July 16 Survey Email

[evnow]

1) Plug the car in every chance I get...Home and work. Basically keeping the battery charged above 80% at all times.

2) Only plug the car in every 4 or 5 days...Basically running the battery to near empty, then recharging overnight and then driving 80 miles before recharging again .

3) A happy medium. Maybe charge every other night.

I'm almost in the same situation as you are in (in terms of daily drive). One thing to note is that if I keep my car fully charged - it allows me to take it to evening drive/dinner to the city - which can be 50 miles. I need to balance this opportunity loss vs possible battery capacity loss. I'll most probably go for maximizing electric miles driven rather than cradling the battery ...

 

[AndyH]

This raises a question I've had for a while now...

I know everybody's driving commute and style etc etc will vary....and each person will have to find the solution of charging that best fits their needs...

But let me ask a specific scenario:

Driving to work is less than 10 miles each way (about 6 miles)...maybe a quick grocery trip or dining out...So make it an even 20 miles a day. I have the ability to charge at home and at work.

Should I:

1) Plug the car in every chance I get...Home and work. Basically keeping the battery charged above 80% at all times.

2) Only plug the car in every 4 or 5 days...Basically running the battery to near empty, then recharging overnight and then driving 80 miles before recharging again .

3) A happy medium. Maybe charge every other night.

Gavin

The answer for lead-acid has been recharge early and often. Lithium doesn't care. There's no need to recharge if there's enough energy in the pack for the next journey.

If one uses a L3 charger for every recharge, it might be better to skip some partial charges, but that's due to possible stress from higher charge rates rather than the need to keep cells full.

We can concentrate on charging when it's good for us and ignore the battery otherwise.

Andy

 

[DaveEV]

Most lithium based batteries have the longest "shelf life" when stored somewhere around half full. Similarly, charging the battery to full or discharging the battery to empty is also hard on the cells. And finally, the faster you charge or discharge the pack, the harder that is on the cells.

So if you normally only drive 20 miles/day, you'd want to charge the to 60% every day, then trickle charge it back up to 60% for the next day. And that still gives you an extra 40 miles of buffer should you need to go farther. Should you need to go farther the next day, charge it up more accordingly.

That does bring up a good question - I wonder if you can set the charge rate from the car? It might be useful to be able to tell it how fast to charge even if it has the capacity to go from empty-full in 8 hours...

 

[evnow]

That does bring up a good question - I wonder if you can set the charge rate on the EVSE? It would be to be able to tell it how fast to charge even if it has the capacity to go from empty-full in 8 hours...

I guess not.

BTW, even the 220V charging is close to trickle charge (C/10 I think is considered trickle, 3.3kw charging would be C/7). Ofcourse you could use the 110V EVSE and trickle charge ...

 

[AndyH]

Most lithium based batteries have the longest "shelf life" when stored somewhere around half full. Similarly, charging the battery to full or discharging the battery to empty is also hard on the cells. And finally, the faster you charge or discharge the pack, the harder that is on the cells.

This is generally true but really doesn't apply to our EV packs for a number of reasons. So we're clear, let's ignore any battery management hardware and/or software for a moment and just talk about a single raw cell.

LiMn has a max cell voltage a bit over 4.2V and a recommended minimum of 3.0V. Charging above 4.2 and discharging below 3.0 will cause cell damage. Cells do have a max charge and discharge rate - gentler is better. If one is going to store a battery and wants to minimize the damage of time, discharge to ~40% and put the battery in the refrigerator. However...

The car's management system isn't going to allow us to use the top or bottom 10%. This is the difference between the 'ultimate' or 'max' cell capacity and the user capacity. 'Our' user capacity of 100% is the cell's 90% charged, and 'our' empty will be 10% charged. The car won't get us get close to the 4.2V or 3.0V zones where damage will occur and is within the zone of long life already.

Likewise charge/discharge rate. It's very likely that the maximum current we'll be able to draw from the pack will be less than 300A. It's very likely that the Leaf's pack will have two parallel strings of cells. Nissan says we'll have 48 modules of 4 cells in series - 192 cells @ 3.6V nominal is a 691V pack. Not likely. 345V is much more probable. The parallel cells will each take 1/2 the load - 150A max per string. If the Leaf uses AESC's 33Ah cells, and we use a very low-performance 5C discharge rate for the cells, the cells are capable of delivering 165A continuous and twice that for acceleration.

So yes - in general I have to agree completely with what you've suggested. In practice, though, we're not likely to be close to the performance limits of the pack.

Cell capacity will degrade over time even if the cell is charged to 40% and stored for 10 years. To paraphrase Les Brown - if we're going to take the hit anyway, we might as well get some mileage out of the pack!

So if you normally only drive 20 miles/day, you'd want to charge the to 60% every day, then trickle charge it back up to 60% for the next day. And that still gives you an extra 40 miles of buffer should you need to go farther. Should you need to go farther the next day, charge it up more accordingly.

I can't point to anything about any of the lithium cells that confirms that this management method would do more than keep one busier than necessary. Since we won't have access to the 'ragged edges' of the battery's comfort zone, then by definition the cell will be comfortable even if we leave the car on the charger 24/7 and only drive 1 mile per day.

I use my road-battery as my rolling test bed for different battery management products. The cells that I've damaged on the bench or on the road have been damaged thru over charge or over discharge. The Leaf just won't let us get get into the danger zone.

That does bring up a good question - I wonder if you can set the charge rate on the EVSE? It would be to be able to tell it how fast to charge even if it has the capacity to go from empty-full in 8 hours...

The devices which with I'm aware (AV and Clipper Creek) are pre-set - we cannot adjust the charge rate via the EVSE. We can move from the Level 2 to the Level 1 device. Later on, we might be able to hack the system and turn the charger down from the 'inside'. But the most likely way to limit the charge rate, should a user desire that, is by selecting the EVSE they choose to use - Level 3, 2, or 1.

Andy

 

[DaveEV]

I can't point to anything about any of the lithium cells that confirms that this management method would do more than keep one busier than necessary. Since we won't have access to the 'ragged edges' of the battery's comfort zone, then by definition the cell will be comfortable even if we leave the car on the charger 24/7 and only drive 1 mile per day.

I use my road-battery as my rolling test bed for different battery management products. The cells that I've damaged on the bench or on the road have been damaged thru over charge or over discharge. The Leaf just won't let us get get into the danger zone.

Right - but have you cycled cells thousands and thousands of times at various depth of discharges over multiple-years to see how various changes in cycle depth affects the amount of energy you are able to store/retrieve from a cell?

Just because Nissan has chosen a 10% buffer at the top/bottom of the pack does not mean that self-imposing a larger buffer will not improve battery life. It simply means that Nissan has chosen 10% as a compromise between maximum range and cell life.

Just like the Tesla has two charge/drive modes - one which lets you use a smaller buffer for when you need to drive as far as possible (the mode used to get the EPA range of 255mi), and a "normal" mode where it doesn't let you charge/discharge as far (where your range is typically around 200mi, or about 20% less).

The devices which with I'm aware (AV and Clipper Creek) are pre-set - we cannot adjust the charge rate via the EVSE. We can move from the Level 2 to the Level 1 device. Later on, we might be able to hack the system and turn the charger down from the 'inside'. But the most likely way to limit the charge rate, should a user desire that, is by selecting the EVSE they choose to use - Level 3, 2, or 1.

The EVSE only tells the car what the maximum charge rate it. The onboard car/charger still controls the actual rate of charge.

So sure - you could use the EVSE to tell the car it only can supply a lower rate, but the proper place to set that limit is on the car.

 

[AndyH]

I can't point to anything about any of the lithium cells that confirms that this management method would do more than keep one busier than necessary. Since we won't have access to the 'ragged edges' of the battery's comfort zone, then by definition the cell will be comfortable even if we leave the car on the charger 24/7 and only drive 1 mile per day.

I use my road-battery as my rolling test bed for different battery management products. The cells that I've damaged on the bench or on the road have been damaged thru over charge or over discharge. The Leaf just won't let us get get into the danger zone.

Right - but have you cycled cells thousands and thousands of times at various depth of discharges over multiple-years to see how various changes in cycle depth affects the amount of energy you are able to store/retrieve from a cell?

Of course not - that's why I talk with and learn from the folks at battery manufacturers that DO that level of testing.

Just because Nissan has chosen a 10% buffer at the top/bottom of the pack does not mean that self-imposing a larger buffer will not improve battery life. It simply means that Nissan has chosen 10% as a compromise between maximum range and cell life.

Just like the Tesla has two charge/drive modes - one which lets you use a smaller buffer for when you need to drive as far as possible (the mode used to get the EPA range of 255mi), and a "normal" mode where it doesn't let you charge/discharge as far (where your range is typically around 200mi, or about 20% less).

Conversely, just because we might only use the middle 5% of a cell's capacity doesn't mean it will do anything. What I'm trying to say is that the SIGNIFICANT areas of concern are those areas at the upper and lower limits of voltage, and upper limits of energy in/out, and upper and lower limits of temperature. Once we get inside the 70% state of charge range, the diminishing returns seem to be offset by capacity loss due to aging.

The EVSE only tells the car what the maximum charge rate it. The onboard car/charger still controls the actual rate of charge.

So sure - you could use the EVSE to tell the car it only can supply a lower rate, but the proper place to set that limit is on the car.

The EVSE only tells the car what the maximum charge rate it. The onboard car/charger still controls the actual rate of charge.

So sure - you could use the EVSE to tell the car it only can supply a lower rate, but the proper place to set that limit is on the car.[/quote]

You asked about setting the charge rate with the EVSE which is what I answered. I agree that if we can't or choose not to select a different EVSE, then we technically can adjust the charger...but the EVSE signal does adjust the charger...and we're not likely to have a utility within the car that allows us to turn the charger down from the inside.

edit to fix the quote..sorry drees.

 

[garygid]

So far, we have not seen any user-accessable charge-rate setting in the Leaf.

We believe that there is a time-of-day clock to control the start of timing and to limit the maximum time period allocated for the charging. For example, charge from 12:10 AM and stop by 4:55 AM to stay within some low-cost-power time slot. However, the charging might not finish, and the cells might not get "balanced".

So far, we do not know how, or when, the BMS/Charger in the LEAF will handle keeping the 192 cells "balanced" (all sufficiently close to the "same" State-Of-Charge).

 

[AndyH]

So far, we have not seen any user-accessable charge-rate setting in the Leaf.

We believe that there is a time-of-day clock to control the start of timing and to limit the maximum time period allocated for the charging. For example, charge from 12:10 AM and stop by 4:55 AM to stay within some low-cost-power time slot. However, the charging might not finish, and the cells might not get "balanced".

So far, we do not know how, or when, the BMS/Charger in the LEAF will handle keeping the 192 cells "balanced" (all sufficiently close to the "same" State-Of-Charge).

And we're not likely to get either of these bits of 'geek level but generally useless to the general user' info until we get the car and/or get the service manual(s).

 

[LTLFTcomposite]

Seems like the "no worries" scenario for the Leaf is if you routinely stay under 40 miles a day and are content to take the other car on those days when you exceed that... and can have it connected for a good eight hours or more at night.

 

[DaveEV]

Of course not - that's why I talk with and learn from the folks at battery manufacturers that DO that level of testing.

...just because we might only use the middle 5% of a cell's capacity doesn't mean it will do anything. What I'm trying to say is that the SIGNIFICANT areas of concern are those areas at the upper and lower limits of voltage, and upper limits of energy in/out, and upper and lower limits of temperature. Once we get inside the 70% state of charge range, the diminishing returns seem to be offset by capacity loss due to aging.

With Nissan Leaf, here's what we know:

24 kWh battery pack.
Some buffer space on top/bottom (how much exactly is not known for sure due to conflicting reports, but estimated to be fairy small, perhaps 10%).

Warranty: Unknown, but based on recent questionnaire, I think a 5 year / 60k mi warranty after which 80% of capacity is still retained is likely.

With Chevy Volt:
16 kWh battery pack.
25% buffer space on top/bottom (using 50% of total capacity).
Warranty: 8 years, 100k miles national - I'd put money on the CARB state warranty being 10 years, 150k miles since it's required of hybrids. GM has stated that they expect the pack to last 10 years, 150k miles.

Now we're comparing apples to oranges since the cells are different, but it seems fairly apparent that using the middle 50% of a lithium pack is not past the point of diminishing returns.

You asked about setting the charge rate with the EVSE which is what I answered. I agree that if we can't or choose not to select a different EVSE, then we technically can adjust the charger...but the EVSE signal does adjust the charger...and we're not likely to have a utility within the car that allows us to turn the charger down from the inside.

My mistake - I should clarify that... Obviously here, there will be some point of diminishing returns as well in terms charge rate and affect on battery life. That said, I think it could be useful to be able set charge rates - Nissan would have to let us know if their testing has shown any difference in battery life - I wonder if that is an additional reason they are initially shipping with the 3.3kW charger instead of the 6.6kW charger...

 

[evnow]

Obviously here, there will be some point of diminishing returns as well in terms charge rate and affect on battery life. That said, I think it could be useful to be able set charge rates - Nissan would have to let us know if their testing has shown any difference in battery life - I wonder if that is an additional reason they are initially shipping with the 3.3kW charger instead of the 6.6kW charger...

Darell had written sometime back that Mitsu actually thinks the battery will be better if fast charged. I highly doubt at the rates we are charging (L1 or L2 - and may even L3 upto 80%) degradation would be material.

 

[hill]

This so-called Nissan survey wasn't put together by Nissan - rather one of (WAY too) many survey companies. The company that I work for also hires different survey businesses, that slap together results that our company is hoping to figure out. This philosophy invariably gives irrelevant results, that simply feed the organization wanting results, exactly what they want to hear. If my business wants to find out what I'm thinking .... why not ask ME ... and NOT go through a 3rd party. Heck ... if a business feels that hiring a survey company gives great results, why not have ANOTHER business ask another business to hire a survey company. That will REALLY make for detached results. The survey companies all seem to do the same thing. They'll usually let you pick (ONLY) one of 4 answers. What if your answer isn't ANY of the stock/irrelevant answers? To bad. Seldom are there any open ended places where you can write out a REAL answer. Well, maybe these surveys are not too bad after all ... because the survey company only wants the hoped for results to be spit out any way ... and so that's all they get.

 

[AndyH]

With Nissan Leaf, here's what we know:

24 kWh battery pack.

24kWh ultimate, total user, total user before 'reserve/limp-home'?

Some buffer space on top/bottom (how much exactly is not known for sure due to conflicting reports, but estimated to be fairy small, perhaps 10%).

Fair enough. Though Perry said in Washington DC that we'll have the middle 80% to work with.

Warranty: Unknown, but based on recent questionnaire, I think a 5 year / 60k mi warranty after which 80% of capacity is still retained is likely.

This is irrelevant to cell/pack analysis as warranty is a marketing and insurance issue. Hybrids will deliver longer cycle life relative to pure EVs, though, so we can expect a pack used consistently to 80% will have a shorter life than a parallel hybrid. I haven't seen any national lab evaluation of the life of a series hybrid pack.

With Chevy Volt:
16 kWh battery pack.
25% buffer space on top/bottom (using 50% of total capacity).
Warranty: 8 years, 100k miles national - I'd put money on the CARB state warranty being 10 years, 150k miles since it's required of hybrids. GM has stated that they expect the pack to last 10 years, 150k miles.

Now we're comparing apples to oranges since the cells are different, but it seems fairly apparent that using the middle 50% of a lithium pack is not past the point of diminishing returns.

Ok - I'll buy this. Sandia Labs tested a couple of cylindrical LiFePO4 cells and while they were on track to return more than 1500 cycles in 'EV mode', they returned more than 8000 'cycles' of the hybrid power pulse test. These are significantly different cycles, though.

But how much do we want/need in the real world? LiMn is very similar to lithium cobalt and lithium polymer and shares the same voltage range. If we keep all other parameters the same (and use an 80% depth of discharge), a cell charged to 4.4V every time will deliver 5 cycles while a partner cell only charged to 4.1V (about 92% SoC) will deliver more than 2000 cycles. That's 200,000 miles of LA4 driving in the Leaf - and about 10 years of Monday thru Friday driving. What more would one want to achieve?

That said, I think it could be useful to be able set charge rates - Nissan would have to let us know if their testing has shown any difference in battery life - I wonder if that is an additional reason they are initially shipping with the 3.3kW charger instead of the 6.6kW charger...

One comment about the charger (don't recall where but do recall it was either Nissan or from a Nissan interview...) suggested that the initial cars will ship with 3.3kW chargers because that's the 'international standard' size. I don't know if it's true or not, but if true we probably won't see 6.6kW until the cars come off the Tennessee line. But that's really a guess.

I'd love to get my hands on some AESC cells and some test results. Eventually...

Andy

Edit...typos...7.7kW charger?! Where did THAT come from?

 

[EVDRIVER]

If the charger is 3.3 kw it is a Nissan mistake and the "standard" is only marketing speak. My guess is it is integrated and can't easily be changed. Even the AV guy I spoke to alluded that it was a mistake.

 

[bowthom]

Hello,
Here is how it broke down at the Leaf presentation for OEVA members at OMSI in PDX.
The cells looked like they were 50 ah (sized like Kokam 50 ah)
Doing the math: 4 cells per battery, series parallel, nets 100 ah @ 7.2V nominal.
48 cells * 7.2V = 345V for the pack (number quoted by the Nissan rep).
345V * 100 ah = 34.5 kWh total battery energy.
34.5 * 70% (safe batt zone) = 24.192 kWh of driving energy.
24 kWh / 240 W/mile (figure quoted by the Nissan rep) nets the 100 mile range (+10% emergency reserve at reduced speed / power).

Since the numbers jived it sounded like the facts to me.

Don

On Edit: The DOE survey stated a 40A 240V service for the charger. That's 9.6 kWh of supply power. At 30A it would be 7.2 kWh input to the charger. At just over 90% efficiency you get 6.6 kWh charging. 24kWh / 6.6 kWh nets the approximate 4 hour charge time. This does not allow for balancing but cells seem to stay pretty balanced when staying inside the 70% safe zone. The series parallel structure makes checking cell balance easy so the Leaf may only perform it when an imbalance is detected.

FYI - doing some calculations on battery life:
1. If lithium batteries are cycled at 70% capacity they will cycle >800 times (Kokam)
a. At 100 miles per cycle that’s 80,000 miles
2. Batteries cycled at 50% capacity will cycle >2500 times (Kokam)
a. At 70 miles per cycle that’s 175,000 miles.
3. Batteries cycled less than 50% capacity will cycle >3000 times. That’s 8.2 years if you charge every day. The battery has an 8-year warranty so it is guaranteed for its full-engineered lifespan.

So it would seem that staying in that 50% to 40% capacity cycle will net the greatest life / miles of usage, bang for the buck so to speak. Constantly topping off the batteries will not gain you anything except an always-full range. It may, in fact, lessen the amount of miles you can drive.

 

[lne937s]

I don't think comparing the Volt's LG battery to the LEAF's is going to be easy. Different batteries, different applications. LEAF uses more of its energy capacity. Volt is heavier due to carrying around two drivetrains and needs more kW output to move it down the road, but gets that output from a smaller battery. LEAF's rated battery output is higher than its motor rating. The Volt lists its motor output slightly higher than their battery is rated. Leaf is harder on energy capacity, Volt is harder on power capacity... We aren't going to know which one lasts longer untill we see real-world results.

However, I think Nissan will be more eager to get the battery modules back because they have reuse plans and they make their own batteries- battery trade-in and upgrade would be a new market for them.

 

[AndyH]

I don't think comparing the Volt's LG battery to the LEAF's is going to be easy. Different batteries, different applications.

Different manufacturers but they're both lithium manganese. They might not perform exactly the same but should be fairly close.

 

[Gavin]

Don...nice post...thanks for the info

I like that the battery is bigger and that the 24k is the useable space...that should help increase the length of service and also ensure a nice range...

I wonder if Nissan can keep the usable range around 100 miles by changing the programming at a later date...

Ie...at 7 yrs the range drops from 100 miles to 80 miles...you head into Nissan dealership and get anfirmware update that changes range from 70% of battery to 80-85% of battery....gets you another couple of years at 90 miles range....yes it decreases life of battery, but then you get a newer, better battery at 9 to 10 years of use....

Gavin

 

[AndyH]

If the charger is 3.3 kw it is a Nissan mistake and the "standard" is only marketing speak. My guess is it is integrated and can't easily be changed. Even the AV guy I spoke to alluded that it was a mistake.

I suspect Chelsea is considered a 'reliable source' in some circles.
http://www.mynissanleaf.com/viewtopic.php?p=11004#p11004

7) When will 6.6kW charging be available?

Not for a few years, it seems. Sounds like it's not been officially decided but seems to be a Gen II thing. Also seems pegged to when the TN plant will take over production, which would make sense since overseas standard is 3.3. Don't know if Gen I's will be retrofittable and at what cost.

8) What is the hump in the rear cargo area?

I couldn't see the pic that was referred to, but the only "hump" I saw was a squared-off one directly behind the rear seats. Underneath is the on-board charger.

So...the charger's not under the hood or integrated with the inverter - it's behind the back seat. There you go - yank that puppy out and install your stack of four Manzanitas - life is good! :lol: