Victron MPPT Error Codes — PV Overvoltage, String Sizing & SmartSolar Diagnosis
Your Victron SmartSolar or BlueSolar MPPT controller is showing an error code — most likely Error 33 (PV overvoltage) or Error 38 (PV input shutdown). The solar charge controller has stopped generating and the battery is no longer charging from solar. This is almost always a string configuration issue, and it gets worse in cold weather.
We review VRM solar data, calculate your string Voc with cold-weather correction, and determine whether the fix is a reconfiguration or a controller replacement.
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Safety note: PV strings can produce dangerous voltages — up to 250V DC or higher depending on configuration. Do not disconnect MC4 connectors under load or in direct sunlight. If you need to isolate the PV string, use the DC isolator switch. Never work on PV wiring without confirming zero voltage with a multimeter.
5-step MPPT error code diagnosis
MPPT errors 33 and 38 are overwhelmingly caused by PV string voltage exceeding the controller's maximum input. Cold weather makes panel voltage rise — a string that works in summer can trip the controller on a cold morning. Start with the error code, then verify the maths.
Identify the specific MPPT error code from VictronConnect or VRM
Open VictronConnect (Bluetooth) or the MPPT device page in VRM. The error code is shown on the main status screen:
Check the error history in VictronConnect under the History tab. If Error 33 only appears on cold mornings and clears by midday, this confirms a cold-weather Voc issue.
Calculate your PV string open-circuit voltage including cold-weather correction
The key calculation: panels in series × panel Voc × cold correction factor
The temperature coefficient for Voc is on the panel datasheet — typically −0.25% to −0.35% per degree Celsius. For a rough UK calculation, add 10–15% to the STC Voc to cover worst-case winter conditions (−10°C ambient, panel at sub-zero before sunrise).
Use the Victron MPPT Calculator at victronenergy.com to verify your configuration. The calculator includes location-based temperature data.
Check whether the string configuration exceeds the controller rating
Common UK configurations that trigger Error 33:
The fix for an oversized string is to reconfigure: reduce panels in series (add parallel strings if needed), or upgrade to a higher-voltage MPPT controller.
Inspect PV wiring for damage or partial shading issues
If the string Voc calculation is within the controller rating but errors persist, investigate the wiring:
Measure the actual string Voc at the MPPT input terminals using a multimeter. Compare with your calculated value — a significant discrepancy indicates a wiring fault.
Assess whether the MPPT controller needs replacement or reconfiguration
Two outcomes are possible at this point:
Reduce panels in series, add parallel strings, or upgrade to a higher-voltage controller. This is the most common resolution and does not require replacing the MPPT itself.
If the string is correctly sized but overvoltage errors persist, the controller's input protection (varistors, TVS diodes) may have degraded from a previous overvoltage event or lightning surge. The MPPT likely needs replacing.
A remote diagnostic can confirm the fault pattern from VRM historical data — we check daily peak PV voltage, error frequency, and whether the issue correlates with temperature before recommending a replacement.
If replacing, ensure the new controller's Voc rating exceeds your cold-corrected string voltage by at least 10% margin. See our VictronConnect setup guide for configuring a new controller.
Why cold weather is the hidden cause of most MPPT errors
Solar panels are rated at Standard Test Conditions (STC) — 25°C cell temperature, 1000W/m² irradiance. In the UK, panel temperatures regularly drop to −5°C or below in winter, especially in Scotland, Wales, and northern England. At these temperatures, the open-circuit voltage of a solar panel rises significantly — typically 10–15% above the STC value. A string that is safely within the MPPT controller's limit at 25°C can exceed it at −10°C. This is why Error 33 is seasonal — it appears in November or December and disappears in spring, leading homeowners to think it has "fixed itself." It hasn't. The underlying misconfiguration is still there, and it will return every winter.
The SmartSolar 150/45 is the most commonly affected controller in the UK because it hits its 150V limit quickly with modern high-efficiency panels. Three 400W+ panels in series produce around 138V at STC — apparently fine — but 155V cold-corrected, which exceeds the limit. Installers who size strings at STC without applying the temperature correction are the root cause of most Error 33 cases we diagnose. The SmartSolar 250/100 gives much more headroom and is now recommended as the standard choice for UK off-grid and hybrid installations.
MPPT error codes — common questions
Error 33 means PV input voltage has exceeded the controller's maximum rating. This is an overvoltage protection trip — the controller shuts down the PV input to protect itself. The most common cause is too many panels in series for the controller's voltage rating, especially in cold weather when panel Voc rises 10–15% above the datasheet STC value.
Solar panel Voc increases as temperature drops. At −10°C, Voc can be 10–15% higher than at the 25°C STC rating. A string that's within limits in summer can exceed the controller's maximum on a cold winter morning. This is why MPPT manufacturers require cold-weather Voc correction when sizing strings — and why Error 33 is seasonal in the UK.
Error 38 is a PV input shutdown — the controller has disabled solar input as a protective measure. Resolve the underlying overvoltage by reconfiguring the string, then clear the error by disconnecting PV and battery, waiting 30 seconds, and reconnecting battery first then PV. If Error 38 persists after reconfiguration, the controller's input protection circuit may be damaged from a previous overvoltage event.
You can add panels in parallel without increasing string voltage — the controller clips excess current above its rated output. But you cannot add panels in series if doing so pushes the cold-corrected Voc above the controller maximum. If you need more series voltage for long cable runs, upgrade to a higher-voltage model (e.g. 150-series to 250-series SmartSolar).
Our remote diagnostic starts from £75 and covers VRM performance data, MPPT error history, PV string voltage calculation with cold-weather correction, and controller health assessment. If the MPPT needs replacing, we confirm the correct model and verify the new configuration before ordering.
MPPT error killing your solar generation?
Tell us the MPPT model (e.g. SmartSolar 150/45), the error code, your panel specs, and how many panels are in each string. We'll calculate whether a reconfiguration or controller replacement is needed.