Sudden Voltage Drop when System Turned On - Related to Combination of Inverter and Charger?

DIY
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1

I have a 12V system in my camper van that includes one Battleborn 100Ah Li battery, a Victron BMV-712 monitor, and a Victron Orion-Tr DC-DC Smart Charger, non-isolated (to charge from the vehicle altenator). I also have a Simplex Power 600W inverter to provide some AC power outlets, in addition to a number of DC power and lighting cricuits. My issue is that when the van is NOT running, and I turn on the system (via a marine battery switch), the voltage as shown on the monitor drops so low that the monitor goes blank in the span of 1 to 2 seconds. There are no sparks, no hot smell, blown fuses, or any sign of a short. If I then start the van, within 15 to 45 sec the monitor relights and the voltage reading returns to over 13V in a few seconds. The monitor shows 100% battery capacity and the history shows a max draw down of 6A.

The inverter and the charger are connected to the same positive buss bar and each has a 60A inline fuse. If I take out either fuse, while leaving the other in and the van not running, the voltage drop does not happen when I close the battery switch. With the van running and both circuits closed (both fuses in place), the voltage drop also does not occur when I close the battery switch. I can then turn off the engine and the inverter will continue to oprate with no problem.

Any thoughts? Thank you

2

Well known issue with small lithium batteries. The internal BMS has a current limit, check your battery spec, probable quite low like 100A. If the current exceeds this value, even momentarily the BMS isolates the battery to stop the BMS burning out.

Heavy duty equipment such as inverters and chargers have a lot of capacitors in them. When you turn on the system these absorb many hundreds of amps for a few milliseconds and the BMS shuts down.

There are 3 ways around it, you have discovered 2.

  1. Use another power source to precharge the capacitors, run the engine first then close the master switch.
  2. Reduce the start up surge, only start 1 item at a time.
  3. Buy/make an inverter precharge device to connect around the master switch. Search here for precharge or google inverter precharge.

Another thing, on the BMV, there is a setting called “Battery reset”, if possible set this to keep SOC so it does not always jump to 100%.

If you battery has a Bluetooth app it should have said it was shut down due to over current.