Fuse individual cells or not?

Are there sometimes reasons when it's more advisable to fuse individually and times it's not so necessary? Or is it a good idea all the time? Odds of problem without? Why not just the one main fuse? Or what will a the main fuse not protect?

I also wanted to mention what I'm doing so you all can stop me if there are any major problems with it. I doubt there is but before I do too much more, better see if I missed something. I'd decided to do 4x2s10p 12v batteries for my 48v ebike and hook them together for 58v or so. This also gives me the option to use them in a home emergency power bank, boat/camper, and any ebike I like by using. 2 3 or 4 at a time. Even throw one in the car for emergency starts.

I'm in the middle of the first one of the 4 and I keep thinking I'd love to do away with this fusing, because it's such a slow process. I never could understand all the technical reasons why these go together like they do, so copying was the easiest for me, and I should get it all after a build or two. I still don't know where the balance leads go, just hope I can find someone to take my pic of the finished product and mark the leads for me when I'm done.

Here are pics my first attempt at this, and a link to the one I'm trying to copy. On the one at the link, viewers didn't seem to think much of his build but I hope I at least got the basics from it correct...another reason I wanted to run this by you all.

What I copied https://www.youtube.com/watch?v=laPbq6OHL0I&t=225s

No idea how to get the "not downloaded yet" pictures to download. Any suggestions for another helpful site, I've tried for 30 min to get a pic to post here, something that is normally no problem to figure out, and this post is partially useless without pictures

I put the picture here.

To me it looks like a 4s10p battery pack.
cell fuses are so if one of the single cells shorts out, it blows out the fuse instead of overheating and possibly melting wires and catching on fire. If a single cell shorts out it acts like a giant fuse that won't blow, all the other cells will dump there current through that cell, hundreds of amps.
Very important to use in a bike pack, if you crash and a cell is damaged it will short out. Thats why tesla uses them for car collision.
You only need to fuse one side of the cell (+ or -), but in your design it looks like both sides of cells need to be fused because of the distance to the bus bars.

As long as you are using fuse wire you are doing it the right way. Its extra work but for safety reason it has to be done.

As far as balance wires, you always start on the negative cell, the cell after that is 1,2,3,4 and always ends on the positive. Never pay attention to the colors on wire connectors, they are all over the place. In this connector the red wire is actually negative. On the connectors the top is where its flat, the bottom is where there are 2 guides to lock the connecter in place.



when I'm building packs I always use one of these 3in1 lithium balance checkers to verify all my wires are good.

Another big fan of individual cell fusing here!
Not sure how to link threads but check out "My battery Builds" thread if you want.

Even more important in my case as I'm using recycled cells...but I would do the same if they were new.

Just another level of safety for "what if" situations

That's a big help, and thanks so much for your reply, JJ, as well as for getting the pics up for me.

OK then, I didn't know all that...you just made the fuse decision and easy one, done deal. I'm using the 34 gauge fuse wire suggested by the youtube guy, something, something "powerwall" ?

That should help with the balance leads, but I may be back once I get the first pack done. If I can just get through one, all else should go well. I'll keep checking for other posts here in the mean time.

Thanks again.

EbikeAus said:

Another big fan of individual cell fusing here!
Not sure how to link threads but check out "My battery Builds" thread if you want.

Even more important in my case as I'm using recycled cells...but I would do the same if they were new.

Just another level of safety for "what if" situations

Click to expand...

Thanks, for the verification, and I'll check that out. For future reference, one can usually just go to the thread and copy/past the URLfrom the address bar to link up the thread.

My cells are from all new, some old stock, Laptop packs, and much better than a year of tedious ordering off ebay. It's kind of addictive, Got lucky a couple of months ago and picked up around 40 packs to go with what I already had, all 8, 9, and 12 cells each for $5.70 each, and all but about 20 individual cells were good, so have plenty to work with now. I've cooled it for now but I doubt I'll ever stop looking for deals.

jonyjoe303 said:

4s connectors a.jpg

when I'm building packs I always use one of these 3in1 lithium balance checkers to verify all my wires are good.
3in1.jpg

Click to expand...

I may look into the wire checker. I ordered the balance cable yesterday, another long wait from China...I'm so cheap.

I also recently go my Capacity Controller in, something I just picked up because they were cheap and they will balance, as well as other things with a nice big digital read out on them. there may be no real use for them with a battery pack but I was hoping, maybe. Here they are and if anyone has messed with them, I'd be interested in any input.

https://www.youtube.com/results?search_query=capacity+controller

A few threads that discuss cell level fusing, if any of the info helps:

https://endless-sphere.com/forums/search.php?keywords=cell*+fuse*&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

There's other threads that don't have it in the title, too.