Anyone else running a cheap Chinese MPPT off a single 100W panel? Sharing my numbers

I picked up a no-name 10A MPPT controller off eBay for about £14 delivered and wired it up to a battered 100W poly panel I grabbed from Facebook Marketplace for £25. Running into a tatty 100Ah leisure battery I've had for a couple of years. Total outlay for the solar side of things was under £45, which felt pretty good.

On a decent sunny day in late spring I'm seeing roughly 4–5A going in at peak, which works out to maybe 25–30Ah on a good day. That's plenty for my use case — charging phones, running a 12V fan overnight, and keeping a small 12V fridge ticking over for a few hours in the evening. Surprised me how usable such a small cheap setup can be, honestly.

The controller itself has no brand markings at all, just a little blue LCD showing voltage, current, and a battery percentage bar I don't entirely trust. It gets warm but not worryingly so. I did stick a proper inline fuse between the battery and controller after reading a few horror stories on here — definitely recommend that to anyone else going the budget route.

Curious whether others are running similarly basic setups and what real-world numbers you're getting. Also wondering if anyone has actually tested whether these cheap MPPTs are doing proper MPPT or just acting as PWM in disguise — I haven't got the gear to check properly myself.

Reply by 48VNerd:

@Foggy95 Nice little setup for under forty quid! One thing worth checking on those cheap MPPT units - a lot of them are actually PWM in disguise, proper bodged firmware slapped on. Grab a USB logger or even just monitor your panel voltage under load. A genuine MPPT should pull the panel down to its Vmp (around 17-18V for a typical 100W poly) rather than sitting close to battery voltage like PWM does.

Also with a battered panel, check if you've got any shading damage causing bypass diode issues - output can look reasonable on a meter but you'll be leaving amps on the table.

What's your battery voltage sitting at end of a decent day? That'll tell us plenty about whether the controller's actually doing its job properly.

Reply by FrankMurray:

@Foggy95 Cracking little budget build! I ran something very similar last summer – cheap 20A unit off AliExpress into a tired 110Ah battery. One thing I'd add beyond what @48VNerd was getting at: keep an eye on the controller's temperature during peak sun. Mine got surprisingly toasty mounted inside a small enclosure. Moved it somewhere with better airflow and efficiency noticeably improved. Also worth logging your actual panel output voltage at midday – my "100W" poly was realistically doing about 65-70W in typical UK overcast conditions, which is actually fine for modest loads but good to know so you're not chasing a fault that isn't there. What are you running off it?

@Foggy95 I ran a nearly identical setup on my boat for about eight months as a backup charging source — single 100W poly into a £12 eBay MPPT, 110Ah leisure battery. The numbers were honestly fine in summer, pulling 4–5A consistently on clear days. Where it fell apart was the bulk/absorption threshold accuracy — I measured the actual absorption voltage with a decent multimeter and found it sitting 0.3V below the claimed setpoint. Over months that'll leave your battery chronically undercharged. Worth doing that check before you trust the controller's own readout. Also, if yours has a cheap LCD display, those tend to read optimistically on watts — I cross-referenced against a clamp meter and found roughly a 12% discrepancy. Still, for £40 all-in as an emergency backup or low-demand application, it's genuinely hard to argue against it.

Reply by Compo27:

@Foggy95 Good stuff — those £14 units are a bit of a lottery but plenty of folk get decent life out of them. One thing I'd add that nobody's mentioned yet: keep an eye on the temperature compensation settings if yours has them. A lot of these cheap units have the coefficient set for gel or AGM out of the box, and if you're running a flooded leisure battery you'll want to tweak that, otherwise you risk undercharging in winter when it matters most. Also worth sticking a cheap inline fuse as close to the battery positive as you can manage — the wiring on these controllers isn't always rated to what's printed on the label. What are your actual harvest numbers looking like on a decent day?

@Foggy95 Nice one for sharing the numbers! One thing worth checking on those cheap units is whether the MPPT algorithm is actually doing proper tracking or just acting as a glorified PWM — a few of the really budget ones claim MPPT on the tin but the tracking is quite sluggish. Easy way to test: watch your panel voltage under load. A genuine MPPT should be hunting around the Vmp (roughly 17-18V on a typical 100W poly) rather than just sitting close to battery voltage. If you're seeing good harvest on overcast days that's usually a positive sign, as that's where proper MPPT really earns its keep over PWM. What voltages are you actually seeing on the panel side during operation?

@Foggy95 Mate, those no-name units often claim MPPT but are secretly running PWM in a trenchcoat — worth slapping a proper clamp meter on the panel input and checking whether the controller is actually hunting for the voltage peak or just sitting there like it owns the place; if the panel voltage is basically the same as your battery voltage, congratulations, you've bought a very expensive PWM controller with an identity crisis. My Renogy Wanderer taught me that lesson the hard way before I eventually caved and went Victron, which my wallet still hasn't forgiven me for.

Reply by Derek1967:

@Foggy95 Running a similar setup here — cheap MPPT off Amazon into a 80W panel I rescued from a shed clearance. One thing I'd add that nobody's mentioned yet: keep an eye on the temperature of that controller under load, especially if it's mounted in an enclosed space. Mine got worryingly warm until I gave it a bit more breathing room. Stuck a small heatsink on the back with some thermal paste and it's been rock solid since. Cheap doesn't have to mean short-lived if you manage the heat properly. What battery voltage are you running, 12V?