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greenleaf avatar image
greenleaf asked

MPPT Voltage Instability

We have been noticing strange behavior from a SmartSolar MPPT 100/50 charge controller and its system partner Cerbo GX.

These two devices are part of a small portable system which provides constant power to a small load in an unmanned and remote area. It is for this reason that we can't easily reboot the entire system. We have only been able to reboot the Cerbo GX through VRM.

The system also consists of a small Phoenix inverter, a shunt, a 12V Lithium battery, relevant breakers on each device, and two PV modules in series.

The system was working fine for several weeks until we began to notice two strange behaviors during bulk and float stages. The absorption stage has been normal.

During bulk charging in the morning hours, the MPPT output voltage and current are sometimes sporadic and contain much ripple. The voltage and current follow one another during this ripple. Bulk stage plots attached below.

Ripple becomes more aggressive during float stage as the day progresses. The ripple during float stage is accompanied with re-bulk attempts even though the float voltage never drops below the rebulk voltage for the required 1 minute to actually trigger an expected rebulk stage. Image of float stage ripple and unwarranted rebulk attempts attached below.

Also, during times of high ripple, all data seems to drop for periods ranging from minutes to hours.

Once the MPPT turns off after sunset, the system does not exhibit any problems.

We have switched over from Magnum and Outback and have been building small and large systems with Victron exclusively for a year now. We have not seen this before.

I have also attached a plot of this MPPT prior to the problem to show normal operation.


UPDATE Aug 1:

The system performance has been getting worse. I have updated the Cerbo GX firmware since it is the only one I can update remotely, and I have attempted several reboots. No success.

The VRM dashboard and Remote Console Dashboard have been frozen and do not display actual real time information. Screenshots attached. Upon exploring the MPPT, shunt, and inverter through the remote console, each of those devices seem fine. The dashboards are just frozen.

Rough Bulk Stage.pngRough Bulk 2.pngFloat Stage Ripple.pngRipple Rebulk Close Up.pngUnwarranted Rebulk Attempts.pngNormal Operation Prior to Problem.pngScreenshot 2023-07-31 11.54.50 PM.pngScreenshot 2023-07-31 11.55.02 PM.png

cerbo gxMPPT SmartSolar
rough-bulk-stage.png (73.2 KiB)
rough-bulk-2.png (69.9 KiB)
float-stage-ripple.png (90.4 KiB)
ripple-rebulk-close-up.png (80.4 KiB)
unwarranted-rebulk-attempts.png (28.8 KiB)
normal-operation-prior-to-problem.png (54.8 KiB)
screenshot-2023-07-31-115450-pm.png (43.6 KiB)
screenshot-2023-07-31-115502-pm.png (53.4 KiB)
14 comments
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mvas avatar image mvas commented ·
Is it possible that the PV voltage is not more than 1 volt above the battery voltage? So the MPPT stops charging. The load discharges the battery. Then the MPPT turns back on?
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mvas avatar image mvas commented ·
A Partial Shading issue?
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greenleaf avatar image greenleaf mvas commented ·
No shading whatsoever.
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mvas avatar image mvas commented ·
What are the charging parameters from the MPPT? What is the Re-Bulk voltage?
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greenleaf avatar image greenleaf mvas commented ·
Absorption: 14 V. Float: 13.5 V. Rebulk: 13.2 V.
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nesswill avatar image nesswill commented ·

Interesting, out of interest what is the battery capacity, make model, what is the weather like where it is (temp). Also the make model of the panels?

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greenleaf avatar image greenleaf nesswill commented ·

The battery is a Simpliphi Phi 1.4 (12V), and the PV modules are 2x 60 cell 370W modules in series. I don't have exact temperatures, but it has been climbing.

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nesswill avatar image nesswill greenleaf commented ·
Thanks.

Can you post a screenshot of the shunt's battery setting please. Also, the MPPT battery setting?

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greenleaf avatar image greenleaf nesswill commented ·
The system is currently deployed, and I can only access it through VRM.

MPPT: User defined, absorption 14 V, float 13.5 V, Equalization 14 V (disabled), rebulk 0.3 V, absorption duration fixed, absorption time 1h (long reason for this), tail current 2.3 A, temp comp disabled.

None of the shunt settings affect the performance of the MPPT. It is just for accurate SOC deternminateion.
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nesswill avatar image nesswill greenleaf commented ·
Thanks, do you have DVCC enabled?
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greenleaf avatar image greenleaf nesswill commented ·
DVCC has always been disabled. The system has performed fine without it.
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nesswill avatar image nesswill greenleaf commented ·
Ok well all the settings look good so we are down to a bad connection or equipment failure.

Sorry I don't have any other suggestions.

Unless anyone else has any other suggestions i guess someone is going to have to be on site to fault find.

Good luck and when you find the problem please post back here i for one would be very interested in what you find.

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greenleaf avatar image greenleaf nesswill commented ·

I have posted an update along with two new images. I am now seeing strange behavior in the VRM dashboard as well as the Remote Console dashboard for this system. The dashboard which displays battery info, AC info, and charger info has been frozen for 24 hours now. Even after a Cerbo GX reboot and firmware update.

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nesswill avatar image nesswill greenleaf commented ·
Someone will need to be onsite to fault find, could just be one bad connection getting worse causing all the problems.
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2 Answers
Marc Heymans avatar image
Marc Heymans answered ·

Is the MPPT programmed to charge a lithium battery?

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greenleaf avatar image greenleaf commented ·

The MPPT is manually programmed to charge this specific lithium battery. These charge parameters have been approved by the manufacturer of the battery.

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klim8skeptic avatar image
klim8skeptic answered ·

@Greenleaf Do you have Smartnetworking enabled between the shunt and mppt?

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greenleaf avatar image greenleaf commented ·
The shunt is only connected to the cerbo GX via VE.Direct.
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