Anyone else running a cheap PWM controller with decent results, or am I wasting my time?

Been running a 30A PWM controller I picked up for £18 off eBay for the past eight months or so on my shed setup — 200W panel feeding a pair of 110Ah leisure batteries. Honestly expected it to pack in within a few weeks but it's still going strong. Temperatures, voltages all reading sensibly, batteries seem to be taking a full charge on a decent day.

I know the general consensus is "just get an MPPT, you'll thank yourself later" and I get the efficiency argument, especially in winter with low light. But when you're on a tight budget and the PWM is actually doing the job, it's hard to justify spending £60-£80 on even a basic Victron or Renogy MPPT when the cheap unit is ticking along fine.

Curious whether anyone else has had long-term luck with budget PWM kit, or whether there's a point where it eventually lets you down — dodgy readings, killing batteries early, that sort of thing. My panels are only 18V Voc so I'm not losing a massive amount to PWM inefficiency, which helps.

Has anyone actually done a proper before/after comparison switching from PWM to MPPT on a small setup like mine — real numbers rather than theoretical percentages? Would love to know if the upgrade actually paid for itself in practice.

Reply by 24V_Geek:

@DaleBen Eight months is a decent run, fair play! PWM gets a bad rep but honestly for a straightforward shed setup like yours it's perfectly adequate. The efficiency argument for MPPT only really stacks up when your panel voltage significantly exceeds your battery voltage — on a single 200W panel into 12V leisure batteries you're probably not losing as much as people claim.

The £18 units do vary wildly though. Main thing I'd watch is the temperature compensation — cheaper controllers often skip it or implement it poorly, and your batteries will thank you for proper voltage adjustments across seasons. Worth checking what yours is actually doing with a multimeter on a cold morning versus a warm afternoon. If the absorption voltage looks sensible you're probably grand. Keep an eye on those connectors too — that's where the budget ones usually let you down eventually.

Reply by DougDixon56:

@DaleBen Similar story here — had a cheap PWM unit running my workshop for coming up to two years now. The key thing nobody mentions is matching your panel voltage properly to the battery bank. Where people go wrong is sticking a 24V panel on a 12V system and wondering why the PWM is wasting half the potential. Get that bit right and honestly the efficiency gap between PWM and MPPT shrinks considerably for smaller setups like yours.

One thing worth doing — keep an eye on the controller's temperature during summer. The budget ones can throttle back or even shut off if they get too warm. Mine lives in a shaded spot on the wall and that's made a noticeable difference to reliability. Eight months solid with no drama sounds promising to me!

@DaleBen PWM and a prayer is basically my whole shepherd's hut's origin story — eventually caved and got a Victron SmartSolar but only after the cheap one quietly cooked one of my Fogstar cells like a very expensive jacket potato 🥔

Reply by Foggy80:

@DaleBen Worth checking whether your panel's Vmp is reasonably close to your battery voltage — that's where PWM really starts to show its limitations. A 36V nominal panel into a 12V battery is throwing away a fair chunk of potential, whereas a proper 12V panel (Vmp around 17-18V) suits PWM nicely and you're not losing much versus MPPT in practice. Eight months of solid running suggests yours is probably well matched. One thing I'd keep an eye on is heat — the cheap units often have undersized heatsinks and thermal throttling can be silent and invisible. Worth touching the case on a warm sunny afternoon and seeing what you're dealing with. Not saying ditch it, just know its limits!

@DaleBen PWM is basically just a bouncer that lets the voltage in but doesn't bother checking if it's dressed appropriately — still, mine ran a Renogy 100W into a leisure battery for 18 months before I upgraded to an MPPT and genuinely wept at the efficiency graphs.