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papen avatar image
papen asked

MPPT is sending current to solar panels

Hi folks,

I have 2x SmartSolar MPPT VE.Can 150/85 rev2 with the latest FW v3.13 and the MPPTs are sending current to the solar panel when there's snow on them.

I checked with a multimeter. The voltage on the panels was lower than the voltage on the battery. The current was also 35A.

Both MPPTs behave the same. :((

Do you have the same experience?


Thanks.

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seb71 avatar image seb71 commented ·

I checked with a multimeter. The voltage on the panels was lower than the voltage on the battery. The current was also 35A.

When there is even a little light, you will have voltage on PV wires. So to be sure what voltage are you measuring, disconnect the PV wires and measure the voltage at the end of PV wires and voltage at the MPPT PV terminals.


Regarding that 35A you measured:

Where? On PV wires?

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papen avatar image
papen answered ·

About the 35A. The current measure at battery wires and PV wires too.

The problem started when it dawned at 8:00 am. I restarted the MPPTs and one started working normally.screenshot-2023-01-22-at-05731.png


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papen avatar image
papen answered ·

Better picture.screenshot-2023-01-24-at-125359.png


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seb71 avatar image
seb71 answered ·

You wrote that you checked with the multimeter and measured 35A.


Also your thread title claims that the MPPT is "sending current" to the PV panels.

I don't know how you came up with that conclusion.


What I do see is that apparently the battery is being discharged, with no obvious load. This could be because some wrong wiring, wrong configuration or some defective component (which reports bogus readings).

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papen avatar image
papen answered ·

35A doesn't show it now, because I have PV disconnected.

Only one string is active now.

In the picture from the mobile and vrm portal, we can see that the battery discharging 356W and "AC load" is 7W (idle workload MultiPlus-II 48/5000/70-48). Somewhere we lose 349W.

Problem is that "PV charger" MPPT dons not display a value below 0. :( . Therefore, on all graphs, the smallest value is 0.

I had to find it with a clamp-on multimeter. And that's why I know that the current flowed right into the PV (about 7A).

Thank you.

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seb71 avatar image
seb71 answered ·

Is this a new system? Or it's an old system with a new problem?

Is anything connected directly to the battery (not through the Lynx Shunt)?

Do you have any DC loads?

What battery? Does it have a BMS?

What is set as the battery monitor?

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papen avatar image papen commented ·

@Seb71 ,

Yes, the system is new (2 months) and works well till now.

No, all are connected through the Lynx Shunt.

No, I haven't any DC loads.

The battery is 16x 280Ah with BMS JK SMART 8-24 200A.

The Lynx Shunt is set up as a battery monitor.

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Alexandra avatar image
Alexandra answered ·

@papen

There are blocking diodes in a solar panel. If it has become a load in the system and not a producer, then it has failed somehow. (Most likely the blocking diodes). It will become hot (so you see the snow has melted/fallen off that one panel). This can happen if the other panels are producing something the power will dissipate out that one.

Remove the panel from the system it is now a hazard.

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seb71 avatar image seb71 commented ·

This can happen if the other panels are producing something the power will dissipate out that one.

This is possible with more PV strings in parallel for instance, but it does not explain the power out of the battery.

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papen avatar image papen commented ·

@Alexandra

If I understand it well, the current can flow from the battery to solar panels through MPPT, but the blocking diodes in solar panels block the flow.

Thanks.

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Alexandra avatar image Alexandra ♦ papen commented ·

@papen

No. The blocking diodes prevent a shaded panel from dissipating energy from other panels.

You diodes have failed in the solar panel. Take the panel out it is dangerous.

The input of the MPPT is shorted when this is happening. (This is why it is important not to exceed the short circuit inout rating of the mppt). The current is therefore flowing from some panels to the other panels, not through the mppt from the battery.

If the MPPT had failed in any way. It would not have worked afterwards.

The MPPTs also have MOSFETs in them. You can't reverse current through a MOSFETs they blow up when you do. (So when you reverse polarity connect your setup that is what happens) in the design of the MPPT the scenario you are proposing is impossible.

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Alexandra avatar image Alexandra ♦ Alexandra ♦ commented ·

@papen

If (and i still maintain the 35aa is not possible) the battery was feeding back then all the panels should have been warm.

Something else is wrong in your system.

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papen avatar image papen Alexandra ♦ commented ·

I agree that something else is wrong because only one panel is without snow. But I can't understand that the current comes from the battery and not from the last panel. The current is measured on the battery.

One note, all the panels have Tigo optimization module. Is something changing?

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nickdb avatar image nickdb ♦ papen commented ·

Optimisers are completely unsupported with victron mppts, this is stated in the docs. Optimisers can cause conflicts with the MPPT's tracking.

It would have been helpful to state this upfront.screenshot-2023-01-25-at-101921.png

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seb71 avatar image seb71 nickdb ♦ commented ·

It would have been helpful to state this upfront

You can say that again. :)

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papen avatar image
papen answered ·

I think that I fined the problem.

MPPTs started to pass voltage to PV terminals. Verified by measurement with PV disconnected.

screenshot-2023-01-25-at-213322.png


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