ev-gavia avatar image
ev-gavia asked

Protocol for charging/equalizing parallel battery bank with Multiplus II

Hello everyone. We have a MultiPlus II with a bank of 4x48V Lithium Iron batteries in parallel (with internal BMS and no communication with the batteries). The batteries are currently at different voltages and we need to get them all up to the same voltage (say, 52.5V) so we can use them. The multiplus has been configured with the correct charge parameters for the batteries. Each battery has its own breaker.

What is the best way to get them charged up using the multiplus?

I was thinking we would switch on just battery #1 (with the breakers off for the other three batteries), let the MultiPlus charge it up, then simply turn OFF battery #1 and switch ON battery #2, let battery #2 charge up, etc and keep doing this for all 4 batteries.

Are there any problems with this? What would you do?

Multiplus-IIbattery chargingLithium Battery
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1 Answer
snoobler avatar image
snoobler answered ·

Get them within 0.1V of each other. Your proposed method should work, but any target voltage is fine.

Alternatively, you can load each battery until they are all at a common load voltage, connect and then charge all at once, e.g.,

  1. Load highest voltage battery.
  2. As it drops to the next lowest voltage, connect the second battery.
  3. As the pair drops to the voltage of the next battery, connect the 3rd battery.
  4. As the three drop to the voltage of the lowest battery, connect the last battery.

IMHO, if this is a new installation, I would prefer to charge each battery to full individually to confirm that they all reach the target charge voltage without issue.

For connections made when there is active current, it's important that the battery voltages are measured AT the terminals with a meter vs. what the inverter might report.

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