Inverter capacitor precharge procedure

[tucsonjwt]

I have a MPP 24 volt 3000 watt all in one inverter and am about to connect my 4 Battle Born batteries connected in two strings of 2 -12 volt batteries in series.

Being an ignorant noob, I need to know the correct procedure for precharging the inverter capacitors. I have a 30 ohm resistor which I plan to connect to a negative terminal of my battery buss bar and touch the other end to the negative lead coming out of the inverter (currently disconnected from the negative battery buss bar.)

Do I have the procedure correct and do I have the inverter turned on or off when I touch the negative lead from the the inverter to the negative buss bar of the battery bank?

I would think the inverter would have to be turned on first, but I thought I should confirm that here first.

Thanks.

 

[BentleyJ]

The problem with the described procedure is having the negative lead disconnected from the bus bar. How much time will it take to connect the negative lead and tighten it down? The caps will start to discharge unless you can keep the resistor in contact while connecting the cable.
A better method would be have everything connected to the + & - bus bars with the DC disconnect or breaker in the OFF position. Then use the resistor to jump across the terminals on the disconnect or breaker for a few seconds then turn on the disconnect or breaker while the resistor is in place. Then remove the resistor and turn on the Inverter.

 

[Texas-Mark]

I would think the inverter would have to be turned on first, but I thought I should confirm that here first.

Leave it turned off otherwise it will try to draw power through the resistor. And as noted above will drain the caps before you connect the negative.

 

[Bud Martin]

Leave the inverter power on/off switch to off position then perform the pre-charge.

 

[tucsonjwt]

So, connect both positive and negative leads from the positive and negative battery buss bars to the inverter with the inverter turned off. Then using the leads of the resistor contact both sides of the circuit breaker/disconnect in the positive cable going from the battery bank to the inverter? Then turn on the inverter?

I thought I saw Will just touch the resistor leads to the inverter negative battery cable and inverter terminal, which is what started me down this line of thinking, but I think the positive cable jumper sounds more controlled.

Thanks

 

[BentleyJ]

So, connect both positive and negative leads from the positive and negative battery buss bars to the inverter with the inverter turned off. Then using the leads of the resistor contact both sides of the circuit breaker/disconnect in the positive cable going from the battery bank to the inverter?

Yes, hold the resistor in place for a few seconds then turn ON (close) the breaker or disconnect, remove the resistor and now the caps are fully charged and the batteries are supplying voltage to the input terminals of the inverter.

Then turn on the inverter?

 

[Quattrohead]

too late

 

[JoeHam]

too late

For what?

 

[MiSh]

FWIW...I understand it's expensive ($280), but BattleBorn sells a surge limiter/resister made speciffically for their batteries for the situation you describe. I have a bit larger inverter and battery bank that I incorporated the limiter into and it works great:

"The CSL500 Current Surge Limiter is a FET-based current limiting device that is to be used with Battle Born Batteries LiFePO4 battery packs when they are used in conjunction with large (greater than 3.5kW) inverter/chargers.
The device is mounted permanently in series between the negative pole of the battery bank and the negative DC input terminal of the inverter/charger. The device protects the battery management system (BMS) from damage caused by the initial current spike that is created when connecting directly to the large capacitors (> 5 milliFarads) that are typically on the DC input side of the inverter/chargers. The device allows the batteries to slowly charge the capacitors (within 1 ms). This soft start avoids the high-current shutoff inherent to the BMS of the batteries."