How to Add a Small LiFePO4 Pack to My Current Setup?

[nolan7]

Hi everyone,
I’m new here, and this is my first post. I hope this is the correct section to post this.

I’ve got a home solar setup with about 14kWp of panels, a Deye SUN-12K-SG04LP3-EU inverter, and a SEPLOS vertical battery (16 cells, ~300Ah, from AliExpress) with a V3 BMS (active balancing). The system’s been running great—no issues so far.

Recently, a friend gave me his old Winston LiFePO4 cells (60Ah each, about 3kWh total). They come with a basic standalone BMS, but I can swap it out if needed. I know this is a pretty small capacity compared to my main battery (only about 20% extra), but I’d still like to find a way to connect it to my system and make use of it.

Here’s what I’ve been thinking so far:

1. Parallel connection with the main cells
I could connect each Winston cell directly in parallel with each Seplos cell. That way, the BMS would think they’re 360Ah cells. (if I set the capacity to 360Ah in Seplos battery app) I think it would work, but it feels like a messy solution, and I’d prefer something cleaner.

2. Parallel connection as a separate pack
Another option is to connect the Winston pack as it is (3kWh) in parallel with the Seplos pack (15kWh). The problem here is that the Seplos BMS talks to the Deye inverter, and any current flowing through the Winston pack’s BMS wouldn’t register with the Seplos BMS. This might mess up current or capacity monitoring.

3. Upgrade the Winston BMS
I could swap the Winston pack’s BMS for a Seplos BMS 200A V3. That way, it could communicate with the main Seplos box. But I’m not sure if it would work since the two packs have very different capacities (300Ah vs. 60Ah). I know Seplos supports parallel battery setups, but I think they’re supposed to be the same size. Would this work anyway?

4. Separate setup with its own inverter
I don’t really want to go this route. I’m not looking to set up a small, separate system with its own panels and inverter. I’d prefer to keep everything tied to my Deye inverter.

5. Use the Deye generator/microinverter input
I thought about this, but I’m already using that port as a smart output for "non-essential" loads, so it’s not really an option.

Does anyone have ideas or suggestions for how to integrate the Winston pack into my setup? I’d appreciate any advice!

Thanks in advance!

 

[Brucey]

Paging @Daddy Tanuki for his Winston experience.

 

[Daddy Tanuki]

Hi everyone,
I’m new here, and this is my first post. I hope this is the correct section to post this.

I’ve got a home solar setup with about 14kWp of panels, a Deye SUN-12K-SG04LP3-EU inverter, and a SEPLOS vertical battery (16 cells, ~300Ah, from AliExpress) with a V3 BMS (active balancing). The system’s been running great—no issues so far.

Recently, a friend gave me his old Winston LiFePO4 cells (60Ah each, about 3kWh total). They come with a basic standalone BMS, but I can swap it out if needed. I know this is a pretty small capacity compared to my main battery (only about 20% extra), but I’d still like to find a way to connect it to my system and make use of it.

Here’s what I’ve been thinking so far:

1. Parallel connection with the main cells
I could connect each Winston cell directly in parallel with each Seplos cell. That way, the BMS would think they’re 360Ah cells. (if I set the capacity to 360Ah in Seplos battery app) I think it would work, but it feels like a messy solution, and I’d prefer something cleaner.

2. Parallel connection as a separate pack
Another option is to connect the Winston pack as it is (3kWh) in parallel with the Seplos pack (15kWh). The problem here is that the Seplos BMS talks to the Deye inverter, and any current flowing through the Winston pack’s BMS wouldn’t register with the Seplos BMS. This might mess up current or capacity monitoring.

3. Upgrade the Winston BMS
I could swap the Winston pack’s BMS for a Seplos BMS 200A V3. That way, it could communicate with the main Seplos box. But I’m not sure if it would work since the two packs have very different capacities (300Ah vs. 60Ah). I know Seplos supports parallel battery setups, but I think they’re supposed to be the same size. Would this work anyway?

4. Separate setup with its own inverter
I don’t really want to go this route. I’m not looking to set up a small, separate system with its own panels and inverter. I’d prefer to keep everything tied to my Deye inverter.

5. Use the Deye generator/microinverter input
I thought about this, but I’m already using that port as a smart output for "non-essential" loads, so it’s not really an option.

Does anyone have ideas or suggestions for how to integrate the Winston pack into my setup? I’d appreciate any advice!

Thanks in advance!

I would go with number three. its guaranteed. I do not use comms but instead work with individual BMS's for each pack and set the SCC and the inverter to avoid issues.

but if i was doing comms, i would do it for all packs.

you could run a dumb BMS and jsut hook the pack up it would charge and discharge as available and needed. honestly I don't think this would cause any real issues other than your SOC reading's. but if tats important then most definitely get a matching seplos BMS. worst case they dies in 10 to 15 years and you replace them and still us the BMS in your system with their replacements.

 

[Brucey]

Another option, run open loop without comms with the batteries in parallel using existing Winston bms?

 

[nolan7]

If the option no. 3 is expected to work, I am OK with that. I thought that only same capacity batteries can be operated in parallel configuration with these BMS. Now I have found Andy's video showing that different capacities do work together. Thank you for helping me. I am going this way.