Seplos BMS

garo

I wasn't able to alter the SOC number but I changed the nominal battery capacity and that somehow brought the battery into action. It is discharging right now and I will let it go until it stops and then charge manually by instructing the inverter. Happily discharging at 11 Amp and providing power to the house.

reklamos

https://www.boards.ie/discussion/comment/118378456#Comment_118378456

You should not need to. On solis you can use pylontech profile and then modify min/max Voltage. Then set timed charge and timed discharge and adjust the Amps. The problem that I see in my case(when the batteries arrive) is that the max Amps I will be able to pull/push is 60 and that is nowhere near 0.5C for 200Ah battery.

graememk

https://www.boards.ie/discussion/comment/118379024#Comment_118379024

Don't you have 32 coming.. so you would have 400ah cell if in a 2p16s

Dont have a solis myself so was only guessing

garo

Ok problem of cell voltage differences solved. Call me an idiot. I had connected the B+ to the negative of the 16th (highest voltage) cell instead of the positive. As a result the pack voltage seen by the BMS was that of 15 cells (49.5V in this case) while the individual voltages were obviously adding up to 52.8. As a result the poor BMS was confused. As only 15 cells were discharging the 16th was at a constant 3.336V. Now fixed but the 16th cell is at a higher voltage now (~90mV when under charge) so will need to equalize. I am going to let the BMS do its job here.

I have the same problem of not being able to charge/discharge at more than 0.3C But I think that's a good problem to have.

reklamos

Yeah, it will be interesting to see how things will go. I've also got 2 seplos as I have not decided if I want 1 big battery or 2 separate ones. Seplos does allow to daisy cain the units.

championc

Just a quick comment based on an earlier comment in the thread - the RS485 to USB adapters do not come automatically with the Seplos units - they are a separate item at $10 each, so having gone through the debacle with the HEYO BMS, I didn't want to leave and option closed off.

And I then got royally fooked over by FedEx. They never sent the bill for the Import VAT to me, and later sent it to debt collectors, with another €50 whacked on top !!!

garo

https://www.boards.ie/discussion/comment/118381347#Comment_118381347

WTF! That sucks. Let me know if I owe you anything.

I will say that the RS485 to USB adapters are super useful. More useful than the LCD tbh as in if I had to chose one I would go for the adapters.

I am currently having two issues with my battery pack:

1) The cells are not balanced. I might just bite the bullet and go for active balancing. Last night as the cells were charging, I saw that one cell was higher than the others (same one as in 3 posts above) and would hit 3.6V quickly causing the BMS to hit cell overvoltage alarm and dial back to 10% charge rate. This allowed the cell to go back under the recovery limit I had set (3.5V) and the BMS would ramp up the amps aagain and this went on for a little while before I really dialled down the charging amps allowing the BMS equalization to do a better (though still not perfect) job. This morning, after sitting idle all night the cells ranged from 3.295V to 3.344V (the cell that was hitting overvoltage limit yesterday). I think the BMS could cope, if I charge at a very slow rate for a few days. Or I could do anothger round of passive equalization. But an active top balance would shorten the process considerably.

2) My SPH3600 inverter charges to 100% fine but then no longer uses the battery in the morning after a full SOC 100% charge.

Same issue as this person here: https://diysolarforum.com/threads/growatt-sph4600-seplos-200a-16s-bms.27929/

I have contacted Seplos but it is late tonight for them and they said they will get back to me tomorrow.

unkel

The interesting thing is that the few times I checked, I found my cells were all within 3-4 mV of each other and I haven't used any BMS / balancing hardware for months now!

garo

Have you ever checked them while they are charging or under heavy load? I find their voltages relatively close - though not as close as yours - at rest but under high amp charge or drain their indicated voltages are quite different.

unkel

I shall check garo! The batteries don't charge from PV this time of year, only during night rate 9 hours @1kW but they do discharge @3kW first thing after night rate finishes 😂

garo

Those miners heating your abode?

unkel

Yup. This winter using zero gas to heat the house. Just some to heat the water (where my 40 solar thermal tubes fall short of doing so)

In other words: mining is very environmentally friendly, if you do it with as much renewables as possible 😁

garo

https://www.boards.ie/discussion/comment/118382382#Comment_118382382

Thanks to Seplos support I figured out the second issue which is related to the first. My cells are unbalanced so one of them is hitting the overvoltage protection every time I charge to 100%. The BMS then goes into standby and waits until both the recovery conditions are satisfied:

1. Individual cell voltage decrease to over voltage recovery threshold.

2. The remaining capacity is lower than 96% of the intermittent power supply.

Both conditions should be satisfied.

The issue here is that once I hit overvoltage protection the inverter does not request any power from the BMS which is in standby mode. So it never goes below 96% unless I manually change the capacity and fool the BMS into thinking it is less than 96% full. And obviously the 100% charged estimate is wrong because of the cell imbalance. If the cells were balanced I wouldn't hit overvoltage protection during normal charging. Going to do a passive bottom balance today as I found two cells hitting 2.9V when fully discharged while other cells remained at 3.2V

graememk

https://www.boards.ie/discussion/comment/118385343#Comment_118385343

Does it not discharge in that state either?

garo

No that's the problem. It doesn't discharge. Now I am not sure if this is a communication problem between the inverter and BMS or a BMS issue. I read somewhere about cutting pins 7&8 on the RJ45. Pack now disassembled and passive equalization in progress.

garo

Top balancing takes forever. Thanks to slave1 for a lend of his power supply. I charged the bank with the inverter until the BMS shut off then broke it up and connected half the cells in parallel (lack of busbars). Now charging at a constant 3.6V. I estimate that the bank had about 200-700Wh of capacity left when the BMS shut off so we are looking at 20+ hours to top balance.

Part of me thinks I should have just let the Seplos BMS handle it. It will take a few charge cycles but it will eventually dissipate enough from the more charged cells to balance the pack. Yesterday's passive equalisation allowed me to put 8.4 kWh into the battery today (from 6kWh yesterday) when charging up from 11% (but that number is likely wrong and could be anywhere up to 16%). So I am getting there.

unkel

Missed that you don't have a variable voltage power supply. I have one too and you can borrow it any time you like (you're not far from me). These yokes are great, I use mine all the time. Might order a spare one just in case this one will go kaput on me (which is quite likely to happen within a few years - cheap Chinese power supply LOL) - would not want to have to wait for it to come all the way from China again

garo

https://www.boards.ie/discussion/comment/118393207#Comment_118393207

Thanks for the offer. I may take you up on it at a later date. The one I borrowed from slave1 is doing alright though it has maxed out at 4.5A due to the banana plug leads. I have 6AWG cables but no lug nuts.

unkel

Mine maxes out at 3A anyway😂

slave1

Good man Garo, you keep making all my mistakes/corrections/learnings for me😁

garo

@slave1 I replaced the banana plug leads with proper 16mm2 wire with ring terminals and amps went up to 10A. I didn't need lug nuts. Just screw open the plastic and put the ring terminal onto the charge post of the charger. More than halves the balancing time so happy days.

Geeyfds53573

Thanks Garo for the updates I really appreciate them and know others do - it does seem that the initial top balance is the frustrating part but learning from what you did it seems it will need to be done with these cells.

garo

I think it is the luck of the draw. You may get cells that are well balanced. But it is only after charging in series with the BMS attached that you will find out if they are out of balance and by how much.

garo

All done and fully operational. I'm sharing a few pictures and comments for those of you who are watching.

This is what the BMS looks like fully wired up. Note the double wires on the positive side both for the BMS and to the inverter. I used 16-6 ring terminals for the BMS and 35-8(positive)/16-8(negative) for the battery and inverter.

DIP Switch and CANBus/RS485 connections.

Wiring to the RS485/USB adapter.

garo

Battery pack connected in series and the BMS wires. The power cables to the BMS not connected yet. They go to the two middle terminals on the right. I labelled the BMS wires as I had to take them on and off a few times when I was balancing the cells. Made life a lot easier. I still checked the voltages on the harness before switching on the BMS to be sure sure.

Setup while balancing the cells. Since I had only 16 busbars I balanced the cells in two halves. Note the cells are connected in parallel. I had to rotate every alternate cell 180 degrees to get the positive terminals in a row. The DC charger was kindly lent by @slave1 and can do 10A. I only got 4.2A with the connectors that came with the charger so used some 16mm2 wire with ring terminals to get to 10A.

Closeup of the ring terminals and charging Volts and Amps. You set the voltage before you connect to the battery - this is important. The charger then goes into Constant Current (CC) if current limited and lowers the voltage to match. As the cells get charged the charger increases it's voltage to compensate up to the max set. If you mess with the voltage knob while charging you could set the charger voltage to a higher voltage like 4V without knowing and end up damaging the cells. Because the display will only show the voltage necessary to get to 10A.

Battery Monitor Software in action. This was before I balanced the cells. You can see Cell09 hit the high voltage alarm (configurable). Note the lighter shading on Cells 6 and 16. These (and 9) are being equalised by the BMS by dissipating power. I think it's only about 1A so will take a while if the cell imbalance is large. But you can let the BMS do its job and not balance using a DC charger if you want. The disadvantage of that approach is that you don't get to use full cell capacity while the equalisation is happening as not all cells hit fully charged/discharged at the same time.

bullit_dodger

That......is awesome to see. Thank you for sharing.

cian1500ww

Anyone have a rough idea on what the customs charges were for purchasing one of the Seplos BMS's?

graememk

https://www.boards.ie/discussion/comment/118402097#Comment_118402097

Im still amazed at how well them batteries sit in the plastic box! Looking good.

When rebuilding the 2 packs with the new cells that are coming (well gonna keep all the new cells together) and merge the older cells. I think i will do a top balance to give me a good starting point.

garo

Thanks. There is just one small problem. The box is not deep enough so the lid does not close 🙄 Another cm or two would have been golden. You can tell from the pic with the DC charger closeup.

Well two problems, it's also not large enough to accomodate the BMS. I would have loved to fit the BMS onto the inside wall. I will probably end up screwing it on the lid and using a makeshift cover.

I am already thinking about buying a second set of 16 cells. The second set will be so much easier to do. And it would mean the end of daytime grid import for me.

A top balance while not essential, is a good way to know where you are at with the cells and that you are getting the maximum capacity out of them.

unkel

We all like the idea of a second set of 16 cells, but surely the financials make no sense at all? Unless perhaps you have a huge PV array, very high electricity consumption and a good delta between day and night rate, without penalties if you reach a certain threshold like 2k units per billing cycle?

Unless of course you can somehow get them dirt cheap. Tried this myself, bought 32 cells from AliExpress a few months ago in what seemed to be too good to be true, and it was. A scam. Got my money back of course but it was a total waste of time..

Anyone care to do the sums on here?