In my current RV solar power wall, I use a 600amp blue sea rotary switch as a quick connect between the Lifepo4 battery and the rest of the 24vdc system (inverter charger, solar charge controller and secondary 24vdc charger). I turn the blue sea switch "ON" before I switch the Aims inverter "ON" and switch the PV breakers on that feed solar to the solar charge controller. When I upgraded from 24vdc/200ah to 24vdc/600ah, my 300amp blue sea switch would overheat and fail. The 600amp switch appears to handle the 'rush'. It still makes a hot sound when the amps rush through it initially. I then turn on the Aims inverter.
Q: Before I switch to my Victron Multiplus II 24v 2x120 inverter/charger, do I need to add a resistor to bypass the power switch and pre-charge my Victron inverter capacitors? Does my blue sea switch act as a sufficient resistor between the battery and inverter, rest of the 24vdc systems?
As others have pointed out, you really need to precharge (for SECONDS) with the resistor to prevent catastrophic damage to the inverter's circuit boards, wiring, and the switch contacts from massive overcurrents as the giant capacitors are suddenly charged from giant batteries. When you connect a capacitor to a hard voltage source (without inductance between - which causes other problems), you dissipate as much energy in the wiring as you store or remove from the capacitor, and the lower the resistance, the higher the current (up to near infinity if the resistance is very low). You want to dissipate that energy in a resistor, which is DESIGNED to turn electrical energy into heat without slagging down in the process, rather than in the circuit board traces, the capacitor "plate" foils, and the tiny area of the switch contacts' initial touch, and do it slowly enough that the resistor can handle the job.
Since you're using a rotary battery switch for shutdown, here's a hack. (It's cheap, except that you may need to buy and swap in a different model of the switch.):
* Use a two-battery selector/combiner version of the switch.
* Hook the battery to the "battery two" connection.
* Hook the precharge resistor between the battery one and battery two connections.
So setting 1 is precharge, setting 1+2 and 2 are battery. When turning on switch from off to 1, wait a few seconds, switch to 1+2 (then onward to 2 if you feel like it). Turning off: switch to 2 and then off (so you don't switch to "resistor in circuit" when there is high current or charging current running through the battery line.)
If your "resistor" is an incandescent bulb, I'd wait until it was too dark to see for at least as long as it had been visibly lit after you started precharging. The precharge goes slower as it approaches even, and switching to zero resistance even when the voltage mismatch is small may still produce damagingly high currents.
NOTE: I 'assumed' the switch provides the resistance/protection given it has 'ignition protection' built in. My Aims inverter/charger has lived happily in this configuration since 2021.
Not sure, but I think "ignition protector" is a metal oxide varistor from the output terminal to ground, to keep the alternator voltage from spiking and burning out your electronics (including maybe the alternator's regulator) if you switch the batteries off when the engine is running (in a typical boat installation). The battery load normally clamps the voltage so that it doesn't go too high, but disconnecting it suddenly while the alternator is charging the battery will cause the voltage to go 'way up for much of a second while the regulator tries to reduce the excitation (which takes a while because of the inductance of the field winding).
