you only charge at cell x pgroup numbers not the whole back cell count
Why?
i been down this road before… he has his own maths
physics
You asked for 1 industrial use
you don’t have a grasp of basic electricity including series, parallel, resistance, voltages yet you think you can spec component for use in a BMS bleed resistors. Well you made me lol pleas get things you do checked by some one before powering them up wouldn’t want you to hurt yourself or others, or give esk8 boards a bad name
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In that use case scenario, it’s being uses as a simple manifold- that’s it, not for the purpose of carrying more current. It’s just a distribution point.
used*
If you think people need to know all these finer details in order to build this stuff, you’re crazy.
I build some of the best packs on the forum, and I’ll take that to my grave.
Well this sure blew up.
Looks like 4x 158 Ohm resistors in parallel for a cell group = ~40 Ohm balancing resistor -> 105 mA balancing current @ 4,20V cell voltage. They probably use 4 large SMD resistors to spread the heat to a larger area, as the BMS’ are conformal coated, so they can’t dissipate the heat as well.
Active balancing systems can move energy between cells where as passive balancing system just burn excess energy away into heat. For example, in an active system a cell at a higher voltage can be balanced by moving energy from it to a lower voltage cell. In a passive balancing system the higher voltage cell is discharged/balanced with a balancing resistor, turning energy from it into heat.
Active balancing is used usually with bigger packs where the actual benefit of saved energy in comparison to the larger size and cost of the BMS can be offset. Active balancing systems are much more complex, larger and expensive in comparison to passive balancing system, but can possible balance at higher currents due to moving most of the energy between cells instead of turning it into heat.
Overcharged cells can grow dendrites that cause internal short circuits in the cell, the severity of the short-circuits can range between a slight self-discharge over time or a catastrophic thermal runaway (AKA fire). The internal short circuit can also just increase the operating temperature of the cell, causing possibly electrolyte vaporisation, which then increases internal resistance (less active transfer liquid through which the Lithium-Ions can flow through) and decreases available capacity.
The cell level fusing protects the pack from thermal runaway in a single cell goes hard short-circuit. For example a single cell in a 5P-group goes into hard SC, this means it essentially becomes a bleed resistor in the very low impedance resistance. Now all the other P-group cells actually start to “charge” the SC cell as it’s voltage crashes, this then causes enough current to flow into one of the cells through the cell fuse to melt/blow the cell fuse, disconnecting the cell from the P-group and stopping the heating process. Ideally this happens before the electrolyte has heated enough to ignite or the cell ruptures from excess internal pressure (although cylinder cells have pressure vents).
Worst case is if the internal SC is somewhere in between a slight and a catastrophic one. Enough where the current flowing into the cell isn’t enough to trigger the cell level fuse, but enough to still heat it up over time to a thermal runaway.
Just putting the scenario out there that if the cell just suddenly goes hard SC by itself and is able to still reach thermal runaway temperatures even with the cell level fuse blown, then you still have a thermal runaway happening in the pack, which can cascade. But this is likely a very rare occurrence.
is very subjective as a design concept. Compare, say cell phone BMS and a Grid-scale energy storage BMS solutions.
Cell level fusing protects the pack from thermal runaways caused by internal short circuits in the cells.
The BMS is there to balance the series cells to same voltage (regardless if bottom- or top-balanced) to maximize the stored energy and give the car diagnostics into the battery packs (temperature, series cell voltages, estimated lifetime, cycle amount, need for service etc.).
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Lots of really good information in there, thank you.
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Active balancing can provide balancing currents into multiple Amps, because it doesn’t turn all that energy into heat, like passive systems do. It just isn’t suited well to small packs, as they can be balanced with passive balancing for a lower cost and smaller board space.
https://www.ti.com/tool/TIDA-00817
I personally just like the extra diagnostics it provides. For example see the actual real cell level voltages and droop and then see how much is lost between the pack and ESC with the battery current info.
Might be related that you can’t pack 13 pins efficiently into a circle. A higher number of pins might work as well and you get more pins.
This might be something with American engineers.
This dude…
If you parallel more conducting material then the current will use all that material. Assuming you bring the ends to the same point.
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I don’t see why they can’t just grab a 14 pin connector, and remove one pin, lol. It doesn’t have to be symmetrical.
Someone who really seems like he knew what he was talking about, seems to be disagreeing with you above? I mean, I am reading that right, correct?
“I’d say that if the battery button top is 8mm it support w/e the current specs for the cell is. If you put alot of these cells in parallell then, the conductor connecting them need to support that amount of current multiplied by number of cells. If you’re refering in your example to one single cell with a 8mm button top, with x thickness of y material (yes material matter too), then no. Using a 10mm conductor of the same material at the same thickness, does not serve a purpose. UNLESS its alot longer conductor, then you need to start applying some math.”
What I meant with my explaination was that if you need X width to support Y current. having 2X wont do anything for you. as in it does not serve a purpose. Are you asking what paths the electrons take on a subatomic level? Cause I havn’t touched electrophysics since uni. Of course the entire conductor conducts. even if the electrons travel in the pathway of least resistance.
Essentially, yes.
I can see how one could reason that as the resistance increases along the path, that it will simply get wider if the surface area exists. Is this not too good to be true?
Use the direct quote system to link directly the quoted text.
Highlight the text you want to quote in your post and click the “quote” button. Makes it easier to go and check the referred text.
I think he means that for a single cell, a 8 mm conductor of a given thickness is going to be able to carry all the current it can provide and 10 mm conductor of the same thickness is not going to provide that much more current capability with a 20% decrease in it’s resistance for a given length.
Do take note of skin effect of with AC currents, where the electron movement moves closer to the surface of the conductor as the frequency increases. But in EV use, we are operating almost completely in the DC region, where all the conducting material is used.
Can you give a bit more clarity/explanation to this statement?
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This is important to understand. @leadBreather you’re off here. series and parallel matter. and miscalculating the amps a pack can deliver and then trying to draw more from it can go catastrophic.
Take these 120 cells at 4.2v that can do 1.5A.
in a 1s120p. setup. that’s a 4.2v system that can do 180Amps.
in a 12s10p setup that’s a 50.4v system that can do 15Amps.
Power is the thing that is the same with the same number of cells. and power is not amps. power is current * voltage.
4.2v. * 180A = 756 Watts.
50.4v * 15A = 756 Watts.
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