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Smart Solar 150/70 MPPT yield limited by Pylontech Bty

Please assist, I have a 48/3000/35 Multiplus II, Venus GX, Pylontech 2000 and 150/70 Smart solar MPPT connected to 4 PV strings. I noticed over a long period that with 3 strings connected and also now with 4 strings connected to the MPPT that at around 10h00 every sunny day my MPPT solar yield drops with about 400W on a 3 string input but 900W on the 4 string input. After long investigation of trends I found that it seems at some point during Bulk charging at which stage the Bty shows 100% for a long time already, the MPPT Pylontech bty voltage graph raises slightly from about 52.26V to 52.3V and then suddenly the MPPT current output drops significantly without any change in the sun exposure. I make use of ESS feed in excess power as well as DVCC with no current limits set or time dependent constraints in any configuration.

I was told that my Pylontech Bty (1 only, proposed 2) is the problem and that the firmware on the Multiplus II version 459 does not handle the excess PV power available very well. As such as the pylontech dictates the MPPT charging algorithm, it throttles the MPPT and also the feed in power to the grid. The proposal is to upgrade the Multiplus II firmware to version 475 which may help. Does anyone know what the reason or solution could be, would not like to buy another pulontech to solve this problem. Attached 2 graphs to indicate the scenario


MPPT - Solar Charge Controller
solar-1.jpg (70.7 KiB)
solar-2.jpg (67.0 KiB)
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@Karel

The newer firmware should be loaded on all the devices including the venus in the system for the feedback to work well. This is good practice when a new system is commissioned.

Hi, all my software/firmware have been upgraded/updated to the latest versions I am aware of, Mulktiplus II now on 2628476 firmware, Venus GX on V2.58, smart solar MPPT on V1.50.

Have seen a V2628471 on documentation but my supplier could only provide V2628476.

Really disappointed at the moment.

Rgds

3 Answers
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Karel answered ·

Multiplus II is back feeding into the grid and not just supplying my load requirements. The pylontech is usually at 100% SOC. I can understand the BMS limiting the charge limit but something (pylontech, multiplus or MPPT) is limiting the back feeding into the grid at what seems to be the point where the MPPT charge voltage increases for some reason. I have done more testing where I disconnected the can-bus on the pylontech to remove the pylontech as a system charge controller and changed the BMS to the VE-bus i.e I assume the multiplus becomes the controller and I still have the same problem.

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Karel answered ·

Hi, the Multiplus is back feeding into the grid, usually about 2000W but have the potential to rise to 3000W. All the tests I have done have indicated that the problem is triggered when the Pylontech battery reaches a voltage of 52.1V. Below 52.1V the MPPT runs maximum feedback to the grid, Above 52.1V the MMPT current drops about 25% . Switched the BMS monitor from Pylontech to Multiplus II and exactly the same happens.

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dgnevans answered ·

Is your Mutliplus II back feeding ie grid tied or just supplying your load requirements. Are your Pylontech at 100% SOC at 10 am. depending on how your system has been configured. The BMS on the battery could have a charge limit which would limit your charge current.

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