I wanted to share my findings regarding an issue I’ve been experiencing with my Victron 100 | 50 MPPT. It seems to be Tracking MPP incorrectly* when external load is turned on, and I wanted to see if anyone else has observed similar behavior or has insights into what might be going on.
Issue Overview
The MPPT efficiency is lower than expected, operating at ~94% instead of ~98%. This is observed when the unit is running under 40 °C.
It fails to properly track the Maximum Power Point (MPP) after 200W, leading to potential energy loss.
I compared it with my Victron 100 | 15 MPPT, and surprisingly, that unit tracks much better under load and reaches an expected efficiency of 98%+.
The setup is as follows:
The MPPT is half a meter away from the Battery Terminal, and the battery is LiFePo4 150Ah 25.6V.
For testing the Victron 100 | 15 MPPT, I have removed the battery wires from the 50Amp controller and connected those wires with an alligator clip.
Points to be noted in the video:
The 3 windows you see on the screen are of the Node-Red Dashboard, which shows the Inverter’s output data, MPPT’s data, and Battery’s data.
The other two are of Victron Connect, showing the Trends of the MPPT, and data of Smartshunt.
In the video, you can see that after the SOC reaches 45%, the grid is cut-off and inverter turns on, and from there you can see the changes in the behaviour of the MPPT tracking.
1. Efficiency Calculation
I calculated the efficiency using Node-RED on Venus OS, using the formula:
(SmartShunt Incoming Power + Inverter Load (5.3W)) / Incoming Solar Power
2. Possible Cause: Solar Side Sensor Issue?
Since tracking drops after 200W when under load, I suspect an issue with the MPPT’s solar or battery’s voltage or current sensor.
If the sensor is misreading values, the MPPT may be selecting the wrong power point, causing it to run inefficiently.
This could also explain why the 100 | 15 MPPT tracks properly—it may not have the same faulty sensor behavior.
3. Limitations
The 100 | 15 MPPT is limited to 15A, so I couldn’t test under the same high load as the 100 | 50 MPPT. However, from what I’ve noticed, it starts after the charging amps are above 7.5 amps, which is around 200W of solar power.
Request for Insights
Has anyone experienced tracking issues or lower efficiency with their Victron 100 | 50 MPPT?
Could a faulty current or voltage sensor explain this behavior?
I appreciate any input or suggestions on further troubleshooting. Let me know what you think! Thanks in advance!
Alligator clips are not reliable for use in this type of situation - even as a test. They are prone to high and varying resistance, which can compromise results.
So the alligator clip I used was for the 15 Amp controller, and the battery cable that I use for the 50 Amp controller is crimped with pin-type lug, so I decided to use them temporarily for testing.
Hi Victron community, I got an update on this issue.
Even after updating to firmware v1.67, which supposedly improves the startup and tracking behavior of the 100|50 model, I’m still experiencing the same persistent issue under load:
The MPPT fails to properly track and maintain the actual maximum power point, especially when the load increases past ~200W.
Hi, I have been experiencing the same issue, except my controller is the 100 | 30 version.
My setup is simpler; I have 2 panels connected in series (~37V Voc each), an old 12V 100Ah AGM battery and a Victron 12V 500VA Inverter connected via a fuse box with short lengths of 8AWG cables. The cable from the fuse board to the battery is longer than between the inverter and MPPT, so the voltage drop (measured with a multimeter) is higher which may change how the power from the MPPT is distributed between the load and battery charging?
If a load was connected (~150VA but I think it was still happening with ~100W too), the tracker would gradually reduce the voltage of the panels until the output was about ~50% of their initial output (e.g. 316W would reduce to 165W) and then briefly jump back up before repeating the cycle.
Initially I tried turn MPPT charging off and on again to reset the MPPT tracker, but disconnecting the load allowed the battery voltage to jump back up and the tracker to stabilize with the expected voltage drop every 10 minutes to re-calibrate the tracking point. If I connected the load again I would see the same behavior as before.
The battery was depleted at the time (~11.5V) because of use the day before so it was less resilient to spikes in the load which may have been contributing to the issue?
To me there is a clear link between the load on the battery and the controllers ability to track properly. Low battery voltage may also be contributing to the issue. Like you my controller was under 40 °C at the time but I cannot confirm there is a correlation.
Here you can see the difference in PV voltage before and after disconnecting the load:
Even after the PV voltage has stabilized, the battery has been charging for a while and the load is reconnected, I still see the tracking getting worse when the load is increased:
I see that your issue is slightly different from mine. From what I can tell, the MPPT is adjusting to a lower voltage and pulling more current, which could still be a bug if it’s not actually operating at the maximum power point.
In the graphs you uploaded — specifically MPPT Power and Inverter Power — they appear to be in sync, and based on that, it seems like the MPPT is indeed tracking the maximum power.
However, I’ll need more details about the earlier part of the data. If you’re in a location where shadows gradually clear between 10:20 and 10:40, the MPPT might simply be following the changing light conditions.
If possible, could you upload a screenshot of the VictronConnect Trends view with Solar Voltage and Solar Power plotted in real-time? Alternatively, you could share the link to your VRM page so I can take a closer look.
