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Discussion Starter · #1 ·
I'm thinking about experimented with DIY DC fast charging. Imagine a situation with no BMS, limited (like six) charge cycles, and the only requirements are quick charging and quick discharging. Used automotive quality 32kw battery pack. Think 25kw use and immediately 15-30kw DC fast charging after use. Battery cooling done during charging.

Here are some of the challenges I've found:
Transforming 3 phase power into DC in a 15kw+ format at a desirable voltage (200-500vdc)
Managing the saturation charge above 4.0v/cell for lithium (nonlinear current)

I guess my real question is: can the core 3.2-4.0vdc charge be done in a relatively crude manner so long as voltage and amperage are supplied until the cells reach 4.0vdc? Then move them to a smarter charger to correctly provide current along the ideal curve for the saturation to 4.2vdc?
 

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Discussion Starter · #3 ·
Define "crude manner". Bottom line, you need to balance the cells or you risk depleting them past terminal voltage or overcharging them.
Instead of charging out of a chademo or factory dc fast charger, it would be directly out of a large DC generator for the 80% to 4.0vdc.
Basically, can the diy dc fast charge just be linear power out of power supply and then the topping up saturation charge on the exponential curve be done by a Brusa nlg513 or similar charger?

Packs would be manually checked for balance between events after six charge cycles. Looks like 400 cells per pack would be incredibly difficult and expensive to monitor via bms.
 

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Discussion Starter · #5 ·
I have not purchased cells yet but planning on two chevy volt packs used together at ~200vdc. Max cell voltage 4.15 min 3.0. Something along the lines of 50s8p would be ideal. In that instance I think I could get away with a 50 cell bms if it was distributed and well labeled. Unusually high capacity loss is acceptable, so long as it's not all during the first charge! I am tempted to purchase a used $1000 load bank to test the generator first before hooking to an expensive battery bank.

I know there would need to be a diode between the charger and battery. The particular generator is a twin motor, induction and brushed commutator same shaft setup. In this instance I believe it is "self-rectifying" and it's 20+ phases based on size, but surely there would be a high level of noise compared to other methods. Do you know of any modern and efficient ways to clean this current?
 

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Discussion Starter · #7 ·
This is the DC shunt generator. My plan is to test voltage and overload condition at ~1900rpm eventually. Initial test will just be 540rpm with the tractor PTO and improvised load bank. Ultimately I'll replace the 25hp 3ph AC motor with a gasoline or diesel power unit.
 

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