ldallan
Posts: 37
Joined: Mon Jan 16, 2017 10:15 am
Delivery Date: 31 Dec 2016
Leaf Number: 000000
Location: Colorado Springs, CO

How often to "Cell Balance"? Weekly? Monthly? Depends?

Wed Feb 06, 2019 5:06 pm

>> http://www.mynissanleaf.com/viewtopic.p ... 77#p541248
Point of fact, you should be charging to 100% roughly once a week, just don't let it sit for too long at a high state of charge - drive it.

I'm wondering what "best practice" is for how often to "cell balance" with relatively newer Leafs from 2015 to the present, including those with Lizard batteries.

I've read the lengthy thread "Cell Balancing 101" http://www.mynissanleaf.com/viewtopic.p ... ll+balance
but that's an older thread from 2011 - 2012.

I've been "cell balancing" my 2015 'S' about monthly. 40k miles, about 14,000 miles per year. 2 or 3+ L2 charges per week (typically to about 85% to 90%). 12 health bars remaining.

I use the ChargePoint L2 station and their smart-phone app for cell balancing. That app provides a handy graph of kW/hr rate delivered every 5 minutes.

I can observe the charge rate ...
  • being about 6.5+ kW/hr under 90% SOC
  • dropping off gradually to 3 kW/hr or less at about 95% SOC,
  • then zero charge rate at 100% SOC, I interpret that as "unbalanced 100% SOC"
  • then three or so cycles of low charging rate to no charging
  • I interpret that as "cell balancing".
  • That takes 3 to 4 hours, depending on the starting SOC.
Last edited by ldallan on Sun Feb 10, 2019 6:26 am, edited 1 time in total.
2015 Leaf S. Bought 2 year lease turn-in with 14,500 miles. Drive about 14k miles/year. Most charging from 'free juice' at nearby ChargePoint or Nissan or other free L2 public chargers within walking distance. ICE is rarely driven pickup truck.

LeftieBiker
Moderator
Posts: 11294
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 30 Apr 2018
Location: Upstate New York, US

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Wed Feb 06, 2019 5:26 pm

Monthly is good, obviously, although I'd consider it near the infrequent end of good. Once a week is probably the most often anyone would need to do it. Thanks for the data points.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

specialgreen
Posts: 227
Joined: Sun Mar 26, 2017 1:21 pm
Delivery Date: 26 Mar 2017
Location: Minnesota

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Thu Feb 07, 2019 1:33 pm

On a related question, it sounds to me like "cell balancing" is wasting energy. When the charge is "tapering," has anyone guesstimated what % of electricity actually gets stored in the battery? I was considering programming my EVSE to stop charging when the taper starts, except on days when I want to balance.
Last edited by specialgreen on Thu Feb 07, 2019 1:45 pm, edited 1 time in total.

LeftieBiker
Moderator
Posts: 11294
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 30 Apr 2018
Location: Upstate New York, US

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Thu Feb 07, 2019 1:38 pm

specialgreen wrote:On a related question, it sounds to me like "cell balancing" is wasting energy. When the charge is "tapering," has anyone guesstimated what % of electricity actually gets stored in the battery? I was considering programming my EVSE to stop charging when the taper starts.


I'm inclined to disagree. During balancing the charger goes off and on repeatedly, letting the cells absorb power slowly. Do you mean the cooling system for the charger running? That may waste a little, but A: I'm not sure it still runs while balancing, and B: balancing doesn't take long, usually. So if you count any extra loss as "waste" then I guess it does. If you figure keeping the pack as efficient as possible to be worth the extra power, then I wouldn't call it a waste...
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

specialgreen
Posts: 227
Joined: Sun Mar 26, 2017 1:21 pm
Delivery Date: 26 Mar 2017
Location: Minnesota

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Thu Feb 07, 2019 1:48 pm

I thought that during balancing, some of the cells are "shunted". What does that mean? I imagined that some current for/from that cell was being discharged through a resistor to ground so that those cells don't overcharge. Reading https://aip.scitation.org/doi/pdf/10.1063/1.4958529

when [the shunt resistor] is in the ON condition, current flows through the shunt resistor, which converts some current into heat and reduces the current which flows to the negative terminal. Reduction of the output voltage is the result"
[sic]

I don't know if the shunted energy is a trivial amount, or if shunting happens outside of charging (maybe it happens all the time).

DaveinOlyWA
Posts: 13698
Joined: Sat Apr 24, 2010 7:43 pm
Delivery Date: 16 Feb 2018
Leaf Number: 314199
Location: Olympia, WA
Contact: Website

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Fri Feb 08, 2019 8:15 am

Generalizing, I would do it every time your expected needs will be 50% of your driving range. I found that frequent cell balancing worked on 24 kwh LEAFs but saw no evidence of anything on 30 (occasionally saw some but not enough variance to say anything really happened) and 40 kwh LEAFs. In fact, my 40 kwh LEAF seems to run on different parameters almost daily.

I charged to 100% 3 days of 5 and each one showed different SOC, Kwh available, and GID count. The variance was well beyond normal fluctuations and did an "up down up"
2011 SL; 44,598 miles. 2013 S; 44,840 miles.2016 S30 deceased. 29,413 miles. 2018 S40; 15,000 miles, 478 GIDs, 37.0 kwh 109.81 Ahr , SOH 94.61, Hx 120.15
My Blog; http://daveinolywa.blogspot.com" onclick="window.open(this.href);return false;

LeftieBiker
Moderator
Posts: 11294
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 30 Apr 2018
Location: Upstate New York, US

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Fri Feb 08, 2019 2:13 pm

I honestly don't know how much power the shunt resistors 'waste,' but given the amount of time they run, the fact that they are only converting power from the highest-SOC cells to heat, etc, I'd say it isn't much. Some balancing algorithms just switch the higher cells out of the circuit, allowing the lower-SOC cells to 'catch up'.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

ldallan
Posts: 37
Joined: Mon Jan 16, 2017 10:15 am
Delivery Date: 31 Dec 2016
Leaf Number: 000000
Location: Colorado Springs, CO

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Sat Feb 09, 2019 7:38 am

LeftieBiker wrote:Monthly is good, obviously, although I'd consider it near the infrequent end of good. Once a week is probably the most often anyone would need to do it.
Thanks for the feedback (and also thx to the other replies)
Thanks for the data points.

And thanks for your time and effort put into moderating the forum. It's MUCH appreciated. I've learned a lot from you (and others).
2015 Leaf S. Bought 2 year lease turn-in with 14,500 miles. Drive about 14k miles/year. Most charging from 'free juice' at nearby ChargePoint or Nissan or other free L2 public chargers within walking distance. ICE is rarely driven pickup truck.

WetEV
Posts: 2666
Joined: Fri May 04, 2012 8:25 am
Delivery Date: 16 Feb 2014
Location: Near Seattle, WA

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Sat Feb 09, 2019 8:23 am

Shunt resisters are 430 ohm across each set of cells. When shunting they draw V^2/R power, or roughly 16/430 or 40 mW each. There are 96 sets of cells, so if all but one was active, total power would be about 3.5 watts.
WetEV
#49
Most everything around here is wet during the rainy season. And the rainy season is long.
2012 Leaf SL Red (Totaled)
2014 Leaf SL Red

flydiver
Posts: 42
Joined: Sun Mar 11, 2018 9:14 am
Delivery Date: 20 Mar 2018
Leaf Number: 337789
Location: Seattle, WA

Re: How often to "Cell Balance"? Weekly? Monthly? Depends?

Sat Feb 09, 2019 8:58 am

WetEV wrote:Shunt resisters are 430 ohm across each set of cells. When shunting they draw V^2/R power, or roughly 16/430 or 40 mW each. There are 96 sets of cells, so if all but one was active, total power would be about 3.5 watts.


You did that in your head, right? :shock:

Return to “Batteries & Charging”