# Leaf pack with many low cells



## kennybobby (Aug 10, 2012)

Have you checked the cell voltages with a voltmeter directly to compare with the bms values? your bms screen has several data fields that seem to indicate that it may be somewhat defective.

Did you make any capacity measurements on the cells when you made the purchase? Obviously you would be more likely to get an exchange or refund if it were requested soon after the transaction.

Did you experience any over-discharge events, such as driving around until the pack was out of energy and all the cells were pulled down low? We all know it can happen when first enjoying the full torque of an EV...

The kia soul cells might be a good investment if the capacity checks okay.


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## Isaac97 (Jun 3, 2019)

The BMS screen is an Android tablet running Leaf Spy Pro in a special BMS-only mode. I have verified that the voltages match.
When I got the cells all the voltages were exactly the same. I did not run capacity checks as the seller claimed that all the cells were at least over 80% capacity. In hindsight that was a bad idea.

No over-discharge except on the range test drive, where the pack went from full to LVC in 25 miles.

The real issue with batteries in this car is the space. The Leaf pack barely fit and a Volt pack won't work at all, else that would have been my choice.


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## john61ct (Feb 25, 2017)

Don't try to make scrapped / used pack work.

Save your pennies and buy new.


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## rmay635703 (Oct 23, 2008)

Leaf cells are an incredibly bad investment, the sheer speed of degradation makes them hard to use
a volt pack from a junkyard you can check with a voltmeter is a much more reliable option


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## john61ct (Feb 25, 2017)

Only a CC-load discharge test gives useful health data other than "dead or not"

Unlike lead, peukert is so close to 1.0 you don't need to use the 20-hour rate, 3 hours is fine if the seller lets you.

Teach them how to do it, and offer to pay double for packs above 95% SoH, true low-mile wrecks.

Industry standard is EoL at 80% for perspective and once the decline's started it only accelerates.

Those bargain days are over I think.


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## Duncan (Dec 8, 2008)

The problem with "buy new" is that "new" is well over twice the price and much much lower quality


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## Duncan (Dec 8, 2008)

Isaac

Have you tried actually balancing your cells? - you can't balance them at an operating voltage 
To top balance them you need to charge them so that they are on the rapidly rising part of the voltage curve

One of the reasons that I suggest this is that "BMS" - Battery management systems used to be notorious for actually UNBALANCING peoples cells 

Try manually top balancing your pack - THEN see what capacity you have


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## Isaac97 (Jun 3, 2019)

Duncan - The Leaf BMS only discharges at about 10mA so it shouldn't be an issue. What voltage would you recommend for top balancing?
I have a Powerlab 8x2 which I could use with a computer to graph discharge tests.


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## Isaac97 (Jun 3, 2019)

What is the easiest balancing method? Should I parallel all the cells and connect a charger or charge each one separately?


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## rmay635703 (Oct 23, 2008)

Isaac97 said:


> What is the easiest balancing method? Should I parallel all the cells and connect a charger or charge each one separately?


If cell pairs are internally imbalanced it becomes a mess


Ideally charging each 3.7 volt cell in parallel with the rest is what you want taking them up via a regulated fixed voltage supply to near the top 90% SOC of the charge range for your chemistry.


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## john61ct (Feb 25, 2017)

Duncan said:


> The problem with "buy new" is that "new" is well over twice the price and much much lower quality


I was not talking about any particular brand / model of cell or pack.

Unless just learning playing around, second-hand sucks and getting poorer value higher risk every month.

So choose the best pack / cell type that you can find, new and from trustworthy sources.


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## Isaac97 (Jun 3, 2019)

rmay635703 said:


> If cell pairs are internally imbalanced it becomes a mess.


For this reason I'll charge the low cells of the modules first. Or use two separate chargers (without common ground) and bring both cells within the modules to the same voltage.



john61ct said:


> So choose the best pack / cell type that you can find, new and from trustworthy sources.


Volume and cost were driving forces in the selection of the Leaf pack. I have the entire pack in the engine compartment and there is no other space for it. Even a single Volt pack would not fit. Do you know of a cell type with better volume density and similar price?


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## john61ct (Feb 25, 2017)

Of course if new cells were offered at a price competitive with secondhand, their quality would be just as suspect.

I'm not addressing your case specifically, do as you please, 

just expressing that over say 5+ years of cycling, normal mileages, I doubt the savings from buying secondhand packs is worth all the extra non-monetary costs and unreliability.

Of course going cheap is perfect for those just learning experimenting etc


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## Isaac97 (Jun 3, 2019)

john61ct said:


> Of course going cheap is perfect for those just learning experimenting etc


My exact use case (as much as I would like my car to be more useful).
EVs are really fun.


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## john61ct (Feb 25, 2017)

If you can get to the individual cell terminals, I believe you can precisely balance them against each other to an average voltage point using

capacitive cell balancing devices, aka "charge shuttling", "transfer balancing"

while still leaving the pairs hooked up in series.

Check out ZHC "battery equalizer balancer"
Shenzhen Huaxiao Technology Co., Ltd

HA02 looks like good value, will do two pairs at a time.


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## john61ct (Feb 25, 2017)

Just realize if the cell **capacities** vary too much, packs are limited by the weakest link, balancing at the top SoC vs the bottom just shifts the same restricted range up or down.

There is still a protective BMS in place with per-cell detection that shuts the whole pack down, right?

Fun is fun until it isn't, boom bad


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## Isaac97 (Jun 3, 2019)

john61ct said:


> Just realize if the cell **capacities** vary too much, packs are limited by the weakest link, balancing at the top SoC vs the bottom just shifts the same restricted range up or down.
> 
> There is still a protective BMS in place with per-cell detection that shuts the whole pack down, right?
> 
> Fun is fun until it isn't, boom bad


Yes. I have an Arduino communicating with the BMS and monitoring all the cells.
Now to take out the pack and disassemble it.


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## john61ct (Feb 25, 2017)

ideally build in redundancies, easy with cheap DIY hardware


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## SeanOrk (Jul 7, 2016)

Isaac97 said:


> Hello all,
> 
> 
> When fully charged (4.10V) .....


Could you tell me exactly how your charging system determines that your pack is "fully charged" please ? - 

..... remembering that a cells terminal voltage is not an accurate guage of being "fully charged"


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## Duncan (Dec 8, 2008)

SeanOrk said:


> Could you tell me exactly how your charging system determines that your pack is "fully charged" please ? -
> 
> ..... remembering that a cells terminal voltage is not an accurate guage of being "fully charged"


The best way to determine that is to plot the voltage as you charge it
You will get a flat slope with a change to a steep slope as the cell is full 

Once you have done that with a handfull of cells then you will know the desired voltage

You are doing this BECAUSE "a cells terminal voltage is not an accurate gauge of being "fully charged" ---- UNTIL it reaches the end when it is


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## john61ct (Feb 25, 2017)

And that SoC vs Voltage correspondence is only meaningfully stable after isolated rest, for say an hour. longer is better for high accuracy.

At the very high reaches approaching theoretical 100%, there is also a "surface charge" effect that can last a very long time. 

Just discharge 0.01% of SoC and you may see a greater V drop than the next 1%.

Finally, that correspondence table, once precisely documented, changes over time as capacity is lost.


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## john61ct (Feb 25, 2017)

The most precise measure is to hold the termination **charge** voltage, observe current acceptance drop, stop at a precise endAmps setpoint, say you use 0.01C 

if you can't find the maker spec, this is how they define Full

then after an hour, measure the cell voltage at rest.

Note most users do not go to this point int normal charge cycling as it reduces longevity a lot.

But maintenance, testing purposes used occasionally NP.


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## SeanOrk (Jul 7, 2016)

Duncan said:


> The best way to determine that is to plot the voltage as you charge it
> You will get a flat slope with a change to a steep slope as the cell is full


That's not the correct method of determining when the charge current should be terminated.


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## SeanOrk (Jul 7, 2016)

john61ct said:


> The most precise measure is to hold the termination **charge** voltage, observe current acceptance drop, stop at a precise endAmps setpoint, say you use 0.01C



That is the correct method of determining when the charge current should be terminated.

Cell life longevity will not be adversely affected unless this method of charge termination is used repeatedly when the terminal voltage is at the cells maximum - 4.2v

I expect the OPs pack has never, while in his ownership, been correctly fully charged.


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## john61ct (Feb 25, 2017)

I was certainly not referring to any specific pack, just offering general information.

Fortunately unlike lead chemistries, with LI rarely or never going to Full inflicts no harm afaik, other than voluntarily leaving that unused capacity on the table


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## Duncan (Dec 8, 2008)

SeanOrk said:


> That's not the correct method of determining when the charge current should be terminated.


Possibly not but it is the one method that will work and does not depend on information from dubious sources on the internet

Remember I am NOT suggesting that you do this all the time but that you do it to determine the correct voltage to use in top balancing your cells


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## john61ct (Feb 25, 2017)

Duncan said:


> Possibly not but it is the one method that will work and does not depend on information from dubious sources on the internet
> 
> 
> 
> Remember I am NOT suggesting that you do this all the time but that you do it to determine the correct voltage to use in top balancing your cells


It **is** the canonical method as used by industry and the research community.

the "not" was a typo


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## Isaac97 (Jun 3, 2019)

SeanOrk said:


> I expect the OPs pack has never, while in his ownership, been correctly fully charged.


Correct. As the cells are not top balanced the charger is always shut off by the BMS before reaching the CV stage.

After removing the pack I will bring all the cells to 4.2 volts, completely discharge, and then recharge for top balancing.
Anyone know how to use Powerlab 8's in parallel? Or series


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## glyndwr1998 (Apr 27, 2013)

Hi isaac97,

I`m sure nissan only charge the leaf cells to 4.14v max. 

4.2v is absolute max votage, you should stay away from this voltage if possible as it will degrade your cells much quicker.

Also, when discharging, 3.5v is the lowest you really want to go.

Anthony.


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## Duncan (Dec 8, 2008)

glyndwr1998 said:


> Hi isaac97,
> 
> I`m sure nissan only charge the leaf cells to 4.14v max.
> 
> ...


That is very true for normal operation -
For Top Balancing you NEED to reach the fully charged position and balance them there

But you normally only do that occasionally


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## john61ct (Feb 25, 2017)

depending on your top balance method there is no need to go to the highest maximum.

So long as it a bit higher than you usually go in normal operations.


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## Duncan (Dec 8, 2008)

john61ct said:


> depending on your top balance method there is no need to go to the highest maximum.
> 
> So long as it a bit higher than you usually go in normal operations.


Disagree

You NEED to get above that straight line part of the graph and onto the rising part 

Otherwise you simply don'y know how much of the capacity has been used


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## john61ct (Feb 25, 2017)

Well yes, above the shoulder.

My normal operating 100% SoC is just below there.

Otherwise you're sacrificing both capacity and lifespan, unless the bank is grossly oversized.

And also, voltage is not the only spec, at different current rates you will be at completely different SoC levels.


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## GregShay (Aug 20, 2016)

Hi Issac,
I actually do not see anything wrong or unusual with the BMS status picture you posted in the discharged state.

Below about 3.5V, the charge curve of the Lithium cell turns downward sharply. This means there is not much charge left once you get down to 3.5V. The minimum discharge voltage of 3.0V is just used as a do not exceed minimum.
So when you discharge below 3.5, it pretty normal for the voltages of the cells to have relatively larger differences, typical as shown in your graph. I do not think this itself indicates the lower voltage cells are bad.

In other words, there is not much charge left below 3.5V. Practically all of the energy in these lithium cells is from 4.1V down to 3.5.

25 mi at what speed? A Porche is going to want you to drive fast (no doubt, no blame!) and power consumption goes way up once you get above about 50mph. My Chevy Volt pulls 23kW at 70mph straight and level. At 35mph it is something like 7kW. And zooming acceleration pulls up to 150kW. Above 50mph, speed makes a significant difference in consumption. Going 
highway speeds uphill *really* eats the battery. I can use half my normally
60miles of battery in 10 miles by driving 75mph on the freeway, uphill (from 600ft above sea level to 1400ft above sea level).

I would have thought you might have been simply using up your 25kWh with fast driving, but the fact that the charge only took 12kWh is more concerning. How was that measured? Actual charge current measured,
or some indirect assumption (like charge rated kW x time)?

Does 12kWh match your consumption rate? In other words, while you were
driving the 25mi, what kW (or what amps x 380V) were you pulling? 

On the positive side, I have seen people collecting data on how rapidly these Leaf cells lose their capacity over years of time and use. The data shows they lose some, maybe 10% to 15%, but I have not seen anyone show data that they go down by half (and your Gen2 are newer and better capacity.)

I can't say what it is yet, but my bet is that your cells may yet be ok.

Cheers


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## GregShay (Aug 20, 2016)

I just looked up your motor / controller.. Nice! but if you are drawing 300A from that Leaf pack, that may be the problem.

IIRC, the Leaf modules are rated for like 100A discharge current. (I have my pack at a lower voltage 72V x 3 in parallel to get to pulling like 400A).

If you are pulling 300A from the Leaf pack, I bet those batteries are getting *hot* and your 'missing 12kWh' is lost in heating the battery pack during your 25mi Porche zoomfest..

Assuming this is true the solution is to split the pack in two, run the two parallel packs of half the voltage (approx 190v), and twice the current.

Good luck!


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## GregShay (Aug 20, 2016)

Hi Issac,
I actually do not see anything wrong or unusual with the BMS status picture you posted in the discharged state.

Below about 3.5V, the charge curve of the Lithium cell turns downward sharply. This means there is not much charge left once you get down to 3.5V. The minimum discharge voltage of 3.0V is just used as a do not exceed minimum.
So when you discharge below 3.5, it pretty normal for the voltages of the cells to have relatively larger differences, typical as shown in your graph. I do not think this itself indicates the lower voltage cells are bad.

In other words, there is not much charge left below 3.5V. Practically all of the energy in these lithium cells is from 4.1V down to 3.5.

25 mi at what speed? A Porche is going to want you to drive fast (no doubt, no blame!) and power consumption goes way up once you get above about 50mph. My Chevy Volt pulls 23kW at 70mph straight and level. At 35mph it is something like 7kW. And zooming acceleration pulls up to 150kW. Above 50mph, speed makes a significant difference in consumption. Going 
highway speeds uphill *really* eats the battery. I can use half my normally
60miles of battery in 10 miles by driving 75mph on the freeway, uphill (from 600ft above sea level to 1400ft above sea level).

I would have thought you might have been simply using up your 25kWh with fast driving, but the fact that the charge only took 12kWh is more concerning. How was that measured? Actual charge current measured,
or some indirect assumption (like charge rated kW x time)?

Does 12kWh match your consumption rate? In other words, while you were
driving the 25mi, what kW (or what amps x 380V) were you pulling? 

On the positive side, I have seen people collecting data on how rapidly these Leaf cells lose their capacity over years of time and use. The data shows they lose some, maybe 10% to 15%, but I have not seen anyone show data that they go down by half (and your Gen2 are newer and better capacity.)

I can't say what it is yet, but my bet is that your cells may yet be ok.

Cheers


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## Isaac97 (Jun 3, 2019)

GregShay said:


> IIRC, the Leaf modules are rated for like 100A discharge current. (I have my pack at a lower voltage 72V x 3 in parallel to get to pulling like 400A).


The Leaf has a 90kw rated motor which means current draw of at least 225A. 300A is not great for the batteries but shouldn't cause 50% capacity reduction.

The car is now back up on jack stands in the garage, so I will report back soon with more information.
Thanks for the help so far!


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## Duncan (Dec 8, 2008)

Re the current that you are using

If the motor has 300 amps it does NOT mean that is what the battery sees

Your controller works by dropping the voltage until the "comanded current" = actual motor current

Motor current x motor voltage = battery current x battery voltage

the voltage to drive current through the motor is very low - 10 volts?
BUT as the motor spins it develops a back EMF - so that has to be overcome

My car (rough numbers)

----------Motor ----------------Battery
Start - 1200 amps 10v = 340v x 35 amps

1000 rpm 1200 amps x 120v = 340v x 423 amps

2000 rpm 1200 amps x 230v = 340v x 812 amps

3000 rpm - 1200 amps - 340v = 340v x 1200 amps --- Controller at 100%

4000 rpm - 900 amps - 340v = 340v x 900 amps - --- Controller at 100%

5000 rpm - 720 amps - 340v = 340v x 7200 amps --- Controller at 100%

With a smaller motor and lower current you are almost certainly NOT maxing out the controller so you batteries probably never see 300 amps

This also shows that splitting up into two paralel strings does not actually buy you anything - unless your controller cannot handle the full voltage


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## Ozpara (Apr 11, 2016)

Great to see another 986 ev on the road.
I had a few weeks of battery balancing before the pack evened out and I fully charged each cell before putting them all together. 
What's the total KW of the pack as I have an 18 KW pack and I only get 70 to 80 kms. I think it's the 265 tyers that don't help the top down also makes more drag.
My pack is an A123 pouch cell setup as this gave me more for the space.
Mine is also on blocks ar the moment getting my battery's redesigned and replacing one cell that collapsed. 
Good luck with the rebalancing


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