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Discussion Starter · #1 ·
TL:DR:
Looking for good options to build out a ~96v (up to 115) pack to drive about 25Kw of output. (AKA 250A @ 96v)
I'm thinking of upping the voltage just a hair to keep amps a bit lower since I'm already at high DC voltages.
For safety, I think I want to build this to be able to break the system into 48v packs when not in use. I'm sure that'll make the bms super happy.
Target is 20-40Kwh of storage. I need to support 250A of sustained drive current.

I see three possible solutions here.
1) LFP/LifePO4 cells.
32cells*3.2v = 102.4v
102.4*100Ah = 10.24Kwh
So, if I use say, 2 to 4 100ah cells in parallel to deliver the amperage I need, this gets pretty approachable. I can add a cell or two to the series config to up the voltage and reduce my amp load just a bit - and allow for puling a cells out of service if I have a failure. Cost: Around 2-4k depending on config/seller/shipping/etc.

2) EV traction pack reconfigure. An interesting pack to me is the BMW i3 pack. It uses something like 48v modules that are easy to remove and reconfigure into a 96v pack. It would be harder to up the voltage if I wanted to. In addition, It looks like about $3k for a likely degraded 22kwh on the open market for these.

3) Custom 18650/26650 cell packs.
This is interesting as I could build custom packs into waterproof pelican style cases. It would be a crap ton of cell welding. After poking around a bit, I've found a similar cost per Kwh unless I absolutely score some epic recycling deals. Seems like similar pricing otherwise and just a ton more fabrication work for me.

Have I missed anything I should seriously consider?
 

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2) EV traction pack reconfigure. An interesting pack to me is the BMW i3 pack. It uses something like 48v modules that are easy to remove and reconfigure into a 96v pack. It would be harder to up the voltage if I wanted to. In addition, It looks like about $3k for a likely degraded 22kwh on the open market for these.
I'm not sure what the advantage of ~48 V in a single module would be; almost any EV pack has at least 8 modules in series and so some combination of modules comes up with a reasonable voltage for this approach

As far as I can tell, the BMW i3 does use 12S modules, so about 45 V nominal. The Volvo Polestar 2 and VW MEB batteries also use 12S modules, but those would not be readily available in salvage yet.

If you want to hit the planned voltage in a single module, you can use Tesla Model 3 short modules (23S) or long modules (25S); a single module would almost hit the target capacity, and two (unfortunately in parallel) would be well up in the target range. Unfortunately because the modules are those two different configurations in the same pack there's no way to use all of the modules from a pack at less than 48S (~180 V).

And as Tim pointed out, there are always the 6S modules of the traditional Model S/X, which could be series connected in pairs for the target fragment voltage, with two pairs in series for operating voltage. Four of these modules from the 86 kW pack is one-quarter of the pack, so a bit over 20 kWh without dealing with any parallel connections.
 

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Discussion Starter · #4 ·
Tesla modules would come down to cost. I think I'd have to run 5s to get the voltage/amp ratio I want.
I have one I used in my RV previously, but would want some in excellent shape for the boat.
 

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Discussion Starter · #6 ·
I found one spec that rated Tesla modules for 225a continuous. I'm wondering if I'll have to go with double packs later but I could live with 22kw of output to start I think.
I found a good deal on a few modules locally so I'm tempted. I kinda like the idea of water cooling the packs anyhow.
 

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Discussion Starter · #8 ·
I'm waiting to hear back from Thunderstruck to validate what I'm doing, I'm thinking 4 or 5 packs. The controller is good for up to 125v but I want to make sure that's reasonable.
Max charge voltage is 25.2, but I think it's better to be a bit conservative and stay a volt or so away from min/max charge levels.
On the one pack I used (which is actually a crappy one) It seemed that the tesla packs like to sag a bit in voltage as they discharge and I'm thinking 5 would keep the voltage over 100 for most of my usage, and give me a little more headroom to avoid driving the cells quite as hard.
 

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I'm waiting to hear back from Thunderstruck to validate what I'm doing, I'm thinking 4 or 5 packs...
That would be "modules" (the blocks within the battery pack; there are 14 in an early Model S/X, 16 in a later S/X, four in a Model 3, and five in a Model S Plaid) in normal terminology, rather than "packs" (a pack is a set of cells or modules in a box; a Tesla car has one pack).
 

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Don't let the forum get to you Willo. You are on the right track and talking to the right company. Thunderstruck gave you the right information.

There's no such thing as a Model S/X. :) Discussing the Model 3, Model S Plaid and Model S modules in the same reply as if all Tesla modules are the same is hilarious. You want used modules out of a Model S or out of a Model X. Technically, they are ALL batteries, not modules.
 

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There's no such thing as a Model S/X. :)
MesquiteTim appears to have difficulty understanding that "Model S/X" obviously refers to the Model S and Model X, which use the same components (drive units, battery, etc). I assume that no one else has this difficulty.

Discussing the Model 3, Model S Plaid and Model S modules in the same reply as if all Tesla modules are the same is hilarious. You want used modules out of a Model S or out of a Model X.
Of course there are huge differences (mostly in size but also in internal construction) in the various Tesla modules, and no one suggested anything else. Traditional (not Plaid) Model S or X modules may indeed be the most desirable of the Tesla modules in this case, but that's not MesquiteTim's decision.

Technically, they are ALL batteries, not modules.
While any set of cells - including a module - is technically a battery (because a battery is "a group of two or more similar objects functioning together"), MesquiteTim apparently doesn't understand common industry terminology, in which a set of cells forming only part of a complete EV energy storage system is called a module; "battery" is typically reserved for the complete set of modules in a case. It's just easier to get useful information if you understand and use common terms.
 

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nah, I'm just poking fun at you for pretending to be such a stickler for accuracy while being inaccurate at the same time, in the same comment

the battery has been around since 1749 so I don't feel the need to change the term to module
 
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