Making a custom battery pack for MiEV

[martinwinlow]

This is a bit of a thread hijack but I was wondering if any battery geek out there has thought of replacing the discrete LEV50's with a 'brick' of 18650's in parallel, 'Tesla-style'? And might this be a comparatively easy yet affordable way around all the problems of sourcing replacement cells that'll fit the original module packaging as well as be agreeable to the existing BMS? Even if we only had the original 16kWh you would still have a very capable city car and possibly at a much cheaper price-point than the larger format/capacity cells that feature in this thread...? Just a thought!

To answer my own Q... 2 rows of 9 (in parallel, obvs) would fit and 18 x 2.5Ah would give 45Ah but even at £2/cell that still the best part of £3k ... plus all the cell holders and not to mention the faff...

 

[MickeyS70]

This is a bit of a thread hijack but I was wondering if any battery geek out there has thought of replacing the discrete LEV50's with a 'brick' of 18650's in parallel, 'Tesla-style'?

See discussion below:
https://www.forums.aeva.asn.au/viewtopic.php?t=5515

 

[piev]

This is a bit of a thread hijack but I was wondering if any battery geek out there has thought of replacing the discrete LEV50's with a 'brick' of 18650's in parallel, 'Tesla-style'? And might this be a comparatively easy yet affordable way around all the problems of sourcing replacement cells that'll fit the original module packaging as well as be agreeable to the existing BMS? Even if we only had the original 16kWh you would still have a very capable city car and possibly at a much cheaper price-point than the larger format/capacity cells that feature in this thread...? Just a thought!

To answer my own Q... 2 rows of 9 (in parallel, obvs) would fit and 18 x 2.5Ah would give 45Ah but even at £2/cell that still the best part of £3k ... plus all the cell holders and not to mention the faff...

Sounds like a good idea. I believe you will discover that packaging a battery is harder than finding cells that fit the package.

Adapting the battery case is not a simple task.

 

[martinwinlow]

Sounds like a good idea. I believe you will discover that packaging a battery is harder than finding cells that fit the package.

Adapting the battery case is not a simple task.

Actually, I think that's one advantage of using 18650s in that there is a wealth of easy and cheap systems to hold cells together in pretty much any arrangement you desire. It would be joining them up electrically as well as providing appropriate terminal connections that will work with the existing BMS PCBs, etc, that may be problematic, I'd have thought. I think, short of a big price drop in 2.5 to 3Ah 18650's, if you were going to go to all that trouble to upgrade what is a fairly old and valueless car (not like they are collectable (yet) or something!) you would be better off spending a bit more and sticking with larger prismatic cells. Anyway, hijack over...

 

[Jiminy]

My son and I designed a replacement cell in CAD that held 14x 2170 Tesla cylindrical cells. They fit in the same space as a stock LEV50 and would require a custom PCB for the top voltage collector. You'd have to print 88x plastic shells. There would be little cooling due to having to hold the cells well. The capacity would be 70Ah assuming 5000 mah per cell. Cost would be attractive IF you bought a Model 3/Y battery module and salvaged all of the cells from one module. It would likely take 3-4 years to do so as the cells are entombed in an epoxy from the Tesla factory. You'd also have to perfect the process of welding wire to the cases of the Tesla cells. Daunting? why yes.

Prismatic I think is the answer but pouch could work. CMU connection details would be the biggest thing to work out.

 

[MickeyS70]

Prismatic I think is the answer but pouch could work. CMU connection details would be the biggest thing to work out.

What about AA cells?

 

[Franco]

I have a contact in Moldova who does these operations, fortunately the cost of recovered Li-Ion cells has dropped a lot in recent years
For my part, I can say that I have managed to do this

https://www.forumelettrico.it/forum/post64104.html#p64104

[translated by moderator]

 

[MickeyS70]

I have a contact in Moldova who does these operations, fortunately the cost of recovered Li-Ion cells has dropped a lot in recent years

Hello and welcome to the forum

For the benefit of everybody, please keep your future postings in English.

Well done on your conversion, but you're right, given the current drop in EV prices projects like yours make no commercial sense.

But DYI battery upgrades of existing 1st gen EVs are a different story. The easiest way to achieve is to use cells with the same form factor, CATL 93Ah are the closest so far that require minimal customizations.

Don't think anybody has been using reclaimed Tesla cells for a triplet (yet) but maybe your contact has some experience/ideas how best to fit and make them work?

 

[Franco]

I don't think rebuilding a battery using 18650s is a good idea, it's true that Tesla does it, but it has quality control of the battery process (very important) and then makes the connections using a wire bonder, an automatic tool not available to everyone: the ultrasonic welded aluminum bridge between the cell case and the collector plate acts at the same time as a fuse (I think it's 16A) and a flexible connection, this allows the module a certain flexibility before the connections are interrupted due to a shock.
Another consideration on 18650s: where do they come from? I hope not from Aliexpress: most of the cells on sale have fake brands and are not reliable over time, if not even have lower performance than declared.
It must be considered that in any case, even if exciting, the work of rebuilding batteries is demanding and requires a series of attentions such as insulation from the external case and the quality of the welding.
As for the prismatic cells available on Aliexpress, the situation does not change much even if in this case the connections on screw terminals are much safer and in much smaller numbers.
So are we hopeless? NO: more and more entire battery packs from damaged or replaced under warranty vehicles are available; in any case the battery must not be more than a year or two old, and in the case of replacement under warranty it is necessary to verify that the problem, as often happens, depends on the failure of an internal VCU or a temperature sensor and not on a serious imbalance.
I have built photovoltaic storage systems and the conversion to electric of a diesel vehicle using Tesla S modules from damaged cars, they have been working for years, unfortunately these modules have a capacity of 238 Ah and are 6s, difficult to divide into 12s 119 Ah, paid over 1000 euros each, but now times have changed and the price of the modules has plummeted given the large offer now available; you need to contact the car dismantling companies authorized to handle electric vehicles or companies that recover cobalt and various metals from EV batteries
The latest upgrades I've worked on use 120 Ah Samsung 12s2p modules from the Fiat 500e, they are very well made and also have channels for a possible heating or cooling circuit (like Tesla)
My contact in Moldova knows the Tesla CAN-BUS protocol and has ready-made interfaces with protocols that can be adapted to communicate with different systems, thus leaving the original BMS in place, but now I know that he has modules available that are much easier to adapt to different situations, the Tesla S module is almost always too big

 

[MickeyS70]

My contact in Moldova knows the Tesla CAN-BUS protocol and has ready-made interfaces with protocols that can be adapted to communicate with different systems, thus leaving the original BMS in place, but now I know that he has modules available that are much easier to adapt to different situations, the Tesla S module is almost always too big

A triplet runs on 88s 50Ah (or 80s for later clones) cells. They are divided into 10x8 cell & 2x4 cell modules, each with its own CMU board.

I gather the only similar format cells are used in BMW i3 packs, however these are welded together (no studs) and would therefore not be easy to adapt.

To use reclaimed cells from other EVs, two challenges will need be to solved: how to fit them and then get them to ‘talk’ to the existing BMU.

We would be very interested in any suggestions…

 

[Franco]

I confirm that BMW i3 uses 12s modules. They are the same as the C-evolution scooter (it uses 3) that I own (I think I was the first in Europe to increase the autonomy of this scooter to 200 km).
As for the possibility of adapting new modules, it is sufficient to reconnect the existing VCUs in the old battery respecting the numbering of both the VCU and the connections to the cells, for each VCU there are also 5 temperature sensors, they must be recovered and glued on the poles of the cells that make up the module (5 sensors for 8 cells each with two poles means that only some poles will host a sensor).
In this way the existing electronics are recovered without adaptation problems.
The biggest problem comes later: the car does not "see" the greater capacity of the new battery and the autonomy remains the same, so the car stops with the SOC indicator at zero while the cells are far from discharged.
To solve this problem I found the right suggestion in the AEVA forum: you need to insert a programmable CAN-BRIDGE that sends the correct data to the car, therefore not based on the capacity of the original battery and its SOH.
The BMW scooter uses the battery until it runs out (116 v) while the iMiev performs a coulombmetric calculation and "sees" the battery voltage only when it reaches the end of the charge, so no hardware modification would be necessary on the scooter except for the autonomy indicator that calculates on the parameters of the original battery, but the scooter does not stop once this has reached zero; to have a correct indication there are two ways: a software modification or the insertion of a CAN-BRIDGE here too.

 

[MickeyS70]

I confirm that BMW i3 uses 12s modules. They are the same as the C-evolution scooter (it uses 3) that I own (I think I was the first in Europe to increase the autonomy of this scooter to 200 km).

What cells did you use to upgrade the scooter?

As for the possibility of adapting new modules, it is sufficient to reconnect the existing VCUs in the old battery respecting the numbering of both the VCU and the connections to the cells, for each VCU there are also 5 temperature sensors, they must be recovered and glued on the poles of the cells that make up the module (5 sensors for 8 cells each with two poles means that only some poles will host a sensor).

Not sure if you have seen the temperature sensors on a triplet CMU, they are tiny, recovering them is unrealistic, better to look for suitable replacements altogether.

In this way the existing electronics are recovered without adaptation problems.

True, but the real challenge is repacking and connecting these reclaimed cells.

The biggest problem comes later: the car does not "see" the greater capacity of the new battery and the autonomy remains the same, so the car stops with the SOC indicator at zero while the cells are far from discharged.

Luckily, that problem has already been solved:
https://myimiev.com/threads/main-traction-battery-upgrade-i-miev.5458/

 

[Franco]

What cells did you use to upgrade the scooter?

Not sure if you have seen the temperature sensors on a triplet CMU, they are tiny, recovering them is unrealistic, better to look for suitable replacements altogether.

True, but the real challenge is repacking and connecting these reclaimed cells.

Luckily, that problem has already been solved:
https://myimiev.com/threads/main-traction-battery-upgrade-i-miev.5458/



I read the first page, I don't have time to read the whole thread now.
The cells for the C-evolution were procured by a dealer here in Italy, but I wasn't particularly satisfied: after two years I had to mount an additional balancer.
For this reason I would never do this job in this way again, I would use compatible modules (Peugeot 308 for example).
I remind you that I have a Peugeot Partner EV, which however mounts the entire iMiev powertrain, with some differences: the BMS is installed inside the vehicle, under the driver's seat, and the battery is divided into two separate boxes, one 32s and one 48s.
My temperature sensors were easily recoverable, they were fixed with a rivet, I repeat: 5 for each VCU.
I did not reconstruct the original modules in my car, I mounted others, respecting the connections, before reassembling I checked the traffic in the CAN line of the batteries and everything was fine, the voltage values of all the cells and all 50 temperature sensors were read, two IDs remain whose origin and meaning I do not know.
For autonomy I found the suggestions in the AEVA forum, then I did a series of tests, in the end I achieved the result.
I still have not understood why the SOC is calculated in two different ways, one for the indicator on the instrument panel and one for the electronics that control the vehicle, I inserted the SOC recalculated with an algorithm that I developed in both Bytes

 

[MickeyS70]

Interesting, but that looks more like a 8s2p module to me?

For comparison a 12s BMW i3 module below…

 

[Franco]

Interessante, ma a me sembra più un modulo 8s2p?

Per fare un confronto, ecco il modulo BMW i3 da 12 secondi…
View attachment 1683

No, it's a 12s 2p