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EVE LF280N Capacity from Docan Power

The other interesting data points to look at are the individual cell voltages when the pack reaches its low cut-off point. This will give you an idea of how closely matched in capacity the cells are.

Also, in this post I gave results of measuring my battery with different meters that I have (none of them lab grade) and had a 4% spread in the capacity results on the same test, depending upon which meter I choose to believe.

When doing capacity tests, the amp hour result is the best one to look at as it negates losses from power used by other devices or losses in connections. This is because the electrons have to flow through all parts of the circuit regardless of which component is using the power, and the amp meter is just counting electrons. Whereas if you look at watts, a bad connection can create voltage drop and thus a lower watt hour reading at the meter.
Hi! Yes this is a good point. Upon voltage cutoff on my capacity test, I had the following voltages on each cell: Cell #1: 2.694, Cell #2: 2.524, Cell #3: 2.811, Cell #4: 2.733

Upon recharging from this point, I can see why cell #3 reaches it's high voltage cutoff before the other cells- it has a head start on charging vs the others.
 
This should not theoretically be the case. Look at page six of the beginner top balance document. The idea is that if your cells have different capacities, top balanced cells will all be discharging at the same rate. By the time you go to recharge, they will be at different levels (in terms of how much capacity is left), but they all went down at the same rate. So when you recharge, they should all get back to 100% at the same point. This theory doesn't quite hold in real life, but it is pretty close.
Yes I agree and initially these were my thoughts exactly. If I a start with all cells at the same exact voltage, then draw same exact power from each cell, then recharge them all with the same exact amount of power each, they would arrive exactly back where they started from- all at same voltage.
However, there must be something more in play here with the physics of the energy flow which I am not comprehending. It could be the assumption that the same amount of energy is leaving each cell, which may not be true. For instance, if cell #3 is at a slightly higher capacity at the beginning, it will always be at a slightly higher voltage than the rest of the cells, which means even if amps are the same, different watts are leaving the cell. There may be other laws of energy working here that I don't understand either.

Another idea is that during top balance I am at very tiny amounts of current, however finishing a charge cycle with bms hooked up I am charging at approximately 30 amps, which could thus exacerbate differences between the cells which would not be apparent during the trickle charge top balance. Also, I am discharging at around 93 amps and charging at 30 amps, discharge could be a different efficiency out of the cells vs charge efficiency into the cells which may affect cells of varying capacity differently. There may also be a slight peukert effect affecting cells of differing capacities differently.

I finished a charge cycle last night at about 25amps up to high voltage cutoff and all the cells were within 15 millivolts which is pretty close. Today I will do the same and do a capacity test for 3 hours down to low voltage cutoff and see if i get any more capacity out of it.

Meanwhile, on my other assembled pack, I have so far completed individual cell capacity testing (at 20amp discharge rates- the max of the tester i'm using) and so far have gotten 285ah & 282ah from the first two cells. This is all pointing to two things- 1) Just as Docan Power stated, the higher the amp draw you test these cells at the lower their capacity (characteristic of cells that failed to make EVE's Electric Vehicle grade) and 2) an assembled pack has much more parasitic loss through bms and associated wiring which is not measured at my shunt.
 
Yes I agree and initially these were my thoughts exactly. If I a start with all cells at the same exact voltage, then draw same exact power from each cell, then recharge them all with the same exact amount of power each, they would arrive exactly back where they started from- all at same voltage.
However, there must be something more in play here with the physics of the energy flow which I am not comprehending. It could be the assumption that the same amount of energy is leaving each cell, which may not be true. For instance, if cell #3 is at a slightly higher capacity at the beginning, it will always be at a slightly higher voltage than the rest of the cells, which means even if amps are the same, different watts are leaving the cell. There may be other laws of energy working here that I don't understand either.
You can't really use the voltage to compare cells, because two cells can be at very nearly the same voltage but have completely different state of charge.

I've lost track here. Did you top-balance your cells before attempting any of these tests. The only way what I described works is if you get the cells to the same state of charge - by either top balancing or bottom balancing.
 
I thought soo too, but I had tested 4 cells together with JBD 150 BMS and I only read 271 AH and 3498 WH, when I tested cells by themselves on the fan tester It was giving 275-277 890 WH

Victron was the worst said 267 - 3471 WH for the 4 cell pack with bms.

So Fan tester dirtectly on cells = highest ah
fan tester with JBD test = middle ah
and victron 500a shunt = least ah
I have a feeling what you may be seeing is difference in capacity when testing at different amperage draws. I'm assuming when you used the fan tester on the cells directly you were pulling a max of 20 amps, with of course no losses associated with bms or bus bars. This would give the highest capacity reading.

Then, when you used the fan tester to test the assembled pack along with the bms, you introduced losses with all the battery cell connections as well as bms losses and you were also drawing only 20 amps max. This would be your middle ah capacity result.

Finally, when testing with the assembled pack, bms and victron shunt you were most likely drawing much more than 20 amps which amplify parasitic losses and super slight peukert (LiFeP04 has very minimal peukert effect though). This naturally would give you your lowest ah capacity rating.
 
I"m using 1/0 cable connected to the victron may be the guage of the wire is eating some ah?

the fan tester I'm using 12 guage silicon wire, its dubro brand.

the vicron would also shut down when the BMS would cut-off so I had to look in the history tab to see where it stopped, this is 1 thing I really don't like about this shunt is that because it has a red power it needs active power to work, as soon as the BMS goes to low voltage the shunt shuts down. I don't know if it has a delay in writing the data.

I think the victron is a good device to get an idea of state of charge, but not a good tool for capacity testing.

I saw will was using something like this and it has a secondary power supply, seems like this would be more accurate:


this way even if the BMS goes to lvc the shut will still be running.
Yes I know what you are saying with the victron shunt shutting down once the bms cuts power upon low voltage shutdown. When I do my capacity tests with the victron shunt I log data every 5min or so in excel and once it is very close to shutoff I log it every minute so I know exactly what the shunt reading was right before cutout.

When the power comes back on i've noticed the history tab will greatly exaggerate the ah consumed & Kw discharge vs what it read right before cutout.
 
You can't really use the voltage to compare cells, because two cells can be at very nearly the same voltage but have completely different state of charge.

I've lost track here. Did you top-balance your cells before attempting any of these tests. The only way what I described works is if you get the cells to the same state of charge - by either top balancing or bottom balancing.
Oh yes I did a full top balance on the cells, a few times actually. Connected all in parallel, followed the guide with positive from lab charger on cell #4, negative from the lab charger to negative on cell #1, verified with multimeter charger was outputting exactly 3.65v before attaching, hooked up and waited until zero amperage passing through before disconnecting.

This, of course gets all the cells to the same voltage but they may be of varying capacities. Also since they were brought up to the 3.65v at a very tiny rate (milliamps) individual cells (may not?) show their differences of voltage as much as if they were being charged rapidly i'm not sure.
 
Yes I agree and initially these were my thoughts exactly. If I a start with all cells at the same exact voltage, then draw same exact power from each cell, then recharge them all with the same exact amount of power each, they would arrive exactly back where they started from- all at same voltage.
However, there must be something more in play here with the physics of the energy flow which I am not comprehending. It could be the assumption that the same amount of energy is leaving each cell, which may not be true. For instance, if cell #3 is at a slightly higher capacity at the beginning, it will always be at a slightly higher voltage than the rest of the cells, which means even if amps are the same, different watts are leaving the cell. There may be other laws of energy working here that I don't understand either.

Another idea is that during top balance I am at very tiny amounts of current, however finishing a charge cycle with bms hooked up I am charging at approximately 30 amps, which could thus exacerbate differences between the cells which would not be apparent during the trickle charge top balance. Also, I am discharging at around 93 amps and charging at 30 amps, discharge could be a different efficiency out of the cells vs charge efficiency into the cells which may affect cells of varying capacity differently. There may also be a slight peukert effect affecting cells of differing capacities differently.

I finished a charge cycle last night at about 25amps up to high voltage cutoff and all the cells were within 15 millivolts which is pretty close. Today I will do the same and do a capacity test for 3 hours down to low voltage cutoff and see if i get any more capacity out of it.

Meanwhile, on my other assembled pack, I have so far completed individual cell capacity testing (at 20amp discharge rates- the max of the tester i'm using) and so far have gotten 285ah & 282ah from the first two cells. This is all pointing to two things- 1) Just as Docan Power stated, the higher the amp draw you test these cells at the lower their capacity (characteristic of cells that failed to make EVE's Electric Vehicle grade) and 2) an assembled pack has much more parasitic loss through bms and associated wiring which is not measured at my shunt.

The bigger the BMS the more loss it will have, a 100 a probably you will loose about 4-5 Ah, the 150 5-6 ah, and like a 200 or so 6-7 ah.
 
Yes I know what you are saying with the victron shunt shutting down once the bms cuts power upon low voltage shutdown. When I do my capacity tests with the victron shunt I log data every 5min or so in excel and once it is very close to shutoff I log it every minute so I know exactly what the shunt reading was right before cutout.

When the power comes back on i've noticed the history tab will greatly exaggerate the ah consumed & Kw discharge vs what it read right before cutout.


which is why fan tester is great, under $100, pretty colors on lcd screen and the has RGB colors also no shutdown & v-sense cables.

It should be the standard for the dollar!
 
This, of course gets all the cells to the same voltage but they may be of varying capacities. Also since they were brought up to the 3.65v at a very tiny rate (milliamps) individual cells (may not?) show their differences of voltage as much as if they were being charged rapidly i'm not sure.
The voltage at the top of the charge curve is very indicative of the SOC. Just look at the steepness of the curve versus a lower SOCs where the curve is very flat. Charging rapidly as in constant current has nothing to do with the shape of the curve above 3.6 volts.
Yes they could be varying capacities but there is nothing you can do to change that physical property. Top balancing is just balancing capacity at the top. Imagine a stack of popsicle sticks of varying length analogous to capacity. You can stack them where they are even at the top or the bottom but you can not change their capacity (length).
 
The voltage at the top of the charge curve is very indicative of the SOC. Just look at the steepness of the curve versus a lower SOCs where the curve is very flat. Charging rapidly as in constant current has nothing to do with the shape of the curve above 3.6 volts.
Yes they could be varying capacities but there is nothing you can do to change that physical property. Top balancing is just balancing capacity at the top. Imagine a stack of popsicle sticks of varying length analogous to capacity. You can stack them where they are even at the top or the bottom but you can not change their capacity (length).
Yes, that's a good point. I think what I meant to emphasize is that even though a group of battery cells are all at the same voltage, their capacities could be, of course, still different. So, after a fantastic top balance is completed where all the cells are at 100% SOC and I then proceed to take say around 500 watts out of each cell on a discharge, that could mean leaving cells 1, 2, 3 and 4 at around 45%, 44%, 46% and 45% SOC. Upon charging these to full at this point, some of these cells have a head start on the others as to reaching 100% so will reach their voltage cutoff sooner than the others.

One could theorize 'well, they all started at the same point and should return to the same point'. Perhaps, but perhaps not. Remember, we got these cells to their top balanced state by connecting in parallel and / or charging individually to 3.65v. I presume the energy's interaction with the cells is different in the aforementioned way versus now discharging and charging in series with a bms involved as well as many other sources of resistance. I believe this is one of the reasons individual cell voltage will drift over time and we need a balancing mechanism in place to bring them back.

This all points towards my idea that if the cells differ from each other significantly enough (be it capacity, chemistry, age, internal resistance, construction methods or materials, etc) they will, upon charging to their respective 100% SOC, all ramp up in voltage at slightly different times. Looks like there may be no real way of dealing with the resulting 'runners' outside of simply draining power from them individually so they line up (closer) with their counterparts, although they will probably only be able to get so close.
 
I managed to complete testing all my cells, individually, using a ZKE Tech EBD-A20H load tester. This tester connects to a computer and generates the pretty graphs, logging voltage and amps every few seconds. Just a chinese tester, but uses independent voltage sensing leads and is seemingly accurate as verified with my Klein DVM. Each cell took approximately 14 hours as this tester maxes out at 20 amps.

The results:
-------------------------------Battery 1------------------------------
Cell-----Ah--------Energy---Internal Resistance--Production Date
--1---285.1Ah---922.81Wh--------0.17mΩ-------------2/6/21
--2---281.4Ah---912.20Wh--------0.17mΩ-------------12/1/20
--3---282.2Ah---914.89Wh--------0.175mΩ------------2/15/21
--4---284.3Ah---921.66Wh--------0.17mΩ-------------2/8/21

Capacity testing assembled pack avg 94A mixed draw (about 20A from 12v loads, 74A from inverter w/ space heater plugged in), measured with Victron BMV-712 logging data every 5 min until voltage cutoff (every 1 min during last 10 min of test):

275.8Ah, 3514Wh
Individual cell voltage at end of assembled pack test:
Cell---Voltage
--1-----2.896
--2-----2.548
--3-----2.708
--4-----2.856

-------------------------------Battery 2------------------------------
Cell-----Ah--------Energy---Internal Resistance--Production Date
--1---279.6Ah---904.51Wh--------0.175mΩ------------2/25/21
--2---278.9Ah---902.38Wh--------0.175mΩ------------2/26/21
--3---281.1Ah---910.30Wh--------0.175mΩ------------2/2/21
--4---280.1Ah---907.80Wh--------0.175mΩ------------2/18/21

Capacity testing assembled pack avg 96A mixed draw (about 22A from 12v loads, 74A from inverter w/ space heater plugged in), measured with Victron BMV-712 logging data every 5 min until voltage cutoff (every 1 min during last 10 min of test):

272.9Ah, 3450Wh
Individual cell voltage at end of assembled pack test:
Cell---Voltage
--1-----2.693
--2-----2.527
--3-----2.795
--4-----2.723


Battery 1 performs very well, cell voltage stays very close to each other (within 10 or 15mv) all the way to 3.65v cutoff.

For Battery 2, cell #3 likes to start climbing faster than the others around 3.5v with about a 25mv delta over the others. I have used a resistor to try to tame this cell's behavior closer to the others. However, after attaching this 6Ω resistor for only about 10 minutes while charging pack at around 5A, once getting to about 3.55v, the other cells climb fast and leave cell #3 in the dust.

I believe I will have to continue to play a bit of whack a mole with the resistor and repeated run-ups to volt disconnect to average out the differences. I imagine it unlikely to get the delta below 25mv overall but i'll be happy with that, given the circumstances.

I began on this journey with a flawed understanding of quality of cells I would be receiving from Docan but after reading on this great forum I now understand there is only so much one can expect from these electric vehicle battery rejects. I have a JK-B2A8S20PH BMS ordered, should arrive in about a month. I believe the 2A balance current will sufficiently keep these cells behaving well together, much more so than my current Overkill Solar JBD BMS could ever do with it's 50mA balance current. Plus, i'll be able to use it when I go 24 volt with these cells, yay!
 
thanks for the results, another reason why I believe the 280N were a better cell than the duds 280K.
No problem Alkaline! I hope they help somebody. I have been able to drain cell #3 a little bit more (I have found a 6ohm works really nice, ends up being around 0.6 amps) and now I'm getting a delta as low as 15 mv at 3.65v cutoff.

As far as how long it will stay that way not sure but we'll see. I think the main thing at play here is cell #3 from battery #2 was made a few weeks before the others so maybe slightly different materials or process was involved in its construction.
 

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