We have a piece of equipment which pulls 4.2 amps 24 hrs a day and rarely pulls anymore power day and night. The equipment is connected through a Victron Smart Shunt and then to Victron MPPT 100/30 solar controller. We also had a Cerbo connected to the system.
We have 2 x good quality 200Ah lithium batteries which the system draws from and connected to the MPPT Solar controller are two Jinko 315w solar panels which are slightly angled away from each other to catch the sun as it tracks across the sky.
Overnight with no sun the battery percentage on the Victron app show a drop in percentage of about 20% which is expected and we consider normal. The battery voltage showing on the Victron app slowly decreases during the night from around 13.4v is usually around 13.1 - 2 volts after the evening hours.
What happens then is as the sun rises we get a slow charge going into the MPPT which increases as the sun gets stronger. So far everything appears to be normal. On a cloudy day in winter we get about 180 watts coming from the panels and the battery voltage displaying on the app increases slightly to around 13.3 - 4 which is fine but then as the cloud clears and we get full sun we suddenly might go from 180w to 385w coming in and we see the battery voltage suddenly spike to up to 14.3 amps which then trip the system into absorption as we have an absorption level of 14.2. What also happen is that the battery percentage suddenly changes from 80% to 100% even though it may have only been charging for an hour or so. WE also have been getting high voltage alarms as the alarm is set at 14.2 volts.
Then the cloud cover comes back over and the incoming watts might go down to 160w again but the battery voltage immediately decreases to around 13.2 and yet the system is still in absorption even though we know the batteries haven't had time to charge up yet.
So in a nutshell we find the battery voltage rises and falls based on the watts coming into the MPPT but the increase and decrease are almost instant. I would have thought that if their were more watts coming into the MPPT that the battery would show a very slow increase in volts as it charges up and then as less watts come in and the system continues to draw power from the batters there is a slow fall in battery voltage and not this roller coaster ride we see everyday.
Can anyone enlighten me if we have a problem or if this is normal as we simply wanting to know the true battery voltage and percentage at any given time
