ripple4
Posts: 63
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: Replace individual battery cells to renew/increase capacity

Sat Dec 08, 2018 6:39 am

On the laptop battery suggestion I found that new laptop batteries packaged for dell laptops cost less $/kwh ($.17/wh) than the china pouch cells i'm currently testing ($.27/wh). the question is do these inexpensive laptop batteries really have the 54wh or whatever capacity that is printed on the battery case. and how much time is required to libertate 4000 cells from plastic cases with 8-cells each in them. also I found there are people who take apart laptop batteries and sell the individual cells in places like Lithuania, and these are as little as $.10/wh, but the capacities range from 1ah to 1.5ah, so they would be mixed and I would need a lot of them. a different angle on it would be the 26650 format battery which also has a strong market pretense and higher per cell ah rating, but these round cells may not pack into the leaf battery case at 40kwh volume due to the interstitial space between the cells. maybe that's a big deal maybe it is not. if most of the battery was in the case and then more of it outside the case, in a second place, then the BMS wires would need to run out of the battery case to balance charge the remainder of the pack, not elegant. thoughts?

if I had a leaf battery shell I could do fitment trials, anyone know where I can get one inexpensively? I'm near Toledo ohio.

I also made the discovery that the 2s3p probably is not going to work with the cells I bought, the reason is that the Nissan metal case modules nest inside each other a little and the difference in the overall height and the nested height is going to prevent 6 cells being stacked. The 37ah cells are not near as wide or long as they could be, but they are more than 1/2 the format of the Nissan cell, so two are larger than the Nissan cell when laid next each other on one layer. they do make 50ah cells with the right size which would net a 100ah capacity in a 4 thick arrangement, but I cannot find 60ah pouches that will work, ie both tabs on one side and <9mm thick. as it stand just using the 37ah cells in the stock 2p2s arrangement will net 26kwh with TMS, more than stock and able to DCQC better than stock, but not the 150 mile range I was targeting.

So far the liquid cooling trails showed me that when the 2s/1p pouch cell pack is insulated on the top and bottom, but not the sides, I can charge/discharge without any cooling at the 30amp rate and the cells stay below the manufacturer 113F limit. I found that they get hotter on charging than discharging at the same current flow. and the copper plate with cooling blocks glued on the edge and the particular of the cooling system I have (small 110v aquarium pump and 3x120mm CPU cooling radiator) cool the cells so that the peak temperature is 8 degrees less at a 30amp charge (92f vs 100F with 80f air), and also the cell bulk temperature returns to albeit temperature more than 90 minutes sooner, that's the big difference there. so the next step is to increase the flow of the coolant and try to hold the water temperature at 5 degrees less than air temp by dropping ice cubes into the water reservoir periodically to simulate the chiller cooling the heat transfer fluid below ambient temp just a little. any other suggestions? maybe I could get a second 30 amp charger and power supply and run them in parallel and get the actual charging rate of a DCQC.

JPet3127
Posts: 1
Joined: Thu Dec 06, 2018 12:21 pm
Delivery Date: 06 Dec 2018

Re: Replace individual battery cells to renew/increase capacity

Sun Dec 09, 2018 10:13 pm

Only testing can answer your question! For me its look too difficult to do. I mean the result is not worth it. However, if you like doing it, I'd be happy to see how it ends.

18650's looks good for your purposes, i think.

ripple4
Posts: 63
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: Replace individual battery cells to renew/increase capacity

Mon Dec 10, 2018 10:01 am

Looking more into it. If i go with two layers of 26650 cells formed into a rectangle 11 cells side to side and 3 cells end to end might be a pretty good solution. maybe leave out 4 cells per layer to let the 4 retainer bolts pass though . it would take 2784 cells to pull this off. at ebay prices of $2.7/cell (for 6800mah cells that have an actual capacity of 3500mah) it would be $7.5k in cells. the Nissan module is 40mm thick, 300mm long and 225mm wide. if the two layers of cells are staggered 1/2 of cell over then the thickness per payer will be less than the 26mm*2=56mm, closer to 35mm leaving some room for copper sheets that could still be Incorporated in a corrugated shape for active liquid cooling in the same way as the pouch cells.

The best part is that even with a reasonable 3500mah/cell the pack capacity will be 101ah with 29 cells in parallel, and the total energy would be 36.5kwh. Then if ~$.5 more per cell is spent to get real 5000mah ones it still should fit in the stock case and provide 52.2kwh.

I have a spot welder and nickel strip so the construction of the module should not be a limiting factor.

ripple4
Posts: 63
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: Replace individual battery cells to renew/increase capacity

Tue Dec 11, 2018 6:36 am

Here is my data for the cooling tests i did. overall the cooling plate between the cells is very effective, and chilling the liquid below ambient temp is worthwhile. with only ambient air to cool the liquid which was a 9 GPH flow rate, it lowered the lithium pouch cells peak temperature 8.4F from 25.6F temperature increase with no cooling to 17.2F with cooling, and then lowering the liquid cooling temperature ~8 degrees below ambeint with ice cubes dropped periodically into the reservoir lowered the cell temperature again to a maximum temp rise of 12 degrees F. The follow-on effect was that after charging was complete the cooling effect from the plate cooling system quickly dropped the cells back down to ambient temperature, or very close.

on the discharge side of things the heating effect was less, with the non-cooled cells reaching 18 degrees temp rise at a 30amp rate and with liquid cooling it was about 11 degrees, the same amount of benefit as the charging scenario.

Image
https://ibb.co/Dt7d2Qq

ripple4
Posts: 63
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: Replace individual battery cells to renew/increase capacity

Tue Dec 11, 2018 8:14 pm

looking into the 18650 batteries further it looks like there are some promising options, but I also really have a concern about the laptop battery approach. namely laptop batteries are considered by many to only have 400 cycles of life, and premium laptop batteries 800 cycles. I would not want to go through a bunch of effort if the battery is at a large degradation amount after only 2 years or so.

on the upside, the cost is amazing. I found that buying new high drain laptop batteries can get me a guaranteed 2600mah cell for $1/each delivered (https://www.ebay.com/itm/162331165709?V ... 2331165709). Since the 18mm diameter is slightly less wide than the 26650 it would be possible to have 16 columns of batteries and since they do not need to be nested, the bolts can fit between cells since they are stacked strait up. cramming a total of 4608 cells in would give a pack capacity, new at least, of 44.3KWH for less than $5000 in cells.

I also looked at the fitment into the Nissan leaf module. using 200 amps as the momentary peak current draw I find that 1awg wire would probably be OK. 1 AWG has cross sectional area of 42.5mm, maybe someone can measure the bus bar in a pack and report how thick and wide the conductors are. anyway, using 1mm/40mm conductor in the module will be very low resistance and I came up with a nested "L" layout with only one place where two conductors need to be between cells. have a look:


Image
https://ibb.co/pdCMmvT

Image
https://ibb.co/PZ7wLFq

Dala
Posts: 64
Joined: Sun Oct 28, 2018 11:24 am
Delivery Date: 01 Jan 2015
Leaf Number: 316851

Re: Replace individual battery cells to renew/increase capacity

Wed Dec 12, 2018 5:54 am

Nice project!

ripple4 wrote:looking into the 18650 batteries further it looks like there are some promising options, but I also really have a concern about the laptop battery approach. namely laptop batteries are considered by many to only have 400 cycles of life, and premium laptop batteries 800 cycles. I would not want to go through a bunch of effort if the battery is at a large degradation amount after only 2 years or so.

on the upside, the cost is amazing. I found that buying new high drain laptop batteries can get me a guaranteed 2600mah cell for $1/each delivered


I have tested a lot of 18650 cells, currently building an EV with them.

These new 1$ 2600mAh cells might be tempting, but remember that these will also degrade to about 2000mAh after 2 years. By starting with cells that are specced at 3000mAh+, but has degraded to 2200mAh, these cells will not change that much in the future since the worst degradation has already happened. This ofcourse depends on the cell brand, etc, so no real ultimate solution.

Also laptop cells are charged to 4.2V and discharged all the way down to 3.0V. So by using them with a leaf BMS, they would only charge to 4.1V and discharge to 3.5V under normal use (3.3V occasional turtle), which would increase the amount of cycles they can do! So an EV application is easier on them compared to a laptop. (Laptops also stay at 100% SOC for most of the time , which is not good for the cells)

Do you need any measurements etc? As said, I have a leaf cell and heaps of 18650 cells.

ripple4
Posts: 63
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: Replace individual battery cells to renew/increase capacity

Thu Dec 13, 2018 6:58 am

Cool sounding project if you make a post about it please PM me, or link it here.

I was researching the excellent suggestion about laptop batteries having short life because of their high utilization strategy in mobile electronics, and battery university website backs this up. (https://batteryuniversity.com/learn/art ... _batteries) It in fact show how much longer one could expect in various charging scenarios. right out of the gate, they say for every .1v that the cell is not charged under 4.2v it doubles the life, and not storing at high charge levels increase life a further 20%, those are freebies with no behavior change. going further, shallow cycling really increases life proportionally to depth of discharge, so where a 100-25 charging pattern might expect X cycles full life, 85-25 would have 2x cycles, and 75-45 would have 5x cycles. expanding capacity to 44kwh will allow very shallow discharges on a daily basis while allowing for 100%-25% 150+mile long trips occasionally. the temperature aspect of it also supports some kind of TMS as heat reduces life.

The only technical issues i can anticipate is that the 80kw acceleration will draw ~220amps from the pack, with 48 parallel cells each one will need to have a peak draw rate of 4.6 amps for at least a few seconds, that might be above what a laptop cell can provide, not that high drain and high capacity 18650 cells don't exist, but they are not $1/each.

Thinking on assembly, i think that using nickel strap material will be needed to connect the cells to the modules internal buss bar, 1mm thick copper might not spot weld easily to the cells, and will prevent any kind of service, whereas if we get 12.7x.25mm nickel strapping and make connections to the bus bar that way i can spot weld everything much more easily and then fold the bars flat to the pack afterwards, the only thing left after that is creating the copper to copper buss bar connections. I want the design to be manufacturerable in anyones basement or garage. maybe the cross bars could be nut and bolted in to maintain serviceability, also i would make the connections on the top of the pack now, to maintain access for cooling hardware on the back of the cells.

it would be great if someone could help test the modules in a car, while i am working to someday make a pack for my car, I commute a long way each day and my 2012 cannot be down. I might consider buying a 2011 leaf with a nearly dead pack, or crash damage etc as my test mule.

ripple4
Posts: 63
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: Replace individual battery cells to renew/increase capacity

Sat Dec 15, 2018 7:49 am

Here is the latest plan for the inexpensive 2012 Nissan leaf cell with more capacity. I am talking about a 35-40kwh usable capacity pack in a 2011-2012-2013 Nissan leaf with active TMS. there seems to be a large supply of the new 2600mah 18650 cells from ebay laptop battery sellers and with cooling and shallow cycling I can see these will last many years and thousands of cycles, if all else fails the extra pack capacity will allow for more degradation and still be useful.

I determined from watching several videos and reading about how tesla and BMW are cooling their cells that tab cooling the cells, as opposed to body cooling the cells will have a more effective result of increasing cell life. both tab and body cooling are a possibility. see video (https://www.youtube.com/watch?v=_jd8REVB-c8). so I think installing silicone heat transfer pad between the ends of the cells and the bus bars will allow the bus bars to be dual use electrical and heat conductors. to connect the cells to the bus bars I plan to use .25mmx12mm pure nickel strapping to connect up to two cells in parallel per strap to the buss bar, which will have a current density of less than 4amps/mm^2 with is the good zone (https://endless-sphere.com/forums/viewt ... 14&t=68005) then I found a 200mm long water cooling block and with the same silicone heat transfer pad I would connect the ends of each buss bar to the cooling block. the silicone cooling sheet has a dielectric strength of 4kv, so it will allow thermal transfer without electrical transfer. Or I could use mica sheet and thru-bolt the copper buss bar and water block for better performance since both surfaces are flat and stiff.

totaling up the cost of cells, the 1mm copper sheets, water cooling block, silicone pads and nickel strapping I'm at about $144/module. can anyone see a way to cut cost out while still keeping manufacturability and functionality?

module cross section:
Image
https://ibb.co/K9T8GyF

overall pack visualization:
Image
https://ibb.co/jDMzwZ4

Image
https://ibb.co/J33FmBZ

ripple4
Posts: 63
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: Replace individual battery cells to renew/increase capacity

Fri Jan 04, 2019 6:51 pm

The laptop batteries that I bought did not work out. I had 11x 9cell batteries shipped in from that ebay link and once I opened the packs and tested individual cells, the truth was revealed. In order to get the 7800mah energy advertised, each needed to be 2600mah, but when tested they were barely 1100mah. they weighed 40 grams each which is consistent with that energy. also one of the batteries did not have wires to balance the cells, just a +/- from the ends of the pack, I thought that was a fire risk.

Image

I guess the two takeaways is don't buy cheap batteries for your laptop, and don't expect the rated capacity at $1/cell. The 1100mah cells would not even have the engery level of the stock 24kwh pack, so that's a non-starter. anyone have a place to get 18650 cells in the 1800mah-2800mah real capacity cells at a 5000pc quantity for a low price? the next step for me would be looking at 26650cells at the 5000mah level and going that route.

Also I notice on these cells that the energy going in from the charger is noticeably larger than the energy released on discharge compared to the 37ah pouch cells. it was just an casual observation, but I'll look into it more. this is called the round trip efficiency I believe. I still have some of the batteries because the ebay sellers did not want the cells returned once I reach out and told them the issue.

ripple4
Posts: 63
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: Replace individual battery cells to renew/increase capacity

Fri Jan 11, 2019 12:42 pm

A note on the laptop-sourced 18650 batteries, looks like electronics and power electronics application are going to differ quite a bit, the distinction is called 'high drain' i think. anyway with the laptop 18650 cells the round trip charging discharging efficiency at 1C was 93%, and the round trip efficiency at 2C was 44%. with 48 parallel cells the current draw per cell on these exact batteries would be .7C at a 20 kw draw, so they would technically work for commuting, but many rapid accelerations would waste alot of power as each cell would be at 3C peak draw at 80kw and i don't think that they can provide that, the voltage sags too much, so high drain is really going to be a requirement.

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