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

mariadumitruiulian

Hi guys! I've gone through all posts in this thread and wow, what a good place to be if you need to build a battery for your solar system.

I am now in a position to order and I have 2 options : get 2 Pylontech US500 and a rack for ~ 3500E (~9KW) or build my own 12KW battery for ~ 2200. I have most important things like cells, BMS, NEEY balancer , switch and fuse in baskets, I just have to press that "pay " button. The only thing that still holds me is how safe is the DIY version in my attic?

I plan to build it in a Schneider metal electrical cabinet 60LX40WX30H laid on the back , have the batteries BMS balancer fuse inside and add a fan for those few hot days in summer... I just want to be 100% sure that this setup would be at least as safe as an off-the-shelf versions.

Few questions now:

Is building in a metal cabinet OK?

Do I need to compress these cells? How much?

Planning to get CATL 228A cells from NKON , are these good ? What is the difference compared with CALB?

What material is used between cells, is just like ordinary 2mm foam that you use under floor?

I have a Sofar HYD5000 EP so the Seplos BMS should communicate OK with my inverter. planning to use maximum 75A for charge/discharge, is 100A BMS enough? Or should I go for the 150A?

For balancing I have a Doctor Charge 50A, bench power supply 30V/10A and a 120A 14V power supply used for car software updates, so I should charge them up to maximum pretty quick. What is the voltage/cell that should be used when I fully charge?

Will the NEY balancer stay connected forever in the battery?

Maybe more questions on the way as I progress, but that's it for now. thank you all for all the information in this thread!!!

unkel

https://www.boards.ie/discussion/comment/120244045#Comment_120244045

The obvious choice is the Seplos. That's what's in most of the cheap Chinese server rack mount battery packs. As far as comms is concerned, it can natively do plug and play CAN comms with the main inverters. But it has significant drawbacks like it can't balance cells.

We're working on a better solution though. A good and affordable BMS with good app and active balancing. Someone has done this before. I've found some code for it for the JK BMS online - @graememk has put in all the hard work, he has made a prototype device that can be added to the JK BMS, that will do the native CAN comms between BMS and inverter. I hope to be testing this device over the weekend and I'll post the results!

Mr Q

https://www.boards.ie/discussion/comment/120244408#Comment_120244408

That sounds promising. I've been looking at the the JK BMS which can also balance but they wouldn't confirm that it would work with the Sofar.

If I knew I could get it to communicate it would be the option I would probably go for.

I purchased a CAN module to add to my current JBD BMS but I'm not so sure it will work as it only has three wires. Does anyone know if the Sofar uses all 4 wires in their comm lead?

darraghsherwin

Are these the cells most folks are using? https://www.aliexpress.com/item/33041721907.html

Trying to figure out which cells to buy

unkel

https://www.boards.ie/discussion/comment/120244828#Comment_120244828

Yep 200Ah CALB cells from either OYE or PWOD stores (somebody showed here recently that's the same company)

Those are expensive though. We have been getting them even in the last few months for around €1300-€1400 for 16 at checkout

unkel

https://www.boards.ie/discussion/comment/120244707#Comment_120244707

I have the JK BMS on my 40kWh CALB pack now since early yesterday morning, seems to be working perfectly so far.

SD_DRACULA

https://www.boards.ie/discussion/comment/120244863#Comment_120244863

@unkel Is that also talking to the inverter natively using the esp hack?

graememk

https://www.boards.ie/discussion/comment/120244707#Comment_120244707

Unfortunately it uses a different protocol, to what the inverters use.

I'll need to double check but I think pin1 is can H and pin 2 is can L the other 2 is for rs485 battery communication.

Jk won't natively talk either.

poker--addict

ok, so battery back up to about 70%, for initial charge and top balance do I need to trickle charge or just let inverter and BMS do it's thing?

at moment inverter is reading battery as 55.3V and BMS says 55.48. Cell volt difference of 0.023

darraghsherwin

https://www.boards.ie/discussion/comment/120244859#Comment_120244859

They are coming in at 1500 on checkout

graememk

https://www.boards.ie/discussion/comment/120245991#Comment_120245991

you can bump it up another volt now then, at 55 V your at 98ish%

poker--addict

Ok. Is there a period of settling and further charging? Floating v equalising?

poker--addict

not showing near 98%?

unkel

BMS don't really know what your SOC is if your chemistry is LiFePO4. Go by the percentage yourself. Rule of thumb for 16S:

48V empty

51V not much left

52V grand in the middle

53V most left

54V full

(both empty and full there have a bit of margin)

andyr24

So was having issues with low voltage alarms and battery just dropping off to 0% on BMS. Was getting roughly 6kwh out of the pack. I had purchased the 200ah cells from Pwod. I rightly or wrongly purchased a second set of cells from Pwod to increase my battery size. However I bought a capacity tester as I wasn't happy with the first batches performance. Battery up and running since mid October.

138ah

138ah

141ah

117ah

123ah

127ah

135ah

135ah

139ah

120ah

124ah

144ah

141ah

117ah

140ah

127ah

So instead of a 10kwh battery I have ended up with a 5.5kwh battery.

Testing new batch currently and between 163ah and 149ah.

This sort of range I can live with.

I was going to do 2 batteries with 2 BMS but now thinking would I be better to just do a 2p16s style battery and try and match cells say a 163ah and a 117ah in parallel and say a 149ah and a 135ah and so on to make the most out what I have?

Did contact Pwod and they said their cells are really 180ah not 200ah.

unkel

They are only advertised as 180Ah I think

What way exactly did you test them? Those results on their own are meaningless. You must test them exactly the way the manufacturer tests them and published the results in the spec sheet. For starters, charge up to 3.65V and discharge to 2.50V at the same C rating the manufacturer does (might be 0.1C or something like that) with a decent capacity measuring tool with very thick short cables from the tool to the battery cell

But yeah your plan is sound, to match the cells so total capacity for the pairs is roughly similar. I used to do that with 18650s I recovered from free dead laptop battery packs when I was making batteries for my eBikes and scooters. There are even online programs for that where you enter your capacity figures and the program suggests the matching groups 😁

championc

Another reason for going with one BMS is that you cannot read the master cells voltages by a PC or via the GitHub script. You can only read the secondary pack voltages (all according to Seplos themselves)

andyr24

Using this tester.

Charged all cells to 3.65v

Then discharged to 2.5v at 20a.

Charged again to 3.65v at 40a just to speed up process approximately got 1ah less into cell. Put all cells in parallel and charged at 10a to 3.65v less than 10ah went into them.

Probably not entirely correct but gave me a good ball park figure of what I have.

mariadumitruiulian

I pushed the trigger and ordered the cells from NKON. i got 280A CALB cells that were 100% tested and all measured over 300A.

Now I will order BMS and balancer from AE . Question about balancer, what's the difference between the classic 5A active balancer ( the one sold by Minerals store with many caps on the board) and the NEEY one, apart from the blue-tooth connection and better visibility? Will both do the job? Is one much better than the other one?

Will order also the Seplos BMS with LCD and bluetooth from Minerals store; Because I don't plan to charge/discharge more than 75A, would the 100A BMS be enough? Thank you!

andyr24

I have both balancers the neey is more controllable as it can set it up to only balance when cells are over a certain voltage which you decide whereas the other one is on all the time which is a bit pointless.

Very happy with the neey keeping the battery in check.

With regard to the BMS your inverter will probably max out at 100amps anyway depending on size.

For the few quid extra I went a 150amp version.

johnbk

https://www.boards.ie/discussion/comment/120244174#Comment_120244174

Answers from my experience

metal case - I made a metal case with batteries on plywood shelf. I have a small amount stray voltage on the metal frame so I am laying thin plastic on the plywood and at both ends. I feel my eve cells need the plastic to be properly insulated.

compression- eve cells I use are compressed with threaded bar and plywood at either end. Not sure it will make much difference but it doubles up as securing the battery to the shelf and ensures there will be no pressure on the busbars. I didn’t torque or use spring as I don’t see the need. Just used my own judgement rightly or wrongly.

I used the foam between cells but I don’t like it so I am putting very thin plastic between them now with no ‘give’ like the foam.

100amp bms should be fine. I used 25mm cable too.

charge to 3.65v, charger amps will drop as it approaches this voltage. I charged one by one and then connected all together to top balance

poker--addict

I don't have capacity tester like that. Any other way to sense check them?

poker--addict

https://www.boards.ie/discussion/comment/120246457#Comment_120246457

Right now BMS showing 51V or about 3.18 per cell, and showing this as 11% charge, does this make sense?

if so, it's discharging too much and I really need it to stop at 15 or 20%?

inverter showing it as 51.7v

so I am unclear how to get the inverter to stop pulling from Battery? The BMS floor is to stop over discharge but not routine?

unkel

You don't have to worry, let the inverter pull as much as it likes. When the BMS don't like it anymore, it will stop it.

johnbk

I have lined the plywood with 2mm plastic (recycled pandemic screens). Plywood is 18mm marine grade. Angle is 30x30x3. The sheet steel is 2mm where the bms is mounted. All inspired by Off Grid Garage

When I was putting up the panels I took off the leaf guard on the gutter. I hate it as it doesn’t work and made cleaning the gutter almost impossible. I’m going to use it to divide the cells. It is really hard plastic.

irishchris

Picked up a neey balancer little while back but held off installing until sourced some t-class fuses as thought may as well do it all while battery powered down.

Now they are arriving just wondering if the balance cables will be looking enough as have two rows of 16 cells. What have others done in this situation and is it possible to extend these balance cables or does it affect the balancing?

graememk

https://www.boards.ie/discussion/comment/120260261#Comment_120260261

Mines Extended, No issues. Yours is all connected via busbars? Not like mine where I have 32 on one row and 32 on another?

edit:

grab a few of these, you can pull the neey data into home assistant quite easily:

https://www.az-delivery.de/en/products/esp32-developmentboard

irishchris

Yes mine is two rows of 16 connected via busbars. Good to know no issue extending if turns out can't reach all cells with my setup.

Assume there is no issue adding the neey cables lugs to the second cell of each of my setup as have the BMS cable lug on the first cell of each.

Cheers for link for those boards, will order one now as be handy to have that info in ha 👍

poker--addict

Struggling to know what exact state of charge is on battery? Obviously won't want it operating down at 10%...

unkel

50.53V is about 15% SOC or thereabouts. Remember my rule of thumb? That's fine, your JK BMS will handle things just fine, if you don't want to go down too far, just set minimum cell voltage to 2.9V or so (instead of the minimum of 2.5V per the spec sheet / standard for LiFePO4)