Is my mppt failing?

DIY
,
21

My setup is that the 2 NNW strings export through the battery so there is continuous export in daylight if the batteries are full.. both MPPTs used to do this but the smaller one has changed over time. Hence my question is my MPPT failing? It seems that it is gradually charging in fewer and fewer instances.

22

I now understand. Do the smaller and larger MPPTs have similar settings? Same firmware?

You could also try switching the two chargers between the two arrays to see what happens then.

Of course, these are basics but I canā€™t think of a solution.

23

This may be blindingly obvious, but it took me a whileā€¦ Iā€™ve had a somewhat similar ongoing problem on my sailboat. At mid-day, just as solar power is approaching maximum, one (or sometimes both) of my MPPTā€™s stopped charging. Since I have no ā€œgridā€ this left me with half-charged batteries at the end of the day. Iā€™m not sure I can see it in the data posted above. But the clue in my case was a discrepancy in the battery voltage as measured by the MPPT and as measured by the battery monitor. The culprit was one or more poor connections in the cabling between the MPPTs and the battery bank. Everything looks fine in the morning. But, per Ohm, with unexpected resistance, as current increases, voltage increases unexpectedly. And it doesnā€™t take much R: a bit of corrosion, a misplaced washer, etc. The MPPT thinks that the battery is charged and shuts off. The battery begs to differ.
On the sailboat, my entire system gets shaken vigorously, from time to time, and the cabling gets put to the test. I cleaned all the connections, simplified the system as much as possible, and increased the wire gauge to one size beyond reasonable, which solved most of the problem. Slightly bumping up the ā€œabsorption voltageā€ setting in the MPPT solved the rest. The biggest culprit, I think, is a ā€œcheapā€ busbar I used as the charging bus. It seems to loosen over time for no reason. So Iā€™ve accepted that I need to throw some money at it. This month, Iā€™m purging all the old stuff and putting in a new Lynx system.
This has probably all been hashed out better elsewhere, but Iā€™m rarely afraid to state the obvious.

24

Thank you @toddster ill check that tomorrow.

25

That will be my next course of action after checking all the connections as @toddster suggests.

Thanks

26

I couldnā€™t find any problem with connections. I ended up replacing the MPPT and the new one works perfectly, I no longer loose one arrays worth of solar generation when the batteries are above 90%.

Iā€™ve contacted my local Victron dealer to see if I can put a warranty claim in.

Thanks for all the replies.

1 Like
27

Part of the emaI I got back from the Victron dealer.. It might help someone:

Sorry the formatting went askew at the bottom.

Why the MPPT Drops to Zero at High SOC

1. Not a Faulty MPPT ā€” itā€™s Control Logic

Victron MPPT controllers donā€™t independently decide to stop producing. If youā€™re using DVCC / ESS, the MPPT will only produce current if the system (inverter + battery/BMS) allows it. When the battery reports 100% and thereā€™s nowhere to send the extra power (loads/grid/AC-coupled export), the controller reduces to zero because the system doesnā€™t request power.

That fits your original post:

  • When SOC hits 100%, one MPPT cuts out while the other continues exporting.

  • Eventually your MPPT started doing this even at lower SOC.

In Victron systems, this can be caused by DVCC control limits (charge voltage, charge current) or feed-in settings.

Typical Causes & What to Check

1. DVCC Charge Voltage vs. BMS Limits

Victron expects the battery/BMS to change voltage limits, not just current limits, when itā€™s ā€œfull.ā€ Some BMS implementations lower the current (CCL) to nearly zero instead of reducing voltage (CVL), so the inverter thinks the battery can still be charged at high voltage ā€” causing the MPPT to shut output rather than feed energy elsewhere.

If your BMS does this, the MPPT will refuse production until SOC drops ā€” because from a DVCC perspective the battery is still ā€œnot readyā€ to handle current, even though voltage is high.

What you can do:

  • Check the BMS charge voltage limit (CVL) settings, especially how they behave around 98ā€“100% SOC.

  • If the BMS only reduces current and doesnā€™t change CVL appropriately, ask the battery manufacturer whether they support Victron-compatible BMS signalling ā€” or adjust parameters if possible.

2. DVCC/ESS Mode Settings

Settings in the ESS Assistant and DVCC control can directly affect when and how MPPTs stop producing:

  • If the ESS algorithm is set to optimise battery life, it may aggressively throttle solar at high battery SOC.

  • Switching ESS mode to Allow Load + Feed-In can sometimes help the system continue exporting even with SOC at ā€œfull.ā€ This was noted in case discussions on similar behaviour.

Try

  1. Switch ESS algorithm ā€” e.g., ā€œOptimized (with BatteryLife)ā€ vs. without ā€” and see how MPPT behaves.

  2. Review Feed-In settings in ESS (limiting export sometimes delays the MPPT operating envelope).

  3. Confirm that DVCC is configured correctly ā€” sharing shunt voltage/current to all controllers helps accurate control.

3. Firmware & Configuration Sync

Sometimes MPPTs behave oddly because firmware versions between the MPPT and GX Device/Cerbo/Multiplus are mismatched.

What to do:

  • Update to the latest firmware on:

    • MPPTs

    • GX (Cerbo/Color Control)

    • Inverter/Multiplus

  • Ensure all devices see the same battery voltage/current via SVS/SCS sharing in DVCC.

Mismatch here can cause one MPPT to ā€œthinkā€ the battery is full while another does not.

4. Hardware Problem / Wear

In the original Victron thread, one user replaced the unit that was constantly shutting down and the problem went away (suggesting the hardware itself was failing).

So if the issue:

  • persisted even after correct configuration,

  • and your new MPPT works fine alongside,
    then it may have been a hardware fault with the original MPPT.

Your description (ā€œI bought a new 100/20 and itā€™s fineā€) strongly suggests the old MPPT may not have been managing voltage/current internally as it should.

Practical Steps to Prevent It Happening Again

Hereā€™s a practical list you can work through:

Review and calibrate battery/BMS interpretation

  • Ensure CVL (voltage limit at full SOC) changes as SOC reaches 100%.

  • If your BMS only reduces current, ask for firmware/BMS parameter changes to include proper CVL signalling.

DVCC / ESS configuration

  • Enable DVCC fully and share battery voltage/current across MPPT + inverter.

  • Try different ESS modes (Optimized with ā€œBatteryLifeā€, etc.).

  • Check Feed-In limits ā€” including grid provider limits if applicable.

Update firmware across all devices

  • MPPT

  • GX / Cerbo

  • Inverter/Multiplus

Test behaviour manually

  • Watch how the MPPT responds as SOC climbs from 90% ā†’ 100%.

  • Look at DVCC charge voltage and current limits live in VictronConnect/VRM.

Hardware check

  • Since you reported the new unit works: that strongly points to the old MPPT being faulty.

Summary
Problem Component Likely Cause What to Check 


 MPPT drops at 100% SOC    DVCC stops request if battery ā€œfullā€   BMS CVL/CCL limits

MPPT output random shutdowns ESS control logic or grid/feed limit ESS mode, export settings

One MPPT behaves differently Hardware or configuration mismatch Swap units, update firmware