k226e01 Battery's

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Dean Williams
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k226e01 Battery's

Post by Dean Williams »

Hello all

i acquired a bucket load of these battery's some time ago.

I have been running my home with these and a few solar panels.

Now I'm working though the battery packs that didn't charge up or were damaged
the idea is hopefully use them in a motor bike.

now my questions
manufactures website says 2.5V to 3.65 19 ohms
http://liionbms.com/pdf/k2/LFP26650EV.pdf.

so i have a variable power supply and have just gotten a load tester.

Given that the battery capacity is 10.2Wh as written on the cell itself

what amperage should i set the capacity tester?

and how do I interpret " internal impedance @ 1 Khz AC MOhms 19

or is that meaning some thing totally different?
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Re: k226e01 Battery's

Post by coulomb »

Dean Williams wrote: Sun, 17 Jan 2021, 19:02 Now I'm working though the battery packs that didn't charge up or were damaged
the idea is hopefully use them in a motor bike.
I think you might have done better keeping the good ones for the motorcycle, and use the damaged ones in hour house energy system. In a vehicle, you want to discharge the battery over roughly 1 hour; in a house battery, over 12 or preferably 24 hours or more. So the currents are much more gentle in the house system.
what amperage should i set the capacity tester?
The datasheet tells you that the continuous discharge rate is 1C, or 3.2 A. I'd use about that if possible. Though if the test involves recharging, set the recharge current to 1.6 A if possible, or run the whole charge/discharge cycle at 1.6 A. Perhaps a little more (say 2.5 A) to shake out the bad ones quicker.
and how do I interpret " internal impedance @ 1 Khz AC MOhms 19
AC impedance is useless for most things. DC internal resistance is much more useful. They often quote AC impedance because it sounds better (i.e. it's a lower number).

Let me guess the DC internal resistance (when new) at 25 mΩ. That means that at the peak discharge current of 13 A (4C), you expect the voltage sag due to that load to be about 13 A × 25 mΩ ≅ 325 mV. So a cell at say 3.3 V no load would drop to some 2.97 V under peak load. You take this into account when working out what maximum power you can expect from the battery.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.
Dean Williams
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Re: k226e01 Battery's

Post by Dean Williams »

brilliant, thank you.
damaged or non charging packs. i have broken these down to individual cells. the packs were 10x4 cells. it seems that a bad pack seems to be only a bad row of 10 cells. or a corroded or melted BMS. I am charging to 2.6 with a cut off at 2.5 volts and am getting a constant correct of 7.4 Wh per cell. when pulling 1 amp. i was pulling 2 amps but the voltage would drop after 3Wh to 2.5 V and everything would shut down. but if i put the volt meter back on i had 2.9 volts. the current tester would start again but shortly shut down again showing 2.5 volts. so now i will try at 1.6 amps. charging starts at 1 amp 3.6V the amps drop to 0 and i have been taking this as being charged?? should i be setting the amps at 1.6 rather than letting it decide what it wants to do?? force ??
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Re: k226e01 Battery's

Post by coulomb »

Dean Williams wrote: Mon, 18 Jan 2021, 14:32 damaged or non charging packs.
Ah! My bad. But note that cells that come from a bad pack may have been damaged by staying too long at a low state of charge. Especially if the BMS has "melted".
I am charging to 2.6 with a cut off at 2.5 volts and am getting a constant correct of 7.4 Wh per cell.
I assume you mean charging up to 3.6 and down to 2.5 V for one cell. The datasheet shows 3.2 Ah and 3.2 V nominal, so that's 10.24 Ah. You are using a slightly narrower voltage range, so I'd expect lower capacity, but only slightly as there is extremely little energy above 3.60 V, and not much below 2.6 V. So I'd guess you should be getting something like 10.0 Ah if they were new. How old are these cells/packs?
i was pulling 2 amps but the voltage would drop after 3Wh to 2.5 V and everything would shut down. but if i put the volt meter back on i had 2.9 volts.
That's the effect of internal resistance. With a 2 A load, the terminal voltage is < 2.5 V, but with no load, 2.9 V. It's like you have an ideal cell in there with a ≈ 0.2 Ω resistor in series. The 0.4 V drop is across this internal "resistor".
so now i will try at 1.6 amps. charging starts at 1 amp 3.6V
Are you saying that the terminal voltage shoots up immediately to 3.60 V with the application of 1 amp? If so, what voltage did the cells start at?

It may be that the cells need a few gentle cycles to "wake them up", reduce their internal resistance, and return more reasonable capacity.
the amps drop to 0 and i have been taking this as being charged??
Yes. You may be suffering a little from the resolution of your cycling machine; maybe anything below 50 mA is rounded to 0 (0.05 A, only one decimal place of amperes shown).
should i be setting the amps at 1.6 rather than letting it decide what it wants to do?? force ??
I don't know how your battery cycling machine works. It sounds like it can limit either the voltage or the current, or probably both. I don't know if it has a way of compensating for internal resistance. For example, you might be able to tell it to assume an internal resistance of say 100 mΩ, and it will then compensate the terminal voltage. So for example, if you specify a limit of 3.60 V and 100 mΩ IR, it will allow the cells to go to 3.65 V when the current is still 0.5 A (V = I×R = 0.5×0.1 = 0.05 V extra). As the current falls to zero, the voltage limit will creep back to the given 3.60 V.

I think you should exercise them at a moderate current (say 1 A) to wake them up a bit, then see what current they will take that will cause the voltage rise or voltage sag to be reasonable, say 0.25 V. Use the internal resistance compensation if it has that feature. At that current and with IR compensation in effect, I'd hope to see at least 8 Ah from each cell.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.
Dean Williams
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Re: k226e01 Battery's

Post by Dean Williams »

coulomb wrote: Mon, 18 Jan 2021, 15:33
Dean Williams wrote: Mon, 18 Jan 2021, 14:32 damaged or non charging packs.
Ah! My bad. But note that cells that come from a bad pack may have been damaged by staying too long at a low state of charge. Especially if the BMS has "melted".
yes
I am charging to 2.6 with a cut off at 2.5 volts and am getting a constant correct of 7.4 Wh per cell.
I assume you mean charging up to 3.6 and down to 2.5 V for one cell. The datasheet shows 3.2 Ah and 3.2 V nominal, so that's 10.24 Ah. You are using a slightly narrower voltage range, so I'd expect lower capacity, but only slightly as there is extremely little energy above 3.60 V, and not much below 2.6 V. So I'd guess you should be getting something like 10.0 Ah if they were new. How old are these cells/packs?
correct, charging 3.6V and current cut off at 2.5 seems to be giving me 7.4 Wh i suspect that is ok as new battery is 3.65V to 2 V is 10.22 Wh. do i have my thinking correct?

i was pulling 2 amps but the voltage would drop after 3Wh to 2.5 V and everything would shut down. but if i put the volt meter back on i had 2.9 volts.
That's the effect of internal resistance. With a 2 A load, the terminal voltage is < 2.5 V, but with no load, 2.9 V. It's like you have an ideal cell in there with a ≈ 0.2 Ω resistor in series. The 0.4 V drop is across this internal "resistor".
Got it, just like a light bulb.
so now i will try at 1.6 amps. charging starts at 1 amp 3.6V
Are you saying that the terminal voltage shoots up immediately to 3.60 V with the application of 1 amp? If so, what voltage did the cells start at?



It may be that the cells need a few gentle cycles to "wake them up", reduce their internal resistance, and return more reasonable capacity.
the amps drop to 0 and i have been taking this as being charged??
Yes. You may be suffering a little from the resolution of your cycling machine; maybe anything below 50 mA is rounded to 0 (0.05 A, only one decimal place of amperes shown).
ok with a cell at 2.5V i connect a power supply set at 3.6V. the battery will immediately start pulling 1 amp. at 3 V this is about .7 amp. and yes at 0 amp or 0.05 amp i stop.
should i be setting the amps at 1.6 rather than letting it decide what it wants to do?? force ??
I don't know how your battery cycling machine works. It sounds like it can limit either the voltage or the current, or probably both. I don't know if it has a way of compensating for internal resistance. For example, you might be able to tell it to assume an internal resistance of say 100 mΩ, and it will then compensate the terminal voltage. So for example, if you specify a limit of 3.60 V and 100 mΩ IR, it will allow the cells to go to 3.65 V when the current is still 0.5 A (V = I×R = 0.5×0.1 = 0.05 V extra). As the current falls to zero, the voltage limit will creep back to the given 3.60 V.

I think you should exercise them at a moderate current (say 1 A) to wake them up a bit, then see what current they will take that will cause the voltage rise or voltage sag to be reasonable, say 0.25 V. Use the internal resistance compensation if it has that feature. At that current and with IR compensation in effect, I'd hope to see at least 8 Ah from each cell.
Ok think i get that. i do not have any internal resistance adjustments, but i can set voltage and amps. at ATM i have 3.6 volts charging. draining i have cut off at 2.5 V and 1 amp. any suggestions?

[ Edited Coulomb: fixed quoting. ]
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Re: k226e01 Battery's

Post by coulomb »

Dean Williams wrote: Mon, 18 Jan 2021, 15:49 correct, charging 3.6V and current cut off at 2.5 seems to be giving me 7.4 Wh i suspect that is ok as new battery is 3.65V to 2 V is 10.22 Wh. do i have my thinking correct?
Ah, yes. I thought their 3.2 Ah cut off at 2.5 V, but you're right it cuts off at 2.0 V. Even so, the difference it slight; I'd still expect some 9.8 Ah from a new cell and using the 3.6 / 2.5 voltage limits.
ok with a cell at 2.5V i connect a power supply set at 3.6V. the battery will immediately start pulling 1 amp. at 3 V this is about .7 amp. and yes at 0 amp or 0.05 amp i stop.
That sounds a lot better. Presumably with the above you had the current limit at 1.0 A.
Ok think i get that. i do not have any internal resistance adjustments, but i can set voltage and amps. at ATM i have 3.6 volts charging. draining i have cut off at 2.5 V and 1 amp. any suggestions?
No, just try a few cycles like that and see if the capacity improves any.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.
Dean Williams
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Re: k226e01 Battery's

Post by Dean Williams »

coulomb. you are brilliant.

it has actually been very hard to get real info on the internet.

i have about 2000 cells. in addition i have maybe a few hundred Makita battery packs, but that will be some time in the future.
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Re: k226e01 Battery's

Post by T1 Terry »

I would try cycling the cells between 3.8v and 2v for 2 cycles at the suggested 1.6 amp max charge/discharge rate.
This will wake up the cells and free up any sluggish tranfer of the lithium ions in and out of both the cathode and anode. We do this with higher capacity prismatic cells that have not been fully charged or cycled for an extended period and they generally come back up to the expected capacity. Then you can return to the safer 3.6v upper and 2.5v lower limit and see what the capacity is then, it should be much closer to the expected capacity.

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Re: k226e01 Battery's

Post by TyTower »

T1 Terry wrote: Tue, 19 Jan 2021, 10:17 I would try cycling the cells between 3.8v and 2v for 2 cycles at the suggested 1.6 amp max charge/discharge rate.
This will wake up the cells and free up any sluggish tranfer of the lithium ions in and out of both the cathode and anode. We do this with higher capacity prismatic cells that have not been fully charged or cycled for an extended period and they generally come back up to the expected capacity. Then you can return to the safer 3.6v upper and 2.5v lower limit and see what the capacity is then, it should be much closer to the expected capacity.T1 Terry
Don't want to be a pain Terry. This is meant in a nice way . Do you have any scientific evidence in any form to support this?
It has been my experience so far that there might be some improvement in the cell doing this ,in the case of prismatics at least, but very little supporting evidence I could find.

A uni video nearly 7 years or so old posted up by Ian George,"LiFePo Battery 101", mentioned the formation of a film on the cathode ,initially the SEI layer, which forms and then "sludges " up with ethelyene carbonate compounds which trap ions and take them out of the movement of ions either way over time . Its supposed to be irreversible. I'm keen to find out more if its known
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