Two brand new Quattro 48/5000/70 instantly trigger battery BMS Short Circuit when connecting DC

Interesting one this — I had something similar last year when I first wired up my 48V LiFePO4 bank (Fogstar Drift cells in a DIY build with a Daly BMS).

The culprit for me was inrush current on initial DC connection. The Quattro's internal capacitors draw a massive spike the moment you connect — we're talking potentially hundreds of amps for a fraction of a second. A BMS set up for legitimate short-circuit protection will see that and immediately trip, even though nothing is actually wrong.

A few things worth checking:

• Pre-charge resistor — are you using one? Victron actually sell a pre-charge resistor specifically for this. Connecting through a resistor first lets those caps charge up gradually before you make the full connection
• BMS short-circuit threshold — what's it set to? Some units ship quite sensitive out of the box
• Cable length and gauge — longer, slightly thinner cable (within reason) can actually help soften that initial spike marginally

The fact you've got two units doing this almost certainly rules out a faulty inverter. That's almost always pointing at the BMS reacting to inrush.

Worth checking the FIDUS BMS documentation — some manufacturers have a specific commissioning procedure for connecting high-capacitance loads. Victron's own documentation on the Quattro mentions pre-charging too if I recall correctly.

Anyone else on here running FIDUS batteries? Curious whether their BMS has adjustable parameters or if it's locked down. Makes a big difference in how much you can tune this sort of thing.

Good shout @Tel1968 on the inrush current angle. Worth adding that the Quattro's internal capacitors are absolutely enormous and will draw a massive spike on first connection — we're talking potentially thousands of amps for a few milliseconds, which most BMS units interpret as a dead short.

The standard fix is a pre-charge resistor before making the full DC connection. I used a simple 100 ohm / 50W wirewound resistor across the positive terminal for about 30 seconds prior to closing the main contactor — lets those caps charge up gradually so the BMS never sees the spike.

Some folks use a dedicated pre-charge relay circuit to automate it. Victron do actually mention this in their installation docs but it's easy to miss. Once pre-charged, the Quattros connect absolutely fine in my experience. What BMS are you running on the new build?

Good point from both @Tel1968 and @Simon1988 — I had exactly this issue connecting my Quattro to a Fogstar-based bank on the boat. What fixed it for me was a proper pre-charge resistor wired in before the main DC isolator. Something in the 50–100 ohm range, rated appropriately, let the bus capacitors charge slowly before the BMS saw any spike.

Worth also checking your DC cable lengths and connections are solid — a loose terminal can cause voltage bounce that mimics a short to the BMS logic.

The Daly BMS in particular seems quite hair-trigger on short-circuit detection. If you have access to Victron's DVCC settings, dialling in soft-start parameters can help too, though the pre-charge method is the more reliable mechanical solution in my experience.

Really important point that hasn't been mentioned yet — pre-charge resistor. Before connecting your Quattro cold to the battery bank, you want to pre-charge those internal caps through a resistor (typically 100–470Ω, rated appropriately) for several seconds. Bypasses the inrush spike entirely and the BMS never sees the short-circuit-level current surge.

Victron actually document this in their wiring guides, though it's easy to miss. A simple pre-charge circuit with a resistor and momentary switch wired across your main isolator does the job — dead simple to knock up for a few quid.

@Tel1968 and @PanelJulie are both right about the root cause, but solving it at the connection stage rather than trying to tune BMS sensitivity is the cleaner fix IMO. The Daly BMS in particular is notoriously hair-trigger on short-circuit detection.

@Wardy has nailed it with the pre-charge resistor — that's the proper engineered solution. Worth specifying though: for a 48V Quattro 5000 you're looking at roughly 47–100Ω, 25W rated minimum for the pre-charge circuit. I used a 50Ω 50W wirewound on my garden office build and it charges those capacitors cleanly in under 5 seconds with no BMS trip whatsoever.

One thing nobody's mentioned — check your BMS short-circuit detection threshold and delay time. The Daly units are notoriously hair-trigger; the default trip threshold can be as low as 200A with near-zero delay. Victron's own documentation recommends a BMS with at least a 1–2ms delay before tripping to allow for legitimate inrush events. Some BMS firmware lets you adjust this directly.