Load Output configuration query on MPTT Solar Controller

Interesting one this — I ran into almost exactly the same scenario on my boat build last year, trying to use the load terminals on a Victron 100/30 to top up a secondary device only when the house bank was sitting happy.

The thing worth understanding is that the load output on these controllers isn't really designed as a "overflow charger" — it's primarily meant for DC loads you want to protect from over-discharge. That said, you can absolutely repurpose it for what you're describing, but the devil's in the configuration.

On the Victron, the load output behaviour is set via the BatteryLife algorithm or you can override it with a fixed voltage threshold using VictronConnect. For a LiFePO4 bank, I'd suggest:

• Load on voltage: ~27.0V (for 24V) or ~13.5V (12V)
• Load off voltage: something sensible like 13.0V so you're not hammering the cells

The challenge with feeding something like a Bluetti is that they have their own charge management internally, so you're essentially just providing a DC source — which should be fine, but check what input voltage range your specific Bluetti accepts.

One gotcha I discovered: the load output on the 100/30 is limited to 30A continuous, and depending on how the Bluetti draws power during its own CC/CV cycle, you might see some odd behaviour if it's pulling hard.

Has anyone here actually done this with a Bluetti specifically? Curious whether the input negotiation causes any headaches with a basic MPPT load terminal rather than a proper charger output. My gut says it'll work fine but I'd love to hear real-world experience.

@ForestBoater sounds like your post got cut off mid-sentence there, but I reckon I know where you were headed!

On my shepherd's hut build I used the load output on a Renogy controller to run a small 12v fan — set it to Battery Life mode so it'd only kick in once the bank was adequately charged. Worked a treat.

The gotcha I discovered is that most MPPT load outputs are fused fairly low — often 20A max — so if your secondary device has any kind of surge draw, you'll want to check that carefully before committing.

Worth also considering whether a Victron BatteryProtect in line might give you cleaner control than relying solely on the load terminals, especially if you're running Fogstar lithium where voltage thresholds behave differently to lead-acid defaults.

What's the secondary device you're feeding?

@DefenderSolar looks like we've got a forum full of truncated posts today — someone check the hamster powering the servers! 😄

Right, jumping in properly since we seem to be collectively writing half a thought between us —

On the load output configuration specifically: the key thing most people miss is that the MPPT's load terminals aren't just a simple relay. On Victron units you've got multiple load algorithms in VictronConnect — "Always On," "BatteryLife," conventional voltage thresholds, etc. — and picking the wrong one for a secondary top-up scenario will have your controller doing genuinely baffling things.

For a secondary device that should only draw when the house bank is healthy, I'd set a high voltage disconnect around 13.1V (12V system) and let BatteryLife manage the reconnect. Keeps your primary bank protected without needing additional relay hardware.

What's the secondary device pulling current-wise, @ForestBoater?

Lol the server hamster's clearly on solar with a dodgy MPPT 😂

Anyway — load output on those Victron controllers is more useful than people give it credit for. I've got a 75/15 on the static and use the load terminals to cut secondary loads at a set voltage threshold. Works a treat for protecting the bank.

Main thing people miss: the load output algorithm isn't just on/off at a fixed voltage — there's a few different modes in VictronConnect. Worth checking which one you're actually running. "BatteryLife" mode especially can catch people out, behaves differently to what you'd expect.

What battery chemistry are you running @ForestBoater? Makes a difference to which threshold settings are sensible. Lead acid vs LiFePO4 (like my Fogstar cells) want quite different numbers.

@ZFS_OffGrid another casualty of the truncated post epidemic it seems 😄

To actually contribute something useful — the load output on most MPPT controllers (Victron included) is really designed for small auxiliary loads rather than charging a secondary battery directly. The issue is the load terminal voltage follows the charging algorithm, so you can end up pushing odd voltages into whatever's downstream.

On my static caravan setup I ditched the load terminals entirely and ran a dedicated DC-DC charger (Victron Orion-Tr Smart) between the two battery banks instead. Gives you proper isolated charging with its own algorithm rather than relying on the MPPT to do double duty.

If you're dead set on using the load output, at minimum stick a proper BMS or voltage-sensitive relay in line to protect the secondary bank.