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Finished my solar powerwall build with 812 cells
Hi there

I would like to give a big thank you! I read and learned a lot here to finally figure out the ideal recipe for building my powerwall from used laptop and ebike packs. It is now fully operational and waiting for solar energy to come. Since I live in southern Germany and right now everything is covered in snow, the powerwall is getting a slow startup phase. It took about a year to harvest and build.

The components are:
  • MPP Solar PIP 3024 hybrid inverter, imported from Taiwan, basically contains a solar charger, battery charger and power inverter
  • 532 Li Ion 18650 cells
  • 3 Generic 60A 7s BMS with Bluetooth from Aliexpress
  • 3 200W mono solar panels

The first pack consists of a large 112 cell ebike battery which was donated for the project. Repacking all cells would have been a lot of work because the cells are glued together with some epoxy. Since the 8p14s pack was in good shape I split it in half and reconfigured it to 16p7s.

The second pack is made of cells from two less good ebike packs, repacked into 20p7s, the third consists of used laptop cells repacked into 40p7s.

Every pack is equipped with a BMS. It will cut off the pack when individual cells voltages are out of bounds or the current exceeds 60A.

The build process was
  • gather ebike packs from a bike shop in the neighbourhood
  • gather laptop packs from work and later from ebay because other sources were dry
  • dismantle, remove welder spots and glue
  • first charge with china TP board
  • settlement phase, sort out cells that discharged to much
  • capacity test on Opus, write capacity on cell
  • enter cell capacities in excel spreadsheet, use rePackr to group blocks
  • spot-weld with the excellent device from
A Raspberry Pi with Bluetooth speaks to the Inverter and the BMS, so I get a good systems status.

Balancing is looking fine, thanks again for this great rePackr tool! The BMS do have a litte balancing circuit too.

A master switch in my main panel allows bypassing the PIP Inverter if needed.

Right now there is little solar energy, it takes about three to five days to charge the pack. At 28 volts the PIP switches over to Battery mode and powers half of our apartment until the pack is down to 25 volts (keeping some energy for standby losses). The PIP switches to Line bypass mode until the pack is charged again. I expect it to stay in battery mode during the summer.

There is still room for one 40p7s, so I will continue harvesting cells but not actively buy more on Ebay.

507PowerWall, OffGridInTheCity, Walde And 9 others like this post
Weiter so !!

Fulstein likes this post
Oh my... Lithium addiction was still too strong and that last empy shelf needed to be filled, so I added one more 40p7s battery made from laptop packs sourced on Ebay. But now it needs to end! Big Grin

System is running nicely, the PIP switches to mains after a couple of rainy days but is generally on battery. I guess I should add more load, right now there is some solar energy being wasted especially when nobody is at home for a couple of sunny days. The fridge would be an ideal candidate but the wiring is a pain... unfortunately I did not yet think of island solar power when designing the appartment's wiring a decade ago.

P.S. Another solar panel was also added to the guerilla setup, a whopping 380 Wp beast measuring 2m * 1m. The advance in solar technology is truly amazing.

Fulstein and RikH like this post
Moin Stefan,

Just curious since I cannot see clearly on the pictures, how did you connect the -ve wire to the bms's and how the +ve to the busbar on the packs?

Keep going!

Fulstein likes this post
Hi Rik! The BMS is wired only into the negative terminal of the pack. I soldered short M6 bolts to the hi power connections of the BMS and to the terminating bus bars. The positive side of the BMS is connected via the thin sensor cables which are directly soldered to the bus bars. I used tiny glass fuses on the sensor cables in my the newest pack to protect against shorts in the BMS.

General update: the fridge is fully solar now, and the coffeemaker and toaster. Thinking of connecting the dish washer too Smile
Fulstein likes this post
Top job! Can you post a link to the BMS and give us some update on how it is going. It looks like a solution for small PW's .

(06-18-2019, 06:27 AM)TroyD Wrote: Top job!  Can you post a link to the BMS and give us some update on how it is going.  It looks like a solution for small PW's .


Hi Troy!

The BMS is from Aliexpress and can be found as Bluetooth Smart BMS in many different versions of voltage and power. The manufacturers web page is here:

You can read more about it in this forum thread:

I meanwhile run 4 of them and everything is fine and stable.

WOW! Nice setup! Quick question....How did you interfaced the SmartBMS with the Pi? I know you used BT, but I'm assuming that you used Android as the OS for the Pi, since I haven't found any code for the BT protocol for Python.
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Hi DomingoRP, I wrote a small python TCP socket server which communicates with the BMS over the Raspberry's built-in bluetooth module. It is basically in a proof of concept state but working fine. The logging and charting happens in my smart home Raspberry running a german open source thing named FHEM.

Edit: I just published the source here
ajw22 likes this post
Congratulations on a sophisticated, fully working system!! Its just exciting to get it all working Smile

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