ripple4
Posts: 17
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018

Replace individual battery cells to renew/increase capacity

Wed Sep 19, 2018 5:54 am

New leaf owner here. lurked quite a bit. i gathered up pieces for an idea around the web and wanted to float an idea to see if i was missing something, what could go wrong and try to get ideas on how to work around any potential issues. I was looking at 32ah 3.7v pouch cells and found that it may be possible to make a leaf battery for less than Nissan is selling for. Alibaba has got 3.7v 32ah pouches for $27/each which times 192 is $5200 + shipping. assuming no volume discount. these cells advertise 3000 cycles, which is more than 9 years of life.

https://www.alibaba.com/product-detail/ ... 10a9o1UCd1

After watching some YouTube about dissembling a 4-cell unit the pouch tab design looks to be unique on the Nissan cells, both side to side and in protrusion from the cell. Also the internal black plastic supports for the cells might not be reusable since the internal connection would need to be in different places. But with ABS plastic and 3D printing a new end cap could be made with new bus bars resistance welded to the generic cell tabs and locate the buss bar connection lugs in the correct spots for the leaf pack wiring. or the cell ends could be wired to connection points and then encapsulated in epoxy with mounting holes that are cast in.

Going further, if one was going to make a clean sheet cell format, since the Nissan cells are ~52mm thick then one could stack 6x 8.5mm pouchs into the same thickness. then it would not be space prohibitive to upgrade from the 2p2s cell arrangement to a 3p2s arrangement and still fit in the stock battery case. also one of the biggest complaints i read is battery cooling. i suggest that since cells are slightly thinner without the aluminum cans and various air gaps, it would be possible to install copper heat conduction sheets every second cell layer and tie the ends opposite of the buss bars with a fluid heat transfer block. the heat transfer fluid i would use something like mineral oil or low viscosity transformer oil, in case it ever leaked. and then plumb each of the 48 heat transfer blocks to a liquid/liquid heat exchanger that connects to the leafs gylcol coolant system. coolant pipes run back to the charger on '11 and '12 cars so teeing into those would be the plan.

proposed layout:
Image

https://ibb.co/e7dk2K


if that was not enough to soak in, they have pouch cells that go up to 50ah in close to the same size format, which would push the stock 22.1kw cars up to 35.5kw in the 192 cell 2p2s. but with 288 cells in a 3p2s arrangement then pack capacity would be 51.8kw, still fitting into the stock battery case and with active temperature management.

Lastly, looking at videos of people who put in G2 cells into old G1 cars, they seem to say that the cars original BMS will not immediately allow the extra capacity, but over time it will learn to use it and give extra miles on the range meter. (http://www.mynissanleaf.com/viewtopic.p ... 2&start=10) so in principle with enough time, the courage to open the traction pack, re-engineer what hundreds of very very smart professionals perfected, might save some money and/or give capabilities not previously possible. it maybe possible to create a battery after Nissan stops supporting the car at the end of the day. Do the experts see problems here? what could go wrong with each step and how could it be worked around? i personally dislike newbie post with grand plans, and if i'm not missing anything i was going to get 6x 50ah cells and make one battery unit cell and attempt to test it, like seeing how fast it can charge without overheating with the cooling sheets. what the real capacity would be of the 50ah 3p2s unit cell within the limits of the BMS voltage cut offs. etc.

opening up pack to get to unit cells
https://www.youtube.com/watch?v=0dBjPwJ_Qaw

opeing up unit cells and looking at pouch cells
https://www.youtube.com/watch?v=WcqaAz1vjlo
Last edited by ripple4 on Wed Sep 19, 2018 8:17 am, edited 1 time in total.

HerdingElectrons
Posts: 72
Joined: Sat Sep 08, 2018 3:20 pm
Delivery Date: 17 Sep 2018
Location: Central Coast, Ca

Re: Replace individual battery cells to renew/increase capacity

Wed Sep 19, 2018 6:44 am

Your proposed layout image/doc isn't displaying for me presumably because I don't have a google account. Do you have a way to upload/display that without being logged into that service?
2018 SL Pearl White, LOVE ProPilot Currently at 4.1-4.5 miles/kwh as I learn to drive pure EV & the weather gets colder.

Sept 2018: AHr= 114.52 / SOH= 99.2 / HX= 99.70% / 14 mV cell delta

2013 Prius 2, 126K & still really enjoy the car

WetEV
Posts: 2369
Joined: Fri May 04, 2012 8:25 am
Delivery Date: 16 Feb 2014
Location: Near Seattle, WA

Re: Replace individual battery cells to renew/increase capacity

Wed Sep 19, 2018 7:05 am

ripple4 wrote:also one of the biggest complaints i read is battery cooling. i suggest that since cells are slightly thinner without the aluminum cans and various air gaps, it would be possible to install copper heat conduction sheets every second cell layer and tie the ends opposite of the buss bars with a fluid heat transfer block. the heat transfer fluid i would use something like mineral oil or low viscosity transformer oil, in case it ever leaked. and then plumb each of the 48 heat transfer blocks to a liquid/liquid heat exchanger that connects to the leafs gylcol coolant system. coolant pipes run back to the charger on '11 and '12 cars so teeing into those would be the plan.


Cooling for the charger and cooling for a battery are rather different.

The charger has a maximum temperature of operation, perhaps over 100C, and as long as it stays cooler than that all is well. Standard automotive component range is -40C to 125C, however there are 150C and 200C components available as well. It is common to have a safety factor between the component ratings and the temperature that the charger stops normal operation because of over temperature.

Battery would like to stay below 35C or so for best life. Normal temperatures that cars with thermal management have as cooling temperature thresholds to are usually in the range of 30C to 40C. Lower than 30C isn't wise due to condensation. The performance types would like NIO EP9 type cooling of the battery, or at least Tesla's cooling. Tesla's cooling will not allow for a full lap of Nürburgring Nordschleife at full speed. A passively cooled battery works out just fine for most of the USA for basic driving needs such as a reasonable commute and around town.

If you wanted to retrofit a battery cooling scheme, you would need to engineer the whole thing.

Nissan has had battery chemistry problems with the 2011-early 2013 models. The 2013 and 2014 are better, and the later cars are better still. Also the BMS isn't an easy problem, both capacity estimation and (in other cars) cell balancing are complex issues that car makers haven't done the best at. And there is potential for improvement of battery life by handling these issues better.

Buying cells off Alibaba doesn't give me warm and fuzzy feelings...

And there are far worse things that can go wrong in Li ion cells than capacity fade. Nissan isn't the worse, unlike all the Tesla fanbouys here might try to tell you. Ford and SSN, GM and out of battery with 50% charge, and the 2012 Zero S.
WetEV
#49
Most everything around here is wet during the rainy season. And the rainy season is long.
2012 Leaf SL Red (Totaled)
2014 Leaf SL Red

ripple4
Posts: 17
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018

Re: Replace individual battery cells to renew/increase capacity

Wed Sep 19, 2018 10:01 am

i changed the picture hosting website, but it still does not show up. i provided a link.

What can i learn from the battery cooling information there. keep max battery temp <35C/95F and don't assume that the vehicle liquid cooling loop can carry away the heat? how does the NIO car cool the battery? I've designed low delta-T cooling loops for industrial equipment and it was sort of easy because i knew how much heat was being produced because its stamped on the motor tag. with this battery cooling idea, its not clear how much heat it will need to remove and how quickly. I suppose charging is the scenario to consider and taking a stab at it with a 85% L2 charging efficiency the heat put into the 24kwh pack with a 6.6kw charger would be .5kwh/hour or 2000 BTU/hour and 1/2 that for a 3.3kw charger in a base/early model. On a 92% efficient 50kw DC fast charge the heating rate would be 8kwh/hour 27KBTU/hour. With these numbers either no cooling is required at all, or a 2-ton chiller is. Just using the mass of the lithium in the battery (295lb 192 cell 32ah) to absorb the heat of charging , assuming no heat transfer to the air or frame of the car, would be 36 degrees F for a 24kwh pack taking a 18kwh charge or 50F for the 570lb 288 cell 50ah example taking a 48kwh charge. so maybe designing the most aggressive active cooling system possible up to 30kbtu/hour with a 10F delta T to ambeit air, while still fitting in the factory battery box is the most practical approach. And then whatever is not actively removed will be left over and so heat the battery.



L2 charging efficiency info:
https://www.veic.org/documents/default- ... ciency.pdf

DC charging efficiency info:
http://www.mdpi.com/2032-6653/7/4/570/pdf

lorenfb
Posts: 1845
Joined: Tue Dec 17, 2013 10:53 pm
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Leaf Number: 416635
Location: SoCal

Re: Replace individual battery cells to renew/increase capacity

Thu Sep 20, 2018 7:30 am

One of the very few interesting threads on this forum!
Leaf SL MY 9/13: 70K miles, 49 Ahrs, 5.1 miles/kWh (average), Hx=70, SOH=78, L2 charges to 100% > 1000, max battery temp < 95F (35C), min discharge point > 20 Ahrs

WetEV
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Joined: Fri May 04, 2012 8:25 am
Delivery Date: 16 Feb 2014
Location: Near Seattle, WA

Re: Replace individual battery cells to renew/increase capacity

Thu Sep 20, 2018 8:31 am

ripple4 wrote:with this battery cooling idea, its not clear how much heat it will need to remove and how quickly. I suppose charging is the scenario to consider and taking a stab at it with a 85% L2 charging efficiency the heat put into the 24kwh pack with a 6.6kw charger would be .5kwh/hour or 2000 BTU/hour and 1/2 that for a 3.3kw charger in a base/early model.


Driving matters as well, perhaps even more than charging. Depends on how you drive and charge.

Power lost in battery is very roughly current squared times series resistance. I^2 * R
Current is power divided by voltage. W / V

Voltage is about 350V to 400V, varies over SOC.
Resistance varies from about 0.1 ohms to about 0.35 ohms, depending on age, direction of current and more.

https://avt.inl.gov/sites/default/files ... af0356.pdf

So with a full power discharge, might be 18kW. Think driving very fast up a very steep hill. Or could get close to that with repeated accelerations and regenerative breaking. (80kW discharge followed by 55kW charge). Round the Nurburgring.

However, unless you are driving round the 'ring, anything close these numbers can't be sustained. So you need a model as to how the car is used.

Suppose you L2 charge for a hour once a day, and drive at a reasonable power for a reasonable commute. Then you get to no cooling, unless the outside air temperature is averaging over 30C or so.

Or you could do a road trip model. Driving at x power, DCQC, repeat. In Kansas in the summer, at 45C. Or Nevada, or Death Valley. Or something like that.

Remember that preventing condensation at any time, coolant leakage even in the case of an accident and mechanical stress under all conditions on the cells are all more likely important.

As a road trip example, I recently did a 160 mile trip with 2 DCQC sessions, total time of 5 hours including stop at the midpoint. Battery temperature went from 18 C to 36 C at the end of the trip. Ambient was about 20 C plus minus 2 C the whole trip.
WetEV
#49
Most everything around here is wet during the rainy season. And the rainy season is long.
2012 Leaf SL Red (Totaled)
2014 Leaf SL Red

ripple4
Posts: 17
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018

Re: Replace individual battery cells to renew/increase capacity

Thu Sep 20, 2018 11:55 am

Thank you for the suggestion to calculate the heating effect using pack resistance. i looked at several websites and got good values to use for the i^2r heating effect, .12ohm for charging and .14ohm for drawing. also in the scenario of the 3p2s module. the resistance should be reduced proportional to the AH increasing so upgrading from 2p2s with 32ah cells to 3p2s with 40ah cells will reduce the resistance, all else being constant, 47%.

http://media3.ev-tv.me/DOEleaftest.pdf
https://www.energy.gov/sites/prod/files ... af5045.pdf

Image
https://ibb.co/chs8uz

This chiller product might be an option for cooling that is a stand alone solution. its a phase change cooler that runs on 12VDC (@30 amps) and can provide 3685 btu/hr of cooling with its own liquid plate heat exchange, which would be just the ticket for the oil-based heat exchange fluid i'm suggesting. it has a COP of about 3, which is much more efficient that peltier coolers. it could be mounted between the body and the under body tray, behind a body panel or in the engine compartment somewhere, being 10*7*6 inches. Assuming no heat transfer otherwise and the stock 24kwh pack 3.6Kbtu is enough to quickly reduce temperature while L2 charging at 6.6kw and also hold temperature drawing on the pack at 17.5KW, which is about 65mph on level ground. and in reality with the heat radiation that normally cools the pack it might allow for much higher draws holding the temp steady. Draws/inputs higher than 30kw will heat the battery regardless with this particular cooler. with the lower battery resistance of 3p2s then the cooler can almost counteract a 50kw DCFC.

keeping the 12v battery charged by itself seems to be an issue reading this forum, let along sucking 30 amps out of it all the time, how could that be worked around? aftermarket 380v/12/24/48v DC/DC converter?

https://uploads.strikinglycdn.com/files ... Module.pdf
https://www.rigidhvac.com/store/product ... 910e-p-12v

1.5kw 380vDc/12vdcDc converter
https://www.mouser.com/ProductDetail/Vi ... U0ug%3d%3d

I understand that condensation would be bad inside the battery case, but does water vapor diffuse into the battery pack once its sealed? could a large pack of descant be put in the pack and allowed to sit for a few days, then removed just before being sealed up, or left in there indefinitely? alternatively, an ardiuno with a hydrometer sensor could be measuring RH in the battery case, and once it got to 90% or close to condensation it could limit cooling.

WetEV
Posts: 2369
Joined: Fri May 04, 2012 8:25 am
Delivery Date: 16 Feb 2014
Location: Near Seattle, WA

Re: Replace individual battery cells to renew/increase capacity

Fri Sep 21, 2018 7:43 am

ripple4 wrote:I understand that condensation would be bad inside the battery case, but does water vapor diffuse into the battery pack once its sealed?


The battery case isn't and can't be completely sealed.

As long as no part of the cooling system gets below the dew point temperature there should be no condensation. Dew point record for the world is 35C. US record is 33C.

https://en.wikipedia.org/wiki/Dew_point
WetEV
#49
Most everything around here is wet during the rainy season. And the rainy season is long.
2012 Leaf SL Red (Totaled)
2014 Leaf SL Red

lorenfb
Posts: 1845
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: Replace individual battery cells to renew/increase capacity

Fri Sep 21, 2018 9:18 am

ripple4 wrote:Thank you for the suggestion to calculate the heating effect using pack resistance. i looked at several websites and got good values to use for the i^2r heating effect, .12ohm for charging and .14ohm for drawing. also in the scenario of the 3p2s module. the resistance should be reduced proportional to the AH increasing so upgrading from 2p2s with 32ah cells to 3p2s with 40ah cells will reduce the resistance, all else being constant, 47%.


If you'd like to determine the resistance of each battery module used in the Leaf's battery, here's a very good inexpensive device;

https://www.ebay.com/itm/New-Portable-B ... 2749.l2649

Resistance values from different modules can be compared and matched when constructing a custom battery system.
From the measured resistance of one of the matched modules and how they're integrated, (XPYS), one can easily calculate
the overall effective series battery resistance. Then one can estimate the battery's internal power loss based on various
loads.
Leaf SL MY 9/13: 70K miles, 49 Ahrs, 5.1 miles/kWh (average), Hx=70, SOH=78, L2 charges to 100% > 1000, max battery temp < 95F (35C), min discharge point > 20 Ahrs

ripple4
Posts: 17
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018

Re: Replace individual battery cells to renew/increase capacity

Fri Sep 21, 2018 4:31 pm

Thanks for the suggestion on the resistance checker. I was looking at battery chargers, I want something that charges at the fastest possible rate and I found this 800w one.

https://www.ebay.com/itm/ISDT-T8-1000W- ... 3465!US!-1

Also I got final pricing in on the slightly higher capacity 40ah cells and it looks like to build the 3p2s prototype module it will be $250 for 6 cells, and $30 in copper sheets and bars, plus the tester and charger So that's pretty reasonable to start testing on. the 50ah cells don't seem to come in the 8.5mm thickness that I was looking for. with the prototype module I would like to primarily measure the heat generated during discharge/charge. and buy a used leaf battery on eBay and compare the two also using the leaf cell as a taemplate to design the cell holders to match. anything else that I could look at without getting in the car?

The cost for just the 192x 40ah loose cells was $5962 delivered which would be the 2p2s 28kwh version. 288x 40ah cells for the 3p2s would be $8944 delivered, but would supply the 41kwh capacity. and maybe if the thermal system works out it could be looked at as a way to get 2019 performance out of a 2011-2015 for ~1/2 the price. open question: does anyone think a GoFundMe would be successful to build one pack and try it out?

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