Getting EcoWorthy BMS to allow solar while at full charge.

Been down this exact rabbit hole with my shepherd's hut build last summer. The EcoWorthy BMS is notorious for this — it cuts solar the moment cells hit 3.65V and then just sits there, even when the pack drops enough to accept charge again. Maddening.

What sorted it for me was adjusting the overvoltage recovery threshold in the BMS parameters. By default it's set almost identically to the overvoltage cutoff, so the BMS never really "wakes up" properly. Drop the recovery voltage by about 100–150mV and it starts breathing again. On mine I had the cutoff at 3.65V and moved the recovery down to 3.50V — made a massive difference.

The other culprit is your charge controller settings. If you're running a Victron or Renogy unit, make sure your absorption voltage isn't constantly hammering the pack at 100% — a slight float voltage reduction gives the BMS room to cycle properly rather than permanently holding the high-voltage cutoff.

Worth noting: this isn't really a fault, it's the BMS doing exactly what cheap BMS units do — being overly conservative. For an emergency backup setup like mine, I actually want a bit of paranoia in the BMS, but not to the point where it's refusing free solar energy on a good Scottish summer day.

Has anyone tried the Overkill Solar BMS as a replacement? Curious whether the more granular parameter control actually solves this properly or just moves the frustration elsewhere.

Gazza24 | Posts: 847 | Location: North Yorkshire

@MPPTGal yeah, classic EcoWorthy behaviour — proper frustrating. What sorted it for me was backing off the charge voltage on the MPPT controller itself. Instead of letting it push to the full 14.6V (4S), I dropped mine to around 14.2V and set absorption time to about 20 minutes. The BMS stops throwing a wobble and the cells still get a decent top-up.

You're essentially taking the decision away from the BMS by not triggering its overvoltage protection in the first place. Not perfect, but pragmatic.

Worth checking whether you've got the 4S or 8S variant too — some batches have slightly different threshold tolerances. What MPPT are you running with it?

JoeFox55 | Posts: 312 | Location: Shropshire

Worth checking whether your MPPT has a absorption/float voltage split you can actually tune properly. I run mine at 3.55V per cell for absorption rather than pushing to 3.65V — the BMS never triggers overvoltage protection and the cells still hit a decent state of charge. You lose maybe 2-3% capacity but honestly on a shepherd's hut setup you'd never notice. @MPPTGal what controller are you running? Some of the cheaper units don't let you get granular enough with the per-cell voltages, which is where the frustration really starts. Also worth double-checking your cell count multiplier is set correctly in the controller — seen a few builds where that's been slightly off and causing exactly this kind of nuisance cutoff behaviour.

ExChippie30 | Posts: 203 | Location: Array

Had this exact issue on my tiny house build. Ended up setting the Victron MPPT absorption voltage to 3.45V per cell rather than 3.65V — keeps the BMS happy and you still get a decent state of charge.

Not ideal long-term but it stopped the constant cutoff loop.

Also worth checking if EcoWorthy have pushed any firmware — mine was running something ancient and a update sorted the float behaviour partially. Still ended up swapping it for a Fogstar-compatible unit eventually, couldn't be doing with the faff.

@JoeFox55 is on the right track re: the MPPT settings tbh.

FormerCop | Posts: 1,204 | Location: Array

@JoeFox55 is sniffing in the right direction — the real fix is telling your Victron MPPT to float at 3.40–3.45V/cell (so ~54.4V for 16S), which keeps you just below the BMS cutoff so it never trips in the first place, rather than fighting to reset it after the fact. EcoWorthy BMSs have a hysteresis gap that's frankly embarrassing — won't re-engage until voltage drops a full 0.2–0.3V below trip, which on a sunny day with low loads basically means you're coasting on nothing until evening. Fogstar cells tolerate the slightly lower float fine, no capacity penalty worth crying about. Sort the MPPT absorption setpoint first, the BMS paranoia mostly disappears.