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Discussion Starter #1 (Edited)
Hi every one,

i am thinking of building a diy battery extender for my 2014 nissan leaf.
after some searching i found these two youtube chanels that have done what i want to do
https://www.youtube.com/watch?v=ZSqGBPBxfUE
https://www.youtube.com/watch?v=UcGoSO_uRXs

and i think i can make it



the leaf has 24kwh battery pack
48 cells in series so 8v*48cels=386v
each cell have 62ah (24.000watt/386v)


i would like to use 18650 li ion cells



i get that i have to highjack the signals from the battery pack's contactors to disengage the battery extender pack when the main pack is disconnected.


what i don't get is how they charge the batteries ( by connecting it in parallel to the main pack it is charged while the main pack is charged )


but how do they balance it ?
so my uncertainty is which battery pack format should i use (i am thinking a 24kw battery pack option a) 18 modules in parallel each being 96s1p b)18 modules in series each being 1s18p


option (a) means that i don't have to make all of them at once and i can add them over time but how can i ballance each module being 96s1p it's large an i have to balance on the cell level



option (b) means that 1s18p per pack ,so each pack is self balancing but still i have to ballance the packs between them


i would love for some wisdom
 

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the leaf has 24kwh battery pack
48 cells in series so 8v*48cels=386v
each cell have 62ah (24.000watt/386v)
Those values are per module, not per cell. These Leaf modules are a 2S2P combination of four pouch cells stacked in a flat rectangular package, so the actual cell voltage and cell capacity are half of what you listed, with four times as many cells (in total) and twice as many cells in series for the whole pack. But there are 48 modules, so your overall pack voltage and Ah capacity are about right.
 

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...
so my uncertainty is which battery pack format should i use (i am thinking a 24kw battery pack option a) 18 modules in parallel each being 96s1p b)18 modules in series each being 1s18p


option (a) means that i don't have to make all of them at once and i can add them over time but how can i ballance each module being 96s1p it's large an i have to balance on the cell level



option (b) means that 1s18p per pack ,so each pack is self balancing but still i have to ballance the packs between them...
Every production EV makes the parallel cell connections at the lowest level, then connects those cell groups in series... this is your option "b", and it is used for the same reason: it is practical to monitor and balance.
 

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Discussion Starter #4
Is there any bms that can handle 96 (cells or modules of 18p1s) in series
If not what alternative do i have ( bms from ebay 12s) and somehow conectem in series?

My onboard charger is 3,3kw what A rating bms should i choose?


And also i think i should us bms .do i?
 

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Is there any bms that can handle 96 (cells or modules of 18p1s) in series
Yes, almost every production EV and plug-in hybrid uses 96 or more lithium cells in series... but of course it can be very difficult to use production EV components in anything other than the intended application. In this case - since you are adding to a Leaf - have you considered using another complete Leaf BMS, but wired to your second pack instead of a Leaf pack?
 

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If not what alternative do i have ( bms from ebay 12s) and somehow conectem in series?
I've always been curious about this.

I suspect the answer is "it depends", but, I don't have a BMS plan for mine yet either. On E-bikes and even motorbikes, running without one is okay, the chain just isn't that long typically. On a car, when you start looking at 50+ or 100+ long chains, you get a couple issues:

1 - The odds of having one bad group in the chain is linearly more likely.

2 - Manually checking them is much more of a chore, so you're less likely to bother, making imbalances go on longer.

I haven't seen an affordable BMS in those ranges though.

...

Also, it's hard to get a clear answer on what exactly a BMS is doing. Is it:

- Draining from the whole chain to charge the lower voltage cells?

- Bleeding off energy from the cells charged first (maybe the weaker cells that filled quickest), and dumping that as heat?

- Something else?

Is a BMS something running only during charging, or all the time? If only during charging, are you then limited to the max current of the BMS? Can the BMS balance cells in the background, independently of what's happening elsewhere or is it an integral part of the connection?

It seems like there's very low level explanations that don't handle any details, and very high level explanations that you'd have to be able to engineer a BMS to understand, and not much for explanations for the layman out there.
 

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Discussion Starter #7
at the previews post have been made some very intresting questions. it would be great if we could get some answers


in my case i would like to ask how would one go about using lets say 8 deferent bms (12s each) this assembly would cover the balance charge or discharge



https://www.ebay.com/itm/10S-12S-13...hash=item4b66a0a2a3:m:mhIUrNt-tJTVl4IEqXPfNog




also could one bms 96s be made using arduino and what funtions would it have to do

top charge or bottom charge
monitor temperature
monitor voltage
 

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Hi

I was thinking to make an extender for Ampera/Volt car. It only has 16kWh.
So i was thinking of doing it like you propose. But i quickly figured out it would not work. The problem is the main battery is 360Vdc something and that means your spare battery would have to be totally the same even Ri, which is not reasonable unless you just buy another Leaf pack. And still there is no guarantee Ri is on par with the first pack. So paralelling directly is out :(.

Then one time i was charging my friends EV when he was stuck. I have an EMW charger which is a large Buck converter. A friend had 200Vdc system and i have like 380Vdc. So charger didnt mind being connected from my car instead to AC source...
That got me thinking... I could use like 4x tesla modules for 20kWh and 96Vdc. Then i could use Boost converter to up the voltage to whatever car would require at the time. Power i think i could provide at 20kW.
This could be made on the drive provided car would drive slow enough.

And then i saw JackBauer playing with DCDC converter of Prius. This is just what we would need! Everything already built with nice water cooled inductor made for 25kW power conversion.

And best part is I could reverse the process, doing buck from AC mains to charge the rear pack with the same equipment. I would have to disconnect at least both HV DC lines from main battery at the time, but that are only two main contactors.
Also BMS would work to protect those cells through both contactors.

To get everything working when car is driving i would use "enable" pin from Volt DCDC converter because it it working only when the car is started.

I still need to make interface board to run this hardware :), that is the hard part...
 

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Discussion Starter #9
I have come to understand that using a leaf bms is the easyest solution and in conjunction with a cellphone and odb2 dongle monitor the pack.

Could someone input how we could implement it (diy 18650 pack 1s18p) 96 in series
With balancing wires in each pack.


Could someone upload a wiring diagram
 

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Discussion Starter #10 (Edited)
I found on youtube the leaf xpack 1.5 video and at the commends someone was saying the following..... Could someone explain how this would work

"I would also use a balance resistor on the circuit so that the relay will only become connected if the voltage between both the vehicle pack and the spare battery pack are equal. This should eliminate any sparks or damage to the relays as well as prevent high voltages and currents being passed between either battery pack once the relays have been fully activated."


What does he mean by balance resistor and how it would prevent the relay from connecting the two packs for if the voltage wasn't equal?
 

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Hi Plefakis,

I'm probably not being 'liked' for posting this...but:

-Please first learn the basics of electronics and (lithium) batteries
-Please practice with low voltage systems (e-bike, home backup, powerpack, etc.) to get knowledge and an understanding of high currents, pre-charge resistors, charging, balancing etc.

By starting with a 24 volt pack you're less likely to injure yourself or others, and it is (usually) safe to touch, experiment, etc.

Please don't jump in the deep part of the pool before you know how to swim.

Splicing into the HV wires of your car is -very- dangerous if you don't know -exactly- what you're doing.

You also need CANbus hacking to incorporate things into your car without running into errors or worse.

a parallel pack can be of different chemistry, but you have to know the details.
This parallel pack could very well supply 90% of the power at certain SOC levels, so it has to be suitable for that.

Once you're sufficiently 'trained' you'll probably throw away the idea of using 18650's because it's much easier and cheaper to use EV battery modules for this purpose, especially if you can use the existing BMS of these modules.
 
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