Hi, can anyone tell me why my inverter is drawing power from the grid when the batteries are 100% charged? This is an off-grid system, with grid connected as backup when batteries run too low. Not sure what details to provide. Inverter is a Victron 48/8,000 Multi Plus ll Inverter/ Charger
See video at 20 seconds
231123 12pm taking from grid.mov
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Many thanks Jason for your time. This also explains why I see the inverter throttle back with what it's sending to the grid under much lower loads with 100% batteries because it's getting hotter now with summer here in the afternoons. I'll do what I can to minimise this. Thanks, Mark
@stretch193 Your inverter is throttling back, assumed because its already hot. A 8kva unit at a temperature of about 50*C will only produce about 4.8kW'ish. As your solar is nearly producing all if not greater than the 4.8kw at times and the inverter is already hot, the rest is going to come from the grid. I have a 5kva unit and when its been running with a 3kW load for 2 hours, I can only get 3.8kW from my 5kva unit.
With the below, the solar is generating 4.64kW. Add the 158w from the battery, the inverter is drawing 4.8kW. Allowing for inverter losses (rule of thumb being 10%), the inverter is outputting about 4.32kW. Your loads are 5.249kW, take away the grid 900w, you get 4.249kW which indicates a inverter efficiency of 88.5%, slightly less than my 10% rule of thumb 4.32 but not far different.
Several things effect the inverter efficiency. The power factor of your loads, the voltage of you AC supply / loads, the temperature of the inverter & batteries, the DC voltage, the volt drop on your DC cables to the inverter, and so on. So many factors that effect the whole system efficiency. As a comparison. my inverter averages 89% efficiency, power factor & inverter temperature being the main causes.
As a test, dont use the inverter or charger for a couple of hours to allow it to really cool down, make sure the ambient temperature of the space containing the Multiplus is less than 25*C, then apply a greater than 8kW resistive load and see what the inverter output is.
