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Discussion Starter · #1 ·
Hi,

I have recently got hold of a few leaf cells, and am researching their charging.

With the lifepo4 cells I already have, I charge them to 3.5v and after charge they settle to around 3.33v.

I intend to charge the cells to 4.1v, that seems to be the general advice from what I have read, I will of course reduce this if advised to do so. The discharge will be cut off at around 3.3v.

What I would like to know is do the leaf cells settle after charge back to a resting voltage, and if yes, what kind of voltage do the settle at?

Also, is there a charge profile curve anywhere that I could download for reference.

Many thanks for your help and advice.:)

Anthony.
 

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I intend to charge the cells to 4.1v, that seems to be the general advice from what I have read, I will of course reduce this if advised to do so. The discharge will be cut off at around 3.3v.

What I would like to know is do the leaf cells settle after charge back to a resting voltage, and if yes, what kind of voltage do the settle at?
4.1 volts as the CV point and waiting until the current drops to C/40 results in a cell that is about 83% charged. A cell so charged settles down to about 4.07 volts. Since you probably will charge less than this your pack will be less charged and the resting settle will be a little more. I would charge to 4.15 volts (it will settle to about 4.12 volts) and then you get about 90% SOC. But if you don't need that extra 7% of range by all means stop at 4.10. But it appears to be harder on the cells when you go closer to the bottom than charging to the top.

Best Wishes!
 

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Doug, do you think my discharge cut off at 3.3v is conservative, or ok. Again, thank you.

Anthony.
At normal temperatures and currents this will be fine. If the batteries are cold then this will be far too high a cutoff. Resting voltage of 3.3 is pretty much a dead battery for this kind of cell.
 

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Hope the formatting stays. Here is what Nissan does in their Leafs:
SOC Pack Vltge Cell Voltage
100% 393.6 4.1
95% 391.2 4.075
90% 388.8 4.05
80% 384 4
65% 376.8 3.925
50% 369.6 3.85
30% 360 3.75
20% 355.2 3.7
15% 352.8 3.675
10% 350.4 3.65
7% 348.96 3.635
0% 345.6 3.6

Nominal Voltage is 3.75 V
Low Battery Warning is at 3.69V
Very Low Battery Warning is 3.64V
Turtle ( Can't drive the car anymore) is 3V

My thinking is simple. If Nissan doesn't recommend going down to 0%SOC, I wouldn't go below that (3.6V)
I charge to 95%SOC which is 4.075V
I typically drive down to 30%SOC - 3.7V
Can I charge above 4.1V, yes, but the lifecycle of the cells goes down. Same thing applies going down below 0%SOC.
Based on my experience, below 3.7v, Voltage starts to drop exponentially.
 

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Discussion Starter · #8 ·
Hi 67GTEV,

that is absolutely great informtion there you have just provided, mny thanks for sharng that with us.

I shall now move my cell paramaeters alittle to help protect them more.

Thank you.

Hope the formatting stays. Here is what Nissan does in their Leafs:
SOC Pack Vltge Cell Voltage
100% 393.6 4.1
95% 391.2 4.075
90% 388.8 4.05
80% 384 4
65% 376.8 3.925
50% 369.6 3.85
30% 360 3.75
20% 355.2 3.7
15% 352.8 3.675
10% 350.4 3.65
7% 348.96 3.635
0% 345.6 3.6

Nominal Voltage is 3.75 V
Low Battery Warning is at 3.69V
Very Low Battery Warning is 3.64V
Turtle ( Can't drive the car anymore) is 3V

My thinking is simple. If Nissan doesn't recommend going down to 0%SOC, I wouldn't go below that (3.6V)
I charge to 95%SOC which is 4.075V
I typically drive down to 30%SOC - 3.7V
Can I charge above 4.1V, yes, but the lifecycle of the cells goes down. Same thing applies going down below 0%SOC.
Based on my experience, below 3.7v, Voltage starts to drop exponentially.
 

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So, if I have 14 of these in a pack, would I set my charger to 116.2V then, or does the charging voltage need to be higher to charge them? ((4.15V x 2 per cell)= 8.3V x 14 = 116.2V)
Unlike with LiFePo4 cells you don't set the CV point above the point you want to charge to. You set the charger CV point to the terminal voltage you want to charge to so in this case 116.2 volts. When the pack reaches this point the charger changes to the constant voltage mode. You can pretty much leave it at this point forever. Typically the charger will shut off when the current has reduced to C/5. C refers to the capacity of the battery in AH. If you have a 90 AH battery C/5 would be 18 amps. If your charger does not even go to 18 amps then the charger would cut off as soon as the voltage reaches the set point. When doing a balance charge on my RC packs I do a C/40 termination. There is not a lot of difference in the state of charge between a C/5 and a C/20 charge because the charge current is reducing quickly in this phase.
 

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Discussion Starter · #11 ·
Hi Doug,

I left my zivan ng3 charger unchanged from the ifepo4 pack I just changed from.

I changed cell parameters to 4.05 and 3.6v.

When the charge was nearly finished ( still set the the old lifepo4 set point) the charger had ramped down from 15 amps at the start of the charge to 4 amps and slowly topping up the charge, at this point the cell voltages were around 4.03v per cell.

I'm quite ok with that set up now, so I'll set th charge cut off when any cell reaches 4.03v, I will know then that th charger was ramping down to very little output at this point anyway.

Thanks all for your help with this, it's much appreciated.

I'll put some pics on later of the leaf cells in the Prius phev conversion. I've got 32 cells in series, I will though after looking at it may have to take out 1 cell as the target voltage is higher than I would like, but it was only the first charge, so so,e tinkering still to do to get to the optimum level.

Anthony.
 

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I am hoping to get 10 Nissan Leaf Modules for Erider Electric motorbike. The TC charger for the original 24 LiFePO4 cells has max voltage of 87.6V. The maximum voltage for charging 10 Nissan leaf modules in series in 84V. I was planning to use a MiniBMS with relay which should cut the AC to the charger once one cell reaches HVC 4.2V. Is there likely to be any problems with using the TC charge to charge Nissan Cells?
Thanks for your input.
 

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Discussion Starter · #13 ·
Hi,

im no expert but using that charger should be ok, but mke sure you dont overcharge the cells.

The nissan leaf cells when fitted to the leaf when i monotor them dont let the cells go beyond 4.15v, I charged mine in the prius phev to 4.1v max but more often to 4.05v

So, if i were in your shoes i wouldnt let the charger get beyond 82v which is 4.1v per cell.

Thanks.
 

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I use a TC charger to charge my 26 Leaf modules, piloted by an Orion BMS. I always charge at 4.1 volts max. If the Orion BMS cannot maintain any of the cell at max 4.1 while balancing, then the charger stops. So it's not based on average pack voltage.
 
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