That's good timing @batalto

So you have time to top-balance the new LiFePO4 cells before case assembly commences.

What's the highest current you have available from a desktop power-supply?

@transparent honestly I don't think I've got anything. I'll have to take a look

The 12A (max) power supply you see in my photo took over a fortnight to top-balance my first set of 280Ah LiFePO4 cells.

You will need something similar, ensuring that it really does provide a rock-steady voltage in the region 3v-3.7v. You don't want your new cells damaged by a power-supply which glitches to a higher voltage/current if you brush against the knobs on the front!

That's why I chose a PSU with a digital set-up. Once I'd 'programmed it' at the start of the fortnight, it wasn't possible to change the settings again unless I pressed the buttons and moved the knob in the right order.

I also verified what was actually happening at least twice a day by using separate multimeters on voltage and current. The voltage drop across the 4mm^2 connection leads was significant. But the very act of top-balancing will sort this out automatically for you.

Please ask for clarification if you want.

@transparent I guess I'll test them first to see what voltage I get

Testing the cells' voltage when you get them will tell you precious more than the fact they use LiFePO4 chemistry (nominally 3.2v)!

I've already pointed this out to wholesalers in China who send me photos and videos of cells 'under test'. They lack understanding of how 'flat' is the SOC curve for lithium technology.

Cells must be under load when tested. When you've got 280Ah of possible charge, the test will also need to be done over a long time.

And in any case, there are very few effective loads which can be driven from each cell at that low voltage. (What about 100 electric toothbrushes?!)

Have a look for a Bench Power Supply with at least 10A output on Amazon Warehouse, ebay and Gumtree.

@transparent I believe the BMS will slowly balance the cells. Its probably not ideal, but then I'm not in the rush? Would there be an issue allowing it to slowly balance vs top balancing?

That's a fair point. It depends on the initial spread of SOC of your cells, and the way in which your chosen BMS undertakes balancing.

A set of sixteen LiFePO4 cells could have one at 20% charge and fifteen at 60%. Once you complete building a circuit, the one cell will effectively 'suck' charge from the others, causing large internal battery currents which might exceed the manufacturers specification.

You really need to keep charge/discharge currents within the 1C bracket. Ie the maximum current applied across a 280Ah cell is 280A.

Above the 1C rate a cell will probably suffer from a lower overall capacity and decreased lifetime.

In practice your set of 16 cells will have a mix of charge anywhere between 10%-50%.

BMS devices have different ways of undertaking balancing. A typical Daly unit contains passive balancing of 30mA-50mA. That means it uses a small resistor to 'burn off' the charge from the cell which it detects has the highest voltage. It re-checks the cells every couple of seconds, gradually removing charge one cell at a time.

At that low level of balancing it could take a BMS unit many months to bring the cells into balance.

Other BMS units have higher balance currents, including some which simultaneously balance multiple cells.

Or you could buy a separate active balancer and allow it to operate alongside the BMS. An Active Balancer removes charge from one or more cells at a higher SOC, stores that energy in an on-board capacitor, and then transfers it to cells with lower SOC.

But check online reviews carefully. There are some very iffy devices being sold for active balancing!

In real terms an effective Active Balancer for 16S LiFePO4 is likely to cost about the same as a 2nd-hand 10A PSU from ebay.

Posted by: @batalto

Case is due in on the 18th of September.

Looks like you got lucky and missed the supply chain issues. Seplos appear to be having big problems fulfilling orders (some of their July orders are not yet fulfilled). I asked for a progress report and have discovered that they now estimate mid-September before they can send out the battery kits. The timeline has slipped from shipping at the start of August to mid-August to late-August to mid-September.

Batteries arrived today. I'm in Holland at the grand Prix... Wife not happy

The second box in the pile is not sealed in the style used by Xuba.

Either it's split in transit and had to be re-taped, or it might possibly have been checked by HM Customs.

I recommend taking photos of the re-taping and any packaging damage, both before and during unpacking. Remember you have a Trade Assurance or Guarantee contract with Alibaba to cover such matters, but you'll need photographic evidence.

One box contains the self-seal plastic bag with the plated copper busbars inside. Check that you have these and that their 'escape'  wasn't the cause of the box splitting!

@transparent I won't be home until Monday, so I'll have to do it then! Thanks for the heads up

batteries are now unpacked. Haven't had a lot of time this week! All cells are 3.305v or 3.304v so very well matched.

Just waiting on the new battery case to arrive and I can put them in and hook it up. I've decided to swap out my Pylontechs for the new battery straight away. The Pylons are just easier to move and manoeuvre. So they will be the ones I can place where needed on the second inverter.