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sjfotos
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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 6:16 am

Hello Mesuge,
Yes, I agree with you on your recommended strategy to Nissan. I think they would be better served to be more forthcoming and more conservative in their claims. I am not at all sure about the GM strategy. I just do not know enough about the variables they are dealing with and the choices they are making in the Volt.

I do think that the Volt rollout is far less sophisticated than the Leaf. The detail in the placement of the vehicles, the number of journalists who have actually driven the car, and the appearance of a vehicle with production values in fit and finish show a much better prepared organization. I am thinking that this will be reflected in the 'choice' of initial buyers by Nissan and additional data before December on battery and range values. I hope I am not proved wrong!
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evnow
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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 6:56 am

100 is the magic number. Go below 100, you won't get that many interested.

If you want 100 miles of hard-driving highway range, it will cost more.

There is no free lunch.
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Rat
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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 2:26 pm

Can battery life can be stretched by charging less often? I'm retired and seldom put in more than 10 miles a day. For longer trips I can swap cars with my wife anyway and she drives less than I do. I could go ten days (in theory) between charging, although of course I wouldn't cut it that close unless I was well under 100 miles in that period. But my question is, is that the best way to charge a battery to preserve life? Does it degrade a battery more to charge up from 90% to 100% 10 times or to go from 0% to 100% one time? Something in between? Jess, can you answer that?
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KarenRei
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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 4:14 pm

Rat wrote:Can battery life can be stretched by charging less often? I'm retired and seldom put in more than 10 miles a day. For longer trips I can swap cars with my wife anyway and she drives less than I do. I could go ten days (in theory) between charging, although of course I wouldn't cut it that close unless I was well under 100 miles in that period. But my question is, is that the best way to charge a battery to preserve life? Does it degrade a battery more to charge up from 90% to 100% 10 times or to go from 0% to 100% one time? Something in between? Jess, can you answer that?
Avoid running it down to 0% as much as you can; li-ion has no "memory", like ni-cd. Optimally, most li-ion EVs prefer to have as shallow of cycles as possible usually hovering somewhere around 60% charge. Most of the damage, however, is done at the very upper and lower ends of the charge range (near 100% charge and 0% charge, respectively). The far upper and lower ends are usually capped off, and what remains is known as the "depth of discharge". Sometimes the lower end isn't totally blocked from usage, but is left as an "emergency reserve". Given the numbers Nissan has provided, it will have a very high depth of discharge.

Basically, to sum up: Charge whenever you get the chance. It won't make a big difference, but if you're super-concerned, stop charging when you have enough charge that going half the distance you usually go in a day would bring you down to 60%. But really, it won't be worth bothering.

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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 4:34 pm

KarenRei wrote:Given the numbers Nissan has provided, it will have a very high depth of discharge.
IIRC, Nissan will use 21.4kwh of the 24kwh (about 90%).
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garygid
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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 6:49 pm

I thought I heard 90% to 10%, but I think 96% to 8% might be relatively easy to do and still have good battery life.
Remember, a series (of cells) battery pack is only as good as its weakest cell.

The Leaf's LiMnO battery chemistry could easily have different limitations, but Nissan has had considerable experience with using it, I believe.
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evnow
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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 7:28 pm

garygid wrote:Remember, a series (of cells) battery pack is only as good as its weakest cell.
Hmmm .... why ?

Except if the cell becomes open ... (or resistence becomes very high)
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garygid
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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 8:34 pm

When the "weakest" series cell starts to get fully discharged, it can get totally ruined by continued "discharging" - which looks like reverse charging to it.
Also, the cell, unless switched out of the series, will likely look like a resistor, dropping the pack voltage quite significantly, and generating a lot of heat.

So, by continuing to operate, the "weak" cell gets weaker, ... and dies.
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evnow
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Re: Battery endurance for every day commuting

Mon Apr 26, 2010 8:41 pm

When the full charge voltage of a cell drops, is that also because of increased internal resistence ?
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KarenRei
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Re: Battery endurance for every day commuting

Tue Apr 27, 2010 12:36 am

garygid wrote:When the "weakest" series cell starts to get fully discharged, it can get totally ruined by continued "discharging" - which looks like reverse charging to it.
Also, the cell, unless switched out of the series, will likely look like a resistor, dropping the pack voltage quite significantly, and generating a lot of heat.

So, by continuing to operate, the "weak" cell gets weaker, ... and dies.
Yeah, Tesla had a pretty good approach to deal with that -- the hybrid series/parallel "brick" approach. Each brick is made of a ton of cells in parallel. The bricks are then linked up in series to form sheets, and the sheets in series for the total voltage. You could outright rip out several cells from a brick and it'll still function mostly normally. Of course, they pay for that approach in terms of assembly complexity due to the large number of cells.

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