I have had experience wiring up 2 x Seplos Mason (horizontal) battery boxes to a SunSynk Ecco 5kW.

The Mason 280L (vertical) use M8 bolts for the terminals, whereas the horizontal version uses (fairly niche) Futronics connectors, available from Fogstar although this crimps on 50mm2 wire. See screenshot for reference to 280L terminals in their promo video.

Looking at the Sunsynk 8.8kW it seems as if it accepts 35mm2 cable and has an M6 terminal (

BIMBLESOLAR.COM "https://www.bimblesolar.com/docs/Sunsynk_Ecco_SG05LP1_UserManual_v10_English-min.pdf"

pages 15 & 16).

Having the 8.8kW inverter means the currents are somewhat larger than are regularly handled. For instance the NH00 sized fused disconnectors are generally rated up to 160A, with NH1 being rated to 250A. https://www.bimblesolar.com/extras/dc-breakers-fuses/dc-fuse-disconnect

It sounds as if you will need 200A fuses since the 8.8kW inverter has a 190A maximum current.

I wired each battery through a 2-pole fuse to a common bus bar, and from that bus bar to the inverter via another 2-pole fuse. This is perhaps overkill, but did ensure an even length of battery connection and avoids the daisy-chain style of connection.

In terms of cabling, I used 50mm2 TWINFLEX up to the per-battery fuse and 25mm2 TWINFLEX for the rest of the connections. The 50mm2 cable was used to get the best crimp to the Futronics connector, but somewhat overkill. Perhaps 35mm2 throughout would be fine.

You will also need ethernet cables (RJ45 etc) to daisy-chain the BMS signal between batteries (if you want BMS communication).

Layout of the batteries is crucial; make sure you know where they will go, have equal length wires and ensure you can route the cables without causing too much stress to the terminals.

Posted by: @chickenbig

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I have had experience wiring up 2 x Seplos Mason (horizontal) battery boxes to a SunSynk Ecco 5kW.

The Mason 280L (vertical) use M8 bolts for the terminals, whereas the horizontal version uses (fairly niche) Futronics connectors, available from Fogstar although this crimps on 50mm2 wire. See screenshot for reference to 280L terminals in their promo video.

-- Attachment is not available --

Looking at the Sunsynk 8.8kW it seems as if it accepts 35mm2 cable and has an M6 terminal (

BIMBLESOLAR.COM "https://www.bimblesolar.com/docs/Sunsynk_Ecco_SG05LP1_UserManual_v10_English-min.pdf"

pages 15 & 16).

Having the 8.8kW inverter means the currents are somewhat larger than are regularly handled. For instance the NH00 sized fused disconnectors are generally rated up to 160A, with NH1 being rated to 250A. https://www.bimblesolar.com/extras/dc-breakers-fuses/dc-fuse-disconnect

It sounds as if you will need 200A fuses since the 8.8kW inverter has a 190A maximum current.

I wired each battery through a 2-pole fuse to a common bus bar, and from that bus bar to the inverter via another 2-pole fuse. This is perhaps overkill, but did ensure an even length of battery connection and avoids the daisy-chain style of connection.

In terms of cabling, I used 50mm2 TWINFLEX up to the per-battery fuse and 25mm2 TWINFLEX for the rest of the connections. The 50mm2 cable was used to get the best crimp to the Futronics connector, but somewhat overkill. Perhaps 35mm2 throughout would be fine.

You will also need ethernet cables (RJ45 etc) to daisy-chain the BMS signal between batteries (if you want BMS communication).

Layout of the batteries is crucial; make sure you know where they will go, have equal length wires and ensure you can route the cables without causing too much stress to the terminals.

 

Thanks for that. Could you provide any pictures of your setup? Also what "yield" in KwH are you getting after losses? I may be going overkill with the 8.8

Kind regards

Stew

I bought a Seplos Mason 280L kit.  The instructions were not that great - I ended up "inventing" a couple of details that were not in the instructions:

The cells are separated from each other with foam pads.  There are also a lot of thin rigid spacers, which are thinner than uncompressed foam pads.  The Seplos instructions don't mention these parts - and they also show bigger foam pads on the cells.  After much consideration, I fitted these to the cells as the pic below - thinking that as the cells expand, it is only the central foam area that expands.  I may have this wrong!?

Also - the bottom of our Seplos box is not flat due to the bracing.  If cells are directly placed there, they will not receive support centrally, but will only be supported at either end. 

I found some incompressible material that I could use to make the bottom flat, and then put a "shelf" on top.  I used 2 layers of Magnesium Oxide board and a couple of blank pcbs to make a level surface.  Then another layer of MgO board on top, to make a sturdy shelf.  MgO is brilliant by the way - similar to plasterboard in that is can't burn, but it's also water resistant and tough.  I will email fogstar - I suspect there is a bit of missing metalwork from my kit.  It wasn't mentioned in the instructions either though 🙁 

A bit more research and I think i need the following:

Posted by: @robl

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I suspect there is a bit of missing metalwork from my kit.

Strangely I think it is the design to have bare strut-work. At least Seplos' product video shows that to be so. This was one of the reasons I went with the horizontal battery box, albeit at the cost of having to use the Futronics connector and associated bother.

Posted by: @makia2023

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3x 50mm2 cabling between battery packs

6x M8 crimp lugs

3x 50mm2 cabling between batteries and DC fused isolator

2x m8 crimp lugs

2x 50mm2 cabling between DC isolator and inverter

2x m10 crimp lugs

I may be missing something but 35mm2 cable is probably sufficient somewhat more flexible and less costly. Moreover sticking to one cable size means you only need to order M6 x 35mm and M8 x 35mm crimp lugs, and you can over-order them for when something goes not crimp well.

Correct me if I'm wrong but it seems as if you're proposing a solution that daisy-chain the three batteries together without any fuses. This may not be ideal, but perhaps you're happy with that. Note that the +ve and -ve connections are on the opposite battery to try and ensure the voltage drop is experienced evenly by all batteries (so contribute equally to charge/discharge). You will have to ensure good contact when stacking two crimp lugs on a single battery terminal, but this may only be slightly more difficult than one lug.

The system I've installed is a two battery variation of the following.

It does protect individual batteries from faults in others, and also allows for a single battery to be disconnected (by throwing the disconnector), albeit ignoring BMS communication. However it is more complex (4 fuse disconnectors plus bus bars).

Posted by: @makia2023

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Thanks for that. Could you provide any pictures of your setup? Also what "yield" in KwH are you getting after losses? I may be going overkill with the 8.8

This is the setup, in a garage well away from people traffic. I've used 50mm insulation to try and take the edge off the cold weather. You can see the 50mm2 cable combined with having to change orientation made my life difficult. Perhaps the twin cable was not the best idea!

I'm not sure what you mean by the "yield". The system is currently well over-specced (5kW with about 6.48kW PV on the roof), and I am disappointed with Sunsynk as their Octopus Flux integration still does not work, leaving the battery at > 85% SoC since it was installed. Their servers may be getting upgraded in the next month or so, although that was the story last month. It is rather poor form to get eFixx to advertise this feature when it is still unavailable! I would find the integration useful to earn more money as well as to keep the batteries warm overnight (from discharging between 1600 and 1900 as we as charging up using off-peak electricity).

@chickenbig 

Neat install !

I've now seen a construction vid from Seplos of the 280L.  They don't directly show the base while filling it with cells - I bet it's an embarrasment to them!  But it's clear they didn't have any more bits to fit there - so the bottom isn't flat.  😣

Have you managed to get the Seplos communicating with Sunsynk?  

Regular RJ45 cable? Any changes to the bms?

I have a 3.6kW Sunsynk (had intended a bigger one, but this one was "spare" and I think probably big enough for us), I'll be connecting it up in the next few days.

Thanks!

Posted by: @robl

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Have you managed to get the Seplos communicating with Sunsynk?  

Regular RJ45 cable?

Any changes to the bms?

I have a 3.6kW Sunsynk (had intended a bigger one, but this one was "spare" and I think probably big enough for us), I'll be connecting it up in the next few days.

The process of getting the Sunsynk inverter to work with the batteries was fraught, but this was because the installer had selected the "Octopus Agile" valuation method which meant the battery was charging/discharging according to what a server commanded rather than what I wanted (and I was unable to change the valuation method because the installer had not given me permission to change settings in the Sunsynk cloud). https://renewableheatinghub.co.uk/forums/energy-storage/my-experience-with-the-selpos-mason-diy-kit/paged/13#post-20361 etc for the series of posts getting more/less confused as time went by.

The connection between inverter and BMS was with the yellow cable that came with the inverter; this is not shown in the above photo because I was still trying to diagnose the charge/discharge issue.

I think I set the inverter to CAN Protocol 0 and limited the charge/discharge current. As for the BMS I can't remember the protocol settings (suspect it was something like Pylontech which might be the default).

Good luck with your installation!

I applied online to Sunsynk to be a user.  Once you have user name and password, you can request a status upgrade - I chose "installer", which means I can setup the inverter how I see fit, given it's a diy install.  There's a level above this which allows firmware upgrades - they won't allow this without checking you know what you're doing!

Alternatively your installer can probably raise your status to "advanced user".  Here's a link:

https://www.sunsynk.org/remote-monitoring#:~:text=Note%3A%20When%20you%20first%20sign,of%20the%20more%20advanced%20features.

A bit of bodgineering below - the 3.6kW sunsynk hasn't got an external fan, so tends to get pretty hot when working hard.  Its big brother that I'd originally planned on does have extra fans.  I've glued on 3 low power fans to it, and a 40C bimetallic thermal switch - I used "fixall" type gap filling glue - hopefully it will all come off if I had to make it "as new" for some reason.  The fans will be below the heatsink, blowing upwards.  There's lots of gaps everywhere so that natural convection can still do something if the fans are off.  If it works well I'll maybe fix it in place better.  

I'm unsure of the sources from which you derived your initial list, but I'm pleased to see it being altered as others contribute to this topic.

Low-voltage/battery cable-sizing is most commonly calculated by manufacturers by using American Wire Gauge sizes (rather than the mm² which we use this side of the pond).
From their tables you need to select the size which carries the maximum continuous current you expect to have.

The industry which has most experience of this is probably the marine sector.
They de-rate current capacities according to conditions such as

• passing a wire through a conduit
• cable length (voltage drop)
• ambient temperature
• the material to which a wire is clipped
• the proximity of other wires which may get hot

The last one suggests that twin-cables should be avoided!
I wonder if @chickenbig would like to comment?

Amongst the reputable suppliers in the UK, have a look at 12-volt Planet.
They have wide-ranging advice on their website, https://www.12voltplanet.co.uk/news/cable-sizes. There you'll find a wire size/current chart of which I'm reproducing this snippet:

The rule-of-thumb is that you shouldn't be drawing current (discharging) from a battery at a current greater than the Ah capacity of that battery.
That charge/discharge rate is called C

If you're building a battery with 280Ah cells, then the maximum continuous current you'll want to draw from it is 280A

Thus if you're starting point is a Mason box with 305Ah cells, you're not going to need a more hefty cable than 50mm²

But you then state that you'll be adding a 150A in-line fuse for each battery...
... thus suggesting a 25mm² wire would be adequate.

The 35mm² wire you're now contemplating is plenty big enough, and will exhibit very little voltage drop.
But cost might also be a considerisation.

Fuses for each battery are certainly highly recommended...
... but shouldn't be the method used to manually isolate a battery of course!
That's the job of a DC-rated relay or trip.

The fuse isn't there to 'protect the battery' either.
If you attempt to draw 4000A from an LiFePO4 battery, then it will happily oblige you!
That's the nature of its chemistry.

The fuse(s) need to blow fast if a connected device fails.
In the event of a component failure in your inverter causing a near-short-circuit, the fuses shut off the energy supply and prevent a fire.

For that reason I recommend (and use) Type-T fuses.

The Type-T is housed in a ceramic body with BS88-standard lugs at each end to accept a bolt.
The fuse body is filled with a chemical powder which ensures complete vaporisation of the internal 'wire', rather than it merely melting at a hot-spot.
It needs to break the circuit instantly, rather than create an arc within the fuse.

You will note that I've made a fair amount of this battery-combiner board rather than buying in ready-made parts.
Sometimes what you really want isn't available.

My four batteries and inverters connect together using very solid copper bus-bars.
Compare that to the plastic-covered terminal blocks you'll see on the photo posted above by @chickenbig

Neither approach is necessarily 'right' or 'wrong'.
I'm posting my photo so that others can better evaluate the options.

We both agree on the need to have non-combustible boards.
Chickenbig mentioned Magnesium Oxide board...
and I've used https://www.fermacell.co.uk/en on which to mount the fuse-holders, DIN-rails and busbars.

a quick note re the yellow comms cable, it works fine with my seplos 280L and sunsynk 5.5 ecco - just set battery type to lithium and plug it into the can bus on the inverter and the can port on the seplos - works fine !! 

@chickenbig 

Re- 280L Seplos vertical kit - I sent photos and a description to Fogstar, about the lack of compression and non-flat base as the kit parts I had, asking if a part was missing.  They replied that other customers had asked similarly, but no - I had all the parts!  Others had used plywood on the base to flatten it.  A bit shoddy by Seplos - unless I am very confused- it really needs an extra piece in the base.  Anyway, the MgO I used will be fine for the task I think.