High-Current, Low-Cost LFP 12.8V Solar Charge Controller? (Amps per Dollar)

Been down this rabbit hole recently whilst speccing out the charge controller for my tiny house build, so figured I'd share some findings.

The metric that actually matters here isn't purchase price — it's cost-per-amp of charge current. Once you start comparing on that basis, the budget end of the market looks very different.

My current shortlist:

The Victron obviously wins on features, firmware quality, and Bluetooth monitoring — but you're paying a significant premium for that ecosystem. If you're genuinely budget-constrained and running a straightforward 12.8V LFP bank, the EPever MPPT units with MT50 display are honestly decent for the money, provided you configure the LFP charge profile correctly in their software (they don't always nail this out of the box).

One thing worth flagging for LFP specifically — you must have a controller that allows absorption voltage to be set around 14.2V and float disabled or set to ~13.5V. Some cheaper units don't allow proper float suppression and will chronically overcharge your cells.

Has anyone run the Fogstar or similar UK-sourced LFP batteries alongside the EPever units long-term? Curious whether anyone's seen charge profile drift over winter months on the cheaper controllers.

Would be interested to know what

@KangooNomad solid framing — and you're right, sticker price is a red herring.

The metric I'd actually push for is amps per pound of lifetime cost, which means factoring in efficiency losses too. A cheap PWM might look great on paper but you're haemorrhaging 20-30% of your panel output versus MPPT.

Running a Victron SmartSolar 100/30 on my motorhome — not cheap upfront, but the Bluetooth monitoring alone has saved me from a dodgy battery situation more than once. You can actually see what's happening.

For budget MPPT that isn't junk, Renogy Wanderer series is worth a look if you're keeping currents modest. But above 30A I wouldn't stray far from Victron personally — the efficiency curve stays flat and the warranty actually means something in the UK.

What panel wattage are you working with?

Curious where everyone lands on the derating question — because that feels like the hidden cost nobody prices in upfront.

Running a Renogy 40A controller at, say, 85% capacity in a warm garden office install versus pushing a cheaper unit to its rated limit in the same conditions... the efficiency gap compounds quickly, doesn't it?

Also wondering whether the LFP absorption voltage precision matters more than raw amps for battery longevity? My Fogstar cells seem quite sensitive to that final stage. Some budget controllers I've looked at have fairly coarse voltage steps which makes me nervous.

@KangooNomad what charge profiles were you comparing across the units you looked at? That feels like it could shift the "cost per usable amp" calculation considerably once you factor in premature cell degradation.

@Nobby derating is exactly where I got burned early on with my shepherd's hut setup. Bought a 40A unit thinking I had headroom, but once you factor in the 25°C ambient correction and the fact it's in a poorly ventilated enclosure, I was realistically getting maybe 28-30A sustained. Might as well have bought the smaller unit.

The controllers that publish proper derating curves (Victron does this well in their MPPT datasheets) are worth the premium just for that transparency alone. Some of the cheaper Renogy units I looked at barely mention it in the docs.

Basically — if the manufacturer won't tell you what the controller does at 45°C, assume the worst and size up accordingly. That's the hidden cost nobody puts in their spreadsheet.

@GazPrice that's a really common trap — the nameplate rating assumes something like 25°C ambient, and if your controller's mounted in a poorly ventilated box or facing south in summer, you can easily lose 20-30% of that rated current before you've even started.

Worth flagging too that with LFP specifically, the absorption phase is quite short compared to AGM, so your controller spends more time at bulk — meaning it's running near peak current for longer stretches. That thermal stress adds up over a season.

My personal rule of thumb now is to buy for the amps you actually need at realistic operating temps, not the headline figure. A genuinely-rated 30A unit will serve you better long-term than a cheap 40A that's thermally throttling half the day.

@GemmaFisher82 spent thirty years watching electricians in sub-stations ignore derating tables and then wonder why things melted — bought a Victron SmartSolar 100/30 for my tiny house precisely because at least Victron publish their derating curves rather than burying them in Mandarin somewhere on page 47 of a PDF you'll never find.