N.E.S.E. with cell level fusing

janpom · May 22, 2020, 6:21pm

Following my recent board fire, I started looking into ways of making battery packs as safe as possible.

One natural choice is the NESE modules. They are easy to use and don’t leave that much room for a user error as traditional spot-welded packs. Also, abrasion resistance is excellent.

One other concept I like is cell level fusing, which (if done correctly) protects against thermal runaway (and fire) in case of any kind of short circuit, including internal battery cell short. This is also what Tesla does for its battery packs.

I thought about ways of combining the two and here’s what I have come up with.

The idea is to use only the unpadded NESE tabs and add custom padding with a fuse:

I decided to put the fuse on the negative side. The reason is that the nickel ring is not held in place by anything. In case it moves it could potentially slide under the fishpaper ring and cause a short. While this seems extremely unlikely, I don’t want to take any chances.

The negative side gets the fishpaper ring to extend the area where the fuse wire is not touching the battery or the tab, which should make it easier for it to pop in case of a short.

I did a few experiments to find out what wire gauge would be appropriate. I have an assorted collection of diodes that I have actually never used. I found out they have wires of various diameters, which came in handy now.

Using a single Samsung 30Q (charged to 3.8V initially and 3.6V when done with experimenting), I tested how the wires will behave under 10A current and under a short circuit. I was looking for gauge that withstands the 10A reliably but at the same it pops as quickly as possible in case of a short.

I used a 0.33 Ohm 50W resistor as load. At 3.8V, this would produce ~11.5A (going gradually towards 10A as the battery looses charge).

I first tested a very thin resistor wire (0.34mm / 28 AWG). No chance to withstand 10A with that one. It popped immediately.

Next, I tried a 0.44mm / 25 AWG wire. First, I used about 3 cm of the wire and that one burned pretty quickly at 10A. Then I realized that I would need a much shorter fuse wire in the NESE, so I tried again with ~0.5 cm wire. That one stood up to 10A just fine:

I then tested a short circuit with the same setup. I took this experiment to my balcony, just in case.

Success! It popped immediately. (Note the wire that shorts the switch directly to the NESE module, bypassing the load resistor.)

Next, I tested the short circuit with 0.50mm / 24 AWG wire to find out if it’s also useable:

It still managed to break the circuit quickly. This wasn’t so convincing though since the fuse wire didn’t pop but rather it desoldered itself from the bigger wire. It would have probably still popped if given a little more time. Anyway, I liked the way the 25 AWG wire handled the short much better so I went with it for the NESE.

Here’s testing the fused NESE with ~10A discharge.

About 30 secs of 10A continuous and nothing happened. (Only the load resistor got really hot. :)) Good!

Time to test the short circuit:

And the fuse wire popped straight away, exactly as expected.

I may need to repeat the experiment with a little more current. So far it looks promising though. The only problem is that the fused tabs are a bit fiddly to make. Should get better with some practice.

What do you guys think about this? Can you see any issues?

Sn4Pz · May 22, 2020, 6:55pm

I can’t contribute anything to the thread, but I’m certainly interested to see where this leads.

Frankly Ii-ion batteries spook me, but I can’t achieve the range and power I want with Lifepo4… So it’s kind of a stalemate

It would be cool to see some collaboration between you and @Agniusm to bring something to the market that any random Joe can buy and use without too much testing or hassle

janpom · May 22, 2020, 6:59pm

Maybe if the NESE tabs were made like this:

Jujo · May 22, 2020, 7:00pm

Are you using some sort of high density foam? Is it affected by constant thermal load?

janpom · May 22, 2020, 7:02pm

It’s just self-adhesive rubber tape that I use as gasket. I don’t think it actually gets hot though under normal load. It may get hot if there’s short but then it doesn’t really matter.

This really was just a proof of concept. I’m very interested in improvements suggestions.

Deodand · May 22, 2020, 8:32pm

I’d not ever use a foam in a battery for pretension. The gas particles that give the foam tension will escape and relax over time causing potentially weak contact force.

Consider maybe a gasket material. I’m planning to use a silicone gasket material for a somewhat similar design to maintain pressure under prolonged compression. This property is typically called compression set. Something like this:

Added benefit of being somewhat fire-proof so as not to add fuel to a potential burn down.

janpom · May 23, 2020, 6:54am

Would something like this be good?

https://www.aliexpress.com/item/33029270136.html

michondr · May 23, 2020, 8:16am

silicon is not that compressable, so it depends if you’ll be able to fit it under the cell in the NESE.

also, silicone costs freackin lot!

Agniusm · May 23, 2020, 11:13am

Sorry to say but from my part i dont see how this could make to productio.
You can ask @janpom how long and fidly it was to make test unit and then think of the proces to make it fast, reliable and cheap in producing them. Believe me, i thought about this and i could not come up with the method.
@janpom. You dont need foam or rubber. If you stick some kapton and then double sided tape, that should suffice. Btw nice job experimenting.
I have a design laying about that incorporates glass 3x10mm fuses. The downside is that the modules are~10mm wider.

janpom · May 23, 2020, 3:43pm

Thanks for your input @Agniusm.

It’s indeed time consuming. I can still imagine doing a full battery pack in one day. Not something I’d want to do commercially but would definitely do one for myself. Even if it just saved the next board I build, it would already be time well spent, not to mention potentially saving property or even lives.

Have you looked at the vid I linked? Any chance of getting the tabs cut like this:

Nice! ~10mm wider is not too bad. I’d definitely be interested.

janpom · May 23, 2020, 3:59pm

Here’s another iteration of my experiments.

Thanks for the tip, @Agniusm. I tried something along those lines. Instead of kapton and double sided tape, I used fishpaper rings, including the centers. They already have the correct shape. No need to cut anything. Plus, the fact that the centers are separated from the rings actually comes in handy – the ring nicely surrounds the button on the tab and the center then covers the button.

I just had to trim the sides of the rings so that I have somewhere to solder on.

This came out much cleaner than the previous version. Soldering on the tabs is pretty painful but I’m getting the hang of it.

Testing the fit:

I inserted the cell into each of the four slots one by one and measured the voltage at the NESE module terminals to make sure the cell has a good contact. It looked good.

I then went ahead and repeated my 0.33 Ohm load resistor test four times, one for each slot. This should discharge about 10A.

I did 10 seconds on each of the first three slots and 20 seconds on the last slot. All was good. Nothing was getting hot except for the load resistor.

I’m thinking of building a small 6S4P battery pack in this way and use it with a 40A limit for a bit and see if it works.

Agniusm · May 23, 2020, 5:26pm

@janpom, i will get the model uploaded so you can look at it. It uses 3x10mm glass fuses, probably can get ceramic one too. I could not test it cause ebay chinese seller sent me 5x15 instead and it takes ages for the stuff to arrive.

janpom · May 23, 2020, 5:51pm

Would SMD fuses be any good instead of the glass fuses since space is a concern? Maybe something like this?

https://www.mouser.com/ProductDetail/Bourns/SF-1206HV10M-2

The length is only 3.2mm. Saves 7mm compared to the 3x10mm glass fuse.

Agniusm · May 24, 2020, 7:06pm

Here is quick edit for the 3x10mm fuse. You could use SMD but the ones are same size only square.
You can get fancy but you will be paying over 60ct per cell for fuse so not that attractive. I think glass fuse would suffice but testing needs to be done.
My approach is very simple and requires little modification to the modules and also simple to install, use and check for the penalty of increased size. I still need to see if the tab could be inserted strait down.5P_base.stl (1.5 MB)

janpom · May 24, 2020, 7:47pm

Same size? The glass fuse is 10mm long. The SMD fuse is 3.2mm long. That’s quite a bit of a difference. Sure, the SMD fuses are more expensive but $0.6/pc I’d still consider acceptable. I suppose the most common NESE flat pack would be 12S4P with 6 pieces of 4P+4P modules. With SMD fuses, you’d save a little over 4cm on the length compared to the glass fuses, which is significant. Seems worth the extra money to me. Also, cheaper SMD fuses can probably be found. I just linked the first thing I came by.

I like your design. Thanks for sharing. This will be my plan B in case the fuse wire approach proves problematic.

mishrasubhransu · May 24, 2020, 7:52pm

This is a great design. Do you have a link for those fuse?

janpom · May 24, 2020, 8:09pm

I did a little more searching for SMD fuses. This one is below $0.30/pc in bulks: https://www.mouser.com/ProductDetail/Schurter/3413032822?qs=tk5EcTX4n4wzBBF6MzsMfw%3D%3D

This one is about the same price, but even smaller – 0603 package / 1.6mm length – but it’s rated a bit too low:
https://www.mouser.com/ProductDetail/Bel-Fuse/0686F8000-01?qs=HXFqYaX1Q2xPwOwhLFPgJQ%3D%3D

mishrasubhransu · May 24, 2020, 8:22pm

I think nyou need to find some in this form factor. Otherwise those flat smd can’t be easily integrated?

Agniusm · May 24, 2020, 8:41pm

I know you can go microskopic with the fuses but you still want some area to support compression. My idea was to use what i have without altering my compression concept too much.
@mishrasubhransu exactly the ones i was talking about. If those could be found shorter, it would save the width by that length.
The glass fuses i was thinking are all over aliexpress and ebay.

janpom · May 24, 2020, 8:45pm

True, I didn’t think of that. Would stacking a bunch of thin SMD fuses on top of each other be any good? That would make them parallel so if N fuses are used in this way, I supposed you’d want to reduce the current rating by the factor of N.