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

Finally got my little setup running last week. It's a 100W mono panel I grabbed off eBay for £35 (slight crack in the corner but no real difference in output that I can see), wired into a Victron 75/15... actually no, I couldn't stretch to Victron. It's one of those generic Wanderer-style EPever knockoffs, no-name brand, about £18 delivered from AliExpress. Connected to a single 100Ah leisure battery I pulled out of an old caravan.

The controller defaulted to "Sealed" battery type and some fairly aggressive charging voltages — 14.6V absorption and 13.8V float if I'm reading the display right. Battery is just a basic flooded lead-acid, nothing fancy. I've read that 14.4V absorption and 13.5V float is a safer long-term setting for that type, but honestly I'm not confident enough to just start poking around the parameters without a sanity check from people who've actually done it.

I'm getting maybe 30-40W peak output on a decent day right now (south-facing, slight tilt, but trees nearby causing some shading mid-morning). Running a 12V compressor fridge which draws about 3-4A when the compressor kicks in. Early signs suggest it's just about keeping up but I'm a bit nervous about the battery sitting low overnight.

Has anyone else dialled in settings on one of these cheap units for flooded LA? And is there a way to actually tell if the controller is doing proper bulk/absorption/float cycling, or does it just lie to you on the display?

Hey @TimHarris, nice score on that panel! Slight edge cracks usually only affect output if they've cracked through the cells themselves — sounds like you got lucky.

Curious which Chinese MPPT you went with though, as the settings vary quite a bit between them. I'm running a Renogy Rover 20A off a single 100W and found the absorption voltage was set way too high out of the box for my AGM battery — dropped it from 14.6V down to 14.4V and it's been much happier since.

Also worth double-checking your float voltage — a lot of these units default to 13.8V which is fine, but some cheap ones I've seen ship with float set above absorption which is just madness.

What battery are you running with it? That'll make a big difference to what settings folk can suggest. 🙂

@TimHarris sounds like @RockyMaker's covered the crack side of things.

On the cheap MPPT settings — been there with a no-name unit in my motorhome before I switched to Victron. Main things I'd watch:

• Absorption voltage — set it properly for your battery chemistry, don't just leave it on default (usually too high)
• Float voltage — same deal, especially if you're on LiFePO4
• Max charge current — a 100W panel will rarely push more than 5-6A in the UK anyway, so headroom isn't really the issue

Biggest problem with cheap Chinese MPPTs is the voltage readings are often slightly off. Worth cross-checking with a decent multimeter at the battery terminals rather than trusting the display.

What battery are you running it into? Changes the advice quite a bit.

@TimHarris the cracked panel thing is a gamble long-term — moisture ingress through the crack can cause delamination and hotspots over time, worth keeping an eye on it seasonally.

On the Chinese MPPT front, I've run a couple of those generic units on my van conversion. Biggest thing is not trusting the default absorption voltage — most of them come set for flooded lead acid at around 14.4-14.7V which will absolutely cook a LiFePO4. If you're on lithium, drop absorption to 14.2V and float to 13.5V minimum.

Also if there's a "load output" on the unit, set the low voltage disconnect conservatively — those sensors are notoriously inaccurate on cheap controllers.

What battery chemistry are you running? That changes the settings conversation completely.

@Chunk48 makes a fair point about moisture — I lost a panel that way on my shepherd's hut build, started as a hairline and by the second winter it had gone milky across a quarter of the cell.

On the cheap MPPT settings specifically — the ones I've seen trip people up are the absorption voltage and float voltage. Most of these units ship with AGM defaults around 14.4V/13.8V, which'll either undercharge or stress a lithium if you've swapped batteries without updating the profile.

With a single 100W panel you're rarely pushing it hard enough to notice wrong settings immediately, which is exactly why they go unchecked for months.

What battery are you running @TimHarris? That'd narrow down whether your current settings are even in the right ballpark.

Jumping in on the settings side — with a single 100W panel into a budget MPPT you'll want to make sure your absorption and float voltages are set correctly for your battery chemistry, don't just leave it on factory defaults. Most of these cheap units ship set for flooded lead-acid at quite aggressive voltages, which can hammer a sealed or lithium battery pretty quickly.

What battery are you running @TimHarris? That's really the starting point for getting the settings dialled in properly. If it's a standard 12V AGM, I'd suggest absorption around 14.4V and float at 13.6V as a sensible starting point.

Also worth checking the max charge current is capped sensibly — a 100W panel will realistically push maybe 5-6A, so nothing dramatic, but no harm in setting a ceiling.

@TimHarris nice little setup for the money! On the settings side, what battery chemistry are you running? That makes a big difference to what voltages you want. For a standard 12V AGM I'd typically set float around 13.5–13.8V, but if you're on lithium you'll want very different figures and honestly a cheap Chinese MPPT with lithium can be a bit sketchy without proper BMS backup. Also worth checking your charge current limit — with only 100W coming in there's no point setting it above about 7–8A realistically. What brand is the controller?

@Nick1982 what figures are you actually running for absorption voltage? I've got a similar-ish setup in my motorhome — single 175W panel into one of those cheap Epever Tracer units — and I've been second-guessing my bulk/absorption/float settings for weeks.

Currently set to 14.4V absorption and 13.6V float for a 100Ah lead-acid leisure battery, but I'm wondering if I'm leaving charge on the table or cooking the battery slightly.

Also curious how long you're setting the absorption timer for — mine defaults to 2 hours but with a small panel that's probably never pulling full current anyway, does the timer even matter much in practice?