, no shunt on the starter battery. System has 3 way switch for DC supply to boat electrics, battery 1 or battery 2 or both in parallel “All”. The shunt on the leisure battery is a 500 amp. When the “All” option on the supply switch is chosen, I see a minus on DC load on the app, and I assume this is due to the balancing happening between the 2 bats while in parallel as the starter battery has a constant draw (Mercathode). I normally don’t see this if the batteries have been fully charged by the PSC overnight. The starter battery has the primary load/draw due to historical install config from the boat manufacturers, as above the Mercathode and other items like auto bilge pumps need constant supply, and leisure bats are optional. I may well swap this, but my 2 question points are, point 1, can I install a second smart shunt on the starter battery, bearing in mind, there may be times where the bats are used in parallel, and independently. Would putting another shunt on the load side of the starter bat help remove the minus I’m sometimes seeing, if so, it will be a lager 1000A shunt due to needing to handle 850mca on cold start. Point 2, I can’t seen to get the solar to engage as the primary source, even changing the absorption and float levels, and again, I’m assuming this is likely to be because the starter bat doesn’t have a shunt so cannot tell the cerbo/PSC accurate levels, especially as that bat has a constant draw. All devices are connected via VE Direct cables as well as via Bluetooth. In addition to this, I’ve also tried with DVCC enabled and still, while the charger is enabled, it always takes preference, seems kind of useless, as surely the solar should be able to be used first!
Please see attached diagram, and thanks in advance for any and all advice.
Hi all, I’ve worked out one of my issues/points thanks to another poster, Shunt / battery monitor not reading the correct SOC/ Amps, missing solar, decreasing daily or other misreading problems and the issues I was seeing was due to my connections for active devices still being mounted on the battery pole, and not on the load side of the smart shunt. I hadn’t considered that in order to be measured correctly, they needed to be moved and mounted to be shunt and not the battery.
I have another question that I hope someone can answer. I will be installing nother 1000a smart shunt to he starter battery so that I can monitor both batteries independently, but my MPPT only has 1 supply out,can I busbar this and supply both batteries? Or will the MPPT get confused with the output it needs to supply? I’ve done a new diagram please could someone help?
The starter battery draws high currents only for very few seconds, and that results in very low energy. And all other loads connected to the starter battery draw only very small currents—albeit often continuously. In all likelihood, more energy is drawn from the battery via these constant small currents than via the rare high currents.
The problem is that the SmartShunt does not measure very small currents at all (in the case of my 300A SmartShunt, the threshold is 0.1A), and that it can only measure small currents exceeding this adjustable threshold with relative inaccuracy. Therefore, a simple voltage measurement is entirely sufficient for monitoring the starter battery.
If you do what you are proposing then you have permanently commoned the batteries together in parallel so they will act as essentially 1 battery. The starter motor will be able to pull power from the house battery via the solar charging wires, which will overheat these wires and the MPPT terminals. Do not do this.
There are a few ways you could do this.
Connect the MPPT positive to the output of the 1,2,All,Off switch and the negative to the bus bar.
Fit a voltage sensitive relay to combine the battery banks when being charged with solar only to the house battery. One of the Victron Cyrix relays will work, not sure which one.
Fit a DC to DC charger between the house and starter battery with the solar connected to the house battery so the starter is charged when solar is running. A Victron Orion will work.
Thanks for the advice, it’s much appreciated, is it correct that they are permanently parallel because of the common, as the 3 way switch has a dedicated positive supply from each battery, so 2 positives, and depending on switch position, parallel can only be fully complete in the “all” position surely, or am I missing something?
And as you say, I do have a phoenix ip43 smart dc-dc charger with 3 out installed already, 2 outs are used, 1 to each battery. When the 3 way switch is in the all position, the MPPT does charge both batteries, when in position 1 it charges the starter battery, and in pos 2 the leisure battery.
The common wires are in parallel by default due to the 3 way switch having 2 positives, one from each battery. Amazon.co.uk
In option 1, connecting the MPPT + to the output on the switch, would the MPPT need regulation as the boat 12v system may have sensitive devices with step downs, and only be rated for 0-15v, or can I assume the output of the MPPT is regulated to normal 12v tolerances? The PV is currently running at 22v.
The DC-DC charger I have seems to be the option 3 you highlight, I cant manually choose which battery to charge via the switch while using the DC charger as the charger is wired directly to each battery, and this is where I was having issues getting the MPPT to be the preferred 1st charge controller, but that then raises a concern, thanks for the advice. I already have the solar connected directly to the leisure battery, so the wiring could melt if starting the engine while on option 2 or on all… If I’m understanding things correctly, is that your view too.
Melting wires depends on the wire gauges to the switch, if everything is suitably sized then all is OK. The issue I raised was creating a parallel connection with thin wires through the MPPT terminals.
