# Gen 1 Chevy Volt Battery reconfigured to 2x 144v sets. Need help with adjusting used NG3 Lithium charger to charge these



## mons2b (Nov 17, 2015)

Gen 1 Chevy Volt Battery reconfigured to 2x 144v sets. Need help with adjusting used NG3 Lithium charger to charge these.

A long time back I obtained these batteries and while standing quite a while they still measure out ok. I have recently been given a used NG3 Zivan charger that was formerly used to charge 144v of thundersky type batteries I think. 

Will I only need to adjust the voltage pot inside? Will the other sittings be "ok" as is? Could someone more experienced charging these batteries and knows a bit about the NG3 please help me?


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## mons2b (Nov 17, 2015)

Anyone have any ideas?


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## cricketo (Oct 4, 2018)

Chevy Volt is NMC, Thundersky is likely LFP. I can't seem to find any docs on NG3 charger suggesting any user configuration. Here is one for example :


https://zivanusa.com/pdf/NG3.pdf



Even if you can adjust the voltage output on the charger, you need to ensure individual cells don't fall out of balance and get sent over their maximum voltage. In other words you want a BMS that has ability to disconnect the charger in case of cell overvoltage condition.


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## mons2b (Nov 17, 2015)

cricketo said:


> Chevy Volt is NMC, Thundersky is likely LFP. I can't seem to find any docs on NG3 charger suggesting any user configuration. Here is one for example :
> 
> 
> https://zivanusa.com/pdf/NG3.pdf
> ...



a BMS is over a thousand dollars US and then you do the currency conversion to NZ dollars. I will be trying without BMS and monitoring the cells manually. At least at first. It has been done before successfully. running the batteries too low is what puts them out of sync. I have two duplicate packs of 144v. cross connecting the cells will provide a limited self balance as well.


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## mons2b (Nov 17, 2015)

What i was really hoping was someone who knows these cells and could suggest a output voltage to set the NG3 to. I could try as is and monitor it closely . WHich may be the case if no one has any ideas


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## cricketo (Oct 4, 2018)

mons2b said:


> a BMS is over a thousand dollars US and then you do the currency conversion to NZ dollars


How much does it cost to build a new house in place of the one that burned down in NZ dollars ?


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## cricketo (Oct 4, 2018)

mons2b said:


> What i was really hoping was someone who knows these cells and could suggest a output voltage to set the NG3 to. I could try as is and monitor it closely . WHich may be the case if no one has any ideas


4.2v is the max for all NMC cells. Ideally you should not charge to the max, so 4.1-4.15 at most.


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## mons2b (Nov 17, 2015)

cricketo said:


> How much does it cost to build a new house in place of the one that burned down in NZ dollars ?


Thats a smart ass comment that is uncalled for.


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## cricketo (Oct 4, 2018)

mons2b said:


> Thats a smart ass comment that is uncalled for.


You're totally right! I should be nicer to people, support and encourage unsafe design and operation of high power systems.


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## mons2b (Nov 17, 2015)

I am looking for the output voltage total from the charger. They charge at a higher voltage than the pack and then ease it back when the pack is at 144. This charger was charging 144v before but with batteries a bit different. I know what the max per Chevy Gen 1 cell is . Im looking for what might be a good output voltage to set this charger to.


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## mons2b (Nov 17, 2015)

cricketo said:


> You're totally right! I should be nicer to people, support and encourage unsafe design and operation of high power systems.


I dont think its unsafe if its monitored and tested. We have strict rules here but nothing says a BMS is compulsory. I simply cant afford one. And I dont own a house either. My aims are to test these things. I dont agree with you and would rather you commented somewhere else


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## remy_martian (Feb 4, 2019)

In the absence of a BMS, you'll need to charge each cell separately....no free lunch.


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## mons2b (Nov 17, 2015)

remy_martian said:


> In the absence of a BMS, you'll need to charge each cell separately....no free lunch.


They are all connected together. They have their balance leads intact. I will check them occasionally to see none are heading out of range


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## john61ct (Feb 25, 2017)

mons2b said:


> I am looking for the output voltage total from the charger. They charge at a higher voltage than the pack and then ease it back when the pack is at 144. This charger was charging 144v before but with batteries a bit different. I know what the max per Chevy Gen 1 cell is . Im looking for what might be a good output voltage to set this charger to.


You need to know the S-count. 144V is a nominal label that does not tell us anything specific.

If 39S them 4.15V is 161.85V 162V close enough termination voltage

If 40S then it's 166V


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## john61ct (Feb 25, 2017)

Going without a BMS is fine

but greater knowledge is needed.

And the gear to properly monitor per cell-group voltages, and to balance your groups manually.

You need to monitor your cell-group voltages when charging most especially so you stop before the first one hits 4.20V

While driving, before approaching 3.2-3.4Voc even higher really best for longevity.


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## remy_martian (Feb 4, 2019)

As long as the battery is open circuit, you can charge one parallel 4V set of cells at a time. Just charge the low SoC ones for now


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## brian_ (Feb 7, 2017)

mons2b said:


> Thats a smart ass comment that is uncalled for.


That's certainly a smart ass comment, but it was entirely called for. If you don't understand what you're doing, you should be less arrogant about doing it, and should expect some blunt warnings.


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## brian_ (Feb 7, 2017)

mons2b said:


> I am looking for the output voltage total from the charger. They charge at a higher voltage than the pack and then ease it back when the pack is at 144.


You clearly don't understand basic electrical concepts - there isn't a pack voltage that you can monitor which is different from what the charger is applying to it, unless you have some substantial resistance in your wiring causing a meaningful voltage drop.



mons2b said:


> I know what the max per Chevy Gen 1 cell is . Im looking for what might be a good output voltage to set this charger to.


Without a BMS, you will know the total of all of the cell voltages in series, but how will you know the voltage of each cell... or more importantly, the most-charged cell?


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## remy_martian (Feb 4, 2019)

The most charged cell would be obvious by thermal observation:









😁


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## brian_ (Feb 7, 2017)

john61ct said:


> You need to know the S-count. 144V is a nominal label that does not tell us anything specific.
> 
> If 39S them 4.15V is 161.85V 162V close enough termination voltage
> 
> If 40S then it's 166V


That all makes sense, but 144 volts isn't even the nominal voltage of the proposed pack. A battery assembled from first-generation Volt modules must be a multiple of 6S (unless the modules are reconfigured by cutting and reworking cell tab connections within the module). He likely thinks that 6S3P and 12S3P modules have nominal voltages of 24 and 48 volts (because they are sold that way), so his "144 V" string is likely 36S3P. GM thinks that a 96S set is nominally 360 V (3.75 V/cell) - and 395 V fully charged (4.11 V/cell) if it matches the second-generation cell characteristics - so 36S is 135 volts nominally (and likely 148 V fully charged if perfectly balanced)... but what would they know? 

The amusing thing is that sometimes two wrongs make a right: the wrong voltage description by incompetent vendors (48 V for 12S instead of 45 V) happens to be close to the fully-charged voltage (48 V for 12S or 144 V for 36S).


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## brian_ (Feb 7, 2017)

For those needing information about Chevrolet Volt batteries, this GM document is a very good start:
VOLT_BATTERY.pdf


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## brian_ (Feb 7, 2017)

john61ct said:


> Going without a BMS is fine
> 
> but greater knowledge is needed.
> 
> ...


All of that amounts to the person operating the charger acting as the Battery Management System... so you still need a BMS, but it can be you.


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## Duncan (Dec 8, 2008)

Hi Mons2b

I'm using Chevy volt cells (possibly even abusing them)
I charge them using a voltage limit - my charger simply charges to that limit and then shuts off

After looking at a number of different Charge/Discharge curves I decided that I would work between 3.5 volts (lower) and 4.05 volts upper

The full Volt (mk1) pack is 96S 
I could not fit all of them under my bonnet so I'm using 84S (one of the 2kWh 12S modules is spare) - I run from 294 volts (empty) to 340 volts (full)

The Volt has seven 2kWh modules and two 1kWh modules

The 2 kWh are 12S - the 1 kWh are 6S

Using my figures the 1 kWh modules should be - 21v to 24.3 volts ---- the 2 kWh modules would be 42 volts to 48.6 volts

Some people say that you should never use voltage for controlling a charger - the Chevy Volts cells ARE a different chemistry to the usual aftermarket cells
This chemistry has a much greater "slope" on the voltage/charge curve - which makes using voltage much more sensible

As far as going out of balance is concerned - despite drawing 28C I still nave not observed any


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## brian_ (Feb 7, 2017)

I assume that Duncan's success with using overall pack voltage to terminate charging and limit discharge results from choosing conservative limits, so that even if a cell group is significantly higher or lower it will still likely be within operable limits. His 4.05 V/cell is significantly different from setting a charger to 4.2 V/cell and hoping for the best.


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## Duncan (Dec 8, 2008)

brian_ said:


> I assume that Duncan's success with using overall pack voltage to terminate charging and limit discharge results from choosing conservative limits, so that even if a cell group is significantly higher or lower it will still likely be within operable limits. His 4.05 V/cell is significantly different from setting a charger to 4.2 V/cell and hoping for the best.


I measured every cell (every group of cells in parallel) both at the low charge and at the high charge 

This is the initial test back in 2017

Voltmeter on both sides of pack - both 149.7v (added together 299.4v)

Using my Celllog 8M I checked all of the cells
max - 3.548v
min - 3.536v
range 12mv
Looking good!

So I charged it
341.6v on the CA
Voltmeter on both sides of pack - both 172.1v - 172.2v (added together 344.3v)

Using my Celllog 8M I checked all of the cells
max - 4.078v
min - 4.064v
range 14mv

So all looking good! 

I have done that three or four times since then - similar ranges - about 14 mV
My CA says 341 when the charger said 340 - I call that a hit!


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## john61ct (Feb 25, 2017)

brian_ said:


> He likely thinks that 6S3P and 12S3P modules have nominal voltages of 24 and 48 volts


Well as stated that certainly needs to be straightened out before anything meaningful can be advised. 

And yes, the farther you stay away from spec-sheet top and bottom, the less critical it is that per-cell/group BMS functions be automated, and the less attention needs to be devoted to balancing

and the longer the cells last.


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## remy_martian (Feb 4, 2019)

I don't think anybody's arguing you can't voltage charge the cells, especially when they are balanced and matched, but how do you charge them at 1C with voltage to max the life of the cells? 

If you're at 5% SoC and you charge at the 80% SoC voltage, how much current is going into the pack at t0? Has to be much more than 1C because the pack voltage is lower. Maybe you're charging at 4C or 5C?

I'd be interested, Duncan, in knowing what your cell temperatures are, say an hour after you plug into a mostly discharged pack.


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## Duncan (Dec 8, 2008)

remy_martian said:


> I don't think anybody's arguing you can't voltage charge the cells, especially when they are balanced and matched, but how do you charge them at 1C with voltage to max the life of the cells?
> 
> If you're at 5% SoC and you charge at the 80% SoC voltage, how much current is going into the pack at t0? Has to be much more than 1C because the pack voltage is lower. Maybe you're charging at 4C or 5C?
> 
> I'd be interested, Duncan, in knowing what your cell temperatures are, say an hour after you plug into a mostly discharged pack.


My charger (BRUSA) is capable of charging at 3kW - but as I wanted the capability to charge at any old mains plug I limited it to 2 kW 
At 2 kW - which is 1/7thC it does not get even slightly warm
Here (Southland) the battery never gets up to the 35C which is apparently optimum
I spent Sunday drag racing - wonderful hot sunny day - highest battery temperature was 29C


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## remy_martian (Feb 4, 2019)

pfft...1/7th C is getting close to the self discharge rate 😂

There's a charmed life....drag racing on a sunny Sunday


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## Duncan (Dec 8, 2008)

remy_martian said:


> pfft...1/7th C is getting close to the self discharge rate 😂
> 
> There's a charmed life....drag racing on a sunny Sunday


1/7th C - will fully charge in .... 7 hours!

The self discharge rate appears to be 10%/YEAR!!

The printer died at the drags yesterday - so I don't have my official times (yet) but I'm told I did a 12.2 second


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## remy_martian (Feb 4, 2019)

Might need to put you in a cage if you bust into elevens 😂


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## mons2b (Nov 17, 2015)

brian_ said:


> I assume that Duncan's success with using overall pack voltage to terminate charging and limit discharge results from choosing conservative limits, so that even if a cell group is significantly higher or lower it will still likely be within operable limits. His 4.05 V/cell is significantly different from setting a charger to 4.2 V/cell and hoping for the best.


I never planned to set for 4.2 and "hope for the best".


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## mons2b (Nov 17, 2015)

Duncan said:


> Hi Mons2b
> 
> I'm using Chevy volt cells (possibly even abusing them)
> I charge them using a voltage limit - my charger simply charges to that limit and then shuts off
> ...


Hello Duncan other people seem to allude that I am ignorant. My Gen 1 chevy pack arrived with different sized modules. Literally big and small ones. I needed 144v as I had originally needed that in lead acid and had a motor and invertor set for that so thats what i needed to do. So I took them apart carefully and put three of the larger modules together in two blocks. They both now years later still sit at 145v. Knowing what you know about these batteries Duncan should I indeed (if possible) try to tune the output voltage on the NG3 charger I am using to about 151 volts? I do not want to mess with its other settings. It was used previously for a different chemistry of lithium but the same 144v.

Edit: there are 3x 12s chevy modules x2 ie in parallel


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## remy_martian (Feb 4, 2019)

^^ You also never have stated how many cells make up this battery you are charging.

You have really bad selective hearing.

^ and you still haven't 🤦‍♂️


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## mons2b (Nov 17, 2015)

remy_martian said:


> ^^ You also never have stated how many cells make up this battery you are charging.
> 
> You have really bad selective hearing.
> 
> ^ and you still haven't 🤦‍♂️


your rather rude. If you cant be nice dont talk. Didnt your parents teach you that?


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## john61ct (Feb 25, 2017)

Fvck being polite.

You are asking for help.

You have been told that you must tell us this information before your questions can be answered.


john61ct said:


> You need to know the S-count. 144V is a nominal label that does not tell us anything specific.
> 
> If 39S them 4.15V is 161.85V 162V close enough termination voltage
> 
> If 40S then it's 166V


If you don't know how to figure that out, then ask for help until you do, use a DMM and videos or pics or diagrams

educate yourself!

And stop tone policing, this is an open forum, and people will communicate however they like.

Or go hire a professional at hourly consulting rates to help you, then you at least nominally have the right to tell them how to interact with you.


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## Duncan (Dec 8, 2008)

mons2b said:


> Hello Duncan other people seem to allude that I am ignorant. My Gen 1 chevy pack arrived with different sized modules. Literally big and small ones. I needed 144v as I had originally needed that in lead acid and had a motor and invertor set for that so thats what i needed to do. So I took them apart carefully and put three of the larger modules together in two blocks. They both now years later still sit at 145v. Knowing what you know about these batteries Duncan should I indeed (if possible) try to tune the output voltage on the NG3 charger I am using to about 151 volts? I do not want to mess with its other settings. It was used previously for a different chemistry of lithium but the same 144v.
> 
> Edit: there are 3x 12s chevy modules x2 ie in parallel


OK so you have three of the 2 kWh modules is series (twice!) - so each is 36S

If you use the numbers that I have been using that will be a "low voltage" of 36 x 3.5 = 126 volts
And a "full" voltage of 36 x 4.05 = 145.8

As remy_martian has said I am using quite conservative numbers
You could safely go up to 4.1 volts - which would be 4.1 x 36 = 147.6 volts 

151 volts would be 4.2 volts - possibly a wee bit too high!


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## remy_martian (Feb 4, 2019)

You're guessing what he has. He's measured the voltage of a pack that's been sitting for a long time. We don't know if there's a dead or weak cell in the mix...just assumptions and guesses when he is squatting on easy info that's been asked several times.

Unless he's in love with you, he ignores efforts to troubleshoot.

Cuz it's pulling teeth for him to tell us HOW MANY FUCKING CELLS IN SERIES?


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## mons2b (Nov 17, 2015)

Duncan said:


> OK so you have three of the 2 kWh modules is series (twice!) - so each is 36S
> 
> If you use the numbers that I have been using that will be a "low voltage" of 36 x 3.5 = 126 volts
> And a "full" voltage of 36 x 4.05 = 145.8
> ...


Thanks Duncan. I will see if the charger can be adjusted that low. If not I wont be able to use it > luckily I can give it back to the person who gave it to me to try if it wont go that low. I think it might not. Isnt the charging voltage different to the cells end voltage? Ie the voltage the charger sees is different to what the cells actually have when the charger disconnects? Or do I understand that wrong? Doesnt the pack voltage drop off after the charger cuts off?


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## Duncan (Dec 8, 2008)

remy_martian said:


> You're guessing what he has. He's measured the voltage of a pack that's been sitting for a long time. We don't know if there's a dead or weak cell in the mix...just assumptions and guesses when he is squatting on easy info that's been asked several times.
> 
> Unless he's in love with you, he ignores efforts to troubleshoot.
> 
> Cuz it's pulling teeth for him to tell us HOW MANY FUCKING CELLS IN SERIES?


Hi Remy_martian

I can vaguely remember him from a few years back when he got his pack - its a Chevy Volt battery same as I have in my car - 

He should definitely pop the covers off and measure each cell!!

Here that Mons2B - measure each cell - I think they will be OK but just in case

With these packs its not that easy to see just how many cells there are - unless you pop the cover !
But once you have measured then put the covers back on for safety


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## Duncan (Dec 8, 2008)

mons2b said:


> Thanks Duncan. I will see if the charger can be adjusted that low. If not I wont be able to use it > luckily I can give it back to the person who gave it to me to try if it wont go that low. I think it might not. Isnt the charging voltage different to the cells end voltage? Ie the voltage the charger sees is different to what the cells actually have when the charger disconnects? Or do I understand that wrong? Doesnt the pack voltage drop off after the charger cuts off?


Yes - a wee bit - but the charger normally normally tapers the charge off and then shuts down -


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## brian_ (Feb 7, 2017)

mons2b said:


> I never planned to set for 4.2 and "hope for the best".


Right... but Duncan does set an overall voltage and let the charger run to that, not monitoring individual cells, so he must keep the target voltage per cell to a much more conservative level. If you were charge to 4.2V/cell without a BMS (whether that is an automated system or you as manual Battery Monitoring Slave), you would be just hoping for the best.


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## brian_ (Feb 7, 2017)

mons2b said:


> Isnt the charging voltage different to the cells end voltage? Ie the voltage the charger sees is different to what the cells actually have when the charger disconnects? Or do I understand that wrong? Doesnt the pack voltage drop off after the charger cuts off?


Yes, there is voltage drop due to internal resistance, so when charging is stopped the cells settle to a lower voltage. This is a bigger effect with lead-acid batteries than with lithium-ion batteries, so while it is a good question, it doesn't seem to be much of a consideration for lithium-ion charging.


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## brian_ (Feb 7, 2017)

Duncan said:


> With these packs its not that easy to see just how many cells there are - unless you pop the cover !


It's actually pretty easy if the modules are exposed, because the segments of polymer frame (the "slices" of the stack) are clearly visible, and each one holds two cells. The Gen 1 Volt battery is 96S3P, so for every three cells (1.5 frame segments) there is one parallel cell group. Thus a 12S3P module has 36 cells, which is 18 pairs of cells so 18 frame segments. If the module has about half that number of segments, it's a 6S33P module. The mechanically combined (bolted directly together with coolant flowing down the whole length) blocks are all visibly comprised of combinations of the small (6S) and large (12S) modules.

The second generation Volt modules are similar, but that battery is 96S2P and modules are 24-cell (12S2P) and 32-cel (16S2P), so they are about 12 and 16 frame segments long (maybe off by one because I think the end frames hold one cell each).

The polymer frame segments are visible in the illustrations in this GM document: VOLT_BATTERY.pdf


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## Duncan (Dec 8, 2008)

brian_ said:


> It's actually pretty easy if the modules are exposed, because the segments of polymer frame (the "slices" of the stack) are clearly visible, and each one holds two cells. The Gen 1 Volt battery is 96S3P, so for every three cells (1.5 frame segments) there is one parallel cell group. Thus a 12S3P module has 36 cells, which is 18 pairs of cells so 18 frame segments. If the module has about half that number of segments, it's a 6S33P module. The mechanically combined (bolted directly together with coolant flowing down the whole length) blocks are all visibly comprised of combinations of the small (6S) and large (12S) modules.
> 
> The second generation Volt modules are similar, but that battery is 96S2P and modules are 24-cell (12S2P) and 32-cel (16S2P), so they are about 12 and 16 frame segments long (maybe off by one because I think the end frames hold one cell each).
> 
> The polymer frame segments are visible in the illustrations in this GM document: VOLT_BATTERY.pdf


This is very true - but as well as the cell "slices" there are end pieces and middle pieces - its easy to get confused
much easier to count the terminations after taking off the top covers
This assumes that (like me) you are too thick to actually use the fancy electronics in the box on the top and are going to take it off and put it to one side


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## john61ct (Feb 25, 2017)

Pretty recent longevity studies show not much point going lower than 4.15Vpc

in a context where capacity utilisation (range) is an issue.

But that was CC only, charge to X and stop, not holding any Absorb/CV stage.

No I did not keep ref links, sorry. 

If range is not a concern, then cycle using the 50% at rest voltage as your "cycling center", going as low as 30% capacity utilisation can extend cycle lifespan by over ten times

everything else being equal.

C-rates in and out are an even greater influence though


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## remy_martian (Feb 4, 2019)

I'd be interested in reading those refs if you ever stumble across them again.


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## Nogasrequired (10 mo ago)

I found this. Might help you reset voltage output on charger.


https://www.zeva.com.au/Projects/RX7/Zivan%20Adjustment.pdf


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## piotrsko (Dec 9, 2007)

Im still having a hard time figuring out how the f he is getting 144v nominal as that would be 36 series cells and there is only 1 sub pack strap interconnector that will support that count and you would need two . at least on my 2011 pack
196, 168, 120, 96, 70, 48 are easy to reach combinations


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## Duncan (Dec 8, 2008)

piotrsko said:


> Im still having a hard time figuring out how the f he is getting 144v nominal as that would be 36 series cells and there is only 1 sub pack strap interconnector that will support that count and you would need two . at least on my 2011 pack
> 196, 168, 120, 96, 70, 48 are easy to reach combinations


Hi Piotrsko

The Mk1 Volt pack is seven 2kWh modules (12S) and two 1kWh modules 6S

He is using three of the seven 2kWh modules is series - 36s - which if using the conservative numbers would give a voltage of 126 volts to 146 volts

If you cut (and replace) the top band its quite easy to unbolt the modules and end up with the separate modules to play with

The picture is my pack - which is six of the 2kWh modules and both the 1kWh modules

Rereading the thread

BMS - if that was ALL I was using then I would be risking a bad failure
But I am using a Batt Bridge





Electric Vehicle Discussion List - Lee Hart's Batt-Bridge Battery Balance Alarm







www.evdl.org





This will tell me if I have a failed cell - which is the information that you NEED from your BMS

IMHO that is ALL of the information that you need
Cells (OEM Cells) stay in balance
Unless they DIE
And if they are going to die then a BMS will NOT keep them alive

So a complex BMS does not "buy you" anything over a simple Batt Bridge


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## cricketo (Oct 4, 2018)

Duncan said:


> Cells (OEM Cells) stay in balance


Is that what the manufacturer of the cells says ?


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## Duncan (Dec 8, 2008)

cricketo said:


> Is that what the manufacturer of the cells says ?


No the manufacturer will include a BMS as the cars will be used for a long time by various numbskulls


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## cricketo (Oct 4, 2018)

Duncan said:


> No the manufacturer will include a BMS as the cars will be used for a long time by various numbskulls


Seems like a contradictory statement - a factory EV will have the battery tucked away out of reach of the various numbskulls, thus arguably fewer safety measures would be required in comparison to various numbskulls on the DIY forums repurposing the cells for a variety of projects. Now with that out of the way, the question wasn't even about the vehicle manufacturers - the question was about cell manufacturers and their recommendations on their proper use. That is considering most vehicle manufacturers don't make their own cells. How does LG Chem suggest their cells should be used ? Do they say things like "our cells never degrade unevenly, thus BMS is not required" ?


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## Duncan (Dec 8, 2008)

cricketo said:


> Seems like a contradictory statement - a factory EV will have the battery tucked away out of reach of the various numbskulls, thus arguably fewer safety measures would be required in comparison to various numbskulls on the DIY forums repurposing the cells for a variety of projects. Now with that out of the way, the question wasn't even about the vehicle manufacturers - the question was about cell manufacturers and their recommendations on their proper use. That is considering most vehicle manufacturers don't make their own cells. How does LG Chem suggest their cells should be used ? Do they say things like "our cells never degrade unevenly, thus BMS is not required" ?


No because when you make millions and they are used for hundreds of thousands of miles there will be times when a BMS is required

However for hobbyists there are a few problems
The biggest one is that the BMS is the LARGEST by far reason that cells fail
You are taking something with a very low failure rate and adding something with a failure rate at least a 100 times as large

For non OEM cells - the actual cell failure rate is probably nearly as high as the BMS failure rate

The other part of the equation is how much the BMS can actually do
It can probably trim in an OEM cell that is a tiny amount different
But if its a non OEM cell that is failing - then all the BMS can do is to tell you its fucked - if its dying its going to die!!

And a simple system like my Batt Bridge can give me the same information for a fraction of the cost and without the failure modes of aftermarket BMS's


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## cricketo (Oct 4, 2018)

Duncan said:


> No because when you make millions and they are used for hundreds of thousands of miles there will be times when a BMS is required
> 
> However for hobbyists there are a few problems
> The biggest one is that the BMS is the LARGEST by far reason that cells fail
> ...


You're talking about some extreme conditions of complete cell failure or near failure. I am asking about gradual cell degradation - does the manufacturer guarantee their cells will degrade at an even rate ? There is a datasheet, there are likely some additional spec sheets and testing reports. What is your position based on besides the personal experiments ?


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## Duncan (Dec 8, 2008)

cricketo said:


> You're talking about some extreme conditions of complete cell failure or near failure. I am asking about gradual cell degradation - does the manufacturer guarantee their cells will degrade at an even rate ? There is a datasheet, there are likely some additional spec sheets and testing reports. What is your position based on besides the personal experiments ?


Personal experience - and reading the results everybody else has been getting

OEM cells are bloody GREAT

Aftermarket cells have an enormously higher failure rate 

Aftermarket BMS's - kill batteries 

Gradual cell deterioration - yep lose 20% after about 1500 full cycles - 

The main thing to do is to have liquid cooling - NOT to avoid high temperatures but to avoid having a few cells continually a bit warmer than their mates
This is why Leaf batteries fail


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## piotrsko (Dec 9, 2007)

THANKS for the reply Duncan, originally didn't see the other 6s string, but surprisingly it's there when I just gave it a hard look, however brian denies that they exist. I just had a real issue getting to 144 nominal without it.
Top band? Are you talking the bolt on interconnect or something else?

Well the OP seems to have gone underground so we now have the 2009 bms great war deja vu. [Buys popcorn, goes outside to look for evidence of nuclear fire in battery pack without bms]


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## mons2b (Nov 17, 2015)

piotrsko said:


> THANKS for the reply Duncan, originally didn't see the other 6s string, but surprisingly it's there when I just gave it a hard look, however brian denies that they exist. I just had a real issue getting to 144 nominal without it.
> Top band? Are you talking the bolt on interconnect or something else?
> 
> Well the OP seems to have gone underground so we now have the 2009 bms great war deja vu. [Buys popcorn, goes outside to look for evidence of nuclear fire in battery pack without bms]


Lol.


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## 52International (Feb 13, 2021)

Another newbie question…

The batteries are all in series and parallel as wired up. There’s no switches in there. Maybe some safety fuses.

How would a bms direct batteries to charge individually?


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## Duncan (Dec 8, 2008)

52International said:


> Another newbie question…
> 
> The batteries are all in series and parallel as wired up. There’s no switches in there. Maybe some safety fuses.
> 
> ...


The BMS cannot direct cells to charge individually - but it CAN discharge individual cells - so it can remove charge from the high cells (actually from the two or three cells in parallel)


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## 52International (Feb 13, 2021)

Duncan said:


> The BMS cannot direct cells to charge individually - but it CAN discharge individual cells - so it can remove charge from the high cells (actually from the two or three cells in parallel)


Oh I see, the sense lines double as a discharging circuit to even things out.

Got it, thanks!

Mark


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## remy_martian (Feb 4, 2019)

To add to that, the discharge current to balance cells is dismally small compared to the charge rate. Especially if you're whacking the pack with a DC charging station and doing full thermal conditioning.

The cells get balanced _eventually_ by a BMS which is why there's a band of zealots on this forum that see no point in adding a circuit that has a higher failure rate than the cells, so their BMS is Battery ("cell" actually, but that wrecks the joke) Meter Surveillance.


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## cricketo (Oct 4, 2018)

EV vendors typically use closely matched cells to build the battery packs, so theoretically if the cells came out of a single donor vehicle they should stay equalized. That is assuming there was no uneven wear for any reason. Now there are two scenarios where that is irrelevant. One, cells that came from some reclaimers are almost guaranteed to be unmatched, as they will likely come from several different vehicles. Two, new cells from the random [Chinese] suppliers. I have two Leaf packs that never fully equalize, as the BMS can't keep up.


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## 52International (Feb 13, 2021)

Thanks for the info. This is quite the learning curve!

The batt bridge idea is interesting, provides basic status. Best part is no microprocessor or software to fail.  You could have one for the entire circuit or multiple for sub circuits. If you had an odd number of cells in series, perhaps you can get tricky with resistor values to match. My mind wanders further and further away until it looks something closer to a bms, which is what you’re trying to prevent.

But it looks to me to need isolation to keep from bringing high voltage into the cab. Shouldn’t there be an opto isolator to drive isolated signals into the cab so you don’t risk high voltage? If the positive or negative get cut, yikes high voltage coming your way.

But maybe I don’t understand how it would be used. I’m thinking about batteries buried in a metal box under the floor boards.


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## remy_martian (Feb 4, 2019)

High voltage stays inside the inverter, inside the motors, inside the battery box, inside the AC compressor, inside the heaters, and inside the HV cables. It never goes in the cab apart from a PTC cabin heater, if you must (I'm a big fan of coolant heater cores).

So, yes, your voltage measurements need to stay inside the battery box and any wires coming out of that box, other than the HV cables and maintenance disconnect, needs to be isolated and only work in the 12V battery power domain.


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## 52International (Feb 13, 2021)

remy_martian said:


> High voltage stays inside the inverter, inside the motors, inside the battery box, inside the AC compressor, inside the heaters, and inside the HV cables. It never goes in the cab apart from a PTC cabin heater, if you must (I'm a big fan of coolant heater cores).
> 
> So, yes, your voltage measurements need to stay inside the battery box and any wires coming out of that box, other than the HV cables and maintenance disconnect, needs to be isolated and only work in the 12V battery power domain.


Thanks, we’re on the same page with that.


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