10kWh LifePO4 DIY Battery Addition..... Here is my write up.

rosmoke · 22-08-2023 10:47PM

Thanks you,

I see folks using Seplos, another one JK smth and the mason box.

What's the go to?

Would you keep it in the attic or build an enclosure outside?

I've HA setup already with inverters connected.

unkel · 22-08-2023 11:17PM

https://www.boards.ie/discussion/comment/121014615#Comment_121014615

I use JK BMS, I didn't like the Seplos I had before. It has an unneccessarily complex menu, poor app, no active balancing and can't handle it if you upgrade to a battery above a certain capacity. But it can communicate directly with inverters, with the JK you will need an additional device

LiFePO4 is safe in the house as long as your attic can take the weight

graememk · 22-08-2023 11:20PM

https://www.boards.ie/discussion/comment/121014615#Comment_121014615

How outside is outside? Garage? batteries need to be within arms reach of the inverter really, dont like the real cold either. Id be leaning more on the inside bit.

LFP cells are rock solid, Id have no issue of having them in the attic.

Seplos and mason are one and the same.

JK is pretty sweet, got good balancing current (2a) vs milliamps on most other bms's

Globalpower has got good reviews from andy in the off grid garage. (but poor balancing so possibly a Neey active balancer needed too)

Main drawback on the JK is that it does not communicate natively with the inverter but you can build a translation board : https://github.com/Uksa007/esphome-jk-bms-can

Also need cable, cable lugs, big crimper, small crimper for balance leads, Isolator, Fuses, (you may already have some as you have a dryness installed.)

16s1p (16 cells) will get you 14ish kwh

16s2p(32 cells) will get you 28ish kwh (Number of cells * 3.2 * cell capacity)

hexosan · 31-08-2023 11:35PM

How long approx should the pack take to top balance when charged at 10a approx. Are we talking hours, days, weeks, months ?

Im aware it depends on the original state of charge, just looking for a ballpark idea.

graememk · 31-08-2023 11:43PM

https://www.boards.ie/discussion/comment/121054291#Comment_121054291

possibly about 3-4 days

hexosan · 01-09-2023 07:00AM

I don’t have enough bus bars so I’ve 8 cells in parallel and I’m using a 10a bench top power supply. So I’m looking at about 2 days per 8 cells.

unkel · 01-09-2023 04:33PM

https://www.boards.ie/discussion/comment/121054540#Comment_121054540

It's going to be extremely slow if you set your power supply to provide 3.65V. Even when the cells are already pretty much fully charged individually at 3.4V or so, you might only get a fraction of 1A. To speed things up, you could set your power supply to 4.2V or so and watch a much higher current. Needless to say, you will need to keep an eye on things then. That said, you won't damage LiFePO4 as long as the cell voltage stays below 4.2V

hexosan · 02-09-2023 10:06PM

https://www.boards.ie/discussion/comment/121057133#Comment_121057133

I’ve it set to 3.65v @ 10a and I’m getting about 37watts on the bench top power supply. All the cells were between 3.302-3.308v when I started. There going about 48hrs now and are at 3.344v.

what sort of time frame am I looking at to 3.65v

hexosan · 02-09-2023 10:07PM

anyone seen something like this as a safety feature. Would like to see a YouTube video of it working

Hot gas sol fire extinguishing device Fire extinguisher for battery box Hot enabling extinguisher

https://a.aliexpress.com/_mP8T1J8

unkel · 02-09-2023 10:42PM

https://www.boards.ie/discussion/comment/121061827#Comment_121061827

If you keep your PSU at 3.65V, it could take another week or two until you reach 0A =>perfect top balance

Your cells will be perfectly top balanced. But you will have lost a small fortune by not being able to use your battery in the mean time. As you can sense from the tone of my post, I'm more of a pragmatic man. Make those batteries work for you and make you money. Rather than let them do a pretty ballerina dance to perfect balancing...

hexosan · 02-09-2023 11:00PM

Would it take the BMS long to balance them out itself ?

putting it up to 4.2v will that knock much off the time to full charge ?

graememk · 03-09-2023 06:57AM

https://www.boards.ie/discussion/comment/121061981#Comment_121061981

What bms?

If it has active balancing it will get there eventually. Passive balancing.. yeah it will never get there

hexosan · 03-09-2023 07:00AM

https://www.boards.ie/discussion/comment/121062294#Comment_121062294

JK BMS

hexosan · 03-09-2023 07:02AM

What if I I only go to 3.4 or 3.5v or is it an all or nothing with them.

graememk · 03-09-2023 07:06AM

https://www.boards.ie/discussion/comment/121062301#Comment_121062301

Jk has active balancing.

Get them to at least 3.5 now that you have started the process.

poker--addict · 03-09-2023 10:50AM

I'm pretty sure I got all mine above 3.5, but still have one or two which seem to consistently dip off the scale first at the lower end, so I am not sure how much benefit comes from fine tuning the top.

unkel · 03-09-2023 12:58PM

https://www.boards.ie/discussion/comment/121062823#Comment_121062823

Cells are not equal, there will always be weaker ones. You got then all above 3.5V, that's your job done. Don't worry about some dipping earlier at the lower end.

hexosan · 03-09-2023 05:13PM

It’s picking up the pace now it took 48hrs to go from 3.30v to 3.340 and in the last 19hrs I’m gone from 3.34 to 3.37v.

I should be done before the winter solstice 🤦‍♂️

unkel · 03-09-2023 06:00PM

You have the patience of a saint. And you mustn't care much about getting them to make you money. I'm the complete opposite myself 😂

hexosan · 03-09-2023 06:14PM

cant do much till Thursday I’m waiting on an Amazon delivery

unkel · 03-09-2023 07:42PM

Cables?

hexosan · 03-09-2023 07:54PM

https://www.boards.ie/discussion/comment/121065271#Comment_121065271

copper lugs for the BMS

hexosan · 05-09-2023 08:34PM

Double checking before I start cutting cables here.

battery to BMS to 125a Dc breaker into the inverter.

is there a need for rotary battery disconnect switch or a fuse on the positive cable ?

BuzzFish · 06-09-2023 02:45AM

You'd want a disconnect and a fuse between battery and BMS in my opinion. See my OP

unkel · 06-09-2023 09:03AM

https://www.boards.ie/discussion/comment/121074821#Comment_121074821

I always use a fuse directly between positive battery terminal and anything connected to it.

hexosan · 06-09-2023 10:03AM

https://www.boards.ie/discussion/comment/121075311#Comment_121075311

What fuse have you used and is there still a need for the rotary disconnect switch on the positive when you have a projoy 125a DC MCB

unkel · 06-09-2023 11:19AM

https://www.boards.ie/discussion/comment/121075532#Comment_121075532

I just use an automotive mega fuse (250A), cheap as chips and will do the job. I also use a battery disconnect switch between this fuse and the inverter positive