question

Minas Papageorgiou avatar image
Minas Papageorgiou asked

Precharge with AC input?

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..

multiple inverters
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2 Answers
mondeoman avatar image
mondeoman answered ·

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.

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Kevin Windrem avatar image
Kevin Windrem answered ·

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.

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