Anyone else running a cheap Chinese MPPT off a single 100W panel — what settings are you using?

Picked up a Wanderer-knockoff 20A MPPT from eBay for about £18 delivered. I know, I know. But I've got a single 100W poly panel on the roof of my Sprinter and a 100Ah leisure battery, and honestly I just need it to not cook the battery over summer. Voc on the panel is around 22V, so nothing scary.

The thing arrived with basically no useful documentation — a folded bit of A4 in Mandarin with a QR code that goes nowhere. I've set it to sealed lead acid (not AGM, just old-fashioned flooded), absorption at 14.4V and float at 13.6V, which seems pretty standard from what I've read. Charge current I've left at the default 10A even though the controller is rated 20A, since 100W ÷ 12V is only about 8.3A peak anyway.

My worry is the equalisation function — it's enabled by default and I can't find a clear way to tell if it's actually firing or just sitting there. Last week the battery hit 14.9V at about 2pm on a sunny day and I'm not sure if that was equalisation kicking in or a dodgy voltage reading. The controller's little display only shows one decimal place so it's hard to be precise.

Has anyone got one of these generic units dialled in properly, or know a reliable way to check whether equalisation is running? Worth disabling it entirely on a single leisure battery that lives in a van?

Nobby43 | Posts: 847

@BoatOllie ha, no judgement here mate — half my setup started life on eBay!

One thing I'd flag with those cheap units is the bulk/absorption voltage settings often ship configured for sealed lead-acid at quite aggressive voltages. If you've got a standard flooded leisure battery, I'd manually set bulk to around 14.4V and absorption to 14.7V, float at 13.6V.

Also worth checking whether it's actually doing proper MPPT or just behaving like a PWM — stick a multimeter on the panel side and battery side simultaneously. If the voltages are nearly identical it's basically lying to you about being MPPT!

The 20A rating on a 100W panel is massive overkill obviously, but that's no bad thing — runs cooler and gives you room to expand later. What battery chemistry have you got?

Running something similar on the cabin — single 100W panel into a budget MPPT I grabbed ages ago.

Main thing I'd watch is the absorption voltage setting. A lot of these units default to 14.8V which is too aggressive for a standard leisure battery. I've got mine set to 14.4V absorption, 13.8V float.

Also worth checking what battery type it's defaulting to — some of these cheap units assume AGM out of the box even if you don't tell it anything.

Honestly for a 100W panel the cheap units are probably fine, the current is low enough that even dodgy MPPT tracking doesn't cost you much. Fogstar do decent budget cells if you ever upgrade the battery side of things though.

DefenderDream | Posts: 1,203

Worth paying attention to the absorption voltage setting specifically — with a standard flooded or AGM leisure battery you want 14.4–14.7V absorption, and these cheap units often ship defaulted to 14.0V or even lower, which means you'll never properly top the battery off. Sulphation risk over time.

Also check whether yours has a genuine PWM fallback mode or whether it's claiming MPPT functionality it doesn't actually deliver. Off a single 100W poly panel the voltage differential is modest enough that a true MPPT advantage is fairly marginal anyway — you're not losing much sleep there.

One practical thing from motorhome experience: if the unit has a load output terminal, don't use it for anything significant. Those cheap load controllers are typically the first thing to fail and they'll take your connected device with them.

JasonPhillips | Posts: 312

Good shout from @DefenderDream on absorption voltage. One thing nobody's mentioned yet — keep an eye on your float voltage too. A lot of these cheap units ship with float set way too high, around 13.8V or even higher, which will cook a standard lead-acid over time. Should be 13.2–13.4V for most leisure batteries.

Also worth checking whether yours actually does proper MPPT or is just PWM in a fancier box — some of the really cheap ones are exactly that. Stick a multimeter on your panel leads under load and compare it to the battery voltage. If they're identical, you've got PWM.

Not necessarily a dealbreaker on a single 100W panel, but worth knowing what you're actually working with!