Is it possible to precharge the MultiPlus capacitors by connecting the AC IN to the grid and putting the switch to charge for a couple of seconds, then disconnect AC and turn on the DC switch to the batteries?
Using a resistor is messy..
asked
Precharge with AC input?
It works, but you need to keep the AC IN powered on and you need to wait about one minute, depending on inverter type and setup. Some models take longer to "charge" their output.
To understand how it works, turn off the inverter, disconnect the battery, put a voltmeter on the DC bolts of the inverter, turn on AC IN and wait a minute or two.
If you disconnect the AC, the capacitors will discharge quickly and there won't be any pre-charge left in them.
NOTE: There will be some "Low battery" warnings triggered by the inverter when starting without battery.
A manual precharge can be constructed from a resistor and pushbutton switch so it doesn’t need to be messy. I’ve also seen people use a 3 position battery switch for precharge. Position 1 has the resistor connected to position 2 where the multi is also connected. Starting in OFF, turn the switch to position 1 for a few seconds, then switch to position 2.
Of course you can still skip the precharge step by moving the switch to position 2 first.
There are also some automatic precharge circuits. REC Battery Management Systems sells one. The Victron Lynx BMS includes one but it’s an expensive solution unless you need the BMS also.
For a Multiplus II 3000/48v I plan to use a pushbutton with a 33 ohm/100 Watt resistor:
Max DC Voltage: 3,65V x 16S = 58,4V
Max power dissipation: 58,4 ^2 / 33 = 103 W
Max precharge current: 58,4 / 33 = 1,77 A
I cannot find any info on the capacitance of the Multiplus II, so how long would it take to precharge with this setup?
I put an LED (don't forget a series resistor to limit LED current!) across the resistor and hold the switch until the LED goes out. On my 12 volt Multi Compact and a 30 ohm resistor it takes less than 10 seconds (don't recall the actual time).
