Not enough that I would worry as long as that imbalance doesn't jump way up under hard loading. That is what we often see when one cell remains considerably below the rest. 23 mv is fine, but 150mv or higher under load isn't.
Modules and instructions for upgrading battery from 24-40 kwh?
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cienporcien
Member
That looks like a lot of work! Any estimate on how long it took?
cienporcien
Member
To me this sounds interesting, keeping the 40kWh BMS by replacing at the cell level. I did this for an old Zero motorcycle by using 7 Leaf modules from a 30kWh pack. A lot of tedious work, , but not hard really. It is hard to know what you did from the photos, was there a lot of metal fabrication, or did you reuse the module metal parts?
cienporcien
Member
This is my 40kWh battery under medium load ( 94A), maybe the big module is toast? Under no load cells are well balanced.
cienporcien
Member
Are these the cells you used? https://szxhbattery.com/products/br...y-cells-with-screws-batteries-battery-lithium
That was the first pack I rebuilt. After that I did a couple more and when you learn some stuff it gets a bit quicker. Now I would do it in a week with all the G10 materials already cut and ready. But I would not advise to do it yourself unless you REALLY know what you are doing. I'm an electronics engineer dealing with different projects for over 30 years. This is just a kind of a challenge which some people noticed and now it might grow into a small segment of my business.
There is only one metal L shaped profile added to stabilize the back pack in case of frontal collision. LH and RH stacks have 1.5mm galvanized metal added. Also I had to cut a bit of rear battery holder on the right side to guide the power cables thru. No metal parts of the modules was reused as they were turned into energy storage. Guiding, cutting and soldering the thin BMS cables is most time consuming. I'm attaching a couple of the pics of the process.
In one of the batteries I added 80°C thermal fuse on each of the bus bars. Really time consuming and overkill but really safe.
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Yes and Starmax is good and trustworthy seller as much as I had business with them.
cienporcien
Member
I'm also an electronics engineer, now retired. Worked with really big chargers for buses and trains for many years. One test was for a train charger at 2200A, 1500V, though the test was performed only for testing the ampacity of the connection system at 150V, 2200A. The first charger of this type is currently being built in France. I like to think I know what I'm doing, though always with an abundance of forethought and caution. Perhaps you could sell a kit of all the custom bits that are needed, plus open source the instructions? I could buy the batteries direct from Starmax and give you feedback and assist with documentation. The car is a 2018 Tekna, and is super nice, seems a shame and a waste for it to go to the dump for lack of a good, economical way to overhaul the battery...
NeguE
Well-known member
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what was the tightening force in nm at the nuts at the cell terminals?
Can you give me a advise about modification at BMS cables ?
I will extend the wires from the bms and I need to find out their order
This is even better. Here the cells are new but the LBC didn't yet adjust itself to them so the SOH and Hx are not realistic.23mV is not bad
Actually the cells were balanced to max 3mV but the BMS isn't as accurate as the battery testers.
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Tightening torque is 10Nm with ordinary bolts and concentric spring washers. If you use bolts with ridges you need higher torque around 15Nm because the ridges of the bolts create braking force. I modified the cables "on the fly". I don't have yet a fixed process for that. I mark each contact with a permanent marker on the contact. I don't use Nissan's numbers but my own. When I assemble the back pack, I leave the wires about 30cm longer and I place the scotch tape at the end for insulation of the tip and place to put a number on. I have some hand written notes if it helps.
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Nice to hear from even more experienced engineer. I'm originally not in voltages higher then 12V and around 10A but I made an exception. I design and make my own electronic projects, one of them will be soon useful and it is SMS beekeeping scale which automatically weighs the hive and reports the yields and some other parameters.
It would be quite some work to make a complete guide and even some kits, but is doable if interest would be big enough. I could document it better when I would upgrade the next battery. Kits would also be nice, but there is quite some work with that, specially with bus bars which I cut from aluminium and drill holes manually yet. If you need more info for your wok I can help. With your experiences you could teach me how to do it.
cienporcien
Member
Is it possible to prepare the packs in advance, then pull the battery and install the packs? Or are things built in place, and need the housing?
ginetto
Well-known member
did you use original compression plates form L and R frontal modules? IMHO rear pack seems well done and well compressed (I'm obsessed with compression
).Some questions:
1) In the rear pack any reason to have cells one in front of the others instead to move in the opposite direction?
2) how the cells are fixed in L,R and read pack?
3) Did you mind to have more "flexible" busbars connecting cells? expansion/contraction could stress cell junctions?
btw well worked pack.
Thanks for your compliments.
Yes, the compression plates are original. It is really well compressed, I hope not too much.
1. Size of the cells determine their orientation. Two pack at the back are facing each other with bolts to enclose all the bus bars and BMS wires and can be glued very well on the outside. Spacers are used to separate the pack coming together in case of a greater force. The mentioned L sape steel bar is there to reinforce the front part of the pack.
2. LH and RH packs are glued together with PU adhesive which is very strong. Cells are in this case facing away from each other. At the end the insulation layer is glued to the cells and then the original stamped sheet covers also glued. Bolts holding the top plates are hand tightened and treated with thread locker. I will attach a couple of pictures from different jobs.
3. The bus bars are solid aluminium. My thinking was this: Cells are glued together only at the edges and have approx. 0.5mm per cell to breathe. I know this is not much but I read a study where they were testing NMC cell expansion and if they are right, then it is enough. Additionally there is around 5mm of hard insulating foam on each side if more space is needed. In case of extreme expansion I had in mind two scenarios:
1. With flexible bus bars cells could deform so much to distort the shape of the stacks and could make a short circuit between the opposing stacks. That would not be very good. Also the flexible bus bars are nickel plated which increases contact resistance significantly.
2. With solid bus bars deformation would cause the laser weld to break and stop further damage. Also aluminium fuses perfectly with aluminium bases of the nuts and oxidation risk is minimum.
I hope I don't need to mention that using pure copper bars are prohibited to be bolted directly to aluminium studs as this almost certainly will lead to problems due to incompatible metals and thus oxidation.
Please, correct me if I'm doing something wrong, I'm always open to learn. Also I hope I helped clarifying your questions a bit.
Yes, the compression plates are original. It is really well compressed, I hope not too much.
1. Size of the cells determine their orientation. Two pack at the back are facing each other with bolts to enclose all the bus bars and BMS wires and can be glued very well on the outside. Spacers are used to separate the pack coming together in case of a greater force. The mentioned L sape steel bar is there to reinforce the front part of the pack.
2. LH and RH packs are glued together with PU adhesive which is very strong. Cells are in this case facing away from each other. At the end the insulation layer is glued to the cells and then the original stamped sheet covers also glued. Bolts holding the top plates are hand tightened and treated with thread locker. I will attach a couple of pictures from different jobs.
3. The bus bars are solid aluminium. My thinking was this: Cells are glued together only at the edges and have approx. 0.5mm per cell to breathe. I know this is not much but I read a study where they were testing NMC cell expansion and if they are right, then it is enough. Additionally there is around 5mm of hard insulating foam on each side if more space is needed. In case of extreme expansion I had in mind two scenarios:
1. With flexible bus bars cells could deform so much to distort the shape of the stacks and could make a short circuit between the opposing stacks. That would not be very good. Also the flexible bus bars are nickel plated which increases contact resistance significantly.
2. With solid bus bars deformation would cause the laser weld to break and stop further damage. Also aluminium fuses perfectly with aluminium bases of the nuts and oxidation risk is minimum.
I hope I don't need to mention that using pure copper bars are prohibited to be bolted directly to aluminium studs as this almost certainly will lead to problems due to incompatible metals and thus oxidation.
Please, correct me if I'm doing something wrong, I'm always open to learn. Also I hope I helped clarifying your questions a bit.
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cienporcien
Member
It all sounds quite correct to me, though I have much more experience with chargers than battery packs. To answer my own question, it looks like most of the assembly is done in situ with the battery case out of the car and in the workshop. Though, wrapping the cells, pre-balancing, and fabricating the bus bars can certainly be done beforehand.
cienporcien
Member
Hi Srečko, I've ordered the same cells from Selin at Starmax, and am getting prepared to do the pack rebuild. Now I understand why you chose those cells, the width and depth match very closely the Nissan cells, which makes it relatively easy to rebuild the pack in the same space and reusing some of the same metal parts. They are also automotive cells, rated to 5C discharge, very important.
Great. Seline told me, that the friend ordered with her. I hope she gave you a good price for NEW cells not refurbished ones.
I recently received custom insulating plates made from G1 material. Quite expensive but needed for ease of assembly and safety. If you need it, please let me know. I have 10 sets.
I recently received custom insulating plates made from G1 material. Quite expensive but needed for ease of assembly and safety. If you need it, please let me know. I have 10 sets.
