Reduction in Battery Charge Capacity?

[outerspace]

Anybody notice a reduction in the # miles predicted for 80% charge? I now have about 3500 miles on the car. I plug in pretty much every night. I let it charge to 100% about once/week. Once I drove it to zero on the dash, but it just kept going the remaining 4 miles home. Could this have damaged the battery so it no longer has the same capacity?

-Not a Battery Engineer

 

[daggad]

Anybody notice a reduction in the # miles predicted for 80% charge? I now have about 3500 miles on the car. I plug in pretty much every night. I let it charge to 100% about once/week. Once I drove it to zero on the dash, but it just kept going the remaining 4 miles home. Could this have damaged the battery so it no longer has the same capacity?

-Not a Battery Engineer

No. There is a hidden capacity in the battery and the Leaf will not let you go all the way down to 0% to avoid damage.

 

[edatoakrun]

http://www.mynissanleaf.com/viewtopic.php?f=31&t=6701" onclick="window.open(this.href);return false;

How's the weather been, lately?

 

[smkettner]

Drive the last 10 miles to home more economically.
The drive a new car cautiously has probably worn off.

 

[TangoKilo]

I charge to 100% all the time and don't bother with the timers. I have not noticed any battery degradation with 11,500 miles so far... :ugeek:

 

[outerspace]

Thanks for many responses, especially link to article emailed to me showing capacity decrease with temperature. Yes, it has been quite cold in Seattle the last couple weeks. I will just have to bump up to 100% charge soon. No problem! Better than buying diesel at $4.10/gal here now.

 

[LEAFfan]

Anybody notice a reduction in the # miles predicted for 80% charge? I now have about 3500 miles on the car. I plug in pretty much every night. I let it charge to 100% about once/week. Once I drove it to zero on the dash, but it just kept going the remaining 4 miles home. Could this have damaged the battery so it no longer has the same capacity?
-Not a Battery Engineer

You may want to make a copy of Tony W's range chart. Ignore the GOM and use your dash m/kW h number to figure out your range (x21 for 100% charge and x17 for an 80%). Remember, the colder battery pack doesn't affect your m/kW h;it's the denser air. I am not going to use my heater this winter so I bought two heated/massage cushions (Homedics/less than ten watts each) and so far, they are working great! If it gets really cold there, you may want the $20 dual heat cushions without massage.

 

[SeaAir]

Like outerspace we live in Seattle. Since the cold weather has hit we are getting 3.5 miles/kWh vs. 4.4 miles/kWh during the summer. The LEAF is garaged overnight so it does not get as cold as it could, but it cools down during the day sitting outside at work. What was a comfortable distance during the summer at 80% is now a little bit tight.

W

 

[GaslessInSeattle]

Like outerspace we live in Seattle. Since the cold weather has hit we are getting 3.5 miles/kWh vs. 4.4 miles/kWh during the summer. The LEAF is garaged overnight so it does not get as cold as it could, but it cools down during the day sitting outside at work. What was a comfortable distance during the summer at 80% is now a little bit tight.

W

We are seeing the same thing.

 

[klapauzius]

Yes, I can confirm that too.

 

[TickTock]

Anybody notice a reduction in the # miles predicted for 80% charge? I now have about 3500 miles on the car. I plug in pretty much every night. I let it charge to 100% about once/week. Once I drove it to zero on the dash, but it just kept going the remaining 4 miles home. Could this have damaged the battery so it no longer has the same capacity?

-Not a Battery Engineer

No. There is a hidden capacity in the battery and the Leaf will not let you go all the way down to 0% to avoid damage.

It doesn't appear so much that there is a hidden reserve, but that Nissan matches the cells very carefully to avoid damage when fully discharged. In the thread below, you can see that the LBW comes right at the knee and you are below the knee by the time you get the VLBW. If the batteries were not matched, you would start to degrade some of the cells.

http://www.mynissanleaf.com/viewtopic.php?f=31&t=6116&start=79

 

[LEAFfan]

It doesn't appear so much that there is a hidden reserve

When I talked to the QC techs at ECOtality, they told me that Nissan told them that the battery pack was 28.8kW hs. They also said there is more hidden than what we LEAF drivers believed and Nissan will not allow us to damage the pack. So even though the SOC gauge may say 1 or 2% at turtle, there is much more really left so as to not damage the battery pack. And when the SOC gauge says 100%, I guarantee you that the battery pack still has much left. When I did a 100% QC charge and my gauge showed 97%, I only had 19kW hs to use.

 

[TickTock]

It doesn't appear so much that there is a hidden reserve

When I talked to the QC techs at ECOtality, they told me that Nissan told them that the battery pack was 28.8kW hs. They also said there is more hidden than what we LEAF drivers believed and Nissan will not allow us to damage the pack. So even though the SOC gauge may say 1 or 2% at turtle, there is much more really left so as to not damage the battery pack. And when the SOC gauge says 100%, I guarantee you that the battery pack still has much left. When I did a 100% QC charge and my gauge showed 97%, I only had 19kW hs to use.

Maybe they have room on the top end, but the discharge curve clearly indicates you are at the bottom when you get VLBW.
The danger of over discharge comes from when you have a long string in series (like the Leaf). Your weakest cell will over-discharge while the rest are still reasonably strong resulting in that cell deteriorating even further. However, since we know the battery controller does have access to the voltage across every cell, it is a fair assumption that it will not let you over discharge any cell. There are quite a few here who can attest to many near-death trips with no noticeable reduction in capacity.

 

[planet4ever]

In the thread below, you can see that the LBW comes right at the knee and you are below the knee by the time you get the VLBW.
http://www.mynissanleaf.com/viewtopic.php?f=31&t=6116&start=79

That's strange. As I look at that graph it seems to be telling me that LBW is well above the knee, and VLBW is just below the knee. The slope doesn't seem to change significantly until about 80% or 85% through the time from LBW to VLBW. I had seen this before, and it was the basis of my advice to myself and others that driving past LBW is no problem, but you should avoid driving past VLBW when possible.

Can you explain your comment further?

Ray

 

[jkirkebo]

When I talked to the QC techs at ECOtality, they told me that Nissan told them that the battery pack was 28.8kW hs.

That doesn't make any sense, we know the specs on the battery cells and modules:

http://www.eco-aesc-lb.com/en/product.html

33.1Ah at 3.8V with 192 cells equals 24,15kWh total.
3,8V/cell times 96 in series equals 365 volts nominal.

 

[TickTock]

In the thread below, you can see that the LBW comes right at the knee and you are below the knee by the time you get the VLBW.
http://www.mynissanleaf.com/viewtopic.php?f=31&t=6116&start=79

That's strange. As I look at that graph it seems to be telling me that LBW is well above the knee, and VLBW is just below the knee. The slope doesn't seem to change significantly until about 80% or 85% through the time from LBW to VLBW. I had seen this before, and it was the basis of my advice to myself and others that driving past LBW is no problem, but you should avoid driving past VLBW when possible.

Can you explain your comment further?

Ray

I think the exact point you call the knee is a bit subjective. We both agree that LBW is above and VLBW is below and driving beyond VLBW should be avoided if possible. (I also agree that it looks closer to VLBW than LBW.)

 

[nogajim]

Remember, the colder battery pack doesn't affect your m/kW h;it's the denser air.

I have seen this stated multiple times in the forum, and it makes no sense to me. None of my other batteries work well in the cold, and the Leaf won't even start below 0. Wht don't people think the temp will affect m/kWh?

 

[TickTock]

When I talked to the QC techs at ECOtality, they told me that Nissan told them that the battery pack was 28.8kW hs.

That doesn't make any sense, we know the specs on the battery cells and modules:

http://www.eco-aesc-lb.com/en/product.html

33.1Ah at 3.8V with 192 cells equals 24,15kWh total.
3,8V/cell times 96 in series equals 365 volts nominal.

Yup. My final voltage was 394 which comes to 4.1V/cell. We are charging at 10A split across the two strings (~1/6 C). So should be pretty close to the slowest discharge curve plotted (1/3 C). Looking at the curve at 4.1 V, it appears there may be ~4Ah not being used. 4*4.1*192=3.1kWh extra on the top. On my last dead to 100% charge, I measured 20.04kWh actually going to the battery so this seems fairly consistant (I am only missing 1kWh which could easily be attributed to the -1/6C charge rate versus +1/3C discharge plot).

So there may be some extra capacity being saved to flatten the battery aging curve, but it's not a 28kWh being only charged to 24, but rather a 24kWh battery only being charged to 20.

Here's the discharge plot from the link jkirkebo provided:

 

[Herm]

Remember, the colder battery pack doesn't affect your m/kW h;it's the denser air.

I have seen this stated multiple times in the forum, and it makes no sense to me. None of my other batteries work well in the cold, and the Leaf won't even start below 0. Wht don't people think the temp will affect m/kWh?

The internal resistance of the pack will be higher at lower temperatures, thus higher IR losses.. but if you drive in a conservative manner it should be reasonable since the currents will be lower, and the pack should warm up, maybe.

A pack pre-heater (one that you control, not the factory one) that brings the temperature up to 70° F or so while the car is plugged in would take care of that problem.. once the pack is warm it should stay that way for an hour or so, more if you insulate it.

Here is one that sticks to the battery case by magnetism, and it shuts off once the temp is up to 45° F, it would be nice if it could be a bit higher:

http://www.amazon.com/Kats-1153-Handi-Heat-Magnetic-Heater/dp/B000BOABS6/ref=pd_sim_sbs_auto_2" onclick="window.open(this.href);return false;

 

[edatoakrun]

...So there may be some extra capacity being saved to flatten the battery aging curve, but it's not a 28kWh being only charged to 24, but rather a 24kWh battery only being charged to 20...

But doesn't available capacity vary by battery temperature?

By how much?