Is it necessary to precharge DC bus capacitors on Multiplus 2 if grid connected?

[gyrex (John)]

As the title says, is it necessary to precharge the capacitors on the DC bus if the Multiplus is grid connected and there’s a supply on AC-In? ie. Will the inverter charge the capacitors on the DC bus via the AC bus?

My system is going live in Monday and I’m trying to avoid massive sparks and arcing when I turn on the battery DC switches. The reason I ask is that when I was preparing my batteries by top balancing them and I initially connected my power supply, the connection to the battery terminals created a massive spark which I subsequently avoided by putting a 32Ω, 20W resistor in series when charging subsequent batteries.

[lxonline (LX)]

You can in theory do that. (But there still may be a spark/arc.) As you are connecting live to live.

[Sebastian]

The sticker on the right side of my MPII says:

Disconnect the supply before making or braking the connection to the battery

So you should have always the DC connected, when AC is at the AC-IN.

I installed a little 3d printed box on my DIN-rail with a switch and two 18 Ohm 50W resistors to limit the precharge current to max 1.5A (50W is a little bit overkill ):

With rising voltage at the output the LED gets brighter.