30 Kwh Leaf showing up on Nissan.ie

BoatMad

simdan wrote: »

Why do people buy svs with the cold pack? I don't understand if you're doing finance why not go for the SVE? Alloys that actually suit the car, proper stereo, all around cameras, cold pack, metallic and leather. These are key factors for me. No brainer for the difference.

P.S. the Nissan website is poor, is not easily understood which options are included. When you speak to different dealers the price and bonuses change..

I got the top end mats and a hard wearing plastic boot protector thrown in. My buddy who also purchased the sve the same day only got the mid range grey mats. I did ask for the boot protector as I have a big dog, so you only get what you ask for I suppose.

The cold pack is very good value at 300 euros the adder to the SVE is nearly 3 k.

Freebies are always upto you , I always get top of the line mats thrown in for free ( play that card at the end )

The options on the leaf are remarkably simple

SV has 30k battery , 6.6 k charger and cold pack options , what could be simpler

cros13

BoatMad wrote: »

Relevant links to support claim , please

From my post last week of the slides Nissan has been circulating internally:





At the same time I posted:

· The 30kW battery will be available as an option on SV and SVE only. The option cost is €3,000.

· The 30kW battery will carry an 8 year, 160,000km warranty. The 5 year warranty remains for the rest of the EV components.

· Production of the new battery starts in December and availability from then on looks good.

· The 30kWh battery will not be available for the eNV200 until mid- Summer 2016 at least.

BoatMad

So the benefits of the chemistry are most obvious when fast charging , but would still be there for slower rates too

The other rates just seem simple mathematical ratios.

cros13

BoatMad wrote: »

So the benefits of the chemistry are most obvious when fast charging , but would still be there for slower rates too

It's an internal marketing slide for dealers so not exactly precise on the technical details.

You'd expect with the chemistry change and the increase in capacity per cell that balancing etc. take up less % of the time and you'd spend more time in the middle of the charging curve.

BoatMad

cros13 wrote: »

It's an internal marketing slide for dealers so not exactly precise on the technical details.

You'd expect with the chemistry change and the increase in capacity per cell that balancing etc. take up less % of the time and you'd spend more time in the middle of the charging curve.

yes I agree, I suspect the advantages show up greatest , when fast charging as would be expected,

of course , given the truthfulness of car companies , it could be they just adjusted the software !!!;)

GreyDad

I would have expected some benefit for non-rapid charging as well, surprised they are saying it's the same

BoatMad

GreyDad wrote: »

I would have expected some benefit for non-rapid charging as well, surprised they are saying it's the same

I dont think its a scientific document !! ( its for salesmen )

BoatMad

BoatMad wrote: »

Relevant links to support claim , please

BoatMad

Deleted User wrote: »

again I suspect the same benefit will accrue at the lower charge rates , just not as obvious. The nissan document is hardly that scientific

GreyDad

GreyDad wrote: »

I would have expected some benefit for non-rapid charging as well, surprised they are saying it's the same

No because it's a larger battery, so on average if you got 21 Kwh in the current leaf usable then that will take around 3.5 Hrs to 100% from 0% @6.6 Kw

With the 30 Kwh, probably 27 Kwh usable then this would be 4.5 Hrs.

The battery will pull more power from the charger for longer in a larger battery because batteries charge at a faster rate at a lower state of charge and the power decreases as the battery charges more and more. Another reason charging beyond 80% takes a long time because at 80% only 6-8 kw will be sent to the battery compared to 45 kw at a low charge %.

As Cross13 pointed out this is more marketing and not due to chemistry changes.

BoatMad

The battery will pull more power from the charger for longer in a larger battery because batteries charge at a faster rate at a lower state of charge and the power decreases as the battery charges more and more. Another reason charging beyond 80% takes a long time because at 80% only 6-8 kw will be sent to the battery compared to 45 kw at a low charge

for lead acid yes, Li tech can be charged at full rate right to knee point if you know what you are doing. There is no need to taper charge, but typically there is a small taper to prevent battery stress . LI has an enormous charge acceptance rate , well in excess of the charger

Theres nothing magic about the 80% level, in reality its around 90%

Another reason charging beyond 80% takes a long time because at 80% only 6-8 kw will be sent to the battery compared to 45 kw at a low charge

Im not sure your right here, I fast charged to 90% I didn't notice any significant change in rate of charge

BoatMad

BoatMad wrote: »

again I suspect the same benefit will accrue at the lower charge rates , just not as obvious. The nissan document is hardly that scientific

No the same benefit isn't observed at 6 kw or 3 Kw.

It's only at the point in charging where the charge current is at the same level at a particular % that the difference is observed.

So at a high charge rate the power falls off quicker than at a low charge rate.

I'm finding this hard to explain.

If at 85% the the charge rate on the fast charger is 6 Kw then there's no difference between using the fast charger than the AC charge point with the 6.6 kw charger if this is making sense ?

BoatMad

BoatMad wrote: »

for lead acid yes, Li tech can be charged at full rate right to knee point if you know what you are doing. There is no need to taper charge, but typically there is a small taper to prevent battery stress . LI has an enormous charge acceptance rate , well in excess of the charger

Theres nothing magic about the 80% level, in reality its around 90%



Im not sure your right here, I fast charged to 90% I didn't notice any significant change in rate of charge

Might not be significant , no but it's going to take longer than 70-80%

BoatMad

If at 85% the the charge rate on the fast charger is 6 Kw then there's no difference between using the fast charger than the AC charge point with the 6.6 kw charger if this is making sense ?

but lithium has a huge charge acceptance rates right up to ( and behind) the upper knee voltage point. Its not like lead acid at all

If the changes in chemistry have improved charge efficiency then that would be seen in all rates of charge

if the changes are merely a result of changing the Chademo control software in the leaf , then its just marketing rather then any battery advantages

the only way you can charge a 30 kWh battery as fast as a 24kwh, is (a ) increase the charging current , or (b ) improve the charging efficiency or ( c ) tweak the cutoff points to run the battery hard to closer to the knee.

if there is greater charging current, then thats fine, but its a function of the DC charge point and the leaf software that didn't utilise the current in the 24Kw battery

BoatMad

Deleted User wrote: »

Might not be significant , no but it's going to take longer than 70-80%

Why, whats the reason , I understand Li very well and I dont understand the reason this would occur.

to be more precise the typical Li charge cycle , is constant current followed by constant voltage charging , This is typically done to maximise battery life over charge time . IN that regard the increased charge time from about 85% onwards is a functioning of charging decisions , not battery chemistry ( unlike Lead acid )

Hence in a 30Kw battery, the decreased time to 80% can only be a function of (a ) increased charger current , or (b ) improved battery chemistry resulting in better charge efficiency

in (a ) no improvement would be seen ( in AC charging ) as , this is not a battery improvement , in (b ) improvements would be seen across all charge levels

The issue here is to separate the marketing hype from the tech

BoatMad

BoatMad wrote: »

Why, whats the reason , I understand Li very well and I dont understand the reason this would occur.

The battery demands less and less current as the voltage rises.

BoatMad wrote: »

to be more precise the typical Li charge cycle , is constant current followed by constant voltage charging , This is typically done to maximise battery life over charge time . IN that regard the increased charge time from about 85% onwards is a functioning of charging decisions , not battery chemistry ( unlike Lead acid )

It charges in a state of constant current until the voltage peaks then as current drops the kw drops.

BoatMad wrote: »

Hence in a 30Kw battery, the decreased time to 80% can only be a function of (a ) increased charger current , or (b ) improved battery chemistry resulting in better charge efficiency

A increased current, but increased current for longer given it's in a constant current stage for longer because it will take longer for the voltage to rise in a larger Ah cell .

BoatMad wrote: »

in (a ) no improvement would be seen ( in AC charging ) as , this is not a battery improvement , in (b ) improvements would be seen across all charge levels

The issue here is to separate the marketing hype from the tech[/QUOTE]

No improvement in AC charging because it will be in a constant Current stage for far longer because you start off with much less current to begin with.

Nothing like a good O'l graph.

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

BoatMad

A increased current, but increased current for longer given it's in a constant current stage for longer because it will take longer for the voltage to rise in a larger Ah cell .

Yes, thats obvious , larger batteries take longer if the constant current phase is held at the same current

Again , if you have a larger battery and you want to retain the same 80% time, at fast charge currents ( aka circa 1-1.5 C) than you can (a) increase the charger current or (b) increase the battery charge efficiency

in fact in LI, there is a issue with fast charging beyond 80-85 as the saturation charge time increases with higher charge somewhat negating the benefit of the extra charging


so either Nissan have not been charging the 24Kw battery at full fast charge rates ( 44- 40 kw) and hence have simply reprogrammed the DC charger to deliver more current or they have genuinely improved the battery efficiency

My view is they have just reprogrammed the fast charger to deliver more current on the basis that testing shows the battery can handle it . They could probably have improved the 24 kw time too. I suspect a whif of marketing here !


in other words, they just have programmed the car to accept a bigger DC charge current, hence improving the charge time , but its not a battery improvement

BoatMad

to put it more simply , if nissan are ( for example ) changing the 24Kwh at 1C then ( for the sake of simplicity ) then if you put 1 Kw of energy back in it will take 1 hour ( assuming 100 % efficiency and linear charge cycles as in 20-80% charge )


if you increase the battery to 30 Kwh and you still charge at 1C then you need to put 30kw in for one hour to retain the same charging time.

nissan can only retain the same charging time by increasing the current the DC charger provides , which suggests that the 24Kwh battery isn't consuming all the rated output of the existing fast chargers

hence it isn't anything to do with the battery chemistry , just a Chademo software change , nissan havent done anything new at all

if they were consuming all the power the Dc charger has available, then they would not be able to retain the same charging time as the smaller battery

Ye cannae change laws of physics, Jim

BoatMad

BoatMad wrote: »

Again , if you have a larger battery and you want to retain the same 80% time, at fast charge currents ( aka circa 1-1.5 C) than you can (a) increase the charger current or (b) increase the battery charge efficiency

You can increase the current depending on whether the battery is rated it V how much heat it will generate.

BoatMad wrote: »

in fact in LI, there is a issue with fast charging beyond 80-85 as the saturation charge time increases with higher charge somewhat negating the benefit of the extra charging

You can't fast charge beyond 80% the battery simply won't request the current at that charge level.

This is the reason the Kia Soul EV charges in roughly the same time at 100 Kw (yes rated for 100 Kw)

Charging at 100 Kw will mean the constant current stage is faster but after this the current will ramp down very quickly because the battery reaches the peak voltage faster so the benefits of 100 Kw charging are not realised on a small battery.

BoatMad wrote: »

so either Nissan have not been charging the 24Kw battery at full fast charge rates ( 44- 40 kw) and hence have simply reprogrammed the DC charger to deliver more current or they have genuinely improved the battery efficiency

Nothing to do with the charger, My leaf charges at 45 Kw until it reaches this peak voltage then drops off gradually as the voltage levels off.

BoatMad wrote: »

My view is they have just reprogrammed the fast charger to deliver more current on the basis that testing shows the battery can handle it . They could probably have improved the 24 kw time too. I suspect a whif of marketing here !

They can't reprogram the charger if you mean the BMS then the BMS has little to do with charging and is really only a tool for monitoring voltages and balancing.

They can improve the 24 Kwh charge time slightly with higher current but it will only reach peak voltage faster before the current starts to drop off again so there isn't a big gain to be had from charging a 24 kwh battery with a 100 Kw charger.

BoatMad wrote: »

in other words, they just have programmed the car to accept a bigger DC charge current, hence improving the charge time , but its not a battery improvement

No it's neither at all.

The battery itself determines the current based on it's voltage it has nothing to do with the charger.

The larger battery means it pulls more current for longer because it takes longer to reach peak voltage where the current starts to taper down and as a result pulls more power from the charger until that peak voltage stage is reached.

With the graphs above you can clearly see this happening.

BoatMad

mad lad, are you an engineer with a background in electronics and charging batteries ?


You are taking lead acid concepts and applying them to Li

Li can be charged at 50C if you want , the battery will never in reality throttle itself , Li internal resistance is so low. ( see the RC guys ) it will continue accepting massive charge currents until it suffers dramatic thermal runaway ( see Boeing)

A charging strategy is set to maximise certain characteristics, in EVs case its usually cycle life and hence battery stress, then its capacity and then fast charging . in other Li applications its different

The Chademo interface would indeed limit current to whatever charge rate Nissan has decided is appropriate for the battery. That charge rate is obviously less then the max the cgademo charger can supply . They would not allow the charger to pump in any old current , the constant current charge rate would be communicated over the CAN interface to the Chademo charger

hence all they have done in the 30 kw battery is raised the DC max charge current in CC mode. hence the 30kw battery charges in the same time . they could not do this is the charger was already providing its max current , which is why you see no effect in smaller chargers. There is no improvement, per se in the battery


its totally different in lead acid , which reacts as you state. its internal resistance during charging rises and in effect " controls charge current "

note the Battery University graph shows a typical Li charge strategy. It does not show the underlying Li charge graph , There are several fast charge strategies proposed for Li ( including pulse for example )

BoatMad

BoatMad wrote: »

to put it more simply , if nissan are ( for example ) changing the 24Kwh at 1C then ( for the sake of simplicity ) then if you put 1 Kw of energy back in it will take 1 hour ( assuming 100 % efficiency and linear charge cycles as in 20-80% charge )

Or to put it even simpler.....

The battery is rated for 67 amp hours so on the fast charger it charges at 110 amps max roughly 45 kw which is about 1.7 C

If by 50% the it's pulling 30 kw form the charger then that's about 78 amps and by 80% it's pulling 8 Kw that's about 27 which is about what I observe.

BoatMad wrote: »

if you increase the battery to 30 Kwh and you still charge at 1C then you need to put 30kw in for one hour to retain the same charging time.

But you can increase the charge to 5 C and it will only charge at 5C for a very short time so it wouldn't have a great impact.[/QUOTE]

BoatMad wrote: »

nissan can only retain the same charging time by increasing the current the DC charger provides , which suggests that the 24Kwh battery isn't consuming all the rated output of the existing fast chargers

People have said to me they sit in the car and turn off the heater while it's charging to speed up charge times, the heater has 0 impact on charge times because by about 40% the power going to the battery would be about 35-40 Kw so there's plenty of headroom to power the heater.

The 24 Kwh battery will consume all the charger has to offer until the peak voltage is reached and starts to level off then the current is reduced and reduced until staying at the fast charger becomes a waste of time.

BoatMad wrote: »

hence it isn't anything to do with the battery chemistry , just a Chademo software change , nissan havent done anything new at all

Nissan have changed the size of the battery this is what's making the difference.

BoatMad wrote: »

if they were consuming all the power the Dc charger has available, then they would not be able to retain the same charging time as the smaller battery

As I said above, it will consume all the power from the charger until the battery reaches a certain voltage then the current continues to fall until such time as the charger shuts off or the charger determines the battery is 100% charged based on the final charge current and voltage.

BoatMad

Sheesh

As I said above, it will consume all the power from the charger until the battery reaches a certain voltage then the current continues to fall until such time as the charger shuts off or the charger determines the battery is 100% charged based on the final charge current and voltage.

NO, Li will consume all available charge current unless you control the charger . the 24Kw battery is charged at approx 1.6 C hence nissan have to program charges with bigger capacities then this to throttle charging current in CC mode

Nissan have changed the size of the battery this is what's making the difference.

actually they have increased the capacity while retaining the same size .



A Li Battery has a virtually flat charge ( and discharge ) curve between 20 and 80%, you are mixing up voltage and current curves

A Li is charged in CC constant current mode ( note " constant ") because of Li massive charge acceptance , you have to pick a particular charge current

The current DOES not drop during the 20-80% phase . its remains " constant", its the voltage that changes ( rises) but in fact the voltage change mainly occurs at the knee point around 85%

You then set a CC termination voltage point, typically to reduce battery stress ( this can be anything from 70-90%).

AT that point you switch to constant voltage charging , note the voltage remains constant hence the current will change ( i.e. decrease as SOC builds )


The only way you can charge a bigger Li battery in the same time is to increase the charge current in the constant current phase , again this is a "constant " current

The charger must have ' headroom ' in its power capacity to allow you to do that .

But nothing has in reality changed in the battery pack , other then Nissan have improved the packaging density

to take a quote from leaftalk

"As for charging, the current 50KW charger only puts out 40KW (380 volts @106 amps at 65%), then it tapers down, so can easily put out the extra 10KW into a slightly larger battery to maintain the 30 minute 80% that everyone keeps going on about."


hence if you put the 30kwh leaf onto a max 40Kw DC charger you would see longer charge times for the 30 kWh battery

BoatMad

heres a little graph of whats happens in Li charging

( sorry cant embed graph)

the blue line is battery voltage , the orange is idealised constant current and the red line is actual typical current profile

As you can see the battery voltage does not vary much in the 20-80% region , in essence the battery accepts full power charging almost constantly over that region of SOC ( state of charge)

note that the current is controlled by the charger not the battery, Li can accept enormous currents but can damage itself so a charge rate of typically less then 2 C is used

A termination voltage point is chosen, in the charger , at that point current is tapered off to prevent voltage stress on the battery, if constant current was continued the terminal voltage would rise uncontrollably , leading to runaway


Hence the while within the linear region, the voltage or current remain basically fixed

to charge at a faster rate or to fill a bigger battery at the same rate the , charge current in the " flat " region must be increased

http://www.em.avnet.com/en-us/design/technical-articles/Pages/Articles/Optimal-Li-ion-Battery-Charging-Maximizes-Safety-and-Performance.aspx

The optimum Li-ion charging cycle

Engineers generally agree that charging Li-ion batteries is simpler and more straightforward than nickel-based systems that demand tight control over charging currents and the added complexity of trickle charging. But while the actual charging process for Li-ion batteries is relatively straightforward, the challenge arises in completing the charging process safely.

The Li-ion charging cycle follows a constant current/constant voltage (CC/CV) cycle. If the battery is deeply discharged (for example, to below 3 V) a small “pre-conditioning” charge of between 0.1 to 0.2 C –– where 1 C equals the maximum current the battery can supply for one hour (for example, for a 500-mAh battery, C = 500mA) –– is applied to keep the cell temperature down until it is able to accept the full current of the constant-current phase.



Fig. 1: Li-ion charging profile using constant current until battery voltage reaches 4.1 V, followed by “top-up” using constant voltage. (Source: Texas Instruments)

When the voltage reaches around 3 V the charge typically transitions to a faster rate (of up to
1 C) until the battery voltage reaches its nominal-maximum voltage (for example, 4.2 V). Manufacturers recommend charging the cell at 0.8 C or less during this phase claiming that such a rate will result in a charge efficiency of 97 to 99 percent while preventing the cell from becoming too warm.

When the battery voltage reaches 4.1 V, the charger switches to a constant-voltage phase to avoid the risk of overcharging. Superior battery chargers manage the transition from constant current to constant voltage smoothly to ensure maximum capacity is reached without risking damage to the battery.

During the constant-voltage phase, the current drops until it reaches around 0.1 C when charging is terminated. If the charger is left connected to the battery, a periodic “top-up” charge is applied to counteract battery self-discharge. The “top-up” charge is typically initiated when the open-circuit voltage of the battery drops to less than 3.9 to 4 V and terminates when the full charge voltage of 4.1 to 4.2 V is again attained. Note that a continuous trickle charge (as used with NiCad and NiMH chemistries) would encourage the production of metallic lithium with its associated safety compromises.

There are other acceptable charging strategies for the initial phase. For example, some techniques charge rapidly by using a constant 0.7 C rate, while others use a constant low rate. The important point to note is that any charging process must switch to constant voltage once the battery’s maximum voltage is reached. Rapid charging to 4.1 V will result in a lower battery capacity at the end of the first stage than slower charging. For example, charging at 0.7 C, although accelerating the initial phase, results in a capacity of 50 to 70 percent at that point, whereas charging at less than 0.2 C takes much longer, but can result in a full battery as soon as the voltage reaches 4.1 V.

Safety can also be compromised if the device powered by the battery is left on during charging. The parasitic load of the device reduces the battery voltage, preventing a smooth transition from constant current to constant voltage even though the battery may actually be fully charged. Continuing to charge at a relatively high current stresses the battery and can lead to long-term degradation.

BoatMad

seriously mad-lad


one more try

IN high capacity Li batteries there is virtually no increase in battery voltage in the linear region, often in the order of millivolts, internal resistance is so low as to mean the battery is an excellent current source , close to a idealised current source

in low capacity Li batteries there tends to be more voltage change , but in practice the 20-80% SOC region , voltage change is around .6 of a volt, IN A SMALL capacity cell. , this is because of its physics, the internal resistance is much higher then a large capacity Li


The posts above take " standardised " Li , typical pouch cells , you need to look at real life graphs for big capacity banks ( my graph is very close)


Hence in practice in the linear region , charging power is almost constant,( almost as there is a small positive slope to the voltage ) battery voltage changes are small and current is CONSTANT throughput the range. The " knee" voltage is much shaper then described in the graph you posted in large banks . constant voltage and constant current = constant power

Lets leave out pre-qualification as the leaf I believe will not you go into that region

Hence charging power is in effect constant throughout the linear region which for a big battery is the longest portion of the charge curve in practice

The graph above is entirely misleading as the main part of the charge cycle is compressed between 3v and 4.1 ( in reality its about 3.4) and looks nothing like that in a big bank


hence for a 24Kw to be fast charged 20-80% SOC, at 1C requires 14,4 kw for 1 hour ( assuming 100% efficiency and 100% linear charge region, i.e. 60% of totoal SOC ) , hence a 30 kw will require a 18kw for 1 hour to charge in the same time


Theres no magic, Nissan command a higher rate for the 30kwh battery from the chademo charger to enable it to complete its charge in the same time as the 24Kwh. If the charger didn't have the power headroom, the battery would not charge in the same time

Theres no way a nissan would allow an " open " current to flow for the battery in charging , what happened if you found a 200Kw charger , you'd massively stress the battery, the Can bus interface on the Chademo controls the max power during the CC cycle

I can do no more here, I dont need to refer to nonsense/stylised graphs found on the internet

If you dont follow this or even accept the Leaftalk comment I dont know what I can do to show you how it works , please look at my graph as its describes the characteristics of large Li banks.

You cannot be suggesting that a 30kwh battery can be charged in the same time as a 24Kwh by not changing the charging power


again, I ask you in all honesty , are you an EE, with knowledge of Li charging

And here's another link using a Citroen EV , same principle,

Department of Energy and Environment
Division of Electric Power Engineering
CHALMERS UNIVERSITY OF TECHNOLOGY
Gothenburg, Sweden 2012

http://publications.lib.chalmers.se/records/fulltext/159633.pdf


2.3 Charging method

A Lithium-ion battery is charged with DC using a method called constant current constant
voltage (CC/CV). As the name indicates, the charge process executes in two steps: under
the first step the current is constant until the voltage reaches a predefined upper value. At
this point, step two begins. The voltage is now constant on the predefined limit, meanwhile
the current is ramped down in order to keep the voltage constant. There are two ways to
terminate the charging process, either by predefine the time in constant voltage mode, or
when the charging current in constant voltage mode drops under a certain predefined value.
By increasing the charging current in the constant current mode the charging time decreases,
but the drawback is ageing and risk of destroying the cells. A compromise between a faster
charging and minimize the ageing is a fact. Regarding the ageing aspect on a battery, the
importance of not violating the different temperature and potential constrains. For more detail
reading about charging strategies and its constrains see reference[9].



So if you got a larger AH battery (I'm not talking physical size like you assumed in an earlier post ) then that that predefined value before constant current and constant voltage takes longer to get to so it charges at a faster rate for longer and not because of a chemistry change or Nissan telling the charger to apply more power.


When the charging starts the DC current increases in steps of 3 A to 124A in six seconds and
then becomes constant. The DC voltage jumps to 329V and during the increase in current the
voltage increases to 343V. During constant current the voltage increases slower, with 0.25V/s.
The AC voltage on the grid dips 10V when the charging starts due to the weak electric grid
and high current drawn from the charger. When the current decreases, the voltage increases
to its original value. After a few seconds the charger is then stopped manually in order to
validate that everything was working.
When the charging is started the second time, the behavior is similar to the previous. The
battery is charged with constant current for 4 minutes and the voltage increases exponential to
363V. The battery is then charged with constant voltage and the current decreases exponential
in steps of 1-2A until the charging stops at 29A, after 23 minutes of charging. The battery
maximum temperature increases from 30 to 38oC during the constant current charging. A
fan is then activated and keeps the battery temperature 38oC or bellow. The battery state of
charge is just below 84%. When the charging stops, at 28 minutes in the plot, the CAN traffic
stops and after a minute the power analyzer is stopped.
In order to charge the battery to 100% the charging must be restarted manually at 33
minutes. The charging from 84 to 94% with constant voltage takes approximately 45 minutes,
about the double as the previous charging from 34 to 85%. When the charging is started the
current is 60% higher than it was when the charger turned off. This is because the capacitance
in the battery needs to be recharged when the charging starts. The current then decreases
exponentially from 49 to 11A

BoatMad

BoatMad wrote: »

heres a little graph of whats happens in Li charging

( sorry cant embed graph)

the blue line is battery voltage , the orange is idealised constant current and the red line is actual typical current profile

As you can see the battery voltage does not vary much in the 20-80% region , in essence the battery accepts full power charging almost constantly over that region of SOC ( state of charge)

note that the current is controlled by the charger not the battery, Li can accept enormous currents but can damage itself so a charge rate of typically less then 2 C is used

A termination voltage point is chosen, in the charger , at that point current is tapered off to prevent voltage stress on the battery, if constant current was continued the terminal voltage would rise uncontrollably , leading to runaway


Hence the while within the linear region, the voltage or current remain basically fixed

to charge at a faster rate or to fill a bigger battery at the same rate the , charge current in the " flat " region must be increased

I agree with some of this except that the current doesn't remain fixed.

In order to charge the battery faster you need to increase the current yes, however I think this is where we're getting our wires crossed pun intended, the 30 Kwh battery will not reach this predetermined state as quickly as the 24 Kwh by which the charger switches to a constant voltage state and the current drops.

So in other words, if the 24 kwh charges at 40 Kw from say 17%-40% the 30 kwh might do it from the same, however that 17-40% gives you more Kwh in the same time because the larger battery stays in constant current mode for longer pulling more power from the charger for longer than the 24 Kwh can.

If you hook up leaf spy you will see the current drop as more Kwh are dumped into the battery and you can graph this activity.

Temperature and age will also effect this ability to charge at a faster rate.

There is one man on the FB EV page and his 2012 I think it is charges at 35 Kw (charger display) and mine charges at 44 kw on the same make of charger simply because as the internal resistance increases the battery is unable to accept the same rate of charge, meaning it reaches that point where it switches from constant current to constant voltage and your battery capacity fades it in effect becomes smaller (not physically of course)

That's it, nearly finished my 4th Night shift, I need a break !

Here's a graph of the Leaf charging via leaf spy. You can see the power drop as the charge % increases.

This will vary due to temperature.



Sleep zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

September1

BoatMad wrote: »

seriously mad-lad


one more try


I can do no more here, I dont need to refer to nonsense/stylised graphs found on the internet

If you dont follow this or even accept the Leaftalk comment I dont know what I can do to show you how it works , please look at my graph as its describes the characteristics of large Li banks.

You cannot be suggesting that a 30kwh battery can be charged in the same time as a 24Kwh by not changing the charging power


again, I ask you in all honesty , are you an EE, with knowledge of Li charging

I think I will be impressed if you manage to convince Mad_Lad. He is very reluctant to change mind.

Theres no magic, Nissan command a higher rate for the 30kwh battery from the chademo charger to enable it to complete its charge in the same time as the 24Kwh. If the charger didn't have the power headroom, the battery would not charge in the same time

I can only add that you can verify that if anyone is still in doubt they can use FCP that displays amperage, you can see that it very quickly drops and for most of charge duration just fraction of maximum FCP power is delivered.

BoatMad

Deleted User wrote: »

Here's a graph of the Leaf charging via leaf spy. You can see the power drop as the charge % increases.

This will vary due to temperature.



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Two things.

First the charge rate is 40 kW , as confirmed by my leafstalk quote , so the FCP has headroom to charge a bigger battery in the same time

The second is the taper charge you are seeing is a charge strategy , ie programmed into the FCP. ( or commanded via the can bus from the leaf , I don't know ) It charges at full almost constant power ( see the straight lines) until about 60-65 % and then tapers ( which is very conservative ). The Li battery could be flat line charged much further then 65 %. ( I wonder why nissan do that , probably cause there at 1.7 C charging which is quite aggressive )


( I should add that in real world lithiums, when you fast charge , because the linear region isn't exactly horizontal , but has a small slope , you do have no other knee point detection then voltage. So if you pick a conservative knee voltage , and you have > 1C charging , you will switch from CC to CV sooner in the charge cycle )

For comparisons see RC charging strategies ( large C held late as possible )

You have to seperate programmed charge curves from the base Li charge characteristics.

In the 30 kW battery. You will no doubt see a bigger power draw then 40 kW in FCP. This is what allows the charge time to be the same

Your curve shows that charging to a high SOC on a FCP is done very conservatively. Which further adds to the issue of why people feel you should not charge above 80 % on an FCP., ie it shows you can and should if that graph is to be believed

It's a very interesting picture Nissan went for a very conservative early taper , ie the change point from CC charging to CC charging. That point could have been later and would allow quicker charging of the 24 kWh battery , but Nissan seem to be playing very safe here

This confirms that if nissan didn't have power headroom in the FCP. The 30 kWh battery would take longer to charge ( assuming they are maintaining similar knee voltage , which I suspect they are )