The output of my solar charger fluctuates from the moment the output power exceeds +/- 1000W. This is clearly visible on today’s and yesterday’s graph coming from Home Assistant. Also a detailed screenshot from VRM shows this. Today and yesterday was sunny without clouds.
I have the same problem on one of our installations. There we have two mppt 250/100 chargers. I don’t think both got damaged at the same time.. I think the bms communication is not stable. Hence the charger starts and stops constantly. I will go on site and try changing the cables and maybe even Cerbo gx. In the mean time did you find the problem and solution ?
I have now disconnected the CAN cable, since CAN with my (unknown) BMS caused problems of which this might be one symptom. I lose any ability to sense the LiFePO4 state of charge, until I grok the BMS’ serial protocol to parse that value out. But actually the batteries seem to charge better without CAN, they used to hit 100% then stop accepting charge until they fell down to ~90%, with a persistent high cell voltage error. Since the change I have not seen the high cell voltage and at the end of solar generation for the day they are at 99%. I will go through the BMS logs to see if I am still getting these swings.
An update. I haven’t found a solution yet, but I have a screenshot of the overall picture. The problem described in the first post occurs between +/- 950W and 1300W. This is clearly visible in the graph below. The problem persists, even when I disconnect the VE direct cable from the solar charger, meaning it operates independently. The only thing I still need to test to see if the problem lies with the solar charger is bypassing the battery BMS. I’ll come back to that later.
Do you by any chance running any heavy load during those times? I got the same kind of behavior with my 100 50 and 150 45 MPPTs. The MPPTs tend to draw less power from the panel during loads and they fluctuate a lot.
I had a similar problem today, suddenly the charger output started fluctuating the same as in your screenshots. It seemed to stop shortly after the cooling extractor fans came on in my plant room, this could be a coincidence or it might be something to do with thermal management in the charge controller.
That indeed seems to show the same behavior. Do you still have the second part of the graph, namely when the output power drops back below about ±1500 W? It’s possible that this behavior appears again then. In my case, this behavior occurs between about ±950 W and ±1300 W. Which type of solar charger do you have?
Sorry, the day clouded over heavily in the afternoon so input was going up and down meaning you would not see it at the other end of the graph. The next day showed the same pattern on the way down like your graph, but the room temperature was up, it is odd that it is between a certain wattage range. My charge controller is a Victron SmartSolar MPPT 250/70 70A.
