So then I get some batteries. . .
So Luke calls me up (you know - the mentally deranged guy we call Liveforphysics) ranting about some batteries that I have to buy. Babbling about how they are $0.18/watt and they would be perfect for my build. Another long story short that includes a frantic trip the the bank 3 minutes before closing an a wad of cash so big it only fit in a coat pocket and we have the following:
Batteries - lots and lots of batteries
2,650 to be exact -> or about 26KWH. To put it in perspective, that is 500lbs of A123 sized batteries. About half a Tessla pack
I went thru several testing rigs - first testing at 20A, then at 100A. I started by trying to bin up the Ah of each bank but got board of that quick. What I am doing now is testing the behavior or the cells under a 3C load
Bank = 2S 12P
Rated Ah = 34.8 AH
Test current = ~100A
Apx C rating = 2.9C
I use 14 x 1ohm 30W batteries in parallel sandwiched between 3 aluminum Infineon cases cooled via a computer fan.
Datalogging at the cell level happens with the iCharger
Datalogging of the current happens with the CA
View attachment 106_Isolator.jpg
This is the GUI for my BMS - here I am only using it to display/record Amps and Ah coming from the CA
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I have started collecting parts on Ebay - this here is a 50mV 100uOhm 500A shunt.
QUALITY! After creating blue lightning by smoking out my first shunt (a story I wont repeat) I learned my lesson -> this ain't no ebike
Ignore the voltage - that is just a pack I use to power the CA. The current is all we are really interested in as we are testing 2S. Unfortunately 6V is not enough to power the CA
View attachment 108_Isolator.jpg
This is how I am going to configure them: Each little bank will be 2S 48P. Rated that would be 140Ah but it is actually more like 120Ah. If I were to run the packs hard - say at 400A continuous it would be more like a 100Ah pack followed by another 20Ah at "normal driving" 150A range.
I went thru a few variations of this laod - currently it is running at something over 2KW. Anyone who has ever tried to dissipate that kind of heat knows.... It is no joke. I am blasting the crap out of that stack of resistors and it is still hotter than hell. At one point it was reaching 230C
Now I have it under control. A 12V 2A PC fan sounds like a jet engine but does the trick.
View attachment 4
I dont know if you have ever tried to open a circuit that is drawing 100A DC -> errrr..... it can be a bit testy and connectors dont last long. For that reason you use a pre-charge resistor. This particular resistor is 1.5ohms 30W and it draws about 5A. First I clip this on then I make the main connections. This keeps the sparks down to a dull roar, especially when disconnecting.
I am starting to prepare the wiring and collect an entire new set of "big boy" tools. This is ghetto - but it will work for what I want to do.
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Yea - that is right. My very own 4/0 cable.
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-methods