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

Picked up one of those Wanderer-style 20A MPPTs off eBay for about £18 delivered. Paired it with a single 100W panel I got secondhand for £25 and a tatty but functional 80Ah leisure battery I rescued from a mate's old caravan. Total outlay so far is under £60, which felt like a win.

Problem is the default settings on this thing seem a bit all over the place. It came pre-set to sealed lead acid at 14.4V absorption and 13.8V float, but I've seen people suggest bumping absorption up to 14.7V for a proper AGM, which mine might actually be — the label's half peeled off so I'm going by feel here. Don't want to cook it, but also don't want to end up with chronic undercharging and a sulphated battery in six months.

Also noticed the controller gets quite warm even when the panel's only putting out maybe 3–4A on a cloudy day. Is that normal for these budget units or should I be worried? There's no fan, just a small alloy heatsink on the back.

Has anyone got a working set of parameters they'd recommend for an unknown leisure battery on one of these cheap controllers? Happy to share more details about what I'm seeing on the display if that helps diagnose anything.

@Squib30 honestly not a bad little setup for the money.

I ran something similar on my cabin build — generic 20A MPPT, single 100W panel, knackered 100Ah lead acid. Key settings that made a difference:

• Bulk/Boost: 14.4V for a standard flooded battery
• Float: 13.8V
• Low voltage disconnect: 11.8V (saves the battery from deep discharge)

The thing these cheap units get wrong out of the box is the float voltage — often set too high at 14.4V which just cooks the battery over time. Drop it to 13.8V and you'll extend that leisure battery's life considerably.

Also worth checking whether yours is actually doing MPPT or just acting as a PWM — a few of these eBay units are mislabelled. Watch the input voltage under load; genuine MPPT will show notably higher than battery voltage.

SmartSolarFan | 📍 South Wales | ⚡ 400W system

@Squib30 cracking little budget setup that! With a single 100W panel you're rarely going to stress a 20A controller anyway, so the main thing I'd focus on is getting your battery voltage settings right rather than worrying too much about the charge current limits.

For a standard flooded leisure battery, I'd set bulk to 14.4V, absorption to 14.4V and float to 13.6V — many of these cheap units default float too high around 13.8V which slowly cooks them over time.

Also worth checking whether it defaults to sealed/AGM mode out the box, as some do. That'll push voltages slightly higher than your flooded battery wants.

What's the battery chemistry — flooded or AGM? Makes a difference to the recommended settings. 👍

Worth double-checking what your battery chemistry setting actually is on those cheap units — a lot of them default to sealed lead acid at 14.4V absorption, which is fine, but some ship with it set oddly low around 13.8V and you'll never properly top the battery up.

On mine (similar eBay unit, ran it on the narrowboat for a season before upgrading to Victron) I ended up manually setting:

• Absorption: 14.4V
• Float: 13.6V
• Low voltage disconnect: 11.8V

Also worth taping over the USB ports on those controllers if it's anywhere damp — they seem to be the first thing that dies.

@Squib30 what's the panel's Voc? Some of those budget MPPTs claim MPPT but are actually PWM under the hood, worth verifying you're actually getting proper conversion.

@BoatEwan is bang on about chemistry defaults — caught mine set to sealed AGM when I had a flooded battery. Was slightly undercharging the whole time.

On the voltage settings for a standard flooded leisure battery I run:

• Bulk/Boost: 14.4V
• Float: 13.6V
• Equalization: off (unless you know what you're doing)

The cheap units often have float set too high out the box — mine was at 13.8V which just cooks the water off slowly.

With a single 100W panel you're not going to hammer the battery anyway, but still worth getting it right from the start rather than wondering why the battery's dying in 18 months.

SussexBoater | 📍 Sussex Coast | ⚡ "It floats (mostly)"

Mine spent three weeks cheerfully overcharging my leisure battery before I realised the display was lying to me about bulk/absorption stage — those cheap units often show "full" when they've barely started. Slap a proper voltage meter on it (even a £6 one from Amazon) and trust that over whatever the controller claims, because the controller is an optimist.

Good shout from @NigeCampbell81 and @BoatEwan on the chemistry settings — that's the first thing to nail down.

One thing nobody's mentioned yet: on those cheap units the absorption voltage and float voltage are often set for a "nominal" 12V battery that's actually targeting 14.8V absorption. Fine for some AGMs, terrible for a tired leisure battery that's already been pushed around.

I'd manually drop float to around 13.5V on an older flooded battery — lets it sit without cooking off electrolyte. Absorption somewhere between 14.1–14.4V depending on condition.

Also worth checking whether yours has a genuine MPPT algorithm or is just PWM dressed up in fancy packaging. Some of the £18 jobbies are PWM controllers with "MPPT" printed on the box. With a single 100W panel you won't lose loads either way, but worth knowing what you're actually running.