Peer Review Request: 24V Off-Grid Mobile System (Dual PowMr Controllers + 4000W Inverter)

Few things jumping out at me here that are worth flagging before you commit to this setup.

Dual PowMr controllers — not necessarily a problem, but you'll want to make sure they're not fighting each other. Are you running them on separate battery banks or paralleling into the same bank? If it's the latter, you really need them both set to identical absorption/float voltages or one will constantly be trying to compensate for the other.

The 4000W inverter concerns me more tbh. On 24V that's pulling around 170A+ at peak. What's your cable run looking like and what gauge are you using? I've seen people fry setups because they underspecced the cabling thinking the fuse would save them. It won't always.

Also — what battery chemistry are you running? LiFePO4 or AGM? Makes a big difference to how you programme those controllers.

From my own motorhome setup I moved away from budget inverter/charger combos pretty sharpish and went Victron. The cost difference is real but the integration with MPPT and the app monitoring alone was worth it. Just saying it's an option if this build isn't fully locked in yet.

Couple of questions that'd help others give better feedback:

• Total solar input wattage?
• Battery capacity (Ah)?
• What loads are you running off the 4000W?

Would be good to see the full schematic if you've got one. Others on here will spot things we might miss in a text description. @Fogstar_fan and a few others have done similar 24V mobile builds, might be worth tagging them in.

@RobJones85 makes good points. One thing I'd add — a 4000W inverter on 24V is pulling some serious amps (170A+ at peak), so your cable sizing and busbar quality really matter here. PowMr gear is budget-friendly but their build quality can be inconsistent; seen a few dodgy units come through the narrowboat forums.

If budget allows, even swapping one controller for a Victron SmartSolar gets you proper monitoring and plays nicely with their ecosystem. Fronius/Victron comms aside though — what's your battery setup? LiFePO4 or lead-acid changes the conversation quite a bit re: charge profiles on those controllers.

@HazelSoul is right to flag those peak amps — but the continuous draw is what kills systems like this quietly over time.

The bit nobody's mentioned yet: cable sizing and busbar quality. A 4000W inverter on 24V needs proper 70mm² flex to the battery, kept as short as physically possible. I've seen setups where the cable run looked fine on paper but had undersized lugs crimped badly, and the voltage drop under load was catastrophic — inverter browning out at 2500W actual draw.

Also worth checking: does that PowMr actually support 24V lithium profiles? Some of their cheaper units default to AGM curves and won't properly bulk/absorb LiFePO4. Run the wrong charge profile long enough and your BMS will start disconnecting under load at inconvenient moments.

What battery chemistry are you running, and what's your actual continuous load requirement rather than the inverter's headline figure?

@LH_Marine hits on something I learned the hard way fitting out my boat — continuous draw is the silent killer. Ran a thermal camera over my cabling six months in and found two crimps running hot enough to melt the heatshrink. Looked fine visually.

On a 24V system with a 4000W inverter, I'd be sizing cable for sustained 100A+ not just the theoretical peaks. Victron's own guidance suggests derating cable runs by around 20% for enclosed/bundled installations — worth factoring in.

Also worth asking: what's the battery C-rating? A lot of cheaper LiFePO4 packs (even decent Fogstar units) will throttle BMS output before you get anywhere near inverter capacity. The weakest link in that chain isn't always where you expect it.

What's the actual use case here — big loads intermittently, or sustained draw?

@ExFirefighter11 nobody's mentioned that a 4000W inverter on 24V also means your DC wiring needs to handle those 170A peaks continuously — and I'd bet good money the PowMr came with cables thinner than my patience for undersized installations.

Victron would've flagged this in the app; PowMr will just quietly melt something and leave you wondering why your static van smells like a bonfire.

Size your busbars and fusing before you size anything else — learned that lesson the expensive way on my emergency backup setup and I still haven't fully forgiven myself.