Only 18 KWh Usable Energy for MY Leaf--Retest Shows 20.3 KWh

[DaveinOlyWA]

The EPA announced last November that the Leaf used 21 kWh of the 24 kWh available, leaving 3 kWh at the top and bottom.

Do you have a reference for this? I haven't ever heard of this info coming from the EPA.

dont need one. have been driving one for 9 months and am pretty confident i know what my Leaf can do. my own measurements and assumptions tell me (granted there will a range of variance) that my battery pack capacity is between 24 and 25 Kw and my usable capacity is between 20.5 to 21.2 Kw

read thru this forum. my numbers are repeated over and over amongst dozens of members here.

 

[SanDust]

Do you have a reference for this? I haven't ever heard of this info coming from the EPA

It's right on the sticker. The EPA runs the car until it can't go through a cycle. Then it measures how much electricity it takes to charge it to 100%. Then it normalizes this number to get X kWh per 100 miles. Just "denormalize" the number and you get how many kWh it measured from the wall to take the battery from "empty" to "full". Assume a charging efficiency of 85% and you get the usable kWh. It might be 100 or 200 wh off because the charging efficiency might not be exactly 85% (I use 87%) but close enough.

[34 kWh/100 miles * 73 miles] X .87 = 21.09 kWh.

 

[surfingslovak]

Smidge graciously uploaded the full EPA report. All things considered, their findings are consistent with 21 kWh usable capacity.

http://www.smidgeindustriesltd.com/leaf/EPA/" onclick="window.open(this.href);return false;

 

[TonyWilliams]

Sorry Tony, but I'm going to have to shoot some holes through that theory. All through the summer, in all of our heat, my m/kW h didn't vary much. The only reduction I saw was when my wife needed the A/C. Otherwise, there was NO reduction in my range nor continues to be in our cooler temps we are having right now. When Nissan did that summer heat testing, I'm sure they weren't hypermiling it so maybe driving it 'hard' will reduce the range more in the heat.

Don't be sorry... we want data!!!

We don't have the heat you do (but we sure have lots of your neighbors in the summer;-), so my personal observations are during the very brief time that temperatures got in the 90F-100F range.

My range [edit: seemed like it] was down, significantly. I didn't do a specific study, but I had planned to. I thought it was YOU who told us that the Nissan engineers in your area were specifically doing heat related studies, and reported verbally to you of a reduction in range? Did I misunderstand that?

 

[TonyWilliams]

Nissan engineers in the Phoenix area doing heat testing report 10-20% range reduction.

do you have a reference? I would love to read that report.

I doubt Nissan will put that in writing for public consumption. So, that falls in the hearsay area.

 

[Stoaty]

It's right on the sticker. The EPA runs the car until it can't go through a cycle. Then it measures how much electricity it takes to charge it to 100%. Then it normalizes this number to get X kWh per 100 miles. Just "denormalize" the number and you get how many kWh it measured from the wall to take the battery from "empty" to "full". Assume a charging efficiency of 85% and you get the usable kWh. It might be 100 or 200 wh off because the charging efficiency might not be exactly 85% (I use 87%) but close enough.

[34 kWh/100 miles * 73 miles] X .87 = 21.09 kWh.

Thanks for that info. I either missed that part of the discussion, or didn't realize the full import. I know that most people consider 21 KWh as the usable portion of the battery, but never thought about the data straight from the EPA.

 

[TonyWilliams]

So, at 118F ambient temperature, the math is (118-70=48/4=12), or 12% reduction in range. It's probably a bit higher than that, perhaps 3F per 1%.

Why would this be? Drag would be less as would rolling resistance and drive train losses. Battery performance would be enhanced. If the AC was on that would definitely reduce the range but since the Leaf doesn't have a TMS I don't see any additional electrical loads if climate control is off.

Only referring to battery performance, not all the other issues you raise. To my knowledge, 20C is the "ideal" temp for this battery chemistry. Temperatures over 130 get into the potential thermal run-away area, so the fancy electronics start cutting back store energy. That's in the service manual.

Also, the battery itself, without fancy electronic management, is outside it's ideal temp at any temperature over 20C.

The only real solution to an answer for this is an actual test.

 

[DaveinOlyWA]

Certainly, I don't know how much ambient heat affects charging, but it definitely affects range above 70F.

Sorry Tony, but I'm going to have to shoot some holes through that theory. All through the summer, in all of our heat, my m/kW h didn't vary much. The only reduction I saw was when my wife needed the A/C. Otherwise, there was NO reduction in my range nor continues to be in our cooler temps we are having right now. When Nissan did that summer heat testing, I'm sure they weren't hypermiling it so maybe driving it 'hard' will reduce the range more in the heat.

its a see saw as you know.

colder weather means denser air, thicker lubes, etc. means lower miles per Kw. but cooler battery so more electrons available for use. (remember we are not using heat/defrost, etc)

warmer weather means better performance or higher miles per Kw but less capacity due to battery management adjustments for temperatures.

now, its obvious all things being equal, that only REAL hot weather affects the Leaf because A/C has much less impact on range than heat/defrost does.

so, the ultimate temps i have determined to be the low 80's. barely enough to require A/C. in fact, at street speeds, i roll down the window and use no A/C at all.

but driving conditions still allow me to approach the "magical" 6 miles/Kw mark.

in the colder weather i am seeing now in the mid 50's to low 60's, the best i can do is 5.2 miles/Kw at "street" speeds. the other day, i spent most of my time driving between 30-35 mph to increase my performance and that is all i could get 5.2 miles which is worse than my worst during Summer driving the same streets at 40 mph.

 

[SanDust]

Just go to the http://www.blinknetwork.com" onclick="window.open(this.href);return false;, sign in, and see the data:

Tue May 3, 13:47:02 Tue May 3, 14:27:42 2.4745 kWh
Tue May 3, 16:30:49 Tue May 3, 16:50:57 1.1203 kWh
Tue May 3, 17:12:17 Tue May 3, 18:22:11 4.2832 kWh

Not trying to give you a hard time but what confused me is that you said the Blink showed kW, which would have been interesting if true and got me excited. But the Blink does not show kW. You're going to the Blink website and using kWh and then deriving an average kW. That's OK but it's different than an instantaneous read out. FWIW I ran the numbers for your first and third entries. They don't match exactly but they indicate the average draw from the wall is more like 3.65 kW than 3.8 kW. That's more like 87% efficiency which is what you generally expect with Li-ion. However it's hard to know exactly what is happening since you have a few unknowns.

 

[SanDust]

Only referring to battery performance, not all the other issues you raise. To my knowledge, 20C is the "ideal" temp for this battery chemistry.

Yes 20C is the "ideal" temperature for Li-ion batteries. But ideal in this context involves a trade-off between performance and longevity. As those drag racing EVs know, you get better performance if you heat up the batteries. It's just like any other chemical reaction. However that extra performance comes at the cost of battery life.

The only reason I can think of why you'd get less range from the battery at higher ambient temperatures is if the Leaf doesn't fully charge the cells at those temperatures. This wouldn't be a bad idea BTW.

 

[DaveEV]

The EPA announced last November that the Leaf used 21 kWh of the 24 kWh available, leaving 3 kWh at the top and bottom.

Do you have a reference for this? I haven't ever heard of this info coming from the EPA.

dont need one. have been driving one for 9 months and am pretty confident i know what my Leaf can do. my own measurements and assumptions tell me (granted there will a range of variance) that my battery pack capacity is between 24 and 25 Kw and my usable capacity is between 20.5 to 21.2 Kw.

Minor correction - no one knows what the actual battery pack capacity is except for Nissan. We only get to see usable capacity from the plug which has been estimated by assuming that a standard L2 charge is ~85% efficient and that a full charge takes about 24-25 kWh. The pack could hold 50 kWh and Nissan's might only let us use ~21 kWh of it and we wouldn't be any wiser at this point. Until we test a cell by itself, we won't know for sure what the actual 100% capacity of the pack is - too many assumptions are still being made.

 

[davewill]

... You're going to the Blink website and using kWh and then deriving an average kW. That's OK but it's different than an instantaneous read out. ...

You can do a little better than that. The Blink website logs kWh usage on 15 minute intervals. Still not an instantaneous measure, but the draw should be constant for most of those intervals. Here's from my last charge:

Arrrrgh! They redesigned the website, and removed the detailed stats!!!! ... OK, I was able to get them from one of the graphs, but only for the latest charge. The detailed history is gone.

• 0.9355kWh = 3.742kW
  0.9360kWh = 3.744kW
  0.9340kWh = 3.736kW
  0.9361kWh = 3.744kW
  0.9374kWh = 3.749kW
  0.9380kWh = 3.752kW
  0.9359kWh = 3.744kW

 

[91040]

The only reason I can think of why you'd get less range from the battery at higher ambient temperatures is if the Leaf doesn't fully charge the cells at those temperatures. This wouldn't be a bad idea BTW.

You may be correct. See: http://www.mynissanleaf.com/viewtopic.php?f=44&t=5582&start=180#p140164" onclick="window.open(this.href);return false;

 

[surfingslovak]

Minor correction - no one knows what the actual battery pack capacity is except for Nissan. We only get to see usable capacity from the plug which has been estimated by assuming that a standard L2 charge is ~85% efficient and that a full charge takes about 24-25 kWh. The pack could hold 50 kWh and Nissan's might only let us use ~21 kWh of it and we wouldn't be any wiser at this point. Until we test a cell by itself, we won't know for sure what the actual 100% capacity of the pack is - too many assumptions are still being made.

Yes, this is a correct assessment. We do however have the specs published by AESC. This has been discussed before and I'm voicing one person's opinion here, but the rated capacity of these cells is 125.78 Wh (33.1 Ah x 3.8V).

There was some debate how the full capacity could be significantly larger, but if you integrate the area below the discharge curve, you see that the rated capacity is pretty accurate. Even if you overcharged the cells to 4.5V, it's unlikely that you would see more than 150 Wh per cell. I looked at couple of research reports for manganese spinel cells from other manufacturers and although they tried different voltages, cell maximum was usually reached below 4.2V, at around 4.17V. Yes, the AESC cells could be different, and we could argue about this ad infinitum, but let's just be clear, the rated pack capacity is 24 kWh, just as Nissan stated in their specs, and the full capacity in unlikely much higher.

This discussion aside for a moment, there are other vehicles we could use as a point of reference. The MINI-E and Volve C30 Electric would come to mind. Both of these vehicles seem to use a similar ratio of usable to rated capacity: 85 to 87%.

 

[Herm]

an easier way to get the actual pack capacity is to work out the exact efficiency of the charger.. all you need to do is to measure the DC output of the charger and the AC intake in watts and then divide, a DC clamp-on ampmeter would come in handy for that... you would also have to measure the DC voltage and that would be the only dangerous part.

 

[surfingslovak]

but driving conditions still allow me to approach the "magical" 6 miles/Kw mark.

in the colder weather i am seeing now in the mid 50's to low 60's, the best i can do is 5.2 miles/Kw at "street" speeds. the other day, i spent most of my time driving between 30-35 mph to increase my performance and that is all i could get 5.2 miles which is worse than my worst during Summer driving the same streets at 40 mph.

This is anecdotal at best, but I did some pretty extensive research of publicly available data from the MINI-E field trial. Reportedly, 10% range reduction was seen for 20 or 30 F drop in ambient temperature. If the cabin heater was factored in, range reduction of 20% or so was reported. Sorry I don't have the link at the moment, but I will try to dig up the data when I get a chance.

 

[SanDust]

This has been discussed before and I'm voicing one person's opinion here, but the rated capacity of these cells is 125.78 Wh (33.1 Ah x 3.8V).

There was some debate how the full capacity could be significantly larger, but if you integrate the area below the discharge curve, you see that the rated capacity is pretty accurate. Even if you overcharged the cells to 4.5V, it's unlikely that you would see more than 150 Wh per cell.

Yes the published specs are a good starting place. The pack capacity also illustrates the problem with having people who aren't really professionals come up with their own measurements. A couple people measured the pack and came up with numbers in the 27 kWh range or something. But this was just an error induced when they measured just the far left area and than assumed the voltage was flat across the entire discharge cycle.

 

[SanDust]

Arrrrgh! They redesigned the website, and removed the detailed stats!!!! ... OK, I was able to get them from one of the graphs, but only for the latest charge. The detailed history is gone.

Pesky changes. No big deal really. Your numbers are very consistent.

I had never really thought about what a 3.3 kWh charge meant. It seems that it's something like 3.75 kW from the wall which suggest something like 3.63 kW to the battery and 3.3 kW at the battery. IOW the 3.3 kW refers to the battery charge.

 

[Stoaty]

I retested my work commute and got the following numbers:

Charged to 80% (226 gids)
Drove 44.3 miles
SOC at end 105 gids
Efficiency center console (not carwings) = 6.2 miles/KWh (assume 6.0 for dash, just to be safe)

Calculations:

Total usable miles = 44.3*(281/(226-105) = 102.9
Usable KWh in pack = 102.9/(6.2-.2) = 17.1 KWh

Conclusions: Previous work commute came out about the same, actually a little better. Either the efficiency number is a made up bunch of crap, or my battery pack has gone from almost 21 KWh usable to 17 KWh usable over a matter of days. Either way, I think this method is totally useless. It also suggests that I can't rely on multiplying the efficiency number by 21 (or 20.4) to reliably predict my distance (although to be sure I suppose I would have to try to drive the 126 predicted miles--6*21--and actually only achieve the 102.9 miles I have calculated by extrapolation).

 

[planet4ever]

I had never really thought about what a 3.3 kWh charge meant. It seems that it's something like 3.75 kW from the wall which suggest something like 3.63 kW to the battery and 3.3 kW at the battery. IOW the 3.3 kW refers to the battery charge.

3.3 kW "at the battery" as opposed to 3.63 kW "to the battery" doesn't seem to make any sense. We know that the battery is able to put out far more power than that, since it can power the 80 kW motor. So are you suggesting that 3.63 kW leaves the charger but only 3.3 kW arrives at the battery? We're only talking about a few feet of wire, running DC at a high voltage and low amperage (less than 10 amps!). It can't possibly dissipate more than 300 watts as heat.

No, I'm pretty sure they are talking about something like 3.8 kW going into the charger and 3.3 kW coming out of it, which would be 87% efficiency. Remember, the charger is liquid cooled, which means it must be generating quite a bit of heat, so a 500W loss there should not be too surprising.

Ray