Fuses, breakers, and BMSs

[TorC]

Edit: Continuing a thread with new title. See post seven for current state.

Working on putting together a system. Off-grid only. Have LiFePO4 cells (EVE280K 16s,2p) and panels (18 REC 365W) ordered, working on quotes for SCC/Inverter. Will replace and expand the domain of a current system which draws the equivalent of about 7kWh/day SCC into FLA, Samlex EVO 2200W. Old system is being moved, so figure I've got a clean slate.

How important/useful is having brand of SCC and inverter the same in terms of programming accessories/comms links/controls/etc.?

Current planning to buy:
2 Outback Radian 4KW inverters (2 inverters more for redundancy than expected load)

Looked at Magnum PAE: no AC/Gen boost, which seems useful to have; matching SCC expensive and not clearly better for me.​

Looked at Schneider SW: Doesn't support parallel operation, would like to have available in case 4kW doesn't quite cut it on occasion for larger draw tools. 7W lower idle spec would have been nice.​

Looked at Schneider XW: Viciously expensive, though nice power output, not clearly better than Outback.​

Looked at Victron: should be fine, but somehow didn't like the feel of what I read on their datasheets.​

2 Outback FM-80 SCC

Have experience with this SCC and like it. Two will comfortably handle the full panel output, and the entire array on one in case of SCC failure should provide enough power to be getting on with.​

Mate3 & hub - Seems to be required for programming and inverter parallel operation.
BMS - read a bunch, but still very unsure what I'll get here. Probably another thread to hash this out.
Breakers, wires, fuses - I've got a pretty good idea in my head what I need, and how it should be sized, haven't quite gotten to laying out specifics. Probably another thread if I need help.

I considered an AIO, but like the notion of modularity in case of failure on the theory that the system degrades less in case of failure with discrete components. And that's before trying to ensure parallel operation.

What I have just figured out is it appears Outback uses proprietary comms, whereas other companies use something more standard. I found this project where someone reverse engineered the protocol for some older Outback stuff, but it looks like nothing Radian is confirmed to work. I tend to very much dislike proprietary anything when I can avoid it. Thoughts on the advantages/disadvantages of this or other brands are very much welcome. Vaguely considered Growatt or similar, but not breaking down or failing that, economically maintaining spares and/or replacing with non-matching replacements, is considered a fairly high priority in selecting components. No SPoF is non-negotiable. I also don't fully trust Growatt idle draw specs.

The proprietary nature of Outback is really what has me wondering if I should move to another brand, but I wasn't as happy with the datasheets on them when I built my comparison spreadsheet.

Notes on any other gotchas or things I might have missed considering here are welcome, too.

 

[TorC]

Well, guess now this is a sizing/planning thread, time to throw the BMS into this thread, too. Battery build is 32 EVE 280K cells as 16s2p. Cells on order. With the planned inverters I figure a 170A sustained draw should be allowed, and preferably possible from a single string in case of failure, although I very much doubt the system will ever see that much demand.

Looked at some of the Daly/JBD/etc., and the feature set is nice. Keeping a spare or three doesn't break the bank, either, which is also nice. Overkill looks pretty good, except it seems one BMS could choke if the second string were down for any reason.

Also tried to look at some of the higher end REC/Batrium/TinyBMS BMS units for reliability and higher power switching. However, if I'm reading right they require an external contactor, with a corresponding small, but non-trivial load, along with being rather expensive once it's on a 48V system. By the time I get two, one for each string, it starts to add up.

At this point I'm kind of spinning my wheels trying to figure this out, so input is appreciated.

 

[viccooper]

I have also been hunting for a new BMS. I have a 400 Ahr 16s CATL LifePO4 bank that uses an OrionJr BMS with an external contactor. This was a good choice 5 years ago but now there are a lot of other options on the market. I would like to use the same BMS that EG4 batteries use but not sure they have a 400 A rated model.
One very interesting BMS I have been following is the DIY BMS by Stuart Pittaway but they are extremely DIY (you have to solder your own boards?) and the pre-built controllers seem to be chronically out of stock. I love the software monitoring, on-board display and shunt integration and he recently added comms to support the Victron Lynx Cerbo GX. A really epic DIY effort!

 

[viccooper]

Also I probably should have posted my thread to this forum but I am also working on a new system. Perhaps we can compare notes? https://diysolarforum.com/threads/o...ep-using-outback-and-other.34462/#post-429529

 

[TorC]

Thanks. Just took a look at your thread, haven't gotten to look at your diagrams yet. At the moment I'm definitely considering one 200A+ FET based BMS on each bank. Unless someone can come up with a good argument otherwise it's set that I'll be doing 16s2p with a separate BMS on each for redundancy. At the price it's quite possible to keep an extra or three on hand to minimize downtime in case of a failure.

Somewhere else on the forum someone found the significant number of parallel power FETS used by one BMS were each rated for the full rated current of the BMS, and used in parallel because it meant ~1/16th the power lost to heat at full output. AIUI, those are the only components that officially handle the full power, so that leaves me feeling quite a bit better about the design and reliability. A component like that used at 1/10th rated power should have a long service life.

 

[upnorthandpersonal]

Just my two cents: I've been using 2 x JK BMS on my 2x16 280Ah cell batteries for over a year and a half now without issues.

 

[TorC]

OK, I have panels, inverters, charge controllers, and main combiner box in my hot little mitts. LFP cells, 4/0 battery wire, and crimp terminals are en route. I'm particularly interested in the breakers/fuses and BMS right now. Wire I can buy to fit appropriate breakers.

Here is the block diagram I've got so far. Looks like I drew an unlabeled breaker on the wrong wire of the SCC. Should be on the pink positive (I think), 80A each.

It's noted on the diagram, but I'm deciding between the 300A JBD relay BMS or the JK 200A MOSFET BMS.

It looks like I can expect the relays to consume ~60Wh/day, plus almost ⅔ the resistive loss of the MOSFET. I expect normally the 4kW inverter would handle everything, but may wish to start a motor with an LRA that could tax the 8kW inverter. I would like to be in a place where I'd still be OK if one battery string were down. Looking for opinions on BMS capacity here.

 

[TorC]

Going to set up my batteries, and each 16s string is one long row. Narrow available cabinet space means a square 2x8 is not practical. The JK-B2A24S20PC BMS I have doesn't have long enough balance/sense wires for this, so I need to extend them somehow. I've seen conflicting reports of max length to extend to - a very marginal 130cm/51" from @Nami here, and someone who reports Hankzor store said 150cm/59", which would work. AIUI, the primary issue with extending is the wire acting as an antenna.

I have some reclaimed 18/4 stranded shielded security wire lying around. Would it be worth using that for part or nearly all of the run, using a butt splice and heat shrink either at original wire limit for wires requiring extension, or near BMS for most/all wires? Or is there a better option?