evguy1369
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Battery pack voltages

Fri Aug 30, 2013 4:01 am

What is the max charge voltage and minimum voltage (discharge) to prevent damage to the battery pack.

stjohnh
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Re: Battery pack voltages

Fri Aug 30, 2013 8:52 am

Well, unfortunately I don't think there is a single answer to this question. Generally, the closer to 100% charge, the more degradation will occur, and the closer you get to 0% the same problem occurs. The pack is made of a bunch of modules (?96 if I remember correctly). "Pack damage" may occur if all cells degrade equally, but I don't think this is the usual situation. Usually one or more of the cells will degrade at a faster rate than others, and it is the weakest cell that determines the range of the car.

Turtle on my Leaf is about 3.000 v per cell, and below that almost certainly increases rate of degradation. That would be 3.000x96 cells=288 volts.
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GregH
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Re: Battery pack voltages

Fri Aug 30, 2013 9:28 am

On the high side usually 4.1V is the cut off for a "full" charge although I've seen 4.125 briefly. Technically you should be "ok" taking it as high as 4.2 or as low as 2.5 if done gently and for a short period of time.. although the Leaf won't let you do that so it's really a non-issue. "damage" is a grey area.. you will do more damage resting at 4.2V than at 4.1V.. you will do more damage at 4.1V than resting at 4.0V.

Best would be to leave the batteries at 3.6V at around 20 degrees C and don't drive the car :)
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surfingslovak
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Re: Battery pack voltages

Fri Aug 30, 2013 9:31 am

It looks like Greg has responded, but I already typed this post, so here it is. Please not that the small differences in voltage could be related to changes made in 2013. We have also seen some variation between vehicles.

---

Yes, it's 96 modules and 192 cells. Since the pack voltage is an aggregate, it can fluctuate a bit after each charge and discharge to turtle mode. The voltage on a full charge is 4.10 on cell basis or about 393.6V on the pack level. I recall seeing something higher than that on occasion, perhaps 0.5 or 1V extra on pack level. The turtle voltage is less clear, and some differences have been observed. I typically saw it around 3.20V on the cell level and 308V on the pack level. A lithium manganese oxide cell is considered to have reached its maximum energy slightly below 4.20V (4.17V are often used). Conversely, a fully discharged cell might reach 2.50V on the cell level. The LEAF does not cycle the cells fully and is reserving about 4 to 5% at the top and about 2% at the bottom.
Last edited by surfingslovak on Fri Aug 30, 2013 9:45 am, edited 2 times in total.

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TonyWilliams
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Re: Battery pack voltages

Fri Aug 30, 2013 9:34 am

surfingslovak wrote:Yes, it's 96 modules and 192 cells. Since the pack voltage is an aggregate, it can fluctuate a bit after each charge and discharge to turtle mode. The voltage on a full charge is 4.10 on cell basis or about 493.4V on the pack level. I recall seeing something higher than that on occasion, perhaps 0.5 or 1V extra on pack level.



96 cell pairs * 4.1 volts = 393.6 volts

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surfingslovak
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Re: Battery pack voltages

Fri Aug 30, 2013 9:45 am

TonyWilliams wrote:
surfingslovak wrote:Yes, it's 96 modules and 192 cells. Since the pack voltage is an aggregate, it can fluctuate a bit after each charge and discharge to turtle mode. The voltage on a full charge is 4.10 on cell basis or about 493.4V on the pack level. I recall seeing something higher than that on occasion, perhaps 0.5 or 1V extra on pack level.



96 cell pairs * 4.1 volts = 393.6 volts

Thanks for the correction, Tony. Yes, that was a typo, sorry about that. I fixed it to avoid confusion.

Stoaty
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Re: Battery pack voltages

Fri Aug 30, 2013 10:18 am

GregH wrote:Best would be to leave the batteries at 3.6V at around 20 degrees C and don't drive the car :)

What is the SOC at 3.6V? Do you have a reference about why this would be the best voltage to store the battery?
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GregH
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Re: Battery pack voltages

Fri Aug 30, 2013 10:28 am

Stoaty wrote:
GregH wrote:Best would be to leave the batteries at 3.6V at around 20 degrees C and don't drive the car :)

What is the SOC at 3.6V? Do you have a reference about why this would be the best voltage to store the battery?

On the Leaf 3.6V (345v) is pretty low SOC.. somewhere between LBC and VLBC? maybe 20% SOC? The differences between 3.6V and 3.8V in regard to battery longevity is probably not that big of a deal.. more important (by far) seems to be to keep it cool.
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surfingslovak
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Re: Battery pack voltages

Fri Aug 30, 2013 10:52 am

While lower voltages are generally better for storage, personally, I would not go under 20% SOC or the LBW in the extreme case. It also depends on how long the battery will be kept at this potential. A few hours, days, weeks or months. I'm on the go and unable to post the discharge graph from the LEAF battery pack presentation, but it matches what Greg said pretty well. Isn't the knee on the discharge curve somewhere between 340 to 350V?
Last edited by surfingslovak on Fri Aug 30, 2013 11:05 am, edited 1 time in total.

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RegGuheert
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Re: Battery pack voltages

Fri Aug 30, 2013 11:04 am

surfingslovak wrote:Yes, it's 96 modules and 192 cells.
There are 192 cells, but there are only 48 modules in the LEAF. Each module contains four cells, with two pairs of parallel cells in series.
RegGuheert
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