Orion 24/12/20 rebulk issue

Been having a similar head-scratcher with my setup in the shepherd's hut and thought it worth raising here.

Running an Orion 24/12/20 between a 24V LiFePO4 bank (Fogstar cells) on the source side and a 12V 200Ah on the load side. The lockout and restart voltages are doing their job fine — no complaints there — but I'm noticing the unit isn't triggering a rebulk properly after the 12V side recovers.

Essentially it charges up, hits the absorption threshold, sits there briefly, then goes into float. So far so normal. But once the 12V bank gets pulled down a bit by the load and should kick back into bulk, it's sluggish about it. Sometimes it takes ages, sometimes it just... doesn't, until I manually reset it via VictronConnect.

Few things I've already ruled out:

• Wiring and connections look solid
• Firmware is current
• Rebulk voltage offset is set to 0.4V below absorption

My gut says it might be related to the source battery voltage being quite stable (LiFePO4 flat discharge curve) and the Orion not seeing enough of a voltage drop to trigger the rebulk algorithm properly. Unlike with AGM where the source side fluctuates more, LiFePO4-to-LiFePO4 setups might behave differently to what Victron originally designed around?

Anyone else running a similar dual-LiFePO4 configuration seen this? Curious whether tweaking the rebulk offset further makes a difference or if there's something in the Orion's settings I'm missing. Static caravan owners with similar DC-DC setups, I'd especially like to hear how you've got yours di

@OldSparky18 the post seems to have cut off before you finished describing the load side — worth completing that so people can give accurate advice.

That said, the Orion 24/12/20 rebulk threshold is something I've wrestled with on my narrowboat. Key thing to check: are you running it in standalone mode or engine-on detection? If standalone, the default rebulk offset is 0.4V below absorption — on LiFePO4 that can cause it to sit in float indefinitely without ever triggering a new bulk cycle, particularly if your Fogstar cells are holding voltage well.

Worth connecting via VictronConnect and explicitly setting:

• Absorption voltage: 28.4V (24V bank)
• Float: 27.2V
• Rebulk offset: bump to 1.0–1.2V

The factory defaults assume lead-acid behaviour. LiFePO4 flat discharge curve catches people out every time.

@OldSparky18 yeah the post got cut off mid-sentence — no load side details, no BMS specs, no mention of whether the Orion is in standalone or engine-off mode. Hard to diagnose a rebulk issue without knowing what's actually on the 12V output side or what your absorption/float voltages are set to.

Also worth clarifying — rebulk threshold and rebulk behaviour are two different things. Victron's documentation on this is actually decent if you dig into the Orion-Tr Smart manual rather than just the app tooltips.

Complete the OP and someone here can probably help properly.

@OldSparky18 your post cut off before the load side details — until you complete it we're largely guessing.

That said, rebulk issues on the Orion 24/12/20 in non-isolated mode are almost always one of three things:

1. Source voltage not recovering above the rebulk threshold — the Fogstar cells sitting at a resting voltage that falls between float and rebulk, particularly if your 24V BMS has a tight absorption window
2. Engine detection / ignition pin wired incorrectly or floating — causes erratic charge cycling
3. VE.Direct polling interval confusing people into thinking rebulk isn't triggering when it actually has

What's your rebulk offset set to in VictronConnect? Default is 0.4V but on LiFePO4 with a flat discharge curve that's often too tight. I've run mine at 1.0V on the narrowboat without issues.

Post the full setup and we can actually diagnose it.

Came across the same Orion rebulk puzzle on my narrowboat last winter — drove me half mad before I traced it back to the BMS on the source bank dropping out momentarily and confusing the charger's voltage history. The Orion essentially "forgot" where it was in the charge cycle.

@OldSparky18 once you've filled in the missing details, worth checking whether your Fogstar BMS has any low-temp or overcurrent protection that could be causing brief disconnects. Even a half-second dropout can reset the rebulk threshold logic on these units.

Also worth noting — are you monitoring via VictronConnect? The history tab will show if the charger is completing absorption or bailing out early, which narrows it down considerably.