ID.3 and other MEB battery packs in conversions

[tom91]

Is there a workaround possible? Like dummy modules?

No not if you need them to be able to balance.

I have had customers try all sorts of setups with very degrees of functionality working, however never reliably.

[skr]

Just wanted to share my experience messing up a 12S module while stupidly trying a 8S cell tap cable without the shroud. Only after disassembling the cable I realized I had killed two fuses - one on each end of module.

I cut the case open with an angle grinder, 1mm disc. Laser welds have great penetration, the fused material goes almost all the way through, so cutting it part way and hoping to chisel it open can only destroy the cast alu lid. Dont cut the ribbon on top side where there is no weld, please.

The epoxy on top of fuses comes off easily with soldering iron with a sharp tip set to ~150C. FPC is made out of PET or similar material, melts easily, remove the epoxy from top of the dead fuses and solder on the new fuse on top of the old one. Be very quick and if possible use non RoHS solder, as tinning the old fuse already starts melting the FPC substrate at 260C. Cover the fuse with some epoxy or adhesive afterwards.

Then reassemble with ALU MIG welder, as I believe TIG would put way too much heat in to the case for my comfort levels. Remember to blow out any alu shavings or dust before refitting the endcaps. Also the cutting wheel may leave some sketchy looking burrs on the inside cutting edge, make sure to remove those, not to fall somewhere dangerous down the road.

Here are some pics.

[Sarek]

Great work there @skr.

I have similar issues with a module.
Having removed both ends, manually balanced and load tested my module, I am confident the issue was with the ribbon at a connection point to the fuse.. the fuse had not blown!

I'm considering connecting wires to the tabs at the point where the ribbon connects at each end of each cell. Basically 'deleting' the fuses. The cells can clearly manage much higher currents. Still using the ribbon for the temp sensors.

Of course I have doubts about this approach but it's never been clear to me what the fuse is there to protect? .. the original BMS, the ribbon or the cells?

Any thoughts?

[EV_Builder]

The fuse protects the ribbon and the joints of the ribbon.
An error is easy made so its best to leave them in place.

[skojon]

Hello, i have trouble balancing. Sometimes it work, sometimes not. I cannot find any info about my issue. Im sending correct CAN packets, but balance status stays at 0. Anyone struggled with similar issue?

[johu]

Here is something to cross-check against https://github.com/jsphuebner/stm32-car ... mebbms.cpp

[tom91]

Hello, i have trouble balancing. Sometimes it work, sometimes not. I cannot find any info about my issue. Im sending correct CAN packets, but balance status stays at 0. Anyone struggled with similar issue?

Yes I had similar issues, so did a customer and so did someone else I spoke to.

No real idea why it did not work, it worked fine then it stopped. Swapped the CMU (cell monitoring unit) and it immediately worked again.

Someone else even just plugged the same CMU back in and it worked again too. So no idea what it was maybe bad or loose connection.

[skojon]

Yes thats the code that i based on. Im sure im doing everything correctly. It just sometimes stops working. I noticed that it somehow depends on cell voltages. If they above 4V its disables, but when it drop, it starts balancing again. Do you know what cell charge and discharge voltages was in volkswagens?

[johu]

Oh, interesting. I have to say I never observed the balancing status that carefully as the pack is perfectly balanced. I can check next time I get up there

[tom91]

Yes thats the code that i based on. Im sure im doing everything correctly. It just sometimes stops working. I noticed that it somehow depends on cell voltages. If they above 4V its disables, but when it drop, it starts balancing again. Do you know what cell charge and discharge voltages was in volkswagens?

Do you have a log of this happening? I can take a look.

[skojon]

I do not have log but i will log it. But i went very deep into it with CAN bus monitor and setting balance flags (example 0x1A55540a to 0x8) just does not turn on balancing (0x16A95471). Funny thing is i have two MEB 8s floors connected in series with very similar voltages to two can buses of my device, and one is balancing and another is not. When voltage drops, it again works like a charm.

[raine]

I do not have log but i will log it.

Hi skojon, did you managed to sort this out? I am also facing similar bahaviour at one of the projects. below 4V seem balancing fine, but then it stops. Not sure if it is precicely the 4.0V, but anyway it stops at hig voltages. First i believed it was the delta getting too high, but manually balanced modules. Now delta is closer ~60mV, no difference.

Thanks!

[dutchlincoln]

If i may ask; why are you disassembling the battery pack instead of using it including the internal BMS?

[skr]

Just a heads up for anyone building with MEB modules-
The captive nuts on busbars are designed in a way that excessive torque may make it start turning inside of the module.
I mistakenly installed one bolt with pre-applied locktite + had nordlock on it, started spinning inside while trying to undo.
Thankfully this was the module I had already bodged the fuses inside, so no biggie, just a few hours of wasted life.

I ended up 3D printing a new "nut holder" + perimeter barrier, lots of filing and supergluing and sketchy mig welding on battery modules later I now have a module ready for work again.

I would advise to use contact grease on these busbar connections, if you are afraid of the bolt coming out - a spring washer and/or a height limiting 3D printed cap could help here probably. If a bolt ever siezes there- it is pretty much game over for the nut holder. Use sane amounts of torque when tightening as well, don't be me.

[arber333]

Just a heads up for anyone building with MEB modules-
The captive nuts on busbars are designed in a way that excessive torque may make it start turning inside of the module
.......
I would advise to use contact grease on these busbar connections, if you are afraid of the bolt coming out - a spring washer and/or a height limiting 3D printed cap could help here probably. If a bolt ever siezes there- it is pretty much game over for the nut holder. Use sane amounts of torque when tightening as well, don't be me.

VW specs for cell module HV contact tightening
M6 x 20mm marked as HV bolt no. 5
Torque 8Nm

Other bolts are structural and must be tightened at 20Nm...ish.
These specifications are critical for ensuring the structural integrity and electrical safety of the battery pack.

I am posting here VW manual, later i will repost it at wiki as well