MPPT 250/70 flapping

Q&A and troubleshooting
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1

Hi all,

I have connected some solar panels (calculated by MPPT calculator) to a MPPT 250/70.
The MPPT is flapping between external and off state.
When going to external control, I see the voltage drops quite fast and the goes off.
When going to off, the voltage keeps very stable to 210V.

When in external state, it’s generating amps and watts, so it works.
But voltage drops directly.

Is this a faulty MPPT250/70? As I connected this one for the first time.
When connecting the same solar panels to another MPPT250/70 to the same system, it all works fine.

The MPPT is 4 years old (never used until now).

Using:

  • 3X Multiplus 2 3000VA (3 phase in Belgium)
  • Cerbo GX
  • MPPT 250/70 TR
  • Sunpower P19- 325-BLK
  • 1 string of 5 panels
  • 7m 6mm² cable

I have another MPPT250/70 with 2x6 solar panels on the same system, so same external control (BMS) and all works fine.

Thanks!

2

As long as the output watts are ok, don’t worry about the pv voltage.

3

That’s it, it is flapping constantly in the state.
When it is then some seconds in external state, then you see amps and watts being generated.
But after some seconds, it goes off again.

That’s the whole clue, the state is constantly off and external control.

4

Disconnect the cerbo from the mppt

5

Maybe a stupid question, but you do have batteries?

1 Like
6

Yes, battery is connected as the other MPPT is working just fine.
I just came home, I thought resetting it (again) to factory defaults.
Now it is generating like expected.

I’m hoping it’ll stay like that for the coming days.

1 Like
7

OK good. I wasn’t sure as you didn’t mention it in your opening post, but you did mention the other MPPT working OK.