diy solar

diy solar

First DIY Battery - Advice Needed

D

Dinobot248

New Member
Joined
Aug 8, 2023
Messages
133
Location
OHIO
Looking to build my first diy 48v 16s lifepo4 battery using the grade B 305ah cells from 18650 battery store for $89 each. I like the JK BMS linked below.

www.18650batterystore.com

JK BMS 8-24S - 150A Continuous - 300A Peak - 2A Active Balancing - JK-B2A24S15P

www.18650batterystore.com www.18650batterystore.com

I have not ordered yet. Still working out some minor details. Questions and comments are below


1. What are you using for the battery level breakers (similar to what is on a Lifepower4 rack battery)? See picture for what is commonly available on Amazon.
2. Other tips or advice are welcome.




Other info

I already have a working system based on Will's design. Only using a single 6500 connected to DC bus bars connected to 6 lifepower4 rack of batteries. Also have a10kw PV array. In case people are wondering why such a large PV array. I have plenty of shade and best solar day for September 2023 has been a measly 20kwh.

I was watching one of Will's old videos from 2 years ago and he paid about $2800 direct from China. Today, it cost about $1440 + $220 for shipping from a US based store.

Seems like the forum users here prefer JK BMS

Eventually as more funds become available, I plan on adding more 15kwh DIY batteries (16s at 305ah).
 

Attachments

  • breaker.png
    breaker.png
    396.3 KB · Views: 8
MisterSandals said:
That knockoff breaker is only rated to 48V. I think a T-class fuse is best for LiFePO4 for safety. If you need a switch, using a properly rated switch is best.

This is probably the worst place to skimp on a safety device.
Click to expand...

As an aside, any comment on those $89 304Ah "grade B" cells? I'm looking to build my first battery and it's hard to argue with that price. So far, I haven't read much about those specific cells, but I'm curious what I might expect from such low-priced cells? Bulging (I'm new to building batteries so not sure why/how-much this matters)? Hard to balance? 300Ah capacity instead of 304Ah? Bruised ego for the lack of a "grade A" label?!
 
Thanks for pointing me to the better breaker. $70 is worth it for the 200A version. The 160A version seems to take at least a month to get here.


Now, I just need the price of the cells to drop back down to $79.
 
Tomthumb62 said:
As an aside, any comment on those $89 304Ah "grade B" cells? I'm looking to build my first battery and it's hard to argue with that price. So far, I haven't read much about those specific cells, but I'm curious what I might expect from such low-priced cells? Bulging (I'm new to building batteries so not sure why/how-much this matters)? Hard to balance? 300Ah capacity instead of 304Ah? Bruised ego for the lack of a "grade A" label?!
Click to expand...
I just had a friend drop off 16 of those cells. All of them were bulged out, some worse than others, The listing says "Potential for some cells to have slight swelling." I have to say that is an understatement at the very least. I am having trouble getting the supplied busbars to fit over the posts without having to swing the batteries all cock-eyed. Not sure how I'm supposed to build the compression frame with the cells sitting all cattywampus.
 
Grab a couple clamps and some plywood, compress them together in blocks of 4. After a couple days you should be able to tape them up and put the battery together.

20231001_124631.jpg

You don't need to go super tight, just snug and you'll have to give it a half squeeze a couple times a day.
 
Rednecktek said:
Grab a couple clamps and some plywood, compress them together in blocks of 4. After a couple days you should be able to tape them up and put the battery together.

View attachment 170268

You don't need to go super tight, just snug and you'll have to give it a half squeeze a couple times a day.
Click to expand...
Huh. I have also heard that you will ruin them if you try to squeeze them back. These are friends batteries and I don't want to be buying them new ones.
 
+ 1 on proper DC rated Breaker
I didn't do it on my DIY packs, but adding it now, as suggested by a Forum Member - when building a 16S pack, put a fuse (Class T or ANL) between cells #8 and #9 right inside the box. If 'all hell breaks loose' this will cut the flow of energy and split the voltage in half at the same time.
 
I've loaded the T-Tocas breakers to 50% of their trip rating with no heating problems. That being said, they're mainly a convenient switch and first level safety device. LifePo4 should really have a class T fuse as close to the battery positive as possible to protect from a "oh $hit" catastrophic event.
 
Rednecktek said:
It ruins them if you try to crank them down Hulk tight right out the gate. If you gently walk them back in it works just fine. Or at least I haven't seen any issues on the multiple batteries I've had to do it to.
Click to expand...
I suggest running the cells down to a lower SOC, and then apply the gentle squeeze as described by others.
Cells tend to bloat as they reach higher SOC, reducing the SOC seems to remove some of the pressure causing this, and allows them to be more easily compressed, slowly and gently back into a flatter (not perfect) form.

I go against most of the advice on this forum and Don't top balance the cells on a bench first before building a DIY pack. I put them into the pack and make sure they all fit well, and then top balance with the cells all in final location. This seems to aid with keeping the worst of the bloating to a minimum, and ensure the cells all slide nicely into their new home without any chance of damage to the shrink-wrap covers, finding they don't quite fit the box you have for them.
 
OffGridForGood said:
I suggest running the cells down to a lower SOC, and then apply the gentle squeeze as described by others.
Cells tend to bloat as they reach higher SOC, reducing the SOC seems to remove some of the pressure causing this, and allows them to be more easily compressed, slowly and gently back into a flatter (not perfect) form.

I go against most of the advice on this forum and Don't top balance the cells on a bench first before building a DIY pack. I put them into the pack and make sure they all fit well, and then top balance with the cells all in final location. This seems to aid with keeping the worst of the bloating to a minimum, and ensure the cells all slide nicely into their new home without any chance of damage to the shrink-wrap covers, finding they don't quite fit the box you have for them.
Click to expand...
Thank you and Rednecktech for sharing your experience and insight. This really helps.
 
These cells are perfect to drop into the Seplos or EEL battery box, let the box do some gentle compression/ holding and just let the BMS sort the cells out.
So far, mine have tracked each other well and I would say you could squeeze the full 305ah+ out of them if you flog them at either end of the charge cycle, but 300ah seems probable if you treat them nice.
Great diy option for well under $2500 for 15kw.
 
You must log in or register to reply here.

Similar threads

J
Advice needed on stand-alone battery backup system
Replies
7
Views
415
Jackie-Hangman
J
T
First time battery bank build.
Replies
11
Views
2K
Aridom82
Aridom82
Disturbedfuel15
First System Build Thread - Another 71kwh DIY
Replies
17
Views
846
Disturbedfuel15
Disturbedfuel15
D
Replacing EG4 with Victron - Advice welcome
Replies
8
Views
585
Brucey
Brucey
iClick
1st time 12v LiFePo4 battery build - continuous discharge advice please (EVE LF304 cells)
Replies
9
Views
213
JeromeS13
J
Back
Top