HM-1200NT + 24V LiFePO4 Battery Inverter Won’t Wake From Battery

Been wrestling with something similar on my static caravan setup and wondering if anyone else has hit this wall.

Running a Fogstar 24V 100Ah LiFePO4 with a HM-1200NT and the inverter just refuses to wake up from battery after the BMS has tripped overnight. Solar kicks in at dawn, charges fine, but if I try to run purely off battery in the evening the inverter sits there doing nothing until I physically disconnect and reconnect.

Few things I've already checked:

• BMS low-voltage cutoff is set to 20V (seems reasonable for 24V LiFePO4?)
• Victron MPPT is waking up fine and pushing charge in
• Battery resting voltage is sitting around 24.8V when this happens, so it's not flat

My suspicion is the inverter needs a higher "wake" voltage than it's seeing when the BMS reconnects, almost like there's a brief voltage sag that confuses it. Has anyone experimented with adjusting the BMS reconnect threshold?

Also curious — is this a known quirk with the HM-1200NT specifically, or would I see the same with other inverters? I'm half tempted to throw a small Victron Phoenix in instead but that feels like overkill just to solve a startup issue.

Could a soft-start relay or a pre-charge resistor circuit help here? I've seen that mentioned for capacitor inrush but not sure if it applies to this scenario.

Anyone else running this combination, or something similar in a garden office or static setup? Would love to know how you've worked around it.

@OldSparky the HM-1200NT has a notoriously high inrush current on wake-up — it'll pull a spike that trips most BMS units before the inverter even fully initialises.

Few things worth checking:

• BMS overcurrent threshold — what's yours set to? Some Fogstar units default quite conservatively
• Try a pre-charge resistor setup between battery and inverter to soften that initial draw
• Also worth checking the low-voltage cutoff on the BMS — 24V systems can trip earlier than you'd expect if one cell group sags under load

Had something vaguely similar with my cabin setup (different inverter, Victron Multiplus) and it turned out the BMS was seeing a momentary spike and latching off. Reset wasn't obvious either.

What does your BMS app show at the moment of cutout — is it logging an overcurrent fault or undervoltage?

@EmmaEdwards82 nailed the inrush problem, but here's the bit nobody mentions — the Fogstar BMS has a recovery timeout that can stretch to 30 seconds after a trip. So even if you sort the spike, people panic and start button-mashing the inverter switch, which just keeps retriggering the fault and the poor BMS never gets a chance to breathe.

My van setup taught me this the hard way. Stood in a layby in the Brecon Beacons convinced my whole system had died. It hadn't. It was just sulking.

Try this: disconnect the inverter load completely, wait a full minute, then power back up. If your Fogstar comes back happy, you've confirmed the BMS is doing exactly its job — just perhaps a bit too enthusiastically. A proper soft-start relay sorted mine permanently.

@OldSparky worth checking your BMS discharge enable voltage threshold too. If the inverter's idle draw is pulling the resting cell voltage below the BMS low-voltage cutoff during that wake-up window — even briefly — the BMS will latch off and won't recover until you manually reset or the timeout @KangooDream mentioned expires.

On my van build I had identical grief with a Victron MultiPlus until I programmed a 2.90V/cell discharge floor into the BMS rather than the default 2.80V, giving it headroom before protection kicks in. Also worth adding a pre-charge resistor circuit between battery and inverter to dampen @EmmaEdwards82's inrush spike — 10–15Ω for a few seconds works well. Some folks use a dedicated relay timer board for this.

@OldSparky one thing nobody's touched on yet — check what voltage the HM-1200NT is actually seeing at startup vs what the BMS thinks the pack is at. Long cable runs with undersized wire create enough of a voltage drop that the inverter's low-voltage cutoff triggers before the BMS even has a chance to object.

Had almost exactly this on my motorhome build. Inverter kept throwing a fault, BMS logs showed nothing wrong. Turned out my 4mm² cable run was about 40% too small for the peak draw.

Minimum I'd say for that inverter at 24V is 6mm², ideally 10mm² if your run is over a metre or two. Sounds boring but it sorted mine completely.

What's your cable spec and run length?

Good shout from @OffGridMax on the voltage drop at startup. One thing worth adding — have you checked the cable gauge between your battery and inverter? On a 24V system people often underestimate how much even a short run of undersized cable will sag under initial load. I had a similar head-scratcher on my setup and it turned out my 6mm² tails were causing enough of a drop that the inverter's undervoltage protection was tripping before it could even complete its startup sequence. Swapped to 16mm² with proper ring terminals crimped rather than just twisted, and it sorted itself immediately. Worth measuring the actual voltage at the inverter terminals during a wake attempt rather than just at the battery terminals — the difference might surprise you.