parallel cells have tiny amounts of current between them and the main current travels through the series connections so maybe the sleds with the paralleled cells and with thick copper connections between would be …as good as ever
I’ve heard this multiple times by several users and was steering away from it but do you really think electrons magically disappear from one point and appear at another???
Hint: No. Here’s an image to explain how much current would flow in a 4P pack where only the last cell is connected to the next series set as is done in most of our setups.
As you can see, not all strips need to be rated to 40A but all need at least 10A and not zero current as implied by others. Otherwise, why even connect them?
Another thing to consider is a buried wire has no place to dissipate heat and needs to be much larger than a aerial wire
You must have missed that he inverted the pluses and minuses. I think he got it right.
My point is that both for the sleds and a welded pack (which is irrelevant to @rpasichnyk’s build as he’s doing something different) you cannot just add wires in the “series” connection. There is current flowing in the “parallel” connections as current has to get from point a to point b. A 1.5" long pure nickel strip (.005" x .25") can take up to 10A before they get really hot in my own experiments. This falls right in line with endless-sphere’s 18650 spot welding how to by nobuo.
If you only add copper to the series connection, you’re going to be running up to (n-1)/nI n = cells in parallel, I = total current, through a single nickel strip. This means lots of heat and an overall inefficient design as your heat generated is I^2R which also means a high voltage drop btw (which ties into that other thread too).
In summary, you should add as big a wire as you can in all connections and not skimp out on parallel connections as that will make your pack inefficient.
I just made it the other way. So you can easily connect the holders by bending the pins on the bottom side and solder them together. I will add parallel connections by soldering a wires between the parallel cells so that the cells can be balanced. One more pack and i have my 12S4P. Made already a 12S8P in a very similar way.
This pack has a couple of advantages:
- very flexible
- cells can be replaced at any time
- easy to build
- you can take it on a plane
- current is shared between 4 lines
- cells are very well protected
- no spot welding necessary and no soldering on the cells
- bit more weight because of the holders (12S4P pack will be 350 - 400g, i guess a standard pack has like 200g of wires and heatshrink)
- 30 mm wider (156 mm total) than a standard 12S4P
Ibeams are strong because all 3 elements are connected (one piece) the strenght of this board also will depend on how the top, the middle and the bottom part are attached. right now one plywood layer on top, and one on the bottom is not enough. you need more intersting project with interesting outcome. subscribed!!
Can we replace the Rload with R(thevenin)??
You remind me of my electrical engineering study …
Oh god. I barely paid attention through all that lol. Norton’s Theorem, Thevenin’s Theorem… Just give me the damn circuit and I’ll solve it without you confusing me is whatI used to think throughout that class
I’m in the class right now and it blows. Learned about op-amps last week @PXSS,
Nonetheless, you should do a FEA on the design because Concentrated Stress Points happen at sharp corners, I would recommend filleting, but you can’t do that now. Side note if you guys have seen road gutter drains sometimes that have this same design of rectangles and ribbage but because their made of metal(steel presumbably) and have a lot of ribbage made into them the, FEA would be useless unless they want to save as much money as possible because they overengineered it.
Where do you study?
UMBC in Maryland, USA
(“up and coming for last 50 years” is the students inside joke)
I went to Georgia Tech. Forever second to MIT… except we don’t have shitty weather.
I study at RWTH Aachen, Germany. We always have shitty weather :\
Look at it again. It’s a 2S4P drawing
look at it again they’re all in parallel
How do you even pronounce that? Do you all just go around roaring??
Do you not see the positive and negative signs??? I’m in bed so I won’t redraw it so you can get it. It is a 2S4P drawing. I know be cause I drew it in all 60 seconds
I’ll entertain the idea that it’s a 1S8P drawing, why the hell would I only connect a load to the negative terminal and nothing to the positive. Connecting such circuit would only short the cells.