26650 build

[rearden]

I am starting my build. I started collecting 18650 but since have come across several hundred 26650 LiFePo in good condition so I am moving to those.

I purchased 4x4 battery holders on ebay.
started with 99 Sb .3 Ag .7 Cu solder and am now trying 97 Sb and 3 Ag
I am using 6.3A slow blow glass fuses soldered to the positive side and 26AWG on the negative side.
I have 12 AWG with up to 16 batteries connected to each strand. The wires will then be connected together at a 1/0 AWG lug.
The pos and neg lugs will be separated vertically with enough length to connect to the appropriate lug on the next battery, come off the front and be expandable toward the rear of the battery by adding another 12g run toward the lug (similar to glubux)
I have not decided upon the inverter, solar charge controller or BMS yet. The goal is to store excess solar energy and use it at night, on demand or grid down. I need advice on those. This design would call for one large BMS.
As each battery will be approx 3V, I will have a 8s or 16-18s and will go as deep as my shelf space can handle as I collect batteries. I think I have enough batteries for 32p at 16s initially.
I am finding that construction is taking longer and costing more than I expected.

Please give constructive criticism: Safety, design, technique, materials, etc. It is early in the construction phase and I can make changes.

rearden

 

[Redpacket]

Looks generally OK, layout looks a bit variable, you might want thicker busbar cable, eg 3 strands twisted together.
Using cable ties or temp insulated wire down the holes between cells might help keep things in place as you build.

My system is LiFePo4

 

[rearden]

Looks generally OK, layout looks a bit variable, you might want thicker busbar cable, eg 3 strands twisted together.
Using cable ties or temp insulated wire down the holes between cells might help keep things in place as you build.

My system is LiFePo4

Thank you for the feedback.
The longer zipties came in last night to connect the blocks together.
The bussbar will grow as the pack grows. Each column of 8x2=16 batteries will get a bare 12 AWG run to the lug.
One of my issues is that I want the ability to expand.

Are your LiFePo4s 26650s?

rearden

 

[Redpacket]

My LiFePo4's are actually pouch & prismatic blocks!

I was meaning using zip ties (thinking about it they might melt!) or anther method etc to hold the copper wires in place while soldering & for better handling strength when complete.

Most people seem to expand by adding more blocks of cells in parallel or build whole new parallel strings.

 

[thunderheart]

I am starting my build. I started collecting 18650 but since have come across several hundred 26650 LiFePo in good condition so I am moving to those.

Good idea!

I purchased 4x4 battery holders on ebay.

How much did they cost?

I am using 6.3A slow blow glass fuses soldered to the positive side and 26AWG on the negative side.

26AWG on the negative as a fuse? Why if you've already fused the positive sides?

And, as Redpacket said, busbar seems kinda thin... What max current you gonna run at?

 

[jonyjoe505]

I have not decided upon the inverter, solar charge controller or BMS yet. The goal is to store excess solar energy and use it at night, on demand or grid down. I need advice on those. This design would call for one large BMS.

For bms I recommend one of the chargery models. I have the chargery bms8t (they have a bms16t and 24t) they are all the same except in how large a series your system is.
This bms uses contactors to shutoff power when the battery is full. Regular bms uses mosfets (which leak voltage) causing voltage surges when they shutoff charging.
I been using mine on my 220ah 4s40p 32650lifepo4 battery and is working excellent, once setup you don't have to mess with it again. With a regular bms I was always having to adjust the bulk setting on the solar controller.
This bms is fully programmable, has temp sensors,loud audio alarm,1.2 amp balancing, LCD screen.

 

[rearden]

I am starting my build. I started collecting 18650 but since have come across several hundred 26650 LiFePo in good condition so I am moving to those.

Good idea!

I purchased 4x4 battery holders on ebay.

How much did they cost?

I am using 6.3A slow blow glass fuses soldered to the positive side and 26AWG on the negative side.

26AWG on the negative as a fuse? Why if you've already fused the positive sides?

And, as Redpacket said, busbar seems kinda thin... What max current you gonna run at?

16x of 4x4 cost ~$30 so twenty something cents per cell for a holder.

12g wire and 16 cell per home run. I checked my math, you are correct, that is light and I need to increase it to 10g, double it or only do a string of 8 per 12g run.
By my calculations, 640 cells in 16s40p (48v) config at 3000VA would need 1.56 amps per cell and therefore 25 amps per string of 16. That is pushing 12g wire. 5000VA in 16s64p would need 1.63a per cell and 26a per string.

as for the 26awg on neg, it can act as a fuse, it is also easy to work with. Should I not use the glass fuses and just use wire as fusing? and then use larger wire for the neg?

---

I have not decided upon the inverter, solar charge controller or BMS yet. The goal is to store excess solar energy and use it at night, on demand or grid down. I need advice on those. This design would call for one large BMS.

For bms I recommend one of the chargery models. I have the chargery bms8t (they have a bms16t and 24t) they are all the same except in how large a series your system is.
This bms uses contactors to shutoff power when the battery is full. Regular bms uses mosfets (which leak voltage) causing voltage surges when they shutoff charging.
I been using mine on my 220ah 4s40p 32650lifepo4 battery and is working excellent, once setup you don't have to mess with it again. With a regular bms I was always having to adjust the bulk setting on the solar controller.
This bms is fully programmable, has temp sensors,loud audio alarm,1.2 amp balancing, LCD screen.

Thank you for this suggestion. I will read up on this one. Any comparison with the Battrium? Which I guess is the gold (and expensive) standard?

 

[rearden]

Pulled apart a bunch more battery packs, I am up around 1000 cells. 26650 3.2v LiFePo4. Some are old, but I am having a hard time finding a tester for 3.2v.

 

[Redpacket]

Apparently an Opus3100 v2.2 can have 3.2V LiFePo4 voltage selected with a switch inside:
https://secondlifestorage.com/showthread.php?tid=1997
You might need clip leads to a larger cell holder

 

[floydR]

many use an opus which has a switch to limit the upper voltage to 3.7 a little highbut from what I have read not too much of a problem with LIFEPO4. you can cut a small hole on the back right left side of the opus to access the switch.
the Opus BT-C3100 and 3400 have the switch.
The cells are much cooler in the 26650 holders need to make new ones for all the cells.



Note the hole is larger than need wanted to be sure I had acess to the switch.



later floyd

 

[rearden]

Thank you for that information.
So if you change the switch, then the voltage charging and discharging profile will be dampened so that it will not exceed 3.7v? and 3.7v is acceptable for 3.2v lifepo cells?
Will the capacity testing cycle also stay within specs which will not harm the cells?
A switch like this has not been found on the Lii-500?

Thanks!
rearden

 

[rearden]

I have built a 16s64p LiFePo4 from 26650 cells.
I purchased 4x4 battery holders from ebay.
2x 18650 battery fuses from batteryhookup.com
.1 and .15 nickel strips
A Kerpu spot welder (a bit weak) and 97/3 rosin core solder to solder the nickel strip to the buss bar.
2AWG and 1/0 as buss bars.
Overkill 100A BMS
Connected to a Solark 12k via 3/0

 

[rearden]

I created 3d printed holders. Lots of learning about 3dprinting, but I hope that I can recover the cost of the printer by what I save in no buying holders. My new holder design locks together, which should make a stronger build.

My next version will probably be a 16s80p.
I need to improve the spot welding reliability. I am using a kerpu welder and it seems weak. I don't want to drop hundreds for a spot welder, but I may have to. I still end up with having to solder 1-2 lbs of solder to get it all together.
Making buss bars out of welding cable is a bit of a pain, but it works.
Anyone have any recommendations for a good, affordable BMS which is >100A? I am using and Overkill 100A for my previous.
The 2x 16650 cell fuses is a bit odd, but no one makes 26650 cell fuses and I was not reliably successful with fuse wire or glass fuses.

Suggestions are welcome.

 

[orangezero]

I created 3d printed holders. Lots of learning about 3dprinting, but I hope that I can recover the cost of the printer by what I save in no buying holders. My new holder design locks together, which should make a stronger build.

Do you have any suggestions for design updates for what you printed? I was going to print "something" to hold my 32650 lifepo4 cells together. I like the yellow.

I have 0.15mm x 10mm wide nickel strip to spot weld to each cell. These will then probably be soldered to some 10 or 12 awg twisted copper wire. I wasn't sure if I wanted to allow for a groove in the print for the twisted wire? Or if I would do something similar for the nickel strip.

 

[rearden]

My biggest problem is warping on the print. It is a major headache. I should be able to get 4 on my print bed, but when I go above 3 it starts curling and breaking things. So far I have only limited success in overcoming it. I used TinkerCAD because I didn't want a steep learning curve. I started out with just printing a ring that I could slip snuggly over a battery. This I replicated it 16 times for my 4x4. I put a 2mm "washer" under the rings to act as a battery stop. I then created a square (box with a box hole) with rounded corners and placed a small square under each corner to help with rigidity and bed adhesion. A challenge was getting the outside frame to work with the connecting "teeth" and corresponding receptacles. Once I got those dimensions correct, I placed box over the 4x4 ring matrix and added half washers along the rim for battery stops. The rings are taller than the outside box. One holder uses 27g of filament and takes a bit over 4 hours. This was my first foray into 3d printing and first time to go from design to print. I am currently using PLA+, but want to try PETG. I have not tried ABS.

I also use .15mm and .1 x10mm nickel strips. A 100mm strip will connect 4 batteries. I did not add any groove for the strips or wire although you could. The battery stop washer is only 2mm.

 

[rearden]

Nearly ready for deployment of battery #2.

16s80p of 1280 LiFePo4 26650, so ~240AH @48vdc or 11.5kwh, 10kwh real world.

3d printed battery holders. PLA+ printed the best.
.15 nickel 26650 mesh for spot welding the neg side.
batteryhookup 18650 fuses cut to a square of 4 for cell level fusing on the pos side.
4AWG large strand copper as buss bars from ebay The pos side is doubled and soldered to each group of 4. The neg side is doubled about halfway down the pack since the nickel battery connections will take some of the amperage.
~1lbs 3.5/96.5 solder, one melted solder tip. Weller 80w.
1/0 selterm lugs and heatshrink. Kapton tape on neg side.
Jiabaida 100A SP25S003 BMS aliexpress
malelectric spot welder. MUCH better than the cheap Kerpu. Think lightning vs rubbing your feet on the carpet static shock. The primary problem is the probes get hot quickly. I have not tried the kweld, but the malelectric will do everything I need and much more.
It will go on the SolArk.

I changed the buss bar material because it was cheaper and the stripping process was time consuming and somewhat dangerous. Stripping 1/0 and 2 welding wire is not easy, but I gave up the flexibility of the fine strands. We shall see what happens when i put it together.

Looking for suggestions for V 3.0.
I have only gone "single stack" because it made the battery more stable and the buss bar routing simpler. I would like to see where I could double stack in maybe a 2x2 or 2x3 config. My BMS limits me to 100A so adding too many p causes issues there and with buss bar size. A better fuse system rather than mickey mouse use of 18650 would be nice. But I have not found 26650 cell level fusing, much less an affordable version.

rearden

 

[OffGridInTheCity]

I changed the buss bar material because it was cheaper and the stripping process was time consuming and somewhat dangerous. Stripping 1/0 and 2 welding wire is not easy, but I gave up the flexibility of the fine strands. We shall see what happens when i put it together.

Just to share - I use 6awg stranded bare copper on my 260ah packs. - https://www.wireandcableyourway.com/6-awg-soft-drawn-stranded-bare-copper-wire No prep work except to cut and bend into proper shape and fuse wire solders easily with 100w iron.

4 runs on each side of the packs. Running up to 300a (14s battery bank) and not even 'warm' at the busses.

 

[rearden]

Prepping for V3.0
16s96p of 1536 LiFePo4 26650, so ~288AH @48vdc or 13.8kwh, 12kwh real world.

I will try a 2x3 configuration of the battery holders. I shall have to see how well they link together and avoid tipping over. It looks like Cura V5 has improved the print speed from around 4hr to 3:15. Warping is the big issue though.
I plan to use #4 stranded bare copper for the buss bars.
My battery source has dried up, so this will probably be the last iteration.
V1 and V2 are are working without issue.

 

[DG98]

It's very odd to me that you're having warping issues with PLA+. I would expect that with ABS. Are you using anything to help the plastic adhere to your printer bed? (Glue stick, hair spray, etc.?) Is your bed an appropriate temperature for the material?

I also print my 18650 battery holders, though mine are 5x5 with tabs to connect them together. I make them exclusively in PETG, both for flexibility of the part and to have a little bit higher temperature tolerance in the finished product.

I'm not sure if your design allows it, but moving from 0.4mm to a 0.8mm nozzle greatly increased my print speed -- and given the nature of the part, it doesn't really affect the quality or "resolution" of the finished print.

Cheers, John