Anyone else using cheap Chinese PWM controllers or is it just me throwing money away?

Ran a cheap 30A PWM unit from Amazon for about eight months on my garden office setup before I finally caved and bought a Victron 100/30 MPPT. The difference was genuinely eye-opening.

The PWM was losing me somewhere around 25-30% of what my panels were capable of on a decent day — you can actually see it when you compare the logs side by side. On overcast days (which, let's be honest, is most of the year in the UK) the MPPT pulls power at voltages the PWM simply can't harvest efficiently. That's the killer difference nobody mentions enough.

That said, I don't think PWM is always a waste. If your panel voltage already closely matches your battery bank, the losses shrink considerably. A 12V panel on a 12V battery with a quality PWM? Probably fine for a small shed load.

The problem is most of us are running mismatched arrays we've cobbled together from various deals on eBay or Fogstar job lots, and that's where PWM really starts costing you.

My honest take:

• Tiny system, matched voltages, low load → decent PWM is acceptable
• Anything over 200W or mismatched voltages → MPPT pays for itself within a season

The cheap Chinese units also had some genuinely terrifying moments with overheating. Woke up one morning to a controller that had clearly been cooking all night. Nothing caught fire, but it concentrated the mind somewhat.

What's everyone else running? Curious whether anyone's done a proper before/after comparison with actual data rather than just gut feeling.

@MarkGibson had almost exactly the same journey on my narrowboat a few years back. Ran one of those generic blue PWM units for a full boating season, convinced myself the panels were just "a bit weak." Switched to a Victron SmartSolar 75/15 and suddenly my Fogstar batteries were actually hitting proper charge states by mid-afternoon.

The real killer with PWM on a boat is the partial charging — you're sat at a mooring thinking everything's fine whilst your batteries are quietly sulking at 80%.

What I'd say to anyone tempted by the cheap stuff: the saving on the controller gets eaten by reduced battery lifespan inside 18 months. Do the actual maths before buying.

The Victron Bluetooth monitoring alone was worth half the price — finally understanding what my system was actually doing changed everything.

@MarkGibson the voltage mismatch loss is what kills people on PWM — if your panel Vmp is sitting at say 18V and your battery is at 12.4V, you're essentially throttling the panel down to match. All that potential just... gone as heat.

What panel configuration were you running? Because depending on string voltage there's situations where PWM can make sense on a strict budget — 12V nominal panels into a 12V bank is at least a closer match.

That said I moved to a Victron 75/15 on my narrowboat setup even for a relatively modest array and the MPPT tracking during low-light British mornings made a noticeable difference. Winter harvesting especially — when every watt counts and the sun barely clears the treeline, you want the controller actually working for you rather than just connecting wires essentially.

Been down this road myself — ran a no-name PWM on the boat for a full winter before upgrading to a Victron SmartSolar 100/20.

What nobody warned me about was how badly PWM controllers handle partial shade. Even one cloud passing over would basically floor the whole harvest. The MPPT kept tracking and pulling what it could. Night and day.

The thing is, the cheap unit worked — it just wasted a surprising amount of what my panels were actually generating. When I finally logged the Victron data against my old notebook estimates, I'd been leaving roughly 25-30% on the table every decent day.

For a garden office like @MarkGibson's, where you're likely running consistent loads, that gap compounds pretty quickly across a season.

My garden office Victron 75/15 paid for itself inside a year — the PWM I replaced it with is now a very expensive paperweight, which is fitting because my office is where I do my actual paperwork.

@CallumHobbs curious what you actually noticed on the boat day-to-day — like did your batteries recover better overnight or was it more obvious on charging speed during the day?

Running a cheap PWM on my narrowboat at the minute and I'm suspicious it's why my leisure bank never seems to hit 100% even when I've had decent sun. Panel specs say 18V Vmp, battery's a 12V AGM. Surely that gap is just getting wasted as heat somewhere?

Been eyeing up a Victron SmartSolar 75/15 but genuinely not sure if the maths adds up for my small setup — only got one 175W panel. Is the MPPT premium actually worth it at that panel size or am I overthinking it?

@MarkGibson same story with my Caddy camper conversion — ran a generic 20A PWM for nearly a year before the penny dropped. The moment that really crystallised it for me was logging Victron's VRM portal data after switching to a SmartSolar 100/20. I could see the absorption and float stages completing properly for the first time. The PWM had essentially been floating my Fogstar Drift 100Ah lithium at whatever the panel's Voc happened to be, completely ignoring what the battery actually needed.

The thing people miss is that PWM efficiency losses aren't just about watts — it's the quality of the charge cycle that suffers. A half-charged lithium sitting at nominal voltage isn't the same as a properly topped battery, and over months that degrades capacity.

The Victron cost me £89 refurbished from a UK seller. Genuinely not a false economy at that price.