Budget 48v LiFePO4 semi-build journey

8to6tech

New member
Joined
Jul 26, 2022
Messages
2
I’ve come across and acquired 4 German made Sonnen 102v 32s8p battery packs and I will be converting them into 2 16s8p 27ah packs contained in one unit. The batteries were picked up from Battery Clearing House in Raleigh NC, link: Sonnen 102v 27.2ah they also have a local pickup option as well as many other packs to choose from. Initial impressions of the pack was that it was clean (didn’t have much of dust or otherwise debris covering the pack), the positive and negative terminals were clean and showed no signs of arcing. It seems like the typical Anderson 30amp connectors fit the stock receptacle decently in the separated double vertical orientation. The case had only minor scruffs and the original warning labels were still present with a pack voltage between 104.3v and 107.8v Looking into the slats on the outside case some cells are visible and appear to be 26650 3.4ah cells with no discoloration or heat markings. So all signs are looking like I got a great beginning point to build from.
The case lids are held together with 24 torx T20 screws (12 on each side). Once opened I was awestruck by the sheer amount and size of the series connections as I’m use to small 24v 18650 based systems. I fully recommend only opening one side at any one time as there’s a significant amount of exposed metal. There is one main pcb board on the front of the pack that has communications ports, what I assume is balance circuitry, and a bunch of other stuff. A second small board is affixed to the main positive and negative bars of the battery and contains what looks to be a 50a fuse and well as a few small circuit components.

The plan:
On the back of the pack in the middle there’s a solid copper bar along with the midway series connection point of the pack. The plan is to split and separate the pack at this point and have two separate 51v packs. I currently have 2 30amp bms units and separate active balancers in transit to complete this build. My main power wires and bms voltage sense leads (separately sheathed) I’m planning to run in the middle of the pack I highlighted red in the pictures which is hollow and clear behind the board. I’m planning to have each bms mounted on the front of the pack.

Initial testing:
I’ve mainly tested the pack unmodified using my 180w small battery tester by makerhawk and a diy forced air cooled load bank that is 10 ohms, roughly 1kw at this packs voltage. Each of my 4 pack reached near/full capacity with the makerhawk before reaching 86v. Looking at the circuitry I do not see the typical mosfets I would expect to see for a bms which is why I stopped at 86v. Testing the series voltages with my multimeter showed they were decently balanced.

I plan to upload a video to YouTube of the full build once I’m further into the build and receive the rest of the parts that are on order. I am also seeing as to how I could parallel the two packs into one 51v ~54ah pack. I am open to all suggestions and critique.
 

Attachments

  • 4C045564-A58C-47CB-AFA7-6E5EEF23733C.jpeg
    4C045564-A58C-47CB-AFA7-6E5EEF23733C.jpeg
    946.3 KB · Views: 62
  • 47CEBB5C-93A3-437D-8B7A-8D87A5B6DE48.jpeg
    47CEBB5C-93A3-437D-8B7A-8D87A5B6DE48.jpeg
    1.3 MB · Views: 63
  • 6ECEF330-5F30-4E4D-9170-BB684C805469.jpeg
    6ECEF330-5F30-4E4D-9170-BB684C805469.jpeg
    1.4 MB · Views: 59
  • F52C73C4-C885-41C5-A980-F9AB675AD131.jpeg
    F52C73C4-C885-41C5-A980-F9AB675AD131.jpeg
    2.3 MB · Views: 53
  • F3C09F34-9990-4E93-9151-95C98A41579A.jpeg
    F3C09F34-9990-4E93-9151-95C98A41579A.jpeg
    2.8 MB · Views: 51
  • 2410BE7F-EDC1-46FA-871B-07E07FF1C64F.jpeg
    2410BE7F-EDC1-46FA-871B-07E07FF1C64F.jpeg
    3.8 MB · Views: 53
  • 97F49552-0B03-4AD6-BE45-BCF938D9F451.jpeg
    97F49552-0B03-4AD6-BE45-BCF938D9F451.jpeg
    1.7 MB · Views: 52
  • F483893F-B251-4E3B-A64F-6893F5DF3B2D.jpeg
    F483893F-B251-4E3B-A64F-6893F5DF3B2D.jpeg
    3.6 MB · Views: 47
  • E951E94D-5028-49FD-BC2F-0CFECB8AD0CA.jpeg
    E951E94D-5028-49FD-BC2F-0CFECB8AD0CA.jpeg
    880.3 KB · Views: 69
Great report! That looks like a really good module / starting point for your project.

Curious -- are the cases standard rack width? I'm currently working on an 18650-based pack to augment my Leaf-based pack. One of my personal dislikes of DIY solutions like mine is the end-product packaging. I'm just used to everything slotting neatly into a server rack!

Cheers, John
 
Re: @DG98 They most certainly will. overall width is 17.375” by 22.25” deep by 3.375” tall. I’ve picked up a 20u rack with a handful of 2u rails from a local data storage company I use to work for. The only caveat I see going this route is the battery packs don’t have mounting flanges for ears to secure the packs in the rack. I havent quite figured the solution for that yet.
 
Last edited:
Back
Top