280ah cells

Gazoo

Dumb Dumb
Just in case someone stumbles across this thread the new group buy is here:

 

Gazoo

Dumb Dumb
I set my Power supply to about .2V higher which would give me about a 5 amp charge, which tapered of fairly quickly. Once the charge current dropped below .5a, I'd bump the voltage a bit until the current was back up to about 5a, then let it taper again. This seemed to let the BMS do a quite a bit of balancing, and I was able to get the pack up to 28.8V without over-voltaging a cell. It tapered off pretty quickly and as soon as the charge current dropped below 0.2a, I shut it off since that's where the BMS stops detecting the charge, and stops balancing.
So I did pretty much the same thing.

I charged the pack and set cut off at 28.2 volts to see if the cells would absorb. Cells started to drift more than 10mv when pack voltage was 27.24 volts. Voltage difference when the charger displayed 28.2 volts was .050mv and pack voltage was 28.00 volts. Charger amps went down quickly. Kept bumping up the charger up the charger slowly until the BMS cut off. At no time was there a voltage difference of 70mv's but that's to be expected. Total charge displayed by the Riden was 269.238ah's and 7215kwh's. BMS displayed 279.56ah's.

I think I can conclude this is as good as it's going to get with my cells unless I add active balancing. Perhaps using a proper charger with higher amps would also help. Now on to the discharge. I was able to get my DROK meter working.
 

ArthurEld

Solar Addict
So I did pretty much the same thing.

I charged the pack and set cut off at 28.2 volts to see if the cells would absorb. Cells started to drift more than 10mv when pack voltage was 27.24 volts. Voltage difference when the charger displayed 28.2 volts was .050mv and pack voltage was 28.00 volts. Charger amps went down quickly. Kept bumping up the charger up the charger slowly until the BMS cut off. At no time was there a voltage difference of 70mv's but that's to be expected. Total charge displayed by the Riden was 269.238ah's and 7215kwh's. BMS displayed 279.56ah's.

I think I can conclude this is as good as it's going to get with my cells unless I add active balancing. Perhaps using a proper charger with higher amps would also help. Now on to the discharge. I was able to get my DROK meter working.
Damn Gazoo it sounds like you are almost done. Good to see you got those last 8Ah.
Do you know where you will set your charge / discharge limits?
I only ran one serial test and one cell took off at about 3.41V so unless something changes I assume I will need to set my limit below that.
I did capacity tests on 16 cells. They were all within 4Ah. But I'm fairly sure mine aren't all 280Ah so there's no way I will get 280Ah from the whole group unless I start swapping cells.

Now I connected them all in serial and I am taking them back up with my BMS.
Since I just finished capacity testing this is basically a bottom balance. So far my cells have stayed together well. We'll see how they do near the top this time.
Some day I will try starting with a top balance. 🙃
 

cwstnsko

Solar Enthusiast
When it was at about 33% SOC, I took one of my packs apart and rebuilt it with the 2mm foam between the cells. The foam sheets I got are 300mm long x so I cut 2 150x180mm pieces from each sheet. This leaves a 10mm edge around the perimeter of the cell without foam, which ensures that the pressure from clamping is being transferred from face to face on the cells, rather than having the edges/corners carrying some of the pressure. I also put some foam on the front and back of the BMS so the hose clamps could also hold the BMS securely on the side of the battery. I also spent a little time securing the balance leads and BT module with tape. This is the current state. The other battery in the background will be next
E3A4F104-284F-42C6-8EFA-A1D82D439B35.jpeg
As the battery comes up to full charge I’ll be able to better judge if this evens out the strap tension over changing state of charge
I didn’t get a good picture of the cells as I was putting on the foam, but here’s a top down shot of one of the gaps. I wouldn’t go thicker than 2mm. My bus bars wouldn’t reach over the posts until I put some tension in the strapsB7EAD373-4A9F-47CC-A691-B9AAECC67456.jpeg
 

Gazoo

Dumb Dumb
Damn Gazoo it sounds like you are almost done. Good to see you got those last 8Ah.
Do you know where you will set your charge / discharge limits?
I only ran one serial test and one cell took off at about 3.41V so unless something changes I assume I will need to set my limit below that.
I did capacity tests on 16 cells. They were all within 4Ah. But I'm fairly sure mine aren't all 280Ah so there's no way I will get 280Ah from the whole group unless I start swapping cells.

Now I connected them all in serial and I am taking them back up with my BMS.
Since I just finished capacity testing this is basically a bottom balance. So far my cells have stayed together well. We'll see how they do near the top this time.
Some day I will try starting with a top balance. 🙃
That was charging. I still expect to get 270ah's discharging. Interesting I am finding my cheap DROK meter to be reasonably accurate...it has a hall effect sensor.

I don't know what I will set my limits at but I want to set about 70% SOC. Definitely less than where the cells started to drift so less than 3.4 volts per cell on the top. On the bottom same thing...set the voltage so the cells don't drift. I am discharging now so I will keep an eye on when they start to drift. It will be somewhere between 28 and 24 volts. As you know the Riden will works good enough for experimenting and using the low amps makes it easy to watch the top and the bottom.

When I take the pack apart to clamp and so on I am going to put cell number 4 that goes high first and make that cell number 8. And put cell number 7 that goes low first and make that cell number 1. I don't know how much of a difference that will make but what the heck. I have plenty of time to experiment.
 

Gazoo

Dumb Dumb
When it was at about 33% SOC, I took one of my packs apart and rebuilt it with the 2mm foam between the cells. The foam sheets I got are 300mm long x so I cut 2 150x180mm pieces from each sheet. This leaves a 10mm edge around the perimeter of the cell without foam, which ensures that the pressure from clamping is being transferred from face to face on the cells, rather than having the edges/corners carrying some of the pressure. I also put some foam on the front and back of the BMS so the hose clamps could also hold the BMS securely on the side of the battery. I also spent a little time securing the balance leads and BT module with tape. This is the current state. The other battery in the background will be next
View attachment 27912
As the battery comes up to full charge I’ll be able to better judge if this evens out the strap tension over changing state of charge
I didn’t get a good picture of the cells as I was putting on the foam, but here’s a top down shot of one of the gaps. I wouldn’t go thicker than 2mm. My bus bars wouldn’t reach over the posts until I put some tension in the strapsView attachment 27913
I admire your build. I like the way you connected the BMS wires. I thought about soldering the BMS wires to the busbars when I have finally figured all if this out and I have heat shrink that I can put around the busbars and wires.

I like the foam too. Would you mind linking to what you used? And maybe take another top down photo of those same cells at 100% SOC? Thanks.
 

cwstnsko

Solar Enthusiast
I'm not sure if this stuff is any better or worse that the neoprene that others have posted, but this is what I ordered, and it is easy to work with
2mm adhesive foam

On the buss bar attachments, I drilled 7/64 holes in the middle and used some tri-lobe self starting screws that I had left over from when I used to assemble my own PCs. The copper is soft enough that the screws self tap (with a little effort and patience) and create their own threads in the holes.
 

Gazoo

Dumb Dumb
So I finished discharging and achieved the same capacity of 272ah's. I watched to see when the cells started drifting and here is what I recorded:

Voltage difference at 25.53 16mv's.
Voltage difference at 25.37 6mv's.
Voltage difference at 25.32 18mv's
Voltage Difference at 25.24 46mv's
Voltage difference at 25.00 102mv's
Voltage difference at 24.55 151mv's lowest cell is 2.969
Voltage Difference at 24.25 177mv's lowest cell is 2.914
Voltage Difference at 24.00 216mv's lowest cell is 2.854
Voltage difference at 23.75 252mv's lowest cell is 2.790
Voltage difference at 23.50 300mv's lowest cell is 2.733
BMS cut off when pack voltage was 22.95 volts Capacity measured 272ah's.

From this I can conclude the sweet spot between the knees on my pack is a pack voltage of 25.35 discharged. I previously recorded 27.25 volts charged. It is very close to these voltages the cells start to drift more than 10mv's.

Next I will charge the pack to 27.25 volts then discharge to 25.35 volts and record the capacity. I am shooting for 200ah's or 70% capacity for long term storage use in a UPS system. According to the attached graph I should be shooting for 60%. I am still going to cycle them every now and then.
 

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Dzl

Unoffical Forum Librarian
Staff member
Moderator
So I finished discharging and achieved the same capacity of 272ah's. I watched to see when the cells started drifting and here is what I recorded:

Voltage difference at 25.53 16mv's.
Voltage difference at 25.37 6mv's.
Voltage difference at 25.32 18mv's
Voltage Difference at 25.24 46mv's
Voltage difference at 25.00 102mv's
Voltage difference at 24.55 151mv's lowest cell is 2.969
Voltage Difference at 24.25 177mv's lowest cell is 2.914
Voltage Difference at 24.00 216mv's lowest cell is 2.854
Voltage difference at 23.75 252mv's lowest cell is 2.790
Voltage difference at 23.50 300mv's lowest cell is 2.733
BMS cut off when pack voltage was 22.95 volts Capacity measured 272ah's.

From this I can conclude the sweet spot between the knees on my pack is a pack voltage of 25.35 discharged. I previously recorded 27.25 volts charged. It is very close to these voltages the cells start to drift more than 10mv's.

Next I will charge the pack to 27.25 volts then discharge to 25.35 volts and record the capacity. I am shooting for 200ah's or 70% capacity for long term storage use in a UPS system. According to the attached graph I should be shooting for 60%. I am still going to cycle them every now and then.
Did you record (or note) the SOC / Ah as well? If so, what was the observed SOC at 25.35V during this capacity test?
 

Gazoo

Dumb Dumb
Did you record (or note) the SOC / Ah as well? If so, what was the observed SOC at 25.35V during this capacity test?
No I didn't. I was more concerned about the millivolt differences. As I recall was there was around 30 amps remaining before the BMS cut off. I can let you know when I do the next discharge. Now that I know the knees I will be watching the amps closely. I will make a note of the amps left when I get down to 23.35 volts.

I want to determine the usable capacity between the knees of my pack and go from there to get around 70% capacity. If all goes well, 25.35 volts will be the cut off. And I will be able to drop down the voltage of the charger to get there. The Riden will help because it counts the ah's going in. The Ah's out is very close to the same that the Riden puts in. Maybe a 2 or 3 amp difference at most.
 

ArthurEld

Solar Addict
I bought a 4 X 2 feet plywood at home depot and had it cut there. The guy could have done a better job cutting it but it will do. You can also order it online and precut to your specs.
I ordered a sheet of plywood cut into 3 equal pieces 32" x 4' so I don't have to strap it to my roof.
We'll see how that goes when I pick it up tomorrow.
 

umdumchuck

New Member
I should have made it more clear so that no one panicked.
All of the orders for 280ah Eve cells that have been paid for will be filled. Even if you do not have a tracking number yet, the cells are there and nearly all are at the forwarders.
They actually have 50 of the 280ah Eve cells left but those I insisted they hold in reserve in case there are problems and some that I have ordered have to be replaced, and I have some here in MI for that purpose too.
Can I get a quote for 8 Pieces 54301
 

Steve b

New Member
Yep I’ll
I received my 8 cells a few weeks ago from china, I haven't tested them or really touched them yet. I've decided to put my RV project on long term hold. If anyone in the Austin, TX area is interested in buying them at my cost - $850, let me know and we can arrange pickup or I can meet/deliver within reasonable distance (I live in Buda and work in Austin near Riverside/I35).
Do you still have these for sale? If so, are they EVE or Lishen? Other specs?
 

Gazoo

Dumb Dumb
Did you record (or note) the SOC / Ah as well? If so, what was the observed SOC at 25.35V during this capacity test?
I posted the following in another thread but I wanted you to know I did not forget you and your question.

The voltages on my last test shortly before the BMS cut off were as follows in order of cell number 1-8.
3.010, 2.813, 3.008, 2.973, 2.934, 2.983, 2.625, and 2.848

And the following are some interesting measurements I noted when the cells drifted more than 10mv's.

Amp hours remaining at 25.35 volts = 25.24. Voltage Difference = 0.010 Capacity = 9%
Amp hours remaining at 25.30 volts = 21.25 Voltage Difference = 0.020 Capacity = 8% Cell 7 volts lower than others.
Amp hours remaining at 25.25 volts = 19.72 Voltage Difference = 0.033 Capacity = 7%
Amp hours remaining at 25.20 volts = 17.59 Voltage Difference = 0.057 Capacity = 6%
Amp hours remaining at 25.15 volts = 16.98 Voltage Difference = 0.066 Capacity = 6%
Amp hours remaining at 25.10 volts = 16.10 Voltage Difference = 0.079 Capacity = 6%
Amp hours remaining at 25.00 volts = 14.64 Voltage Difference = 0.102 Capacity = 5%
Amp hours remaining at 24.90 volts = 13.57 Voltage Difference = 0.110 Capacity = 5%
Amp hours remaining at 24.80 volts = 12.71 Voltage Difference = 0.122 Capacity = 5%
Amp hours remaining at 24.70 volts = 11.96 Voltage Difference = 0.132 Capacity = 4%
Amp hours remaining at 24.60 volts = 11.20 Voltage Difference = 0.140 Capacity = 4%
Amp hours remaining at 24.50 volts = 10.58 Voltage Difference = 0.150 Capacity = 4%

As you can see when the pack of the voltage approached 25.30 volts is when the voltage of cell 7 dropped below the other cells.

When the charger cuts off and my cells are full there is only a 0.083 voltage difference between the cells thanks to parallel top balancing.
 

Dzl

Unoffical Forum Librarian
Staff member
Moderator
I posted the following in another thread but I wanted you to know I did not forget you and your question.

The voltages on my last test shortly before the BMS cut off were as follows in order of cell number 1-8.
3.010, 2.813, 3.008, 2.973, 2.934, 2.983, 2.625, and 2.848

And the following are some interesting measurements I noted when the cells drifted more than 10mv's.

Amp hours remaining at 25.35 volts = 25.24. Voltage Difference = 0.010 Capacity = 9%
Amp hours remaining at 25.30 volts = 21.25 Voltage Difference = 0.020 Capacity = 8% Cell 7 volts lower than others.
Amp hours remaining at 25.25 volts = 19.72 Voltage Difference = 0.033 Capacity = 7%
Amp hours remaining at 25.20 volts = 17.59 Voltage Difference = 0.057 Capacity = 6%
Amp hours remaining at 25.15 volts = 16.98 Voltage Difference = 0.066 Capacity = 6%
Amp hours remaining at 25.10 volts = 16.10 Voltage Difference = 0.079 Capacity = 6%
Amp hours remaining at 25.00 volts = 14.64 Voltage Difference = 0.102 Capacity = 5%
Amp hours remaining at 24.90 volts = 13.57 Voltage Difference = 0.110 Capacity = 5%
Amp hours remaining at 24.80 volts = 12.71 Voltage Difference = 0.122 Capacity = 5%
Amp hours remaining at 24.70 volts = 11.96 Voltage Difference = 0.132 Capacity = 4%
Amp hours remaining at 24.60 volts = 11.20 Voltage Difference = 0.140 Capacity = 4%
Amp hours remaining at 24.50 volts = 10.58 Voltage Difference = 0.150 Capacity = 4%

As you can see when the pack of the voltage approached 25.30 volts is when the voltage of cell 7 dropped below the other cells.

When the charger cuts off and my cells are full there is only a 0.083 voltage difference between the cells thanks to parallel top balancing.
Is the "amp hours remaining" based on the nominal ~280Ah, or the measured ~272Ah? In either case, that doesn't sound too bad, especially for your (UPS) application where full discharges will probably be quite rare. And in an emergency you can always change the parameters to wring an extra 5% out of your pack.

If I am understanding your situation/model correctly, you are targeting an upper limit of ~70% SOC, and your weak cell limits the low end to ~5% SOC, but you plan to limit discharge to 25.35V or ~10% SOC to stay out of the knee.

So with the 70% storage SOC, your maximum usable energy would be 65% and your planned usable energy would be 60% or 280Ah x 25.6 x 0.6 = 4300Wh

Am I on the right track?
 

Gazoo

Dumb Dumb
Is the "amp hours remaining" based on the nominal ~280Ah, or the measured ~272Ah? In either case, that doesn't sound too bad, especially for your (UPS) application where full discharges will probably be quite rare. And in an emergency you can always change the parameters to wring an extra 5% out of your pack.
That was based on the 280ah's nominal capacity. I have since changed it to 275ah's nominal capacity. The total capacity of 272ah's is equal to 97% capacity. I am happy with that. Power outages are rare here even with Tornados and bad storms. But we do get alerts and warnings. I can start charging the pack if a storm is expected. In the event of a power outage I will have more capacity.
Am I on the right track?
While I have not measured the exact total capacity between the knees I know it's at least 240ah's. 70% of 272ah's is 190.4 ah's. I think 70% will be ok since I will be cycling the pack monthly. So that would be 4874.24wh's and well within the knees.

I am still learning as I go here. Thankfully I have plenty of time to experiment. It's been great to learn what I have from other forum members and pass it on. Applying what I have learned hands on is a different experience and I have a better understanding of things.
 

Dzl

Unoffical Forum Librarian
Staff member
Moderator
That was based on the 280ah's nominal capacity. I have since changed it to 275ah's nominal capacity. The total capacity of 272ah's is equal to 97% capacity. I am happy with that. Power outages are rare here even with Tornados and bad storms. But we do get alerts and warnings. I can start charging the pack if a storm is expected. In the event of a power outage I will have more capacity.
I remember hearing about one system that can monitor NWS/NOAA weather alerts and automatically top off the battery bank if a weather alert is active in your area. I thought that was a pretty damn cool feature if it works well.

While I have not measured the exact total capacity between the knees I know it's at least 240ah's. 70% of 272ah's is 190.4 ah's. I think 70% will be ok since I will be cycling the pack monthly. So that would be 4874.24wh's and well within the knees.
One thing to bear in mind though is that the 70% SOC that you referenced above (from the graph), is an upper storage limit, not the total usable capacity.

If your storage SOC is 70% (and based on that graph and what I've read elsewhere it should be less than or equal to 70%), the only way to attain 70% usable capacity is to discharge all the way to zero, but since your weakest cell cuts off while the pack is still at ~4% (If I understand correctly) your maximum usable capacity would be 66% if you are comfortable with the weakest cell hitting zero and the BMS disconnecting. Or if you disconnect at 9% SOC as you mentioned that would give you 61% usable capacity (assuming 70-9%). Of course you could increase this by charging the pack prior to a storm like you mentioned.

Does this make sense or am I misunderstanding your scenario?
 
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