Fuse cells 18650 diy pack

[bikegeek]

Hi,

I've seen this videos:

1) https://www.youtube.com/watch?v=5EE4TsuzD_Q

2) https://www.youtube.com/watch?v=raBWFsPlx7w

My question is, why diy battery builders are not using fuses for every cell from the pack? What are the disadvantages?

I want to build a pack like this and I don't know if it is any problem with this method.

 

[bikegeek]

It is very good information but still doesn't answer my question.

Why people is not using this method of fusing every cell? All information I read is in favor of using fuses for every cell.

 

[amberwolf]

Likely that most of them are not even aware of the possibility when they actually start building, and dont' think of it themselves.

But also probably because most dont' have time, money, materials, inclination due to the complexity of assembly, and really don't believe anything will ever go wrong that it would stop.

At least, not until their bike (and whereever it's stored in) burns up because of it. :/

And realistically, there are other factors, like space between cells, ventilation, etc., that might make the fusing pointless if something did go wrong with a cell that caused it to overheat sufficiently, as it could start a chain reaction. And many ebike pack builders don't have the space on their bike for a pack with the internal spacing to keep cells apart in the case of an overheated cell failure.


Tesla's packs do use this fusing, and cell spacing....

 

[bikegeek]

I don't think is more difficult than building a standard pack.

I've attached a picture of what is inspiring me and what I want to do in the future.

 

[Hillhater]

1) You don't actually need a "fuse" on each cell....just a "fusible connection".
2). Those fuses will protect the cells, but not prevent the pack from potentially causing fires.
3). That method of cell connection ( soldering) is likely to promote early cell failure
4). There are 18650 cells available with inbuilt current limiting and over /under voltage protection....if you are so inclined

 

[Syonyk]

I've attached a picture of what is inspiring me and what I want to do in the future.

You do realize that every 18650 spec sheet out there says, "Do not solder to cells"?

 

[Lurkin]

The key question was: fuse or not to fuse? why?

The more fuses you use, the more points of safety, but also failure can occur. This can leave you stranded without knowing where the shorted fuse is. The fuses in your picture look like PPTA fuses - these are designed to deal with temporary shorts (unlike a glass fuse) so if the situation causing the short is temporary the circuit will go back to normal, for the most part, avoiding this problem. The advantage of this is that the fuses do not require replacement so long as they have not been damaged in the process. https://en.wikipedia.org/wiki/Resettable_fuse

The primary purpose is to protect against damage caused by shorts within the pack, rather than heat or just cell explosion (happy to be wrong here).

I agree with Amberwolf for the most part, most ebike builders probably do not consider than anything will go wrong/ external pack fusing is adequate for their purposes. I note em3ev uses PPTC fuses in their packs as discussed on their website, but I have not disassembled one to work out what level the fuses are at. Some of the more commonly available materials often used for ebike packs, like dovetailed cell spacers, don't really provide space for these fuses. They are designed to have the nickel run and spot welded directly onto the cell without anything inbetween. Again, if there was an easy product that was fusable per cell to be used instead, I think we would see more of this. It's certainly something I'm considering, but would prefer to use a pre made plastic structure to hold the cells/nickel strip spacing rather than a hot glued fused pack. I believe Spinningmagnets had found a nickel strip type design which has this type of fuse built into it.

Tesla packs have both individual fusing of each cell and a beasty fuse for each module. There is a youtube video of a bloke shorting the pack deliberately and watching the individual fuses go. The individual fuses for Tesla packs look different to what you have in your picture, pretty sure they are just a nichrome wire (or similar) which burns through when too much power attempts to go through (happy to be wrong on this).

Oh yeah, please get a spot welder. Soldering cells heats the cell inorder for the solder process to occur to fix the nickel or wire to the cell, which isn't good for it. Some have the artful skill of being able to do this quickly, but I think its worth investing in a spot welder. The JP Welder on this forum has had excellent results, is low cost and designed to be used with a commonly available car battery. I'm not aware of a good reason (other than soldering iron availability and spot welder cost) that justifies continuing to solder 18650s. The welded end product is also arguably stronger than that of a soldered pack - leading to less shorts within the pack to start with.

 

[bikegeek]

Ok, my answer is clear now, is good to have a fuse on every cell but could be a problem if is not made right.

I have a spot welder made from a MOT and I've made a 10S4P pack using 0.1mm nickel strips and BMS but after that I realized I could make things better. Now I want to rebuild that pack with fuses for every cell and make another pack from used cells.

I know is not OK soldering cells but I was thinking welding a small piece of nickel and on the other end of the nickel strip to solder the fuse. This treatment only on the positive side. I don't have problems with putting things together, my only concern was if using fuses is OK or not.

I have added some pictured with fuses used in teslas battery packs and how I want to welder nickel on cells.

 

[Hillhater]

if you are re-using cells from laptop or powertool type packs, try to keep the original welded pairs together and treat them as one cell of double capacity.
you can then simply solder your fuse links onto the tabs to join tabbed pairs.
half the number of fuses needed.

 

[Lurkin]

Are progress with your pack?

 

[bikegeek]

Not yet, I'm waiting for some bits and parts to come from China.

I received the fuses.

I have a question, I have the option to buy laptop battery with 2.2 euro/each or 2.4 dollars/each, is this a good price? What should I look for? They have a lot off them and I can choose.

 

[999zip999]

No there's a guy in poland selling cells and packs and cells.
In the : Items for sale new section
Brand New Cells 18650. Member Tumich. Check it out.

 

[Hillhater]

I have a question, I have the option to buy laptop battery with 2.2 euro/each or 2.4 dollars/each, is this a good price? What should I look for? They have a lot off them and I can choose.

Cell price depends entirely on the brand and model , capacity, etc of the cell.
For example,...a Sony VT 5 would be cheap at 5.0 Eu each
But a UltraFire of any type would be overpriced at 0.1 Eu !

 

[Lurkin]

The point is - you are going to quite an extent to build a decent battery. Laptop packs are rolling the dice unless you can identify what cells are contained in them to start with and confirm the source is providing quality cells before purchasing them. You may well be spending $ and finding out later that they are rubbish.

If you think about how much time and effort you are going to, it doesn't really make sense to use laptop cells unless you are broke and have no other opportunity cost for your time I.e. no job. Doing the per cells testing is really, really time consuming (it's well documented on here is you look) unless you are willing to spend more to have a larger test set up. Otherwise, your better off buying quality new cells. Tumich is selling cells internationally, but it may be worth seeing if anyone local to you is selling cells and their pricing. Freight is usually the killer on batteries, ignore pricing that doesn't include freight it's just a tease.

I think you need to go back to the beginning and work out what battery capacity you need - this will dictate the cells you require based on the physical parameters of your pack fitment. You may well find the size of the battery pack made from low capacity cheapo cells is bigger than ideal - hence new, reliable, quality, high capacity cells is usually a far better idea.

 

[bikegeek]

Thanks for your info.

I've bought from Tumich 40 new cells NCR18650PF and made a pack that is on my bike (10S4P) and I'm planing make it bigger 10S5P already (it dose not have more then 5 charges so I can add one more parallel).

Now I just want to test and play. The price of 2.2 euro was for a laptop battery pack (at least 6 cells inside). And on this pack I would like to test the fuses and all other features I want to add.

But I was making a calculation and I have to buy 60-90 cells of 18650 (10-15 laptop battery packs) to get 40 maybe 50 "good" cells. The total cost would be ~35 euro for 15 laptop battery (about 90 cells). And I'm hopping to get 2000 mAh of each cell. That would allow me to make a pack of 8 Ah (4S) or 10 Ah (5S) with a minimum cost.

Brand new cells would cost me 40 x ~2.5 euro/each = 100 euro + transport = 110 - 120 euro. From 35 euro I thing is a long way but who knows?

Do you have a better solution for new cells? I mean a good cell (bigger than 2000 mAh) cost ~2.5 euro, right?

The motor that I want to use for the pack is a 36V 250W geared motor that will need 12-14 A at peak.