Let's back up a bit to understand the problem and understand the terms.
All inverters have a bank of large capacitors tied parallel to the DC battery inputs. When the battery is first connected to the inverter, these capacitors appear as a dead short to the battery, and a huge surge of current flows till the capacitors charge up to the same voltage as the battery. The capacitors will charge in a fraction of a second, but the current will start out at a very large value. It is only limited by the total resistance of the circuit and since LiFePO4 has an internal resistance of fractions of milliohms, the total circuit can be measured in fractions of milliohms so the current could start out in the thousands of amps.
The huge surge of current can be problematic in a couple of ways.
1) The surge can damage components in the BMS and the inverter capacitors.
2) If the BMS sees the current as a short circuit, it will shut off discharge and may require a manual restart of the BMS.
To alleviate this problem a precharge
resister (Not a pre-charge capacitor) is put between the battery and the inverter till the capacitors charge up. The resistor will limit the current to something reasonably low. (I try to size the resistor to have a current in the 2 amp range in order to keep the spark barely detectable....but you could safely go to a higher current.) The capacitors will hold a charge for a few seconds, so you can then remove the resistor and directly hook the battery to the inverter. From then on, the capacitors will stay charged even if the inverter is off. It is not till the battery is disconnected from the inverter that the inverter capacitors will discharge.
So.... when do you need to use a pre-charge resistor? There are different opinions on this, but I default to the safe answer of 'always'. Others are less strict about it.
If you find the inrush current trips the over-current protection of the BMS..... then you really should use a pre-charge resistor. Some batteries (such as SOK) have a very aggressive short circuit detection algorithm and they will trip almost every time.... even at 12V.
* In general, the higher-wattage inverters are going to have larger capacitor banks so the surge will be greater and will be more problematic.
* In general, if you have batteries in parallel, the total circuit resistance will be less so the surge will be greater. However, with multiple batteries, the surge might be spread out over multiple batteries and therefore not trip the BMS.
Even if the BMS does not trip, there is always the concern about damaging something in the BMS or in the Inverter. I can't quantify how hard the surge is on the equipment. I have seen people argue the damage is minimal to none and others argue there is a reasonable likelihood that something will fail each and every time the surge happens. Others claim the damage is cumulative and it will make equipment fail over time. I don't know what the reality is..... and that is why I recommend always using a pre-charge resistor.
(The other reason I always use the pre-charge resistor is that the spark scares the shit out of me even when I am expecting it
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