Sonnen 2.1Kw battery DIY

[sollap]

Hi All,

I'm new to the forum, and solar power in general. I'm trying to pick things up, but if I say something below that doesn't quite make sense, please call it out. I may have more info to back it up, or I may just be wrong in my assumptions.

I recently acquired a pair of Sonnen/Sony/MuRata 2.1Kw LiFePO 48v battery units, and I'd like to make use of them without damaging them. They are designed to be part of a specific system, and are overseen by a battery management unit that I don't have. That said, they do appear to have an internal BMS which may allow me to use them without the external control and without purchasing new BMSes. Does anyone have experience with these batteries that they can share?

I took one of them apart and found two battery packs in each unit. The packs are 25.6v each and use US26650FT cells in a 8S14P layout. The cells are 3.2v, 3000 MaH according to MuRata, who I believe is their manufacturer. The ratings on the unit match the math for those cell values.

Behind the faceplate, there's the main terminal board with a shunt resistor and a small duplex wire which goes into the unit - I assume as current sense. There's a separate board with Renesas 16bit MCU (R5F21368MNFP) which handles the serial comms to other batteries and the battery management unit. I don't know if it's RS485, Modbus, or something proprietary. The MITSUMI IAM-A61 comm connector is an oddball and doesn't lead me anywhere.

That comm board connects to the main board via a 22 pin connector. The main board is populated with SONY branded chips that I can't find any details about. CXD5244R, CXD5243R, etc. The main board has a daughter board, and another small board with what appears to be an antenna. WiFi? Bluetooth? Seems odd to have an antenna buried so deep into the case.

The main board then plugs into each battery module board using a 30pin connector each. There aren't any components that I can see on the backs of these battery pack boards, but they are tightly mounted and soldered to strips of metal coming out of the packs. It's possible some small smd components are hidden back there.

There are enough contact points on each board for the 8 stings of batteries in each pack. There's a connector with 4 wire pairs which go around the pack into blobs of white silicone. I assume these are temp sensors. There are eight 22ohm resistors and some small smd components on the boards. The wires feeding the + and - to these boards are thin, maybe 18 gauge or so. The battery pack's main terminals are connected directly to the cells.

Back on the main board, there are 16 transistors arraigned in 2 rows of 8. I think these control passive balancing of the cell strings through the resistors. The big question is if this is done internally, or if the external unit calls the shots. Given all the microchips on here, I'm thinking it's capable of handling the cells by itself. What do you think?

How would I go about testing to find out if the internal BMS is working on it's own?

 

[sollap]

I decided to extend the BMS' cell contact points to outside the unit so I could reassemble it and monitor the cells as they charge.

Initially the unit showed 52.8v with one of the cell packs showing these voltages per string:
3.29
3.31
3.30
3.31
3.30
3.30
3.31
3.30

I used a variable power supply to set a constant charging voltage. Once the current got down to 130mv, it seemed to just hang at that rate. I'm not sure what that means, if anything. Testing shows the new cell voltages as:
3.32
3.33
3.33
3.33
3.33
3.33
3.33
3.32

The second battery pack inside the unit has identical voltages to the first.

It looks like the internal BMS is working. Next step is to get it a real charge - from the sun. I'll be monitoring along the way.

 

[cobratom]

How did this come out? Did you figure out how to communicate with the BMS? I know when the batteries are plugged in together and are turned on they communicate via RS485 and the little light turns green when all is good on the front of the battery face.

 

[sollap]

I got busy with some other projects and put these batteries aside for a little while. I did find the RS485 pins on the connectors and tried some Modbus probing, but I wasn't able to get it to respond to any inquiries. I also charged the battery to a higher voltage than I did previously did, but that started to show some battery strings maxing out at 3.34 while others went to 3.45. The balancer on the bms was not able to bring the lower voltage strings up, probably due to physical limitations on those strings (old cells). Once I get some time, I will get back to these. They do hold about 1.3kw of usable energy each so I want to get them fixed up and into my solar system.

 

[epiparts]

I bought 4 of those packs myself from this youtuber. I am not sure if I can mention it here or not but I will add the link to one of his videos talking about these particular sony battery packs. hope I dont get in trouble and let me know if anyone has done any work with them. thanks

 

[sollap]

When I started working on these batteries, I saw that he had sold them. He was out of stock though, which was too bad. I had heard these Sonnen batteries had a problem with the BMS and that's why so many of these packs ended up on the market. Presumably, the bad BMS could have allowed damage to some of the cells. At the very least it made further work on the internal BMS parts seem fruitless. Hopefully, that rumor is not entirely true. I can't recall where I saw it.

I've learned more about LFP since I started this and plan to take my test battery to a higher state of charge. It may be that it needs to be closer to 3.5v/cell for the internal BMS to do it's thing. I had been so concerned about over-charging or under-charging the unit that I may not have given it a fair chance.

Here are a couple of links with some info about the batteries. It may not be useful to you, but I thought I would pass it along.
2.1kWh Energy Storage
Cylindrical Lithium cells

 

[sollap]

In the image below, the front board is upside down from how it's normally mounted. The 8pin chip circled in red is the 485 transceiver chip. Pins 6 and 7, indicated in purple, are the A and B lines. I think - but I am not sure - those pins went to the second column of pins on the front connectors (indicated in red). Definitely, it used the top and bottom, I'm just not sure if it was the second or third column of pins. It's been a while since I looked at it. You could trace the pins from the chip to be sure.

 

[Grogdor]

Thanks for the writeup and pics, just cracked into one of these. Found this thread with "cxd5243r" as there's not much else out there for Sony/muRata IJ1101M.

The 100A fuse is blown, it's showing 3.29v on all strings. I'm contemplating this BMS retrofit for use as a "house batt" out in the bush, or maybe stick in the rack with the UPS but that seems like a waste. Will bring the internal resistance tester next week and attempt to suss out what kind of shape these strings/cells are in. Who knows with this BMS and what they've been through, and annoyingly there's no date codes anywhere on/in this box!

Sad to hear the onboard BMS isn't robust, but may discourage wasting time on poking at the RS485 :D Especially if a replacement BMS is <$100 but a bit wary of the JK stuff, seeing all the "issues" threads around. Any suggested alternatives?

 

[sollap]

That's a nice video, it's similar to what I did to mine. I used a JBD BMS. I think JK and JBD are the most popular low cost BMS' around. They both have issues, but given their cost they seem to be good enough. I'm happy with mine despite the quirky software, lack of active balancing, etc.