Dj avatar image
Dj asked

Feeding back to grid,no matter

Hi guys, sitting with a complex 4x 48/5000 MPII parallel system. (All the same serial no) with 3x 15kwh (900ah Total) BSL batteries. 28x 555w panels on 450/200 mppt

Problem is I keep feeding back into the grid. No matter what setting on Ess I go.

Have been ticking all the boxes on installation side this past week on dc cable size and length and ac cable size and length. Even downgraded my ac and dc cabling as to thought it might have been to thick.

Had an external meter in just for performance boost but even took that out of the picture to try and eliminate any potential problems.

Next step is to run System without bms and see if the problem is still active ,as it seems like the batteries keeps discharging into the grid.

Just checking to see if you guys might have any advise on this or have had this problem.

Adding a few photos but still need to finish up making neat as this week has been hectic trying to find a solution!!



ESSmultiplus in parallelfeed-in limitgrid paralleless grid setpoint not reached
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1 Answer
marv2097 avatar image
marv2097 answered ·

Hi @Dj I am having very similar problems to you. I am working through some testing to rule out cabling and other variables. I have a pair of MP-II 5000 and I have done similar with ensuring cables are the right lengths, torqued correctly, firmware matching etc.

I have been swapping both the AC and DC cables between the two units and testing with a 4000w grid setpoint to force charging. One of the units is consistently doing nearly half the charge current of the other. Swapping all the cables between them rules this out so its I can only think this is either a faulty unit, internal differences in the internal resistances or a software bug.

When there is excess solar this either shows as constant discharge or constant export. I found this changes depending which of the units I make the master. This I suspect is due to how the master is measuring its output and sending sync and duty cycle info to the slave which either exports too much or too little.

Both units run fine when are used on their own but when as a pair they dont balance out. I will be doing a post soon with all my findings and asking to see if there is anything else I can check as I am not sure what else to do with it at this point.

Good luck getting to the cause of things with your system.

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Dj avatar image Dj commented ·
I have a theory that I will test this week and will aso let you know how that goes… please if you find anything let me know.

I do see there is a few people struggling with this and do hope we can get this sorted.

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