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EVE LF280N Capacity from Docan Power

Delta Sierra

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Aug 22, 2021
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Im posting here and deleting my previous post. I initially ordered 8 of the new style LF280K cells from Docan Power but emailed Jenny Wu @ Docan before purchase making sure the cells I was to receive were not going to be bloated. She advised the cells do have a slight bulge to them and recommended I take delivery on the older style LF280DK (EVE 280N I believe, as the LF280DK is just their internal naming for these cells.) as these cells have no bulge and satisfy a few of my other concerns.

I received them via ups promptly and they were in great physical shape. Barcodes show the oldest one manufactured on 12/1/2020 and newest one on 2/26/2021 so looks like they have been sitting around for about a year before I got them. I assembled them into two separate 12.8v packs with an overkill BMS on each of them. I ended up using .125" thick aluminum plate cut just wider than width of cells and just shorter than their height, one plate onto each end of the group, with 8 hose clamps banding them together tightly. Also used some 2mm thick rubber sheet in between each cell and the plates on the end for protection.

Wanting to go with a flexible connection between each cell rather than a rigid bus bar, I chose to arrange them physically in parallel and built my own 'bus bars' with 2/0 AWG cable and tinned copper lugs, hydraulically crimped. They actually have about 33% more cross sectional area than the 2mm x 20mm bus bars that came with the cells, can move slightly to account for cell expansion / contraction as well as have excellent contact area when tightened- unlike solid bus bars.

I initially connected in parallel with bus bars and top balanced them at 3.65 volts with a cv/cc charger until amps went to near zero. I then used my cables to series connect the cells for each pack, attached the bms and torqued each nut to 3 Nm.

For the capacity test, I put the assembled pack into my RV and connected my Victron BMV-712 smart monitor shunt in line between inverter neg / trailer neg & C- lead from bms so the shunt measures everything, without anything else bypassing shunt. I then reset history of smart monitor, connected 1000w heater to inverter and started logging data into excel every 5 minutes for the 3 hours it took to run the battery to the 2.5v per cell cutoff. Average amp draw through the tests were around 92 amps.

Ended up getting only 275.8 AH out of battery #1 (one test) and 272.9 AH out of battery #2 (ran two tests, exactly same result). These AH numbers are from the Victron app where it says "Consumed AH". Under history tab, discharged energy shows 3.5Kw for all the tests. In excel, I ran a formula that added up all the wattage drawn from the pack from each sample point and got 3514 watts for battery #1 and between 3477 (test 1) and 3487 (test 2) for battery #2.

I'm assuming the watts I would be expecting from these packs would be approximately 3.2v * 4 * 280 AH = 3584 watts correct? So- bottom line question here- did I get screwed on buying these cells or no?

I do realize that there is energy loss on the battery side of the bms that the shunt is not measuring, for instance the battery and bms temps raise approximately 6 and 12 degrees respectively and of course all the connections are not zero resistance either and get slightly warm to the touch (never hot). I'm assuming over the course of a 3 hour test it would be fair to expect 50 to 100 watts of energy loss from this?

So, perhaps I got a fair deal? Please let me know if my methodology for capacity testing these cells is correct and what your thoughts are as to my purchase from Docan :) I emailed Jenny Wu, will see what kind of resolution if any at all she may have for my situation.

Attached a few pics, they will eventually both be in a plano box wired in parallel for 7 kw of power and eventually in series for 24 v

batt2.jpgbatt1.jpg
 
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It's possible that your shunt isn't perfectly calibrated. Unless you're using lab grade, calibrated equipment, I would expect a +/- 10% error margin, but hopefully less from a Victron. Even if it is accurate, unless you paid for legitimate "grade A" EV cells, then getting over 270ah from a 280ah cell isn't too bad.

273ah is 97.5% of 280ah, and 276ah is 98.6%. I wouldn't be upset.
 
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.
 
It's possible that your shunt isn't perfectly calibrated. Unless you're using lab grade, calibrated equipment, I would expect a +/- 10% error margin, but hopefully less from a Victron. Even if it is accurate, unless you paid for legitimate "grade A" EV cells, then getting over 270ah from a 280ah cell isn't too bad.

273ah is 97.5% of 280ah, and 276ah is 98.6%. I wouldn't be upset.
I see what you are saying about the shunt however, the victron manual states current and voltage measurement are +/- 0.4% and 0.3%, respectively. Can't imagine being anywhere near 10% off.

I did pay for what was advertised as Grade 'A' Eve 280ah cells. I do agree with you that I am getting pretty near advertised capacity though. However, I do see Will is passionate about stating if your batteries don't pull at least their advertised capacity, you got ripped off :(

I appreciate everyone's response thanks guys!
 
I see what you are saying about the shunt however, the victron manual states current and voltage measurement are +/- 0.4% and 0.3%, respectively. Can't imagine being anywhere near 10% off.
The 10% is general. Your farthest number is 2.5% off. The closer is 1.4%. that can be the difference in a few degrees difference during testing. It's CLOSE by any standards. It's going to be exceedingly difficult to prove to the seller that those cells are lower in capacity if they're that close to spec, without using professional measuring equipment.
I did pay for what was advertised as Grade 'A' Eve 280ah cells.
They wouldn't have been made in different years if they were a matched grade "A" pack. Did you get test reports that match the serial numbers? Cells aren't "matched grade A unless you get a test report for that specific cell from the manufacturer. The CELLS, individually, might be grade "A" but if they were manufactured that far apart they most likely won't "match".

Most of the actual EV cells I have come from the same S/N set, they were made on the same day. A handful are even sequential.
I do agree with you that I am getting pretty near advertised capacity though. However, I do see Will is passionate about stating if your batteries don't pull at least their advertised capacity, you got ripped off :(
I don't think you got "ripped off" unless you actually paid for matched and batched cells.
I appreciate everyone's response thanks guys!
Happy to attempt to help!
 
Testing cell capacity by testing an assembled pack can be good in some ways and bad in other ways. It gives you the capacity at the battery level, which is what is meaningful for how you would actually use it. That's good. Unfortunately, the capacity of the battery is driven by the lowest capacity cell. One cell will get to 2.5V before the others, and that will cause the BMS to cut off discharge.

This is also why it is good to know the capacity of individual cells, so that you can assemble batteries with more closely matched cells. You may have four cells with over 280Ah, and four with less. If you put the higher-capacity cells together, that battery will actually have more than 280Ah of capacity. When the lower capacity battery cuts off the higher capacity battery may be able to sustain your loads a bit longer. If you put lower capacity cells in with the higher capacity cells, the batteries will both cut off earlier.
 
There's some error when you multiply by a flat 3.2v but cut out at 2.5v. Depends upon what voltage you started at and how fast the curve drops to 3.2v and then falls off to 2.5v at the end.
 
Testing cell capacity by testing an assembled pack can be good in some ways and bad in other ways. It gives you the capacity at the battery level, which is what is meaningful for how you would actually use it. That's good. Unfortunately, the capacity of the battery is driven by the lowest capacity cell. One cell will get to 2.5V before the others, and that will cause the BMS to cut off discharge.

This is also why it is good to know the capacity of individual cells, so that you can assemble batteries with more closely matched cells. You may have four cells with over 280Ah, and four with less. If you put the higher-capacity cells together, that battery will actually have more than 280Ah of capacity. When the lower capacity battery cuts off the higher capacity battery may be able to sustain your loads a bit longer. If you put lower capacity cells in with the higher capacity cells, the batteries will both cut off earlier.
Thank you Horsefly, this is a really good point!

Jenny from Docan Power got back to me and asked if I have tested the cells with either an EBC-A40L or EBC-A20 battery tester and generated a graph. I am actually looking unto buying a CBA V Pro like what Will uses to test battery capacities, minus the amplifier. For a little over $200 I would be able to test my batteries very accurately (over 99% accuracy) and like horsefly said, be able to assemble matched packs. Only bummer is the max draw is 200 watts. But then again, testing each cell individually this would still be around a .22 C rate.

I looked into the EBC-A40L on amazon and they are over $300 without many reviews, the EBC-A20's that I've seen on amazon are about half the price of the CBA V but there are no reviews on them and don't look like they would be very accurate.
 
Thank you Horsefly, this is a really good point!

Jenny from Docan Power got back to me and asked if I have tested the cells with either an EBC-A40L or EBC-A20 battery tester and generated a graph. I am actually looking unto buying a CBA V Pro like what Will uses to test battery capacities, minus the amplifier. For a little over $200 I would be able to test my batteries very accurately (over 99% accuracy) and like horsefly said, be able to assemble matched packs. Only bummer is the max draw is 200 watts. But then again, testing each cell individually this would still be around a .22 C rate.

I looked into the EBC-A40L on amazon and they are over $300 without many reviews, the EBC-A20's that I've seen on amazon are about half the price of the CBA V but there are no reviews on them and don't look like they would be very accurate.
I don't have the EBC, but I will say that I reluctantly got a battery tester, and thought it was expensive for something I would only use once, but I end up using it all the time. I can use it to test the ratings of power supplies, usb chargers, alkalines, and my vape batteries.

I would definitely recommend getting a tester, it's a cool gadget to have around.
 
A strange phenomenon I've noticed with this battery is that when charging is almost done (around 98% capacity) and voltage starts rapidly climbing up through 13.8 and beyond, voltage on cell #3 is about 30 to 40+ millivolts higher than the others (cells 1,2 & 4 remain pretty close).

Once the voltage cutoff is reached and things settle down, the cells are all very close in voltage. However as soon as it starts discharging same thing happens, cell #3 much higher volt than the others.

So, what I am trying is rapidly charging from 98% to full, then discharging back to 98% and repeating over and over to allow BMS to balance that one cell. Hopefully they will all reach voltage cutoff at same time eventually.

Strange as I top balanced this pack initially.
 
I don't have the EBC, but I will say that I reluctantly got a battery tester, and thought it was expensive for something I would only use once, but I end up using it all the time. I can use it to test the ratings of power supplies, usb chargers, alkalines, and my vape batteries.

I would definitely recommend getting a tester, it's a cool gadget to have around.
Oh that's good to know :)

Yes and I've seen it can also be used to test power supplies and solar panels too
 
Get the little fan tester from amazon its more accurate than the victron shunt, I have the 500A.
 
A strange phenomenon I've noticed with this battery is that when charging is almost done (around 98% capacity) and voltage starts rapidly climbing up through 13.8 and beyond, voltage on cell #3 is about 30 to 40+ millivolts higher than the others (cells 1,2 & 4 remain pretty close).

Once the voltage cutoff is reached and things settle down, the cells are all very close in voltage. However as soon as it starts discharging same thing happens, cell #3 much higher volt than the others.

So, what I am trying is rapidly charging from 98% to full, then discharging back to 98% and repeating over and over to allow BMS to balance that one cell. Hopefully they will all reach voltage cutoff at same time eventually.

Strange as I top balanced this pack initially.
Instead of charging fast, trickle charge it (<20w) so that #3 is always balancing and not climbing in voltage, this will allow the other cells to “catch up”.

That or try and bleed off cell 3 with a resistor.
 
Instead of charging fast, trickle charge it (<20w) so that #3 is always balancing and not climbing in voltage, this will allow the other cells to “catch up”.

That or try and bleed off cell 3 with a resistor.
Hi! Yes I actually ordered a 6ohm resistor and wired it up with some alligator clips and have successfully used it to bleed off some power from the cell.

What I've noticed is I the more I let the battery sit at the top of its charge, the less meaningful individual cell voltages become. It helps if I discharge it to 80% or 90% then start another charge cycle, making note of which cells are high. Then, I can apply the resistor to those cells for like 2 minutes each and repeat the process. It is working well.

My theory here is that the cells are not matched at all so even though I top balanced them very well, all that did is get them all to 100% capacity. Which, with differing capacities means when you charge back up from a discharge some cells have a head start vs others so they reach their cut off voltages at different times, thus requiring me to bleed off excess energy from some cells. I guess this is kind of like a bottom balance?
 
Get the little fan tester from amazon its more accurate than the victron shunt, I have the 500A.
I may try that, but I have a feeling the victron shunt is going to be much more accurate than a little Chinese fan tester. After all, the little fan tester itself utilizes a shunt to measure current as well.

I am now using an EBC-A20H battery load tester to test each cell by itself. The first one from my better functioning pack tested at 285ah so I will keep at it and update here.

I have a feeling the BMS itself, combined with all the connections of an assembled pack, has more energy wasted than one would think vs testing individual cells.
 
My theory here is that the cells are not matched at all so even though I top balanced them very well, all that did is get them all to 100% capacity. Which, with differing capacities means when you charge back up from a discharge some cells have a head start vs others so they reach their cut off voltages at different times, thus requiring me to bleed off excess energy from some cells.
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.
 
My theory here is that the cells are not matched at all so even though I top balanced them very well, all that did is get them all to 100% capacity. Which, with differing capacities means when you charge back up from a discharge some cells have a head start vs others so they reach their cut off voltages at different times, thus requiring me to bleed off excess energy from some cells.
That is correct, that a top balanced pack is not matched. I saw a good example that explains the difference between top balance and bottom balance with cells of different capacities. Imagine had a group of sticks of varying length. the length is the capacity and bottom balancing is analogous to holding the sticks in your hand and taping them on a table until the bottoms all line up. The top will be uneven and the shortest stick will hit high voltage first and presumably trigger the BMS to shut down. The analogy also works with top balancing if you turn them over and line them all up at the top. Then the weakest cell will hit the bottom first and also trigger the BMS. Either way the capacity of the pack will be limited by the weakest cell.
I have not seen any evidence that a top balanced pack will not remain balanced at the top as long as you do not disturb that balance by over discharging. Just like the group of sticks of uneven length, the cells which are different capacities can never be considered matched. In my mind, matched means equal capacities under similar tests.
 
I may try that, but I have a feeling the victron shunt is going to be much more accurate than a little Chinese fan tester. After all, the little fan tester itself utilizes a shunt to measure current as well.

I am now using an EBC-A20H battery load tester to test each cell by itself. The first one from my better functioning pack tested at 285ah so I will keep at it and update here.

I have a feeling the BMS itself, combined with all the connections of an assembled pack, has more energy wasted than one would think vs testing individual cells.
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
 
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This is the one I have it has v-sense wires:


my main wires are 12 guage and the v-sense wires are 24 guage futaba servo wires.

I don't think you can beat it for the price.
 
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