ripple4
Posts: 80
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 Feb 14, 2019 10:26 am

Update: After trying 5+ different kinds of 18650 lithium batteries, from high spec LG HG2 to no-name generics I’m pretty certain that 18650 is not the way to go. The weight to energy to cost ratio is not where it needs to be, if I could find 3000mah 5amp drain cells for $1.50 each, it would be one thing, I cannot. As it stands the best 18650 I tested had 1600mah between 4.13 and 3.3 volts at a 1.5amp discharge rate, and weight 42 grams and costs $1.75. Fitting out the pack like I showed in a previous post with 4700 cells total ends up at a specific energy of 7grams/watt hour and the cells would cost $8100 for pack energy of 28kwh.

Now the update is the EBL 26650 cells I got my hands on. these guys provide 4.8AH between 4.13 and 3.3 volts are rated at 1200 cycles, which is 3x longer in shallow cycles, so its there. I am hoping that I can get these for $3/each (currently $4.35/each from ebay), and in the high density arrangement I came up with, which I think is really cool, I can get those numbers to move in the right direction. The specific energy would be 5.0gram/watt hour, and a pack energy of 47.5kwh and a cost of $7800 in cells. There is a lower density layout that is 37.5kwh and $6K.
My next steps are to find a high volume-low cost supply for these batteries and again, make one module and test the cooling approach I talked about before. I didn’t have a chance to test it on the 18650 because I didn’t want to waste the copper bus bar materials since the cells could not have worked.

https://ibb.co/DbsYpX7
Image

https://ibb.co/zSYWBQf
Image

I did find a new tool to help investigate cells, I found that if I X-ray them I can see how many wraps they have in the cell, how big the center pin and from that the square area of the electrodes. The 18650 that performed the best had a center pin diameter of 6.5mm, and 19 wraps of the electrodes, this means each wrap is .29mm thick and it has 13,000mm^2 of area. Then 26650 has a center pin diameter of 3mm and 31 wraps for an electrode area of 26,250mm^2, twice the 18650! And the energy works out to 5mm^2/milliamp hour for the 26650, and 8.3mm^2/milliamp hour for the 18650. The EBL 26650 also has a thicker layers at .37mm, so that might indicate durability or other robustness.

https://ibb.co/4my6pgc
Image

Also I really could use an empty battery shell to do fitment work on, if anyone knows of one in the SE Michigan area, please PM me. Lots of people sell the leaf modules, but the cases must be scrapped.

jlsoaz
Posts: 700
Joined: Sun Jul 08, 2012 12:57 pm
Delivery Date: 10 Oct 2012
Leaf Number: 24218
Location: Southern Arizona, USA

Re: Replace individual battery cells to renew/increase capacity

Sun Feb 17, 2019 12:18 pm

Hi - do you happen to know where Nissan is as to whether they will allow their own shops to replace individual cells? Maybe this is common knowledge, but I have just been wondering about it and ran across this DIY type of thread.
Former lessee 2012 SL
http://www.pluginamerica.org/surveys/ba ... hp?vid=229
2017-October: bght 2013 Volt
will buy 150+ mile BEV when they become less expensive on used market
opinions expressed are my own

GerryAZ
Gold Member
Posts: 2201
Joined: Mon Nov 22, 2010 6:47 pm
Delivery Date: 12 Jun 2011
Location: Phoenix, AZ

Re: Replace individual battery cells to renew/increase capacity

Sun Feb 17, 2019 6:58 pm

jlsoaz wrote:Hi - do you happen to know where Nissan is as to whether they will allow their own shops to replace individual cells? Maybe this is common knowledge, but I have just been wondering about it and ran across this DIY type of thread.
Yes, LEAF-certified Nissan dealers can replace individual modules if they become defective (not just capacity loss). There are a few reports in other threads on this site.
Gerry
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015; traded 8/10/2019 at 82,436 miles
White LEAF 2019 SL+ purchased 8/10/2019

cwerdna
Posts: 9569
Joined: Fri Jun 03, 2011 4:31 pm
Delivery Date: 28 Jul 2013
Location: SF Bay Area, CA

Re: Replace individual battery cells to renew/increase capacity

Sun Feb 17, 2019 9:02 pm


'19 Bolt Premier
'13 Leaf SV w/premium package (owned)
'13 Leaf SV w/QC + LED & premium packages (lease over, car returned)

Please don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

jlsoaz
Posts: 700
Joined: Sun Jul 08, 2012 12:57 pm
Delivery Date: 10 Oct 2012
Leaf Number: 24218
Location: Southern Arizona, USA

Re: Replace individual battery cells to renew/increase capacity

Sun Feb 17, 2019 9:38 pm

GerryAZ wrote:
jlsoaz wrote:Hi - do you happen to know where Nissan is as to whether they will allow their own shops to replace individual cells? Maybe this is common knowledge, but I have just been wondering about it and ran across this DIY type of thread.
Yes, LEAF-certified Nissan dealers can replace individual modules if they become defective (not just capacity loss). There are a few reports in other threads on this site.
Ok, thanks, good to know.
Former lessee 2012 SL
http://www.pluginamerica.org/surveys/ba ... hp?vid=229
2017-October: bght 2013 Volt
will buy 150+ mile BEV when they become less expensive on used market
opinions expressed are my own

jlsoaz
Posts: 700
Joined: Sun Jul 08, 2012 12:57 pm
Delivery Date: 10 Oct 2012
Leaf Number: 24218
Location: Southern Arizona, USA

Re: Replace individual battery cells to renew/increase capacity

Sun Feb 17, 2019 9:39 pm

cwerdna wrote:^^^
Yep. http://www.mynissanleaf.com/viewtopic.p ... 80#p458180 is an example of one.
Ok, thanks.
Former lessee 2012 SL
http://www.pluginamerica.org/surveys/ba ... hp?vid=229
2017-October: bght 2013 Volt
will buy 150+ mile BEV when they become less expensive on used market
opinions expressed are my own

ripple4
Posts: 80
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 Feb 22, 2019 7:33 pm

Feel free to use this invention/design for any non-commercial application. For commercial applications contact me and we can work something out. I completed a micro pack assembly to test out my process and also test how well the silicone heat transfer pad will cool the cells in the micropack before building a full size leaf module. The U shaped micro pack will show the ½ thickness buss bar that will be in the full size module between – and +, and the remote cooling blocks will allow the buss bars to also act as the cooling heat conductors.

The hard part about assembly is the devilish details in the process of attaching all the parts, I wanted to make it so that with modest cash the process could be reproduced, so a multi-hundred dollar spot welder will be needed, so long as it can provide ~1200amps to a parallel electrode weld handle. I made a few handles before settling on my own design. The electrode have to be independently supported by springs to get good welds, once the power hits the metal turns to jelly, and if the electrode comes off the surface it arcs and sprays metal everywhere, its nasty.

The file can be downloaded here:
https://www.thingiverse.com/thing:2748339

It uses 2x ¼” diameter 4” long RWMA class 11 (75% tungsten 25% copper) electrodes threaded about ¾”up each end with ¼-20 threads, the points were formed on a drill press with a lathe cutter in the vise and the threaded the same way, with the die in the vise. That way it threads strait, tungsten copper is hard. Also this way the points and threads can be easily redressed as they wear out. The weld process is direct energy AC with a phase-fired SCR as the control mechanism, also known as a spot welder. The spot welder I used was a current feedback controlled, 480v/30amp input, but only 5.3v output, but with up to ~2500amps though. The .2mm pure nickel strap takes more power than the thinner, plated steel straps. There are several 3kva/kw spot welders on eBay (SUNKKO 709 or similar) that might have enough power for .2mm Ni, or maybe two layers of .1mm strap could be used. The straps need to conduct 17 amps peak when connecting two cells. And that puts the current density at 6.5amp/mm which is the maximum, 4.5amp/mm is the recommendation for best performance. .1mmx12mm should be enough for single cell connections. hmm..maybe I should only do single cell connections since the staggered cells are not suited for doubled up cells anyway.... To make sure the welds are good, I do a 90 degree pull test, if the welds pull out the strap, and I can see though the hole, it’s a good weld. If the strap peels off in the middle of the weld, it’s weak. The negative side of the battery is thinner than the positive side and so it needs less power, I used a longer 10 a/c cycle, cooler 1000 amp weld for the negative side so the electrode points did not press into the can. Then on the thicker positive side I turned the power up to 1250 amps, but cut the time down to 5 A/C cycles and that was also used for welding two layers of .2mm strap. I used 1 a/c cycle for upslope to cut down on sparking, you tube videos of welding batteries always have spark flying everywhere, that does not make for good welds.

https://ibb.co/w0sXTpL
Image


Connecting the strap to the 2mm thick copper buss bar was not as easy as I had thought it would be, it won’t spot weld on. I think I will try blind copper pop rivets for the module assembly, which is cheap and easy for the home hobbyist. However, for the micro pack I laser welded it. I know this is not a practical solution, since multi-kw lasers are expensive, but for the curious, it worked really well and here are the weld details.

https://ibb.co/Mp06nKs
Image


My next steps will be to test the micro pack with various charge and discharge currents that represent the important conditions the module will see, just at 2/27ths of the current. Then I’ll wrap it in insulation and measure the heating effect with no cooling, and then with cooling, like I did with the pouch cells, and document what I find.

Here is the assembly steps of the micro pack and how the silicon heat transfer pad is cut, installed, and folded into the module. The picture I posted awhile ago shows this from an end view but in real life the details are apparent. The silicon pad is sticky like chewing gum so it conforms to the surfaces for good heat transfer, I hope.

https://ibb.co/HKSHTBB
Image

ripple4
Posts: 80
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 Mar 04, 2019 2:16 pm

I hope if someone sees/follows this thread here, they feel free to speak up and make a suggestion or a comment, getting feedback is the point here.

Here is an update on the cooling performance of the micro 2s2p 26650 pack. I found I have to drain the pack prior to starting the charge at the same rate, so both lines here had a 1.2amp discharge rate (7500w simulated motor power, like a slow drive in a parking lot) to 3.3v/cell and the DCFC started right after. The cooling really makes a difference in a way I would not have expected, the pack is able to stay in constant current mode for a longer amount of time with cooling, and so then finishes faster, 15 minutes faster at the simulated 50kw DCFC current rate. The innovation here is that the pack is remotely tab cooled. Or in other words, the liquid used for cooling is only on one side of the module and the heat is drawn out in the same buss bars that conduct the high currents. And where the cooling effect interfaces the cells is on their tabs. Like I linked to in a previous post this arrangement is supposed to cool the cells from the inside out, and lead to longer life.

I’ll get some back up runs to confirm this. Also do a run with ice in the reservoir for simulated refrigerated cooling . This data is only using ambient air passing through a CPU water cooling radiator, no chiller yet.

https://ibb.co/Fmc6rQ5
Image

Also I did some work developing the nickel strap to buss bar rivet idea. The rivets did not form how I wanted out of the box. It had a long tail end and I can rotate the strap on the rivet, not good. I figure I can just crush that in a press/vise with smooth jaws and can get a nice crowned back, so its strong and it does not rotate then . I’m waiting on .15mmx10mm nickel so when I get it I’ll make the 18 rivet / buss bar sample and post how that looks.

https://ibb.co/GH6FQDS
Image

jrhirsch
Posts: 2
Joined: Thu Apr 25, 2019 12:41 am
Delivery Date: 25 Apr 2019

Re: Replace individual battery cells to renew/increase capacity

Sat Apr 27, 2019 9:03 am

I've also been considering a complete pack replacement with the newer 5000mah 21700 cells. It would take about 2,000 for a 36kw pack. I've seen them for $5 per cell in quantities of 1,000 or more. Definitely not cheap even with an extra 50% of range.

They would be packed without the plastic sleeves for better cooling in 48 3d printed plastic modules using the stock bus bars and connectors. The cells are much lighter than stock so the pack would weigh about the same.

$10,000+ for a battery pack is too much so in the meantime I'll be checking the pack with Leaf Spy and see if I can refurbish it by replacing the lower capacity cells with good used ones. The cost could be well under a $1000 if not too many cells are bad. Even that is not cheap considering the range might be extended just 15 to 20 miles. But as any Leaf owner knows, that extra range is like gold!

How do you hook up multiple cells to coolant using conductive bus bars?

jrhirsch
Posts: 2
Joined: Thu Apr 25, 2019 12:41 am
Delivery Date: 25 Apr 2019

Re: Replace individual battery cells to renew/increase capacity

Sat Apr 27, 2019 9:31 am

OK I understand how the coolant lines are insulated by the rubber tubes.

There's another cost effective option to replacing the entire pack with new cells. Sell the old Leaf and buy a 2013 or newer model that has had the pack recently replaced with a lizard pack. The prices aren't that much more. I've seen them for $7,000 to 8,0000. Subtract the sale of you old car and that's just $3,000 to $4,000 to upgrade with very little labor.

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