Tesla Module BMS Balance Issue

[65NW]

Is anyone familiar with the battery modules BMSs from a Tesla model S?
these are 5.3kwh modules running on SimpBMS.
REV A module board, says "PCBA, BMB, WIRE-CLIP"

When simpBMS put the pack in balance mode, the lowest two cells of one module begin to jump up and down. (cells 10 and 11 on the serial monitor)
when balancing is off, they are steady voltages.
This is on a new install and the batteries are not yet equalized.

Has anyone seen this behavior with the Tesla module BMSs?
How do the Tesla BMSs work normally?

 

[sunshine_eggo]

I would assume it's the balance current influence on voltage readings or bad connections.

Not many use Tesla modules around here. They tend to be a LOT more expensive then DIY batteries of larger capacity and comparable to new 5.12kWh LFP batteries, and they are dramatically more dangerous.

 

[shifty]

I would assume it's the balance current influence on voltage readings or bad connections.

Not many use Tesla modules around here. They tend to be a LOT more expensive then DIY batteries of larger capacity and comparable to new 5.12kWh LFP batteries, and they are dramatically more dangerous.

In most metro areas where they scrap functional teslas for minor body damage, you can find the 5.2kwh modules for around 300 a piece. BMS adds another 30 bucks or so per module. I totally agree with the safety assessment, but I haven't been able to find any LFP that aren't a few times more expensive. I'm actually in the planning phase of another build and was considering the tesla modules as an option. Do you have any links to any alternate products around that same $/U?

 

[Lt.Dan]

In most metro areas where they scrap functional teslas for minor body damage, you can find the 5.2kwh modules for around 300 a piece. BMS adds another 30 bucks or so per module. I totally agree with the safety assessment, but I haven't been able to find any LFP that aren't a few times more expensive. I'm actually in the planning phase of another build and was considering the tesla modules as an option. Do you have any links to any alternate products around that same $/U?

The Ruixu and SOK basic batteries are $1199-1299 for 5.12kWh. You might be able to find less on sale or less-quality brands

 

[sunshine_eggo]

at $300 each, that's a pretty good deal. I certainly haven't found anywhere in my metro area that would go for that price.

18650 store has grade B 305Ah cells for $75 last I checked. That's the equivalent of 3.9kWh for $300 + BMS.

The 6S config of the tesla modules means you're running 15% higher current for a given power vs. 8S (24V) / 16S (48V) for LFP.

 

[shifty]

at $300 each, that's a pretty good deal. I certainly haven't found anywhere in my metro area that would go for that price.

18650 store has grade B 305Ah cells for $75 last I checked. That's the equivalent of 3.9kWh for $300 + BMS.

The 6S config of the tesla modules means you're running 15% higher current for a given power vs. 8S (24V) / 16S (48V) for LFP.

Thanks, that's pretty cheap, and yeah that's a good point on the tesla batteries. They're not really 5.2kwh in practice. Decisions decisions...

 

[65NW]

My pricing chart from this spring put my 2s3p pack, with bms (900usd) at about 125usd/kwh. I did not price diy LFP packs because im not interested in building one.
the "AK price hlx+" is what I paid locally for my previous 4s pack after hazmat shipping to Alaska. I ended up driving my tesla packs up this summer from SAC, CA.

anyways, thats off topic. hoping to find someone with tesla module exp.
will it balance cells that far out given enough time or is that indicitive of an error?
they are currently balancing with load output off, checking them every few hours.

 

[mrconstantin]

i have many packs with tesla S 6s config , also i use B class with is 7s made also with tesla, dot have any problem to balance.
On Some pack if the cell have wires not ribon the wires can oxidate and have problem on contacts with battery plate.

I dont use simp bms because is expensive , u can do same thing with an esp32 board

I prefer the setup because u dont need other balancer for the packs.

Also can use this boards with any li-ion packs if u can find it

 

[65NW]

On Some pack if the cell have wires not ribon the wires can oxidate and have problem on contacts with battery plate.

yes, I have wires and a few of the ones on the bottom of the pack were unbonded. I spot welded a tab on and soldered to it. I was unable to solder the wire directly to the alu plate. I think they use an ultrasonic welder in the factory. have you had to rebond wires? how did you do it if so?

i have many packs with tesla S 6s config , also i use B class with is 7s made also with tesla, dot have any problem to balance.

I dont use simp bms because is expensive , u can do same thing with an esp32 board

I prefer the setup because u dont need other balancer for the packs.

and this is with the tesla bms board and you are using the esp32 to put them in balance mode? do you have more info on a tool to talk to the module BMS?

Also can use this boards with any li-ion packs if u can find it

do you use the boards you have from modules or do you buy tesla bms boards specifically for the balancer?

 

[65NW]

After letting them sit several hours in balance mode, it does not look like they are doing anything (presumably this is very slow and would take a long time to see any progress). Im pulling those modules from my pack and will manually balance them in my shop before adding them back in.

 

[mrconstantin]

After letting them sit several hours in balance mode, it does not look like they are doing anything (presumably this is very slow and would take a long time to see any progress). Im pulling those modules from my pack and will manually balance them in my shop before adding them back in.

The balance is resistive so will take some time if u have modules with cell wires w up this means is a problem there, and with few cell in parallel in pack will be unbalance when charge discharge.

I made a project to talk with invertor protocols and i take also data from tesla battery boards like SimpBms how is expensive simp is about 400-500$, u can do same thing with esp32 with max 100$. U can see it in my thred post wit the jk can interface.

For HV battery for inverter Like Fronius, Sungrow, Solax i can use an full pack and can take data without open all battery, and the B class have 30kw so is ok for used.

Some people change the Tesla board from battery with orion boards or other after market bms. If u communicate with them u have an good bms and can put it on any pack.

 

[Jacob_]

You can always get a Active balancer 3a + , that you can balance your modules from time to time...
That should solve your problem, dont let the Simp bms do the balance...there is so much a BMS can do...the less...the better...

 

[dag84]

I have had good luck getting Tesla modules for under $300 I recently drove from KC to Louisville to pick up 11 modules for $1,000 plus driving expenses. They all work and tested very close to each other Ah wise after spending 2 weeks testing them. They are the 4.5 kwh version not the 5.3, but still very useful.