… Also if there is a short between main terminals of the battery then, I think, the following should happen: The currents through all cells will be very high and there will be one fuse which blows first. This will automatically increase the currents through other cells in the same P block, so their fuses will also blow. So basically all fuses in (at least) one P block will blow, and the battery will be saved.
Soooo, to clarify, using a more conductive material than say nickel has no negative effect on the pack.
To really clarify: using more conductive than nickel is a benefit for the pack on all series connections for sure but on parallel connections it MAY be better to use high resistance stuff.
@sash can u or someone tell me are the cell level fuses also the parallel connections? So in a situation where one cell in a p group were to internally short I guess it’s voltage will drop way low and then the rest of the p group cells would try to balance it as always but now with a lot of current through the p balance connection and if that’s thin it will burn up n disconnect the single bad cell from its p connection and prevent the other p cells from dumping into it. The one bad cell is already a goner and the benefit being decreasing heat in the cells beside it with the hope that one hot cell isbt enough to go to thermal runaway and it needs a couple. . A cell level fuse just being a very high resistance connection. Is this right? I see the cell level fuse thread but its big n hoping someone can summarize grabbing the nuggets n kernels.
You guys are so smart
Sadly it’s basic basic electronics and that’s why I really want to understand it which is possible if it’s explained in numb nut terms
@Hummie I think that you are basically right. But I don’t want to pretend that I am expert on cell level fusing. I’ve read through several long threads about it and considering to use it in my next battery build, but I am not sure yet.
Currently, I don’t use any fuses in my esk8, because I don’t want a fuse to blow on me when I am riding. I thought that cell level fusing is a safer option, because if one fuse blows you can still ride your board.
My impression is that it has not been widely tested yet. For example, which fuse wire to use? If it is too thin then fuses will blow when you don’t want them to blow, if it is too thick then fusing defeats its purpose and will not save a battery from thermal runaway.
It also depends a lot on the design of the pack, on the length of fuse wires, on the material and weight of busbars, on the amount of open space around fuses, etc.
Basically, the only way to figure it out is to try and find out what works for you.
I need to build a 10S4P battery in two layers. It looks that so far only @michaelcpg has managed to build a 2 layered battery with fusing. So this is really a new territory.
Tesla uses cell level fusing, but it is a different story. In cars they have huge numbers of cells in P groups. So their batteries can produce high currents even if fuse wires are thin. Several blown fuses should not make much difference.
In esk8, where people typically use 4P or 3P setups, it is much more sensitive to the gauge of fuse wires, etc. So I am not convinced about cell level fusing.
Why would you ever wan’t to use a less conductive material. If your using the same material in your connections there will be no uneven discharge/charge from the cells.
Am I missing something?
I probably wouldn’t go as low as 18 awg. I think 20 awg would be best IMO.
I think that a fuse wire is “a less conductive material”. The whole point is that it is less conductive, and if the current is too high it heats up and blows. Other than fuse wires I also don’t see a point in using less conductive material.
Now for series connections you need to use conductive material to produce the current you need from your battery without heating the connections. For parallel connections you don’t really need very conductive material because there is not much current going through these connections. (Ideally, if the cells are identical to each other, where should not be any current going through parallel connections.) So you can use less conductive material for parallel connections. But the only benefit of it is saving a couple of dollars on your nickel strips.
and don’t forget gorgeous! and amazing! and humble!
Yeah ofcourse the fuse is adapted after the kind of load your application is capable of.
Hummie states that it may be benefitial in other cases. I don’t see it though.
@jinra Thanks for the clarification.
One question is bugging me. @chaka says to put fuses on positive ends of cells. In the design that I have in mind, I want to put fuses on pluses and minuses in an alternating way. I am can eliminate any possibility of shorts. (Planning to separate fuses from cell by fiberglass plates.)
Is there any electrical reason why I should not do this? (Uneven current distributions, or something like this?)
18 awg being thicker than 20. But…if cell level fusing IS simply a very thin parallel connection and done in a board as apposed to a Tesla, and a cell were to out-of-nowhere short, and then its p neighbors would not just be balancing but shorting as well, (mistaken in what I wrote about above and it would be shorting all the p cells if one cell were to short). Makes sense to have a thin enough p connection that it would break the circuit so as not to continue shorting the other three cells but how often does a cell short out of nowhere anyway and more so I thought the large majority of fires were due to a cell being charged that was damaged and in that instance does it ever even short in the cell before or even after thermal runaway has started? The fuses maybe only are good for a rare instance of a cell internally shorting. Is that rare or the norm for a lead-up to runaway?
I fused both ends, but I think positive only is sufficient.
Is there any difference between fusing both ends or only one end of a cell? I mean, it is enough to interrupt electrical current only in one point, right? But in youtube videos about cell level fusing, they usually fuse both ends.
Fusing both ends would be the same as putting two fuses in a series connection. It should not add anything. Actually, I think it might be even worse than fusing one end because it would increase the probability of accidental blown fuse (due to a defective fuse, bad soldering, vibration, etc). Am I missing anything?
I was asking the following: I want to fuse only one end of cells, but I want to put in on plusses for one half of all cells and on minuses for the other half of the cells. Is there any reason why it can be bad?
Why would the neighbour p short? The cells are only connected to eachother with the fuse. When the cell draws too much A (be it from a short or a bad cell from over discharge) the fuse will melt and seperate the cell from the group. The rest of the group remains intact.
Edit: The rest or the remaining group would not short but will draw a higher current.
I was meaning that when the one cell has an internal short the other cells beside it in the same p will also be shorting through it until the fuse breaks the connection. A safety feature which makes sense only when shorting happens in a cell but when does shorting happen in a cell?
i have all the same questions.
my thoughts were that the fuses allow a gentle overload cascade to happen that will eventually burn up all the cell fuses in the p group, disabling the pack, and i have to assume burning up the balance lead as well if the BMS doesn’t sense some dumb shit happening and switch off.
so then what… you replace the cells?
so after reading this whole thread repeatedly while trying to take the occasional break in order to draw pictures of urinating esk8ers, i was lead to the conclusion that having cell “go dud” inside a welded p-group was somehow super-bad-time, either the cell would drag everything down with it and not accuratelty balance things any more, or something worse like extra heat …
except i’ve never seen any of this happen and i’ve had every kind of bad battery come across my bench conceivable. I’m not saying i’ve seen everything, i must assume that i have not. but i have seen packs with far less than adequate cells sitting in the middle of a 4P group doing nothing but mildly affecting range and full charge voltage.
I am also trying to decide if cell level fusing worths extra efforts needed to build a pack (and also maintain it, replace fuse wires, etc.).
In the known cases of thermal runaway, would cell level fusing have prevented it? If one cell goes on fire, then I guess the whole pack will even if all fuses burn.
Does “internal shorting in a cell” happen to anyone?
But I am definitely going to do this:
What’s nice with the @chaka method is that he left behind a nice thingiverse design for anyone to adapt it