BMS is now connected, I had a build my own cable. Honestly, you think that if you bought a battery system they could chuck in the cable. It's just a n un-needed layer of hassle 

Firstly, can I say that the conversation over the last 15 pages has been incredibly useful to someone entering this space without much background knowledge. The detailed explanations (and references to 'future readers'!) are exceptionally appreciated.

I'm at the battery ordering stage at the moment. There's a UK supplier called Fogstar that seems to have universal acclaim and are not hugely more expensive than sourcing cells directly from China.

They've got Grade A and Grade B 280Ah cells available on backorder.

The Grade B cells are a bit cheaper and their website essentially claims that they'll still be decent and perfectly suitable for home battery energy storage. My daily usage is around 8kWh so I'm considering saving £500 and buying the Grade B cells as I've no need for as much as 14kWh so even if their capacity was 13kWh I'd be perfectly happy. I'll likely be using a 3kW inverter so I don't believe this will stress the cells too much for their Grade B classification to be a concern in my use case?

My worry is whether they are likely to die sooner/have other issues beyond minor capacity variations.

Fogstar's website suggests that Grade B batteries get a bad name due to genuinely defective 'Grade C' getting sold by some unscrupulous suppliers.

Any thoughts?

Thanks for posting here @korwraith  And I think we'd be interested to know what strategy you're attempting to follow by installing a LiFePO4 storage battery. 🙂 

I have two 'live' storage trials here: one grid-tied and one off-grid. Neither is functioning as it should, but the grid-tied one is very much worse than it should be for a professionally designed/installed commercial unit. It also uses LiMNC cell chemistry, which is more commonly installed in EVs. They have the lowest mass per coulomb (less heavy per unit of charge), which is great for fast acceleration. But it's an odd choice for a domestic storage battery. My house doesn't need to accelerate anywhere fast.

The LiFePO4 chemistry holds less charge per Kg of mass/weight. But it can last at least 5x longer than LiMNC cells. So it's taken over from Lead-acid batteries for home storage.

In time I expect LTO (Lithium Titanate) will replace LiFePO4. It's already available, and slightly easier to manufacture. It only offers 2.4v per cell, but can be discharged below -20°C which allows it to be kept outside the thermal envelope of a house in the UK.

So for the present time, Lithium Ferrous Phosphate is the way forward. It's difficult to manufacture the cells and Chinese companies have a monopoly on that knowledge.

The 280Ah cell is currently the optimal capacity for LiFePO4 manufacture. Either side of this, the cost per Ah rises and production yield decreases.

I've looked at the Fogstar website pages on their LiFePO4 cells which @korwraith directed us to.

I like the design of the terminals which EVE is supplying them with via Fogstar. It has two bolts for each busbar, the fixing points being offset from the axis of the connection into the stack of plates which make up the cell. That overcomes the issue of applying just enough torque to bolt-down a busbar (8Nm) but not enough to loosen the 6mm stud from its aluminium threaded hole. Most DIY installers struggle with this, but would be much more likely to achieve a good solid connection with the Fogstar variant.

I'm in two minds about the value of buying B-grade cells, even if supplied directly to Fogstar by EVE themselves.

If I knew which parameters they'd failed during final test & inspection then I'd be more confident. There's a big difference between the outer casing being slightly too large/small, and the consequences of a failure for electrical/chemical reasons.

The Fogstar cells are about 30% more expensive than I'm paying to import EVE cells using maritime transport. But by the time I add in Fogsar's labour and a secure storage warehouse, it seems a fair price.

The description above is an attempt to explain technical issues without delving into lots of physics and engineering terminology. If I've inadvertently failed to adequately explain a point, please say so!

@transparent Thank you for your thoughts. The alternative to Fogstar would be the likes of Luyuan/Basen/Xuba.

I note you specifically recommended Xuba earlier in this thread, are they still your top recommendation? I contacted them on Alibaba and they've quoted $1970 for 16 x 280Ah EVE, DDP. This is significantly cheaper than Fogstar but also cheaper than Luyuan's self-declared Grade B which makes me wonder about the quality of the cells. 

I'm not the best forum member to provide battery purchase guidance based on price.

The reason Luyuan is more expensive is because their main agent is Amy! She has a well-deserved reputation for providing high-specification lithium cells to end-users in Northern Europe and USA. See a discussion of her renown on the DIY Solar Forum. If you want to pay a bit more to have an absolute guarantee of top quality product and customer service, then go to Amy.

I'm not an end-user, but a commercial developer, working with other engineers to create a new storage control device.

I will therefore be making ongoing orders for lithium cells over the months & years as our prototype work expands. So it wouldn't be good for a Chinese seller to supply me with a duff cell!

That gave me the credibility to approach a different company (not Luyuan) and build a working relationship with another (as yet unknown) agent. So instead of sending a general RFQ (Request for Quotation) via the Alibaba system, I just wrote directly to a Chinese company which I knew was supplying cells to members on the DIY Solar Forum!

That company was Xuba, and the agent is Brian Chen. I simply told him that my company required a long-term working relationship based on trust.

He knows that I will post comments about Xuba here in the RHH Forum, and that others are therefore likely to buy similar lithium cells from him. He may not be the cheapest. That wasn't the most critical factor I was looking for.

What I sought was reliable product which comes from the trust-relationship. That means I don't need to waste valuable engineering time to undertake capacity checks on every cell that Xuba supplies! We can get on with our R&D work instead.

I've opted for Fogstar's 280Ah Grade B cells x 16 at a cost of £2048.

Once I'd accounted for Alibaba's 'insurance' fee, payment fee and credit card foreign currency fee there was only about £160 of savings when going down the China-supplied route. Granted the Alibaba seller (Xuba/Docan) claimed they would supply Grade A cells but I've read enough on the DIY Solar forum to understand that this USUALLY means decent quality Grade B, so I expect I'd be receiving the same cells from both Fogstar and Alibaba. Given that, I think the £160 premium for having a UK point of contact in case of any issues is worth it.

Luyuan's price for 'guaranteed' Grade A cells with certificates etc. was significantly higher than Fogstar's Grade B price and I don't believe I require such high spec/matched cells for my home battery.

I plan to follow the same build path as @batalto and will order a the Seplos DIY kit with 200A BMS (quoted $668 DDP including battery to inverter cables & RJ45 USD adapter, plus whatever fees Alibaba adds so probably closer to $700).

I've also ordered a Solis Energy Storage 3.0kW inverter (RAI-3K-48ES-5G) with WiFi dongle (£720).

That brings me up to approx £3380 so far with some smaller purchases of tools/cabling/misc. to follow.

@korwraith that sounds very exciting. I’d suggest you start a new dedicated post for your project where you can find regular updates.

Posted by: @korwraith

...approx £3380 so far with some smaller purchases of tools/cabling/misc. to follow.

In my experience, the final expenditure on tools, cabling, connectors, fuses, trips and enclosures cannot be described as 'smaller purchases' 🤣 

In fact it's very much the case that what you do by way of the interconnections and safety devices is precisely what we'd appreciate you sharing here on the forum.

Anyone can buy a pallet of hardware to satisfy their energy requirements. It's how you then implement it which everyone else wants to hear about!   ... preferably with photos.

There's a relevant discussion about BMS (Battery Management System) units over on the topic PV Sizing and Approvals. That links takes you to a comment by @simonstengineer who kicked off the debate.

I suggest @korwraith and @batalto might want to see what's being said about the Seplos BMS units in their Mason boxes.

@transparent Thanks for the thread recommendation.

I've watched the same Off Grid Garage video re the Seplos BMS' ineffective balancing feature.

My hope is that the lack of significant BMS balancing won't have have much of a real-life impact if I do an initial top balance of the cells and generally only pull 7-10kWh daily from their supposed 14kWh capacity.

I think I remember Will from DIY Solar suggesting in one of his videos that an active balancer is unlikely to be required in a situation such as mine...

Worst case an active balancer can be added at a future date.

Posted by: @transparent

In my experience, the final expenditure on tools, cabling, connectors, fuses, trips and enclosures cannot be described as 'smaller purchases' 🤣 

Additional expenditure currently at £80 🙃 (wheeled dolly to sit battery on, torque wrench, adjustable DC power supply).

If it helps, the current 'best deal' for an Active Balancer for LiFePO4 16S battery is here on Banggood. Unlike AliExpress, their price includes shipping and VAT.

However, can I suggest that you don't buy without 'checking in' again here. I've just filed a technical query with the company who I believe actually manufactures that unit. I'll explain more once I receive a response.

I noticed the guy from off-grid garage liked this balancer + disconnector = BMS.  That is, in addition to active balancing, it detects over or under voltage on any cell, and over/under temperature, and can stop charging or discharging due to this.

I think you still need a DC fuse, and also a mechanical disconnect switch.

https://www.aliexpress.com/item/1005003104573871.html?pdp_npi=2%40dis%21GBP%21%EF%BF%A160.06%21%EF%BF%A142.64%21%21%21%21%21%400b0a3bb916677520992023667e2aa2%2112000030977333522%21btf&_t=pvid:d8e9c100-e3be-4960-a019-3eed1a718ae3&afTraceInfo=1005003104573871__pc__pcBridgePPC__xxxxxx__1667752099&spm=a2g0o.ppclist.product.mainProduct