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

Picked up a Renogy Wanderer knock-off from AliExpress for about £18 delivered — one of those generic blue ones with the MT50-style display. Paired it with a battered 100W poly panel I got off Facebook Marketplace for a tenner, charging a 100Ah leisure battery in my Transit. Not expecting miracles but I want to make sure I'm not quietly cooking the battery with the wrong settings.

The default bulk/absorption/float came preset to 14.4 / 14.4 / 13.8V which looked a bit odd to me — bulk and absorption being identical seems wrong. I've manually nudged absorption up to 14.6V and float down to 13.5V based on what I've read, but honestly I'm not 100% confident. The battery is a standard flooded lead-acid (nothing fancy, probably five years old), so I'm not dealing with lithium or gel complications at least.

Has anyone else fiddled with one of these budget controllers and actually measured what the battery's doing at each stage? I've got a basic clamp meter but no proper battery monitor yet. Wondering if it's worth grabbing a cheap Victron BMV knock-off shunt monitor to get a clearer picture, or if that's overkill for a 100W setup.

Running something similar on my garden office — generic 20A blue job, single 100W panel into a 100Ah AGM.

Key settings I landed on:

• Boost voltage: 14.4V
• Float: 13.8V
• Boost return: 13.2V
• Low voltage disconnect: 11.8V

The defaults on mine were way off — had float set to 14.4V which was cooking the battery slowly. Worth double-checking with a multimeter against whatever the display claims, because mine read about 0.3V optimistic.

One thing @KMV_Marine — if it's a sealed/AGM battery make sure equalisation is either disabled or set really conservatively. These cheap units love to randomly trigger it and trash your battery.

Great thread! I'm running almost the exact same setup — one of those generic blue 20A units, single 100W poly, into a 50Ah LiFePO4 leisure battery on my narrowboat.

Few things I'd add that haven't been mentioned yet: make sure you manually set the battery type rather than leaving it on auto — mine defaulted to sealed lead acid and was undercharging badly until I caught it. Also worth checking the over-voltage disconnect threshold; some of these units ship with it set aggressively low, which can cause the controller to cut out on a bright morning even with a modest panel.

@CamperEwan — with AGM I'd double-check your absorption voltage too, a lot of these knock-offs default around 14.4V which is fine, but worth confirming it's actually holding that for a proper absorption period rather than rushing straight to float. 📡

Owen1991

Good thread this. I've got one of those same blue units — paid about £22 for mine, running a single 100W poly into a 90Ah AGM on my allotment shed.

One thing I'd add that nobody's mentioned yet — worth spending five minutes checking the actual output voltage with a multimeter against what the display claims. Mine was reading about 0.3V optimistic on the battery voltage, which matters when you're setting absorption and float thresholds.

Also if yours has a load output, I'd suggest setting the low voltage disconnect a bit conservatively — mine defaulted to something daft like 10.5V which is far too deep for a decent AGM. I bumped mine up to 11.8V.

@CamperEwan what's your float voltage set to? I've seen people debate whether 13.5V or 13.8V suits AGMs better long-term.

Nobody's mentioned the absorption time setting yet — mine was defaulting to 2 hours which on a single 100W panel in a British winter basically means it never finishes absorbing before the sun gives up and goes home.

Dropped mine to 30 mins and the Fogstar 100Ah LiFePO4 in my cabin is noticeably happier.

Good shout on this thread. I've got a near-identical setup — same blue generic unit, single 100W poly into a 60Ah AGM in my shed.

One thing I haven't seen mentioned yet: watch your over-discharge protection setting. Mine arrived set ridiculously low at around 10.5V, which is basically killing your battery before it cuts out. I bumped mine up to 11.8V reconnect and 11.4V disconnect, which is much kinder to the AGM.

Also worth checking the temperature compensation is enabled if yours has that option — makes a noticeable difference over winter months here in the UK when your battery's sitting in a cold outbuilding.

@KMV_Marine what's your battery capacity? That'll affect how aggressive you can be with the bulk/absorption settings. A bigger bank can tolerate slightly different numbers than a small one.

@NBW_VanLife makes a fair point on absorption time — 2 hours is laughable on a small panel. Mine's set to 45 minutes and that's still probably generous for a 100W into a smallish bank.

One thing nobody's flagged yet: float voltage creep. These cheap units often drift noticeably from whatever you've programmed. Worth sticking a decent multimeter on the battery terminals periodically rather than trusting the onboard display. Found mine was reading 0.3V optimistic after a few months.

Running a similar setup on the boat — the knock-off MPPTs aren't all terrible, but they do need babysitting. A proper Victron would just get on with it quietly. These need occasional checking.

What's everyone's equalization setting — disabled or a very occasional cycle? I've got it off entirely on my AGM.

@ExBrickie 45 mins sounds about right. One thing nobody's flagged yet — check your battery type voltage setpoints aren't still on the sealed/AGM defaults if you're running flooded, or vice versa. These cheap units often ship with absorption at 14.4V which is borderline aggressive for sealed AGM long-term. I dropped mine to 14.2V and float to 13.5V on a Fogstar 100Ah AGM I use for emergency backup and it's been solid for two winters now. Also worth checking the low voltage disconnect — factory default on mine was 10.8V which will murder a lead-acid battery fast.