18650 Insulator Rings - Redundant?

I noticed everyone seems to be using the peel-n-stick insulator rings (usually made from fish-paper).
But I also noticed that a lot of 18650's (mine included) already have an insulator ring under the shrink-wrap.



Seems kinda silly to be adding insulation on top of 2 layers of stock insulation (ring + wrap).
What do you guys think?

The fiber washers do not shrivel and shrink when they get hot.

Also, sometimes the conductive metal can is exposed due to vibration or a crash. These fiber washers are cheap. Personally...I would not consider ever building a pack without them.

spinningmagnets said:

The fiber washers do not shrivel and shrink when they get hot.
Also, sometimes the can is exposed due to vibration or a crash. These fiber washers are cheap.

Click to expand...

The *white* in the previous photo is a plastic insulator ring, here's a photo of it (from IMR Batteries) without shrink-wrap:


So your vote would be to just add the additional insulator ring on top of the two levels of protection that already exist?

I am starting to get the feeling that 18650's didn't used to come with the stock insulator rings, and now everyone is just accustom to adding them. Perhaps I should be asking if there are any documented instances of stock plastic insulator ring failing? (not talking about shrink-wrap).

Although 18650's are frequently used in ebike battery packs, they were designed for cordless tools and laptop computers. If you do not add the fiber washers, it is likely that your pack will be fine.

However, even though the possibility of a cell developing a short is very rare, it does sometimes happen.

Here is an article I wrote, and I consider it to be one of the most important things I have ever done...

"What's inside an 18650 cell, and why it's important"
https://www.electricbike.com/inside-18650-cell/

If a cell or it's interconnects on teh positive end heat up enough, and there is pressure on the interconnects that could then press it thru a melting (or softening) plastic layer(s), then the existing plastic rings are insufficient.

A paper insulator ring could not be pressed thru under the same conditions, and would then prevent a short across the cell group.

Up to you if you want the extra layer of safety, but if I were to build an 18650 pack, I'd be using them.

Because the edge of the nickel strip can be very sharp and easily pierce through the wrap and existing insulator, that's why you add that extra layer of protection

Thanks for all the responses guys.

I think for the most part, its a "better to be safe than sorry" scenario, given the minimal cost and ease of application.

If the connection between cells heats up for any reason, it will melt plastic at a much lower temperature than it takes to ignite a piece of fishpaper. Its just something else in the way of a direct short and that can never be a bad thing...

For the $2 it costs to order 100 of these cardboard/fiber cell insulators it's well worth the piece of mind not having t think about a potential short somewhere with a 1kw battery between your legs... Might take a tad extra time but it's worth it imho

For the casual reader in the future...if you are contemplating building your own ebike battery pack...don't "save" $2 on avoiding these fiber washers, and then make a $500-$800 pack that has LESS safety built-in...

I fully agree , but Someone should tell the big commercial ebike battery manufacturers ..EG Bosch.. , who rely on the cell manufacturers insulator ring in their packs.
https://endless-sphere.com/forums/download/file.php?id=215053

Cost. Even a few cents per pack adds up when they make enough packs, so....

It's all about profit margins.

Almost certainly, even if they had known problems costing them millions in recalls of packs due to shorts due to lack of the rings, they'd still save the money and not install them.

Pedego was almost bankrupted by their first foray into using 48V packs (compared to the initial 36V packs). They survived.

Banking on the odds, you will likely be fine when building a pack without the $2 worth of fiber washers. So I guess the question becomes...are you willing to gamble?

Sorry guys, but if the big boys like Bosch dont use them , its not to save a dolla or two...they know what the financial and commercial risk is if they have a failure or two due to that insulation ( they make a LOT of packs.
I suspect they have done their testing, probably specified what type of ring is used and figure there is no advantage in extra rings.
Maybe you guys are stuck in a 2010 paradigm when cells didnt have these insulating rings factory fitted. ( some still dont). And we now have a mindset that automatically thinks these extra rings are a must.

Bosch packs:

* Don't use nickel strips with scissor-cut edges
* Don't have someone potentially going overboard soldering stuff to the interconnects
* Weld strength and other mechanical support is evaluated to ensure the cell block is adequately stiff to prevent chaffing
* The battery enclosure has been carefully designed to adequately support the cell block to prevent chaffing
* The design will have been validated with physical vibration tests

The home battery builder does approximately none of these.

Prototypes, one-offs and low-volume parts are always over-specced to ensure a conservative design because failure costs outweigh the potential savings of using less material/parts. Mass-manufacturing is where you invest the time & money to find out how material you can shave from a design so it's still just about good enough for the job.

TLDR: the home battery builder would be an idiot to try and save $2 leaving out these insulating rings as a safety feature: you are not Bosch.

Use em on a homebuilt pack for sure. Because you don't have the factory grade nickel strips.

Of course Bosch (etc) packs are much better quality,..but if you expect a few microns of fish paper to protect against chafing of sharp burr edges on your nickel strips, you are fooling yourself.

I can't tell the readers how many home built packs I have seen where the builder bought a big roll of nickel ribbon, instead of nickel bus material that was laser-cut and professionally de-burred on an industrial scale. Then, the builder cut the nickel ribbon with shears and didn't de-burr the cut.

But...deleting fiber washers saves you $2.

Also, Bosch packs have a BMS that prevents them from providing high amps. A home pack-builder might design a pack that gets hot. 500W from 36V is 14A, and using a common 5P pack, that's roughly 3A per cell. Fiber washers will not stop the pack from getting hot, but if it does, the shriveling plastic will not cause a short when the nickel ribbon on the positive end crosses the positive nipple and negative shoulder.

But...deleting fiber washers saves you $2.

Bosch uses a hardcase and internal padding, along with high-quality insulating tape, as a safety measure against crashes and long-term vibration. I have seen countless home-built packs that had a single layer of shrink wrap, and are mounted inside a cloth triangle bag (you should insert thin padding and hard side-panels for crashes).

But...deleting fiber washers saves you $2.

Crap materials can look the same as quality materials, especially from China. Bosch uses quality materials. Bosch packs (on ebikes and cordless tools) will shut down the battery permanently for a variety of faults, but many builders do NOT use that kind of BMS, if they use a BMS at all...

The insulating rings I have used before were quite substantial: approx 0.5mm thick.

My friend was a pedago dealer back in the day andI told him toget a fire box with a vent to the outside for the battery Before the melt down. They make cheap product for big profit. Look at the components they put on their bikes trailer brakes xcetera cheap cheap cheap. Yes I've been to there place in Irvine cheap

Use the rings if you're a home builder.

Maybe they're overkill if you have an integrated system where the controller can't be hot rodded, and the pack has built in temperature sensors, and the welds are robotically done for uniformity, and the cells are highly quality controlled, and the connecting strips aren't accidently nickel plated steel.

If you already do all that when you home build a pack, they're possibly redundant. After seeing several commercial packs that melted thru the white washer under the shrink wrap, and then shorted a hole thru the top of the can, I would still use them even when taking the other steps.