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

Burned through three of the cheap eBay specials before my Victron SmartSolar paid for itself in dignity alone. 🔥

Seriously though, the maths isn't complicated — those £12 PWM units are basically just a voltage switch with delusions of grandeur. You're losing anywhere from 20-30% of your panel output compared to a decent MPPT, and in a UK winter when you're scraping every photon off a cloud-covered sky, that loss genuinely hurts.

That said, I won't be completely snobbish about it. If you've got:

• A tiny system (say, 100W or under)
• Matched panel voltage to your battery bank properly
• No plans to expand

...then a PWM isn't automatically criminal. It's just aggressively mediocre.

The real false economy trap is buying three duff ones trying to save money. First dodgy unit torched a wiring loom in my van build, second one decided 28V was a perfectly acceptable float voltage for my Fogstar lithiums (narrator: it was not), third one just gave up on a Tuesday for no apparent reason.

Spent about £85 in total on rubbish before caving and getting a Victron 75/15 for £65 from Bimble Solar. Still running two years later without a single drama.

Anyone else got a graveyard of cheap controllers under their workbench, or am I just catastrophically unlucky with electronics?

Cleggy83 | 📍 Yorkshire | ⚡ 400W panel / 200Ah LiFePO4

@MoorKev Ha, "dignity" is doing a lot of work in that sentence mate 😄

I'd push back slightly though — there IS a valid use case for the cheap PWMs if your panel voltage closely matches your battery voltage. Running a small 12V panel into a 12V lead-acid setup, the efficiency losses aren't catastrophic.

Where people go wrong is chucking a 36V panel at one and wondering why their batteries never charge properly. That's not the controller failing exactly, that's just mismatched kit.

My proper gripe with the cheap units is the protection circuits — or lack thereof. Overvoltage, reverse polarity, temperature cutoff... all theoretical on paper, none of it reliable in practice.

Spend £40 on a decent EPever and you're in a different world without necessarily jumping straight to Victron money.

Renogy_Pro | 📍 Narrowboat / Shepherd's Hut | ⚡ 800W / 400Ah LiFePO4

The bit nobody mentions: PWM dumps your panel voltage down to battery voltage. So that lovely 36V panel you bought? Now it's pretending to be a 12V panel. You've just thrown away roughly 60% of your potential harvest before a single electron reaches your battery.

On my hut install I ran the numbers properly — a £180 Victron SmartSolar MPPT recovered its own cost within one UK winter purely through harvesting those low-angle November panels that a PWM controller would've basically ignored.

@Cleggy83 With LiFePO4 specifically it gets worse, because cheap PWM units have no idea what a lithium charge profile looks like. You're essentially hoping for the best, which isn't a strategy, it's a prayer.

False economy doesn't cover it. It's an expensive false economy. The worst kind.

MuddySkipper | 📍 Array | ⚡ Garden Office Build

Genuine question for the thread: does the MPPT vs PWM efficiency gap actually close in summer when panels are running closer to Vmp anyway?

I'm mid-spec on my garden office build and trying to decide whether the Victron 75/15 is justified at roughly 3x the cost of a decent-ish PWM unit. My panel array will be 200W on a south-facing lean-to roof, feeding a 100Ah Fogstar Drift LiFePO4.

@Renogy_Pro — the panel voltage loss point is what's making me lean toward MPPT. My planned 2S configuration would give me ~44V Voc which a PWM can't really use properly anyway, right?

Is there a wattage threshold where the maths genuinely tips toward MPPT being worth it, or is it always worth it regardless of system size?

RussMartin | 📍 Derbyshire | ⚡ 600W / 230Ah LiFePO4

@MuddySkipper The efficiency gap narrows considerably in summer when your panels are running warm and close to battery voltage anyway — that's the dirty secret MPPT sellers don't shout about. Where MPPT genuinely earns its keep is winter mornings; cold panels produce higher Voc and MPPT harvests that extra voltage properly rather than just clipping it. My old 20A PWM was genuinely fine through June and July. October through February though? Night and day difference once I switched. For a garden office with predictable modest loads, I'd honestly say: start cheap, monitor your actual harvest with a decent meter, then upgrade when the data tells you to rather than because someone online told you to. Evidence-based spending and all that.