I have a BMV-712 Smart Victron battery monitor, and 2 mppt 75/15 regulators. 1 monitors my campers rooftop solar panels, the other monitors my external solar blanket.
Battery monitor shows 13.33v and SOC 82%.
Sun is out →
the rooftop solar regulator is showing battery voltage of 14.4v (! NOT matching the battery monitor) and hence charge state = ABSORPTION.
solar blanket regulator is showing battery voltage 13.34v (matching the battery monitor) and hence charge state = BULK. This makes sense to me given the SOC is 82.
Why is the rooftop solar monitor showing such high voltage? This is problematic as it will not allow state to be ‘BULK’ charging.
What is the likely issue please?
So maybe the cable to the rooftop is a little too thin and has voltage drop?
If you put them in VE.Smart bluetooth network (if available for your equipment) the rooftop MPPT will use the shunt voltage, and correct for the voltage drop.
Hi and thanks for the information.
The mppt and roof solar always used to quickly recharge the 2 lithium batteries up to 95-100% when we were parked up in full sunshine, before going into absorption and float. Hence the cables are ok.
Now it seems to be in absorption at 80%SOC which i think is not appropriate given there is still 20% of the battery capacity to fill.
Even now, at 87%SOC the mppt is showing at being in FLOAT.
Something is wrong as if i was to drive the car with the dc-dc charger connected the batteries would be 100%SOC in a relatively small timeframe.
Something is confusing(?) the mppt to think the batteries are nearly full.
Can i reset it perhaps?
If the battery is 13.3V and the MPPT is 14.4V you have a cable problem between the 2 units, the MPPT is working OK, the 1.1V loss is the issue. As it used to work it is possibly something that has vibrated loose so check everything is tight, check the fuse, check any isolators. Do you have a multimeter to check voltages, they are great for finding voltage drop.
Do you have isolators like the types shown, they have a poor reputation for developing high resistance.
Hi. I checked the VE Smart Bluetooth network and actually created a new one and attached thge Battery Monitor and both MPPT’s. Suffice to say the Rooftop Solar MPPT is now showing same voltage as battery monitor and in fact. Has over today gone back to BULK charge and I am seeing expected amps into the battery. Time will tell if this resolves the issue completely but for now at least i think your suggestion has resolved the issue. Many thanks
Just to reiterate: If the voltage was resolved by sending it via VE.Smart network, it still means that without that network, you have a big voltage difference.
Ergo, like others mentioned, somewhere in the cable, cable connector, fuse, you have a bad connection with a large voltage drop. You should still fix it, as it will still generate loss, even if VE.Smart is compensating for it.
To reiterate the post above, the MPPT will be reporting 14.4V because it is getting that figure from the SmartShunt via the VE Smart network, it is not the actual MPPT output voltage, that will be something like 15.5V if you measure it with a meter.
You are losing more than 30W in heat somewhere in your cable run which could result in something overheating.
Please have a look at your system, as said above you are hiding a problem not solving it.
