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Discussion Starter #1
Hello all, I have just completed my conversion of a 1963 Beetle to EV, using 5 Tesla modules from a MOD S and an HPEVS AC50/CURTIS 1238. I am using the Dilithium BMS...As you are probably aware, each Tesla module is made up of 444 18650 batteries connected in 6S 74P to make 6 cells. I have 5 battery modules, so therefore I have 30 Cells..38 of the cells are at 4.06 volts and 2 cells are at 3.8..I need to balance all cells so they are equal BEFORE I plug in the onboard charger! I need a way of charging these 2 low cells up to 4.06, so I am looking for some suggestions of how to do this. Working with these Tesla modules is not like working with individual Cells (like CALB for example) The BMS is actually working to lower the voltage on the 38 good cells down to the 3.8 of the 2 low cells, but this seems a bit backward as it will take week or so, when all I really need to do is charge the 2 lower ones. Any ideas???
cheers
Bob
 

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Just a helpful hint... your terminology makes the post a bit confusing, and will be more confusing if you ever discuss cell capacity.

I am using the Dilithium BMS...As you are probably aware, each Tesla module is made up of 444 18650 batteries connected in 6S 74P to make 6 cells. I have 5 battery modules, so therefore I have 30 Cells..
The module is made up of 444 18650 cells connected in 6S 74P to make 6 cell groups.
A "battery" is a group of cells connected in series. In an EV (such as a Tesla), there is one battery, but it is too big to build in one piece so it is made up of modules (14 or 16 in a Model S).
Referring to a group of many cells which are connected in parallel as a "cell" (rather than a "cell group"), and referring to a single 18650 cell as a "battery", are the parts which can be confusing.

You don't have 30 cells, you have 2220 cells, in 30 groups.

Anyway, the voltage of each cell group is the same as the cell voltage (because the cells in a group are in parallel), so your voltage levels still make sense. :)
 

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Discussion Starter #3
Thank you you Brian, but my question was how to charge an individual cell group, do you have any suggestions in this area?? Have you actually worked with one of these modules
Thanks
Bob
 

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Best is to charge the cell-groups by connecting directly to the bus bars, charging via balance-wires can be done but please be gentle on the current, like 1A max.

But...yes there's a but...

Why are these cellgroups out of balance??

In my experience this happens mostly when coolant from the modules ends up on the positive end of the cells, where it creates resistance and thereby drains that cell-group.

and now the bad news: I've never seen anyone successfully recover a module from this situation, maybe it can be done if you're fast to the problem (before the coolant creates a permanent resistor) you might be able to flush the coolant away with alcohol.

Please be careful and double check why the cells were drained.
 

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Discussion Starter #5
Many thanks Boekel, that's certainly an area to investigate, I purchased the Tesla Modules from EV West in California and they tell me they have seen this condition before and they have been able to recover, but I will certainly investigate your theory
Thanks
Bob
 

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Many thanks Boekel, that's certainly an area to investigate, I purchased the Tesla Modules from EV West in California and they tell me they have seen this condition before and they have been able to recover, but I will certainly investigate your theory
Thanks
Bob
Ah good than at least you have some warranty.

did you by any chance measure the voltages some time before ? and know if the imbalance has increased or not? or it's been there from the beginning.

also is it in one module? and can you reach that module for inspection?
 

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Discussion Starter #8
Hi Boekel, yes these two low cells have been there since I received the batteries. I have a total of 5 modules 3 behind the rear seat and two in the front where the petrol tank used to be.. I moved the modules around so that the two modules with the low cells are in the front where they are easy to get to. I have concluded that my best course of action will be to return these two modules for replacement. There does not appear to be any suitable charger capable of individually charging a cell group, but I am going to wait until I receive some more responses...
Bob
 

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Hi
I just use a simple power supply
The one I got on TradeMe (Kiwi EBay) cost me $40 and will charge up to 16v and 3 amps

Set the Voltage to the max for your cells
 

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Discussion Starter #10
Many thanks Duncan, how did you connect the charger to the cell group? did you charge through the tiny balance wires?
Bob
 
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