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diy solar

Beginner DIY EVE 280AH Prismatic LiFePO4 cells system

And just to clarify my last post when I said "..charged them to 3.60V..."
what I should have typed was "
...I set the BMS to 3.60V or 14.4V for each 12v Battery..."
Because I wanted to complete the last and final charge to 3.65V with my PS unit during the Top Balancing phase.
 
Another update!
Top Balancing completed (extremely long process for a bank of this capacity despite most cells were at 3.60v) then using my 6a PS it totalled a tad over 6 hrs to bring all cells equally to full capacity!

But the first capacity test wasn't too impressive slightly disappointing ?.

However the cells were discharging equally within each battery and depending on which BMS I selected for monitoring the cell imbalance were 0.005v , 0.010v , 0.011v and 0.004v.

One thing I noted was as the bank discharged from 2% to 0% (edit: 2% to 0%=cell capacity) the cell imbalances climbed and alternated between 0.004v and 0.102v.
(However, as the bank is currently recharging a good thing to note is all cells have returned to their original minimal cell imbalance readings as listed above)

My setup is temporary during testing phases on my table top, all leads are approximately same length, and only 3ft lengths at 35mm² x 2 (75mm² total) connecting the inverter/charger to the battery bank bus bars, and using custom made bus bars to connect the battery bank in parallel to complete the bank. The bus bar is 25mm X 3mm (75mm²) copper.

My set up of four 280ah batteries @ gives a total of battery bank capacity of 1,120ah.

My initial test results maxed out at 1,089ah ?.

I'm going to repeat the test after the loooonng recharge to full capacity of my bank.
I'm using my Victron BMV 712 BM and shunt for this capacity test. It's relatively new and only in use for the past two months on board.
And I disconnected and removed it from my boat for the testing phases as this is an extremely accurate piece of equipment.
And while I inputted the correct settings for my LiFePO4 cells (as opposed to the lead acid that's its measuring presently) I then made the rookie mistake of forgetting to actually "reset history", so I'm going to hold my hand up and suggested that maybe the lack of resetting has somehow given me an inaccurate reading??

I'm open to opinions here though ?
 
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On a slightly different note I couldn't get my android phone to connect to my Overkill BMS kept getting a popup of "Enter Password" and got no further it simply froze.

So uninstalled it and despite following the setup on Overkill website and BMS manual all three links by Overkill on their website, their pdf manual and also an email link that I recieved from Overkill support none of them worked???

Ironically the link in Will's website was the only android Overkill BMS app that worked but it's still not the same screen as he shows on his YouTube review.
But honestly i didn't mind the appearance of the app as it now works and there's an impressive array of data that can be fine tuned and I can connect and disconnect at ease and repeatedly without issues ?
 
Capacity testing over and satisfactory results.

I set the low disconnect to 2.6v and max disconnect to 3.6v and still pulled the 1,120ah, which I'm happy with as I could have drawn more AH by maxing out the low and high disconnect settings.
Also with individual 4s batteries averaging 10.8v when the test was over and despite some deformation in the Cells as delivered, as I mentioned earlier in the thread I'm happy with the test end results.

My tests were carried out at an average cell temperature of 21°C to 25.5°C and a rate of 0.125C discharge.

While theoretically I could have carried out a 0.2C test as the EVE specs state for test results.

I had to reduce my test loads because rather than stressing a new and 'costly' inverter, as I was getting periodically 'overload' warnings from my inverter at the 0.2C load. I stopped the test, recharged the bank and used a domestic heater pulling an average of 1,697w hence the 0.125C load testing.

Also I repeated logging the voltage recordings at every 10% of battery bank discharge. And again the cell imbalance was minimal until almost cell depletion. However when recharged each time cell imbalance returned to stable minimal imbalance readings.

Few Questions here guys;
With a minimum cell imbalance during normal charge and discharge, does this suggest healthy cell internal resistance?

Also out of curiosity would ye insist on a 0.2C testing for new cells? And why?
 

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Finished making the cell compression frames this evening, using 304L Stainless Steel 6mm (¼") flat bar welded into a frame structure.

Also I'm placing 6mm polycarbonate sheets inbetween each cell as insulation just incase for some reason there's a rip or tear in the flimsy aluminium EVE cells coating, and marine ply at the ends.

While others have used similar insulation sheeting like FR4 and HDPE it was easier to source polycarbonate from a local supplier.
And the melting point of polycarbonate isn't too far off that of FR4 .
Also I realised his evening I'll have to make new bus bars also, as those supplied for joining the cells are too short as the 6mm polycarbonate has increased the distance between the cell terminals.

So tomorrow I'll disassemble my bank and fit everything and share the pics.

These projects can be time consuming? but the experience gained from these builds is immeasurable.
 
I've no affiliation whatsoever with Overkill Solar and the only reason I purchased them was following Will's suggestion in one of his videos. So while I may suggest in my limited opinion as a beginner they are fantastic with a huge amount of data that is available and also programmable/changeable with limited pc/IT skills.....I love them for their simplicity.

They are not the cheapest by far but do allow the user to control a considerable amount of cell autonomy over some of the cheaper BMS's.

Also I purchased them as I'm new to this battery DIY building (but not new to R&D and building). But because Will stated they are a very good make and build and the company undergoes testing of their BMS's and supplies test sheets to collate their test results, (which are then supplied with each BMS), hence their slightly dearer costs to reflect the companies input.
Also I've had a few emails to and from from Overkill customer support who were extremely helpful and reasonably quick with responses.

Using my Victron 500a shunt for the capacity testing and taking readings, I've played around with a few iterations of cell capacity percentage figures, (including those supplied when I asked Overkill solar customer service ) for the EVE cells. These readings were different to those supplied in the BMS program. And I've since changed them again going by the Shunt's accuracy.
So here's a screenshot of the final iteration of voltage readings I've inputted into my BMS.

These voltage readings appear to reflect a fairly accurate cell capacity percentage.

While I'm not a guru and still learning this fascinating discipline, it's a reasonably accurate reflection on the EVE 280ah Prismatic LiFePO4 cells capacity voltages. Over time I will be keeping an eye on the bank and may update the readings again but the changes won't be substantial.
 

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3 out of 4 almost finished
 

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Looking around for battery terminal posts, and came across these20230321_093950.jpg

but most of them are brass/zinc compositions and poorer conductivity.
What are people using as battery posts?
 
Bit of a disappointment with no responses to VTE for their copper cored Bush through posts.
I was interested in this one
SmartSelect_20230324-185113_Chrome.jpg

But since I got no replies from either the US or EU offices I decided to make my own. They use nickel plated steel threaded bar but the copper cross section of the insert doesn't appear extremely thick, but still its rated for 300 -400a.
SmartSelect_20230324-185148_Chrome.jpg
 
So I made mine out of 30mm X 6mm copper bar which I cut into 55mm lengths for the flange and then with two 30mm X 30mm placed on top.
Drilled and tapped the flange for M10 thread and drilled the smaller plates 10mm.
With the whole lot secured with a 10mm nut I then machined the smaller 30mm X 30mm squares into round posts.
And soldered them externally under compression.
20230323_130629.jpg20230323_164116.jpg20230324_182326.jpg
 
Bit of a disappointment with no responses to VTE for their copper cored Bush through posts.
I was interested in this one


But since I got no replies from either the US or EU offices I decided to make my own. They use nickel plated steel threaded bar but the copper cross section of the insert doesn't appear extremely thick, but still its rated for 300 -400a.
That sucks with no reply! I've ordered from them with no issues but never needed to contact them. Good to know!
 
These builds can be time consuming, nearly there though. And probably going a little OTT but as I'm building batteries for a Marine build I figured I'd do it right first time out.
As I don't want any eyebrows frowning on me from any insurance brokers when I'm renewing my Marine ins.
Here's where I'm at, at present.
 
Where the heatsinks are mounted, I swapped out the M3 screw with longer M3 Stainless machine Allen capped screws. And fitted 6mm (¼") polycarbonate sheets, which I also drilled and countersunk.
And gluing an additional piece of Marine Ply on to the end plates of my 4s batteries, I then fitted the BMS securely to the battery pack with counter sink brass screws.
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With a Marine build everything has to be solid and secure. So I guess taking the time now hopefully will pay off in the long run, as it should be another thing less to worry about to go wrong! (Hopefully)
 
Finished the boxes too, marine ply and three coats of waterproof bund epoxy resin.
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Happy enough with the battery posts, as the resistance reading is the same as when I touch both leads directly to each other!

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And finally with the three coats of epoxy...
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Theres a frame on the base plate that the 4s pack squeezes tightly into and that stops the pack from moving around within the battery box. And there's another piece of teak 25mm (1") thick placed on top of the cells with double sided tape, (Seen in the last photo of my last post).
But not yet fitted in the photo, I have an EPDM (Ethylene Propylene Diene Terpolymer) gasket which is glued to the box frame and also to the teak.
When the lid is screwed down the teak holds the cells completely snug.
 
If anyone is interested in also doing a Marine build hopefully the photos and explanations aren't too confusing.
 
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