Multiple LiFePo4 banks in parallel

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cruisey1987 asked Apr 21, '20

Multiple LiFePo4 banks in parallel

Hi all,

I'm currently designing a home solar system that will use Winston LiFePo batteries to store excess energy.

To keep the initial costs down, I'm going to use 16x 300Ah cells in series to make a 48V 300Ah bank. I'll be using the GWL BMS123 to manage the batteries.

This bank will be connected to a Victron Quattro inverter and 18x Solar panels via 2x Victron MPPTs. I'll also have a Colour Control GX module setup in the ESS config

I'd like to design the system in such a way so that I can add additional battery banks of the same type later in parallel to the original one to give more storage. As far as I can tell, this is possible with the BMS123 system, I'll just need additional BMS kits per bank. However there's a line from the manual which has me confused

Multiple battery packs parallel
When you have to connect multiple packs parallel, you need 1 complete BMS per pack. You can connect the signal relays on each End Board in series. For instance: with 3 packs parallel, you can run the charging signal through from the first End Board Charge relay to the second Charge relay and through the third Charge relay. This signal can switch an enable/disable or power relay. The same goes for the Load relays in series.

If anyone has any experience with this kind of setup, can you please help me figure out what they mean by connecting the relay signals in series?

Also if there's any other advice for connecting banks in parallel, I'm all ears

Lithium Battery battery

2 |3000

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Answer 1 · 2020-04-21T15:35:00Z

nebulight answered · Apr 21, 2020 at 03:35 PM

This is more a question for BMS123 than it is for Victron. But to answer your question, the "Allow to charge" and "allow to discharge" signal wires that you hook up to your devices (in the case of allow to discharge the Quattro and allow to charge the MPPTs, but you'll need MPPTs with the on/off connection) will have to go in series from one BMS board to the next so that if one BMS detects an over/under voltage condition, it will shut off either the inverter or the charger since they are in series. It's like a daisy chain. However the allow to charge

If building a system from scratch it's more expensive to do it this way. Most systems will put the cells in parallel before putting them in series. ie Two 3.2v 300ah for a 600ah 3.2v cell group. Then you series connect the cell groups to make a full battery. However if your plan is to add them later, this isn't the best method because the capacities wont' match. If you are okay with a BMS per battery, then this is fine.

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cruisey1987 commented · Apr 22, 2020 at 09:56 AM

Ah okay, so I'd wire them like an OR gate, so if any of the battery banks send the stop charging signal the charge relay will open. And same for the Load relay. Does that sound right?

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