Anyone else using cheap Chinese PWM controllers or is it false economy?

Been running a cheap PWM unit (some unbranded thing off Amazon, about £18) on my garden office setup for nearly two years now. Still works, which surprised me honestly. But I've definitely left efficiency on the table — with a 200W panel and a 12V battery bank I'm losing a fair chunk compared to what an MPPT would squeeze out, especially on those grey winter days when you really need every watt.

The thing is, for small setups it's hard to justify a Victron SmartSolar when the controller costs more than everything else combined. But I've been reading that even a mid-range EPEVER MPPT pays for itself within a season if your panel wattage is decent.

What's actually getting on my nerves is the lack of any monitoring. No Bluetooth, no app, just a tiny LCD that I can barely read without my glasses. Victron has absolutely spoiled everyone with the VictronConnect stuff.

So I suppose my question is — at what panel wattage does it stop making sense to use PWM? Is there a rough rule of thumb people actually use in practice, or is it more about the battery chemistry involved?

Also curious whether anyone's had one of these cheap units outright fry their batteries. Running AGM at the moment but considering a Fogstar lithium pack for the van conversion I'm planning, and I wouldn't trust a £18 controller anywhere near that.

Suspect the answer is "just buy an MPPT and stop being tight" but interested in whether anyone's genuinely made PWM work long-term.

@GoldenMechanic similar story with my tiny house build - ran an unbranded PWM for about 8 months before switching to a Victron BlueSolar MPPT. The difference in winter was genuinely shocking. Same panels, noticeably better charging on grey days.

The maths eventually made sense for me - the MPPT paid for itself through recovered energy within a season or two, especially with UK winters being what they are. PWM is basically telling your panels to operate at battery voltage rather than their optimal point, so you're just leaving power on the table constantly.

That said, if your array's small and your loads are minimal, cheap PWM isn't the disaster people make out. It's when panel voltage significantly exceeds battery voltage that the losses really stack up.

@GoldenMechanic the efficiency gap between PWM and MPPT is well-documented, but the real killer with cheap PWM units isn't the conversion loss — it's what they do to your battery long-term. Most of these unbranded units have deeply questionable charge profiles. I measured mine with a proper analyser and it was terminating absorption phase far too early, which was quietly sulphating my AGMs.

If you're running a small panel array (say, under 200W) with a 12V system where panel voltage roughly matches battery voltage, PWM losses are tolerable. Beyond that, you're haemorrhaging yield.

My current setup uses a Victron SmartSolar — expensive upfront, yes, but the Bluetooth monitoring alone has saved me from several costly mistakes. Fogstar lithium paired with a properly configured charge controller makes a noticeable difference to cycle life.

The £18 gamble sometimes pays off. Mine lasted three months before cooking itself.

@GoldenMechanic £18 for two years is genuinely decent ROI — my shepherd's hut laughs at anything that costs less than a pint and outlives expectations, but the dirty secret nobody mentions is that a PWM controller is essentially throttling your panels down to battery voltage, so on a cold Scottish morning when your 20V panel could be singing at peak efficiency, your £18 box is just… not having it.

Ran one on the boat briefly and the Victron MPPT I swapped to paid back the price difference in about four months of harvested ampere-hours I was previously throwing away.

The maths only doesn't work if your panel array is already matched perfectly to your battery bank voltage — which, let's be honest, almost nobody's is.

@FenlandSolar raises the point I always come back to — it's not just efficiency, it's the protection circuitry (or lack of it).

Had an unbranded PWM on my narrowboat before I knew better. Worked fine until it didn't, and "didn't" meant a slightly cooked battery bank because the low-voltage disconnect was lying about its setpoints by nearly 0.4V. Multimeter and a load test revealed it pretty sharpish.

The real calculus is:

• Known load, small system, good batteries → cheap PWM probably fine
• Lithium cells (Fogstar, etc.) → absolutely not, the BMS disagreement can get spicy
• Unattended installation → I'd want a Victron or at minimum something with verifiable specs

For a garden office that someone checks daily? Probably acceptable risk. For a boat that sits unattended for weeks... different conversation entirely.

Great thread this. I'd add that the efficiency gap actually widens in our rubbish British winters — when you're already scraping 20-30% of rated output on a grey November afternoon, losing another chunk to a cheap PWM isn't academic anymore, it's the difference between your batteries recovering or not.

That said, @GoldenMechanic two years of solid service is nothing to sniff at. I ran a similar unit on my allotment shed for eighteen months before upgrading, and honestly it did the job for a small 12V setup with modest loads.

My rule of thumb: if your panel array is worth more than about £150-200, spend the extra on a decent MPPT — Victron if budget allows, EPever as a reasonable middle ground. Below that threshold, the maths on a cheap PWM can still stack up.

@Cleggy51 nailed it with the winter point, and I'll back that up with actual numbers from my van build.

Running a no-name PWM for the first winter — brutal. I've got a 200W panel feeding a 100Ah Fogstar lithium, and on a grey January day in Scotland I was pulling maybe 4-5A. Swapped to a Victron SmartSolar MPPT the following autumn, same panel, same miserable sky — regularly seeing 7-8A from identical conditions.

That gap matters enormously when you've got maybe three usable hours of weak sunlight and you're trying to keep a leisure battery topped enough to run heating overnight.

The boat taught me the same lesson even harder — marine environments destroy cheap electronics fast, and you really don't want to discover that mid-Channel.

For a static shed? Maybe gamble. For anything you're depending on, the MPPT pays back surprisingly quickly.