Ziporah, Belgium 48V 3KVA powerwall

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ziporah

Member
Joined
Apr 26, 2021
Messages
47
Hello from Belgium, so I started my journey on this forum quite some time ago and have been reading a lot of threads carefully.
I have a grid connected system installed with 11 kVA solar panels, spread over 2 inverters.
One power-one 5K-OUTD and one goodwe 5K-ET, which has a BYD 14.4 KVA battery system connected to it. Unfortunately the 14.4 KVA doesn't cover the electricity needs when we have several cloudy days in a row. And since we have quite some in Belgium, I decided to start collecting cells and try to offload a part of the system to a secondary solution. On sunny days, I am backfeeding to the grid, so in my initial setup will just be using an apc ups of 3KVA with 48V battery pack. One of my main loads are my raspberry pi systems and synology NAS which are always on. I used to have an always on server, but I managed to transfer everything to a cluster of several raspberry pi's, which already greatly reduced the power requirement.
I started collecting cells when corona started, so I've been testing, disassembling packs, trying to get more cells, we all know the story. I noticed the offer from the fogstar guys, and couldn't resist, so I also bought 600 cells at a very good price.
I've collected lots of powertool cells, some old e-bike and step cells, below is my current status of collected cells:

1633380557085.png

The idea is to build 14S40p packs with these cells. Wolf already suggested not to mix the US18650V3's with the rest, so I'll be using them to replace my Lead Acid batteries in another (smaller) apc ups, but the rest of them are selected to be used in any or all of my upcoming systems. They all pass the full test cycle of charging, resting, low drain, +80% capacity, most of them even are +90% cap.
I'm planning to build 14s40p packs with DALI or jkbms and use cell level glass fuses on each cell.
Negative poles will be soldered or spotwelded, just don't know yet how to handle it.
This is my 7 day past usage of the circuit I'll be using to provide the power from the cells:
1633380859428.png

as you can see, I'm well below 1KVA, and living in Belgium => 240V meaning I would be pulling around 20A from the pack.
At 40 cells per pack, that would bring me down to 0.5A per cell. I'll probably start with the DLG cells, since they are brand new and can take 6A per cell. This should be very mild for them and then I'll be adding a second string as I finish the next packs. Now here's the point were I need more input.
I'll have to figure out the size of the bus bars (need to do some forum digging for that probably). I have 6mm2 copper wire and 4mm2 copper wire that can be used.
Second I have to find out which cells can be combined together and which I should leave aside.
I know I shouldn't mix ICR and INR in the same packs, so I won't even go that road, but I do need 560 cells to create a second and even third pack if I want to store my excessive solar. Last month I backfeeded 130kwh and had to pull 64kwh back from the grid. backfeed produces me 0.04 cents, but pulling it back in at any other time costs 0.26 cents, so you could understand why I want to store more for cloudy days.
That's all for now, I'll be adding more information as I'll be making my next steps in the project and try to figure out how to connect and tune the apc ups to behave the way I want it to behave. I was initially planning to get one of those chinese inverters, but I managed to get this ups much cheaper then the inverter and it basically does what I require it to do (for now)
I can't connect an inverter to my power-one solar panels directly as I'm still receiving 300€ certificates for every 1000kwh I produce. Same for the 5k-ET, can't alter the setup or I loose the certificates (50 € /1000kwh) and this one is a HV system.
 

ziporah

Member
Joined
Apr 26, 2021
Messages
47
After reading some more on the bus bars, I'll be sizing them with 2X6mm2 or 3X4mm2, which should result in a total 24mm2 at the junction point.
This should be enough for 120-130Amps on a 48V pack.
I'll be going for 14s40p packs, with twisted busbar and glass fuses on positive terminal.
I should be getting 11,744wh * 14 * 40 = 6576,64 wh or 6.5kwh in my first pack.
The other packs will have smaller kwh, since the first pack will have the best cells.
With my current ups, the max power is 3000VA, thus 62,5A over 48V. 40 cells in the initial pack => 1,56A per cell.
My fuses are limited to 3A, so these should be fine.
As soon as I add my second pack, the current should lower to 781,25mA per cell.
Adding a third, will go down to 520,83mA per cell, which is the max target current I want to have for each cell.
The lower the better, but I won't be pulling 3000VA for anytime soon. For now I'll be capping the load to 1000VA to be sure I don't abuse the packs.
 

ziporah

Member
Joined
Apr 26, 2021
Messages
47
I spent some weekends working on my battery packs. First I stripped several meters of 5x6mm2 cable. Cut them to 60 cm, then paired them between my electric drill and the vice, twisted them untill they were 55cm.
ED4318B1-4A5B-42FD-85BC-5BB15F8E077A.jpeg

I created a simple mold and used that to create 14 pairs of busbars.
6099E2F2-9E46-4C82-8D54-87DAB7CED3AD.jpeg

then I got my small press and provided all of them with a connector.
F3C42C5C-D239-4E71-BA2E-91C6FA29067C.jpeg

I first cut them all to the same length. I made sure they were all at the same length, note the marks on the cardboard, then pushed them in the connector, crimp the connector and then I put them in this shape:
====\
\==<connector>

This should hopefully make it easier to put enough space between the packs and connect them without shortcircuits or sparcs (hopefully)
 

ziporah

Member
Joined
Apr 26, 2021
Messages
47
After testing some of the fogstar batteries, I believe they will serve me fine. They have a rated cap of 3000, this is the result from full charge down to 3V.
CF838C36-2797-4294-9868-78B4DFE25909.jpeg
I didn't test them down to 2.5V, but I'm pretty sure they will reach the 3000mah rating if I discharge them down to 2.5V. I'm planning on charging to 4V, discharge to 3V, so the useable capacity will probably vary between 2600-2800 mah per cell. I started building the first pack. 40 cells in holders, fuses of 5A on positive side, 0.3 mm copper wire on negative side, with solder connected to the busbars. I initially tried spotwelding the fuses to the positive side with a kweld, but that didn't work out, and since I was planning on soldering the negative side as well, I just started soldering on both sides.
I first put some solder on both side of the cells while they were in the holders. Then I put on the busbars with tie wraps.
76E116BF-32BF-45D8-80A5-CF7BED48422D.jpeg
I connected the negative side first, then turned it around and add the fuses on the positive side.
66333458-1A78-46D8-93FB-EC094B9E5510.jpeg
83909779-F16F-42B9-962D-5DC51795C31D.jpeg
after a few hours work, this is now my first pack. I measured the IR 1.44 mohm, 3.62V

F7C8B29B-3EF9-40EE-81D9-EC8B76FC7444.jpg

Lessons learned:
try with kapton tape below the busbars, when soldering the fuses to the bars, the seem to melt into the battery holders.
cut the fuses shorter before soldering them, this makes it easier to put the other side to the busbar.
put the fuses in the twist of the busbar, each row in the opposite direction.
 

ziporah

Member
Joined
Apr 26, 2021
Messages
47
And so I created my second pack today...
with kapton tape on both sides.
negative side kapton perhaps isn't required, the soldering goes really fast on that side and the busbar isn't that hot after soldering all of the wires. I might take the soldering outside, to lower overall pack temperature, so the bars and batteries will cool down much faster then now in my (in house) garage, where it is 18-20 degrees on this sunny day.

82A79449-A8B6-4307-91CA-ACC733D50A32.jpeg E1DF96D3-E6C5-48EE-85B2-904DEA32F9F4.jpeg
66333458-1A78-46D8-93FB-EC094B9E5510.jpeg 5E7D50DD-7E45-4320-B846-BC4198037233.jpg
overall I'm pleased with the result, 12 packs to go ...

Note to self: buy thermal camera to scan the pack after it is finished, making sure nothing is wrong with one of the cells.
If anybody has any good suggestions for affordable types...
 

ziporah

Member
Joined
Apr 26, 2021
Messages
47
Today I fired up my soldering iron again for some personal time.
F594E43D-23B3-412B-BC3B-BD7BEDD58236.jpeg
a few hours later, these two beauties are ready. I’m getting the hang of it. I’m way more handy with my soldering iron then with the spotwelder, so I’ll stick to soldering the packs instead of trying to weld them. 10 more to go…
 

jdeadman

Member
Joined
Mar 28, 2017
Messages
959
Looks nice. What I like to do is use the Twisted copper in a rectangle and then Solder on a length of High strand Count flexable 8AWG copper for making the packs connections to each other. this allowed me to have a little bit of fudge room to make the connecting easier.
 

ziporah

Member
Joined
Apr 26, 2021
Messages
47
@jdeadman You can set the twisted wire straight and then connect the packs with a flexible wire with crimped connector on both sides. I believe this will work better then trying to solder flexible wire to the twisted copper.
 

jdeadman

Member
Joined
Mar 28, 2017
Messages
959
@jdeadman You can set the twisted wire straight and then connect the packs with a flexible wire with crimped connector on both sides. I believe this will work better then trying to solder flexible wire to the twisted copper.
I actually find it quite easy but I have a 100W iron and use triple wound 14 awg wire. Also using 63/37 solder I find makes it easier as well
 

ziporah

Member
Joined
Apr 26, 2021
Messages
47
I have a 150W iron, works like a charm. Didn’t have any regrets ordering it here in Belgium.
 
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