taper on fast charger when at high SOC

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rawlins02

Well-known member
Joined
Jan 29, 2017
Messages
99
Location
southern Delaware
I've had my 2014 Leaf S for just over 2 months. Yesterday I used a fast charger for first time on an extended road trip. I was very surprised at how slow the rate of charge became after SOC reached about 75%. I started at around 25% and noticed I was gaining about 1% every minute or two. Went for a walk. 40 minutes later it had reached 78%. I noticed what I think was a rate of charge displayed on the machine. The value was decreasing, and I think it said 2 kW, down from 5 kW. I see from posts here and elsewhere that tapering is normal. After one hour the charge was at 87%. I get the feeling that level 2 charging at 6.6 kW is a better option at high SOC, in times when we need close to 100%. On a level 2 I can go from 40% to 100% in just over 2.5 hours. I wouldn't normally charge to 100%, but yesterday I was driving over 100 miles and really could have used the full charge. I may have been able to get the 70 miles to home, without having to charge again, if I could have fast charged to 100% on the fast charger.

So.....does it make sense to avoid trying to get above 80-85% on fast charge? Or am I missing something?

Good news is I'm getting around 70 miles on my 2014 S on highway driving (60-65 MPH) in 40 degree weather. Averaging about 4 mi/kWh. I think my battery can hold about 20 kWh.
 
How cold was it when you were charging? I forgot the numbers, but the owners manual states that a quick charge is 30 minutes on a comfortable day. It can be 90+ minutes if you get very far away from ideal temperatures.

Edit: also, quick charging above 80% is contraindicated in the manual as well, at least for the 2017 model.
 
BenTheRighteous said:
How cold was it when you were charging? I forgot the numbers, but the owners manual states that a quick charge is 30 minutes on a comfortable day. It can be 90+ minutes if you get very far away from ideal temperatures.

Edit: also, quick charging above 80% is contraindicated in the manual as well, at least for the 2017 model.


OK I see fast charging is recommended up to 80%. Air temperature was 43F at the time.
 
Charge rate at high SOC really depends upon battery internal resistance. Therefore, cold temperatures and battery degradation both tend to reduce the charge rate. My 2015 will charge at rates equal to the L2 rate as it approaches full charge in moderate temperatures so there is no benefit to switching to L2 as long as nobody is waiting for the DCQC. I suspect your 2014 is similar. DCQC charge rate on my 2011 really dropped off at high SOC due to the higher internal resistance of the older batteries.
 
GerryAZ said:
Charge rate at high SOC really depends upon battery internal resistance. Therefore, cold temperatures and battery degradation both tend to reduce the charge rate. My 2015 will charge at rates equal to the L2 rate as it approaches full charge in moderate temperatures so there is no benefit to switching to L2 as long as nobody is waiting for the DCQC. I suspect your 2014 is similar. DCQC charge rate on my 2011 really dropped off at I high SOC due to the higher internal resistance of the older batteries.

Good to know this. I will consider charging on DCQC above 80% if needed. I'll assume there's no harm and that the rate will be no slower than L2.

BTW - For the weekend trip I drove ~280 miles, mostly highway. A total of five charging sessions, four on L2 and one on fast charge. Of the five, four were free. 280 miles for $6 equals over 100 miles per gallon equivalent.
 
Here in Austin we only have three L3 DC quick-chargers in the metro area. One of them, at Town North Nissan, is perpetually blocked by a vehicle placed there by the dealership and has an out-of-order sign on it. *sigh* I don't know the status of the L3 charger in South Austin, but the other L3 DC quick-charger I know about is in the downtown area and usually working. As a new owner of a used 2011 Leaf I hadn't ever tested my quick-charge port so a month or so ago I gave it a brief test.

My SOC was around 70% when I pulled up to the charger, so it started pumping 27kW into my l'il Leaf. But the taper was immediate and after about 10 minutes the rate was down to around 9kW or less. I pulled the plug at 80%, satisfied that the QC port worked if I ever wanted to use it again. Here are the salacious details thanks to Leaf Spy Pro -

8z7q1Ht.png


Just an FYI, confirming what you saw & others also explained.
 
@Zapped That's an insightful chart. Good to know. I pulled the plug at SOC of 87% with an incoming rate of < 3 kW, based on the charging machine display.
 
Zapped said:
Here in Austin we only have three L3 DC quick-chargers in the metro area.

You seem sad about this, but I am jealous. We only have one L3 Chademo station in Louisiana and Mississippi states combined! Fortunately for me it is in New Orleans.
 
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