Is this a bad idea? Battery Protect Manual Bypass

Been thinking about this one a fair bit lately, particularly after a situation on the narrowboat last winter where the Victron Battery Protect tripped and left me without the heating pump at an inconvenient moment.

So here's the scenario I keep mulling over — your BMS has fired the ATD signal, Battery Protect has opened, loads are cut. Fine, it's doing its job. But what if you know the reason it tripped (say, a rogue cell voltage reading that's since recovered, or you accidentally ran things too hard overnight), and you just need to run one specific load to get yourself out of a sticky situation?

Is there a sensible way to implement a manual bypass — properly fused and switched — that lets you selectively energise a critical circuit while the protect is open?

I'm thinking something like a heavy-duty rotary isolator wired in parallel around the Battery Protect output, with a big warning label saying "DO NOT USE UNLESS YOU KNOW WHAT YOU'RE DOING." Not something you'd leave enabled, purely an emergency get-out.

The obvious concern is that you're circumventing protection that exists for a reason, and if the BMS tripped because of a genuine fault you could cause real damage — or worse.

On the motorhome I've got a Fogstar Drift 100Ah with its own internal BMS, so the protection layers are a bit different there.

Has anyone actually done this? Is there a smarter way — maybe via Victron DVCC settings or a secondary small battery that stays live for critical loads?

Curious what others think, especially those running lithium setups where the BMS is doing the heavy lifting.

@MrBodge65 the narrowboat scenario is exactly why I wired a manual bypass toggle on mine — though I did it properly with a clearly labelled warning sticker because future-me is an idiot who forgets things.

Key consideration: your Battery Protect exists to stop you killing the battery, so bypassing it means the BMS is now your only line of defence — and if you've got a Fogstar Drift or similar with a decent BMS that's probably fine, but if you're on older cells then you're one distracted afternoon from a very expensive mistake.

In the van I'd never bother, but on a liveaboard where heating = survival, a labelled, fused bypass toggle seems entirely reasonable.

@MrBodge65 Done similar on the boat myself. The real risk people gloss over is bypassing the BP without any overcurrent protection on that bypass path — if something's already drawing hard enough to trip the BP in the first place, your bypass wire needs to be rated accordingly or you're asking for a fire in the bilge.

What actually caused your BP to trip? Low voltage cutoff, or overcurrent? Because if it was low voltage protecting the bank, manually overriding it to run a heating pump could finish off your cells. That's the bit that makes me skeptical of blanket "just fit a bypass" advice.

Worth knowing why it tripped before deciding the BP was the problem rather than a symptom.

@ExBrickie raises the point I was going to land on — overcurrent protection is non-negotiable if you're bypassing the BP.

What I'd add from my motorhome setup: the Battery Protect is doing two jobs simultaneously — low voltage disconnect and reverse polarity protection. A lot of people only think about the first one when planning a bypass and completely forget the second.

If your bypass toggle is wired carelessly and someone connects a load backwards during a fault scenario, your LiFePO4 cells will have a very bad day with absolutely nothing standing between them and disaster.

My approach was fitting a proper rotary changeover switch rather than a simple toggle — BP circuit in one position, direct bypass in the other, never both simultaneously. Labelled it clearly with a Dymo label. Belt and braces.

The narrowboat/liveaboard use case genuinely justifies the extra effort here.

@ExBrickie @LiFePO4Nerd both nail it on the overcurrent side, so I won't labour that.

My actual question though — has anyone tested what triggers the BP to trip before reaching for a bypass solution? On my van build I had similar grief and it turned out to be a dodgy crimp causing intermittent voltage drop, which the BP was reading as a low-voltage event. Fixed the crimp, problem gone.

Bypassing a safety device to work around what might actually be a symptom of a wiring fault seems like the wrong direction. Particularly on a narrowboat where a thermal event is a genuinely nasty scenario.

What was the actual trip condition @MrBodge65 — did you pull the logs from the BP via VictronConnect? Because if you haven't diagnosed why it tripped, a bypass just papers over it.