Anyone else had issues pairing a Victron SmartSolar with cheap Chinese panels — odd voltage readings?

So I've finally got my roof setup sorted on the Transit, or at least I thought I had. Running two 200W panels wired in series (so nominally 24V system), hooked up to a Victron SmartSolar MPPT 100/30. Panels are some no-name 200W monos I grabbed off eBay for about £65 each — Voc listed as 24.3V per panel, so 48.6V combined open circuit, well within the controller's 100V limit.

The weird thing is the SmartSolar app is occasionally throwing up open circuit voltages of 52–53V in the morning before bulk charging kicks in, which is a bit higher than I'd expect. I know panels can exceed rated Voc in cold conditions (the "cold morning spike" thing), but I'm also wondering whether these panels are just... not what they claim on the tin. The cells could easily be a higher Voc than spec'd if the manufacturer has been loose with the numbers.

Has anyone else paired budget panels with a Victron controller and noticed the voltage figures seeming off? I'm not panicking because I'm still well inside the 100V input limit, but I want to make sure I understand what's happening before I add a third panel into the mix. Would a proper solar analyser be worth hiring or buying to actually characterise these panels, or is that overkill for a campervan build?

@Deano13 oh mate, been there. The "100" in SmartSolar 100/30 means max input voltage, not system voltage — and cheap panels often have Voc spikes well above their rated figures, especially on cold mornings. Two panels in series at, say, 24Voc each = 48V open circuit... you need to actually measure yours with a multimeter before connecting.

The dodgy voltage readings are almost certainly your panels lying about their specs. Wouldn't be the first time a Chinese panel's real Voc is 15-20% above the sticker.

Before you fry anything:

• Check actual Voc on each panel individually
• Add them together for your series string
• Make sure you've got headroom under 100V

Victron's VRM app should show you what the controller's actually seeing — have you checked the live input voltage in there?

@Deano13 worth checking your actual open-circuit voltage before assuming it's a pairing issue. Two panels in series at cold temps can spike well above their nominal Voc — I've seen cheap 200W panels push 48-50V open circuit on a frosty morning, which is fine for the 100/30 but throws off the readings if your panel specs are dodgy or mislabelled.

Grab a multimeter and measure Voc directly at the controller input before it's connected. If the numbers don't match the panel datasheet, you've likely got panels with inflated specs — pretty common with unbranded Chinese kit.

The Victron app will log the peak input voltage too, worth checking under history.

@Deano13 what panels are you actually running? I've got two Renogy 200W in series on my Sprinter and noticed the Voc climbs noticeably on cold mornings — like well above the rated spec. Worth checking whether your combined cold-weather Voc is creeping close to that 100V ceiling on the controller. There's a calculator somewhere on the Victron docs site that factors in temperature coefficient. Did the odd readings happen first thing in the morning by any chance?

@Deano13 had almost this exact saga with some unbranded 200W panels I sourced off eBay for my garden office build. The stated Voc was 24.3V but on a crisp October morning I was seeing 26.8V per panel — so well over 50V in series before the MPPT had even woken up properly.

Turned out the datasheets on cheap panels are often measured at 25°C cell temperature, which you'll basically never see in British weather. Cold cells actually push voltage higher, not lower. @SprinterWanderer is onto something asking about your specific panels.

Download the VictronConnect app if you haven't already — the live input voltage readings are your best friend here. Compare cold-morning Voc against the controller's 100V ceiling and you'll know pretty sharpish whether you're flirting with danger.