JRP3
Posts: 395
Joined: Sat Feb 26, 2011 12:04 pm
Delivery Date: 26 Jun 2015
Contact: Website

Re: Leaf Range in Colder Weather

Mon Mar 14, 2011 10:45 am

Balancing a SE/CALB cell at 3.4 is not going to be as accurate as doing so at 3.5 because the voltage is not as directly representative of SOC at 3.4. Real world my cells will take a good amount of charge at 3.4, meaning that I can have two cells both showing 3.4V but at different SOC. At 3.5V the cells will not stay at that voltage while taking more charge for very long. The further you get into the curve the more accurately voltage represents SOC. So yes you can balance cells at lower voltages but it will not be as accurate as going to higher voltages in the steeper part of the curve.

AndyH
Posts: 6383
Joined: Fri Apr 23, 2010 3:43 pm
Location: San Antonio

Re: Leaf Range in Colder Weather

Mon Mar 14, 2011 4:11 pm

Thanks for the confirmation. ;) The good news is that the Leaf doesn't use LiFePO4. It might be better to move the CALB stuff to another thread.

The fact remains that lithium - and especially LiMn and LiCo - can be capacity balanced throughout the entire charge/discharge curve because of the sloped curve. This means that the Leaf doesn't have to wait to balance until the end of charge and comments about waiting until 80+ percent are irrelevant.

JRP3
Posts: 395
Joined: Sat Feb 26, 2011 12:04 pm
Delivery Date: 26 Jun 2015
Contact: Website

Re: Leaf Range in Colder Weather

Tue Mar 15, 2011 5:34 am

AndyH wrote:Thanks for the confirmation. ;) The good news is that the Leaf doesn't use LiFePO4. It might be better to move the CALB stuff to another thread.

The fact remains that lithium - and especially LiMn and LiCo - can be capacity balanced throughout the entire charge/discharge curve because of the sloped curve. This means that the Leaf doesn't have to wait to balance until the end of charge and comments about waiting until 80+ percent are irrelevant.

I'm not sure I confirmed what you are suggesting. The point is that with LiFePO4 you really aren't doing much balancing at 3.4V since SOC can still differ. You need to get further into the end of the charge curve. Balancing is getting cells to the same SOC. Since 3.4V is not accurately representative of SOC at that point you aren't really balancing. They may get closer but it may not be close enough.
What you suggest about the LiMn LEAF pack having a steeper curve may be true, but I have yet to see a charge curve for the LEAF pack.
I'm not the only one questioning your assertion: http://www.mynissanleaf.com/viewtopic.php?f=27&t=2746&p=69018#p69018
Finally, 80% charging is not really at 80% SOC since Nissan limits the usable size of the pack. Charging at "80%" may actually be charging at closer to 70% since the full pack capacity is not accessed.

AndyH
Posts: 6383
Joined: Fri Apr 23, 2010 3:43 pm
Location: San Antonio

Re: Leaf Range in Colder Weather

Tue Mar 15, 2011 6:46 am

One can absolutely balance at 3.4V because I've done it. Works just as well and just as consistently as balancing at 3.6V, which I've also done (hmmm...and am doing right now. My bike is getting topped off at 3.6V per cell, and my solar storage pack is being balanced at 3.7V.)

Again - the Leaf is not a LiFePO4 vehicle so NONE of this applies!

Voltage is a second order indicator of SOC. And because of the relatively flat charge/discharge curve of some members of the lithium family, it's more difficult to positively track SOC until reaching one of the ends. But that's one of the main reasons manufacturers are using LiMn (aside from the price...) -- because the sloped charge/discharge curve provides an easy way to track SOC throughout the cycle.

Did you order a Leaf, JRP?

JRP3
Posts: 395
Joined: Sat Feb 26, 2011 12:04 pm
Delivery Date: 26 Jun 2015
Contact: Website

Re: Leaf Range in Colder Weather

Tue Mar 15, 2011 10:52 am

No, I'm sticking with my converted Fiero for now. It does what I need and I spent too much time working on it to give it up. Also, unlike the LEAF, it's available in my area ;)

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