Significant solar voltage drop at Sungold Inverter

Had this exact issue on my narrowboat last summer. Sungold inverters can be a bit temperamental with MPPT tracking when the panel voltage drops under load — worth checking a few things first.

What to look at:

• Cable runs and connections. Voltage drop over long DC cable runs is a classic culprit, especially on a boat where you're routing around awkward spaces. Check every connection for oxidation.
• The inverter's input voltage threshold — some Sungold units will throttle output if the incoming PV voltage dips below a certain point, even briefly.
• Are your panels wired in series, parallel, or a combination? Under partial shading, a series string can collapse badly if one panel underperforms.

On my setup I found a dodgy MC4 connector was the main offender — looked fine visually but had maybe 0.3Ω of resistance across it, which was enough to cause noticeable voltage sag under load.

If you've got a decent clamp meter or a Victron SmartShunt, logging the voltage over time while the inverter ramps up load is really useful for pinpointing when the drop happens — transient vs. sustained tells you completely different things.

What's your panel configuration and approximate cable run length? That would help narrow it down. Others on here may have had the same Sungold quirks — I know @GridFugitive mentioned something similar a few months back in the DC wiring thread.

@PennineNomad makes solid points about the MPPT tracking. One thing I'd add from bitter experience with my static caravan setup — check your cable run length and gauge before anything else. I had a maddening voltage drop last autumn that turned out to be undersized 4mm² cable on a 6-metre run to my Renogy panels. Swapped it out for 6mm² and recovered nearly 18V at the inverter under full load.

Also worth checking your MC4 connectors for oxidation — the damp British climate absolutely murders a dodgy crimp over winter. Victron's SmartSolar logs were what flagged it for me originally; if your inverter has any monitoring capability, pull the data before assuming the worst.

@PennineNomad @StormyHiker — both good shouts. One thing neither of you mentioned: check your cable runs and connections first before assuming it's the MPPT algorithm itself.

I had a similar voltage sag on my setup and spent ages tweaking inverter settings before realising I had a dodgy MC4 connector dropping nearly 2V under load. Classic symptom is the drop gets worse as current draw increases.

For EV charging specifically (which I do off my array), even a small resistance in the DC side gets amplified massively once you're pushing serious amps. Worth doing a proper volt-drop calculation on your cable gauge vs run length — the Victron documentation has decent guidance on this even if you're not running their kit.

A cheap clamp meter and a multimeter testing under load will tell you more than any settings menu will.

@NQ_Sparks fair point on the cabling — though I'd push further and say don't just check connections, actually pull them apart and re-terminate if there's any doubt. Had a dodgy MC4 on my static caravan setup that looked absolutely fine visually but was dropping nearly 8V under load. Nightmare to diagnose.

Also — what gauge are your cable runs @PennineNomad? On my boat I had undersized cable between panels and MPPT controller which made the voltage drop look like an inverter fault when it was nothing of the sort. Took me an embarrassingly long time to figure that one out.

What's the actual panel-to-inverter distance? Longer runs need heavier gauge than most people budget for. Victron's cable sizing tool is worth a look if you haven't used it.

@NQ_Sparks and @BayTim have covered cabling well. What I'd add specifically for Sungold units: check the input voltage range in the MPPT settings against your actual panel Voc. I've seen these inverters fall out of MPPT tracking when panel voltage dips below the minimum threshold under load — the unit essentially stumbles trying to re-acquire the MPP and you get a cascading voltage drop.

On my narrowboat setup with Victron MPPT controllers I can log this behaviour clearly, but Sungold's own monitoring is fairly basic. If you have a clamp meter, watch the current draw as voltage drops — if current spikes momentarily before collapsing, that's your MPPT hunting.

Also worth ruling out partial shading causing a secondary voltage step — even minor shading on a series string will do this and looks identical to an MPPT fault initially.

Something nobody's touched on yet — and this caught me out badly when I was commissioning my garden office system — is panel orientation drift under load.

What I mean is: my Renogy panels were fine at open-circuit voltage, looked perfect on paper, but the moment the Victron MPPT started drawing serious current, a slightly shadowed cell in one panel was dragging the whole string down. Not a connection issue, not cabling resistance, just one rogue panel behaving like a bottleneck the moment it had to actually work.

Worth going out with a clamp meter while the system is under load and measuring each panel string individually. The difference between idle readings and loaded readings told me everything @LH_Marine's input voltage range check was hinting at, but with a clearer culprit to point the finger at.

Partial shading is sneaky like that.