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Mixing Tesla Modules with Laptop Cells
#1
I am currently in the process of building my Powerwall. I have built 11 out of my 14 80p 160Ah cells (and tested all of them before) and I have all my fuses, relays, connectors, etc.
The Sunny Island ready to go and the Batrium is on its way.

I am now facing a slight dilemma: My plan was to start off with the 8kWh battery and expand it as I was going to continue testing cells and building packs. However, I have now come across some Tesla Modules and now I am considering to use these. They will not run with the infrastructure as I had planned it (the modules are 6s and I was planning for 14s). Hence, my idea was to repurpose my 160Ah blocks: 
-run a 2s3p system of Tesla modules =12s222p (699Ah)
-Use my 160Ah and the remaining cells to build 2 packs of 700Ah
And then run a 14s system of mixed tesla modules and my own packs. 

What are your thoughts on this? I realize that the Tesla modules should be inherently more balanced than what I built, but there is also no guarantee that my packs (or any DIY packs) will be balanced. 
How have you dealt with Tesla's 6s configuration?

Best, 
MM
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#2
Hrmm, interesting situation. 12s is pretty low for a 48V. Your range would be 38.4V - 49.2 (3.2 - 4.1V). Most inverters would probably shut down if set for 48V, or trigger overvoltage if set for 48V. Unless you have an inverter that can take a wider ranger of voltage. I'm not personally aware of those.

The other option is to have two completely independent systems. But, this would be double the equipment/work

I would not add laptop cells to the tesla cells to bring them 14s. The only way I'd recommend doing something like that is to use new cells to make those 2 packs. Otherwise, you could end up with a lot of work the bms would have to do. Those tesla cells are probably in lot better condition than those laptop cells.
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#3
I dont know much about the tesla modules, but I have seen individual tesla cells for sale.
Can you dismantle the tesla modules and reconfigure to 14s?
That way you could add your existing cells in parallel as well to increase capacity
chuckp likes this post
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#4
Partially agree with Oz. If dismantling is a possibility, then reconfigure to 14s. However, I would not parallel laptop cells with the tesla cells either, at least not at the pack level. Perhaps make a separate string of 14s*p of the laptop cells and then parallel the strings together, but not the packs. IMHO
Proceed with caution. Knowledge is Power! Literally! Cool 
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#5
I see Magnum Inverters used with Tesla battery packs here and there in various youtubes.  If you look at Mangum 48v Inverter specs the voltage range looks great for 12s (e.g. 3v*12 = 36v  to 4.2v*12 = 50.4v).    Magnum Inverters seem well respected in the literature, they claim 94% efficiency (AIMS is 88% peak) - so I would view them as a 'production level' choice if you wanted to go that way.


There may be other inverters as well - but I agree with above, if you go Tesla you should stay with their config and that means finding equipment to match. You could reconfigure your laptop cells to 12s with same ah as Testla battery and run as a parallel battery.
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#6
(10-13-2019, 06:26 PM)OffGridInTheCity Wrote: I see Magnum Inverters used with Tesla battery packs here and there in various youtubes.  If you look at Mangum 48v Inverter specs the voltage range looks great for 12s (e.g. 3v*12 = 36v  to 4.2v*12 = 50.4v).    Magnum Inverters seem well respected in the literature, they claim 94% efficiency (AIMS is 88% peak) - so I would view them as a  'production level' choice if you wanted to go that way.


There may be other inverters as well - but I agree with above, if you go Tesla you should stay with their config and that means finding equipment to match.  You could reconfigure your laptop cells to 12s  with same ah as Testla battery and run as a parallel battery.
Thank you for the research, but I have already bought the Sunny Island and my PV system & accessories are also run by SMA so I would like to stick with their products. 

I could take them apart, but that would be a hassle and a waste of materials. 
I am planning on connecting each of the modules in parallel at a cell level - i.e. solder a wire capable of about 20A between each of the modules individual busbars. I would do this for two reasons: The BMS needs individual leads per pole of each cell and I am not a fan of strings in parallel. That would ensure that at least all module cells have the same voltage. 

I see the problem with mixing balanced cells (tesla modules) with unbalanced cells (laptop modules). This, of course, assumes that the modules a rebalanced. 
To somewhat lessen that problem I have thought about three strategies: 
1. Add more cells to my packs than necessary and observe the imbalance between my packs and the tesla modules during cycling, adding or removing cells from my packs as necessary. This will give me some flexibility regarding the adjustment of the Ah of each pack. It also allows me to add some cells later if my packs age faster - effectively "rejuvenating" them. 
2. Shallow cycling: I know that this can sometimes lead to more imbalance, but I plan to set the BMS to 4.05-4.1V max charging voltage to prevent the overcharge of some batteries.
3. I am considering to do an X arrangement of the tesla modules. I.E. have two modules as 1-6s, two as 9-14s, one as 2-7s, and one as 8-13s.
That way my packs are in parallel with the Tesla modules and not in series, which should reduce imbalance and is basically the same scheme as me adding my packs as a 12s configuration on parallel.
I.e. Packs a,b,c,d,e,f, in the following connecting with my packs g,h,i,j inbetween:


  1. a---g---b
  2. a---c---b
  3. a---c---b
  4. a---c---b
  5. a---c---b
  6. a---c---b
  7. h---c---h
  8. i ---d---i
  9. e---d---f
  10. e---d---f
  11. e---d---f
  12. e---d---f
  13. e---d---f
  14. e ---j---f
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#7
I have 14 modules and I can tell you. Good luck taking a module apart, they're glued to never come off and they're naked so they can easily short.

Magnum and Outback both support custom voltages when using the advanced router and the mate3 respectively. Without the extra controllers you won't be able to set your max and min voltages.

The only inverter I know that has the profile out of the box to work with 2 Tesla modules in series is Sigineer (12 and 15kw versions)
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