When we started to make these battery blocks, we added these fuses on each cell, mainly to isolate a cell if it shorted. The role of these fuses is not to protect the unit against an external short circuit, but exclusively to disconnect the defective cell. For protection against an external short circuit, a main fuse is required for all the blocks in series. We had chosen to use fuse wires of 5 to 6 amps, If these fuses do not burn when the unit is in short, it is because the cell is unable to supply sufficient energy.This can be seen in the test of the last block which is insufficiently loaded. Sory for my bad english.

The fuses that don’t blow are obviously connected to high-ir cells, that’s why they don’t blow, the cells can’t push enough current. That’s why we need fuses that blow at 2A maximum

Double fuse adds resistance in the shorting loop, that lowers the max short circuit current, might be just enough so the fuse doesn't blow. You can determine the max current output as following: Current = tension / resistance So you'll get different result if the cell is charged or discharged ! Once you have your cell's voltage, you just divide it by all the resistance in serie (for the short) : 1rst fuse res + internal res of the cell + second fuse res + 2 x Bussbar res And you have your maximum current output. It's clear that 2 fuses add resistance and lower the current, and that it is to be taken into account for the choice of the fuse. For this use I would personnaly choose a fuse just above the draw per cell in normal use. If not, this is impossible to detect a short in this case ! But then it might become too resistive and lower the efficiency of the pack.. (Sorry for my bad english)

Kinda why Ive been using the glass fuses from the start. I wonder if those that didnt pop have a dirty wire where the solder is so it didnt "connect" the best. Interesting for sure. I love these type of videos!👍👍

Fusing both sides doesn’t make sense, just extra work. Kirchhoff’s law means current in = current out, so one side is OK unless you think the body of the cells will short to each other. But in these holders they won’t. Also the fuse wire should be in tension somehow, so when they break they disconnect quickly. In the Slo-mo you can see some of the fuses broke but continued to arc across.

I use miniature glass protected 2A fuse. I tested it with degradated cell less than 100mAh of residual capacity, high internal resistance and tested at low voltage (3V), it blow immediately. Best use glass protected fuse that are of constant lenght and perform always very good.

I would like to see some current measurement to see how much actual current it takes for 1 fuse wire to blow connected to a single cell. Also an IR rating of the batteries in which the fuse wire does not blow.

no it`s not boring thankyou

Cell level fusing is to protect the remainder of the pack in the event an individual cell goes to a short condition. So a 1S40P pack (as per your demonstration) with one shorted cell could dump a minimum of 20 amps if the pack is in a very low SOC. Conversely the same pack in a high SOC could dump nearly 200 amps (assuming 5 amps per cell). I believe your current fusing scheme is correct and should be continued. You are correct in your comment about do we really need two fuses per cell. 2 fuses per cell (one on +ve and the other on -ve terminal) just means the weaker fuse will blow first as is a series circuit. A single fuse will work just as well. If you wish to protect the pack as a whole, then a circuit breaker or fuse at the pack level is required. The sizing of that protection will have to be less than the maximum current capability of the pack. Using the numbers above, and say you wish to limit cell protection to 5 amps, then a 1S40P pack may have a 160 amp circuit breaker which limits each cell to 4 amps. This would protect the pack (assuming the cell level fusing is at 5 amps). I'm currently working on a battery design for 1S144P pack for an EV conversion of a Suzuki Jimny. 28 of these should give me some serious capacity and range.

It's called internal resistance the battery 🔋 has so much internal resistance that is can not produce enough amps to blow the fuse

That cell is incapable of producing enough current to blow that fuse.

To me, this shows exactly what fuses are supposed to do. The purpose of a fuse is to protect the pack from a *single cell* that goes bad/shorts. Its not about every fuse blowing if the pack shorts out. In the case where 1 cell was left on 4.2v pack AND the case where the pack was 3.2v - there is not enough amps in the short circuit to melt the fuse wire. So the question - will an individual cell catch fire if its externally shorted... (not necessarily).... which is a different that if 1 cell shorts (within itself) within a 40p pack where there's 39others to flow / burn the fuse wire.

Glad to see that you are back to making videos!

But as I can understand ... the idea to use that kind of fuses is to isolate a shorted cell from the rest of the pack, in order to avoid a collapse of the entire pack and avoid the faulty cell to heat and even catch fire. In order to protect the entire pack from a short circuit, should be enough to fuse the positive terminal of the pack with the correct current you need for your system to work in normal operation.

I am eager to hear more thoughts about your safety concept. Like the fuses, but you have very little isolation in the setup for unwanted touching with metal objects and stuff.

I think that the one battery fues not cut is from the battery. I think the battery is gives lower ambs that could not cut the fues

Interesting wonder what amp of fuse wire was used I like to use the Bussman BFW-1 1amp wire which actually takes more than one amp to blow but worked in my tests. I only tested with single cells so makes me want to try a whole pack now.

How about this for a possibility. Some momentary event happened that shorted out the pack many hours before the fire started, but due to one or two cells with high IR, the pack didn't then read 0V and was presumed by the batreon to still be healthy. In reality though the pack was changed from a 200Ah pack down to a 4Ah pack. The pack continues to get charged at the normal rate, but as it's now only two cells with high IR they're just heating up all day long. At 4pm the heat gets too much and the cells catch fire.

I have a test i would like you to do! Create a pack like you have here of 4.2 volts and use cc cv step converter to run a known resistance and use your Bluetooth cell meter to measure and record each cell at intervals and also the heat of the cells to illustrate the different esr and quality of different cells as some are built for higher and lower ability in their discharge characteristics especially over time as some cells can get a lot hotter than others! 👍🏻

Boring - NO. Educating - YES. :-) Really like your live testing. I think the low volt test shows that the cels can't produce enough power to blow the fuses....

I would think that resistance overall plays a role, not just the internal resistance of a cell but, also that of the fuse wire, the amount of solder which is after all just a lead and tin mixture which is also not perfect and the length of the fuse. Pete, did you not spot weld some of your battery pack fuses? Would that not be a game changer in the way the fuses would re-act??

Seems a new way to test the internal resistance of the cell!lol

the fuse wire also blows depending on ambient temp and is greatly affected by any air going over the fuse wire it self

This is not a boring video really enjoy your video

Got them blue PLATO cutters!

1:27 my packs have fuses on both sides and have a pack fuse to protect the cell fuses from shorts across the main terminals.

thanks a lot for repeating this test cause now I could see the relevant part in the timelapse video.

as i have said to many people many times dont go overboard on the fuse thickness i think if these had been high current drain cells the fuses would of blown easy but as they are low current flow cells they dont have the power to melt the fuses that have been used

check the battery internal resistance before parallel

Very informative. Thanks

Interesting tests. Thanks! Regarding the low voltage short test... I think when SOC is so low like that, short-circuit amps are much lower and cell is much less likely to get hot enough to cause any problems and/or enter thermal runaway. Just my guess though.

Thanks Pete for the additional testing at the expense of your time from the day job (or even your free time)! Are you able to check the size and type of wire that was used to fuse the donated disaster pack? It could be a less conductive wire that has a higher resistance (steel vs aluminium or copper). This might also explain why the fuses didn't blow and the terminals got too hot to hold. Regardless of outcome, thanks for the extra investigation you're putting in to the "decommissioned" pack!

That was worthwhile Pete - I think we can take away that the fuse gauge is too thick for the lowest voltage. Higher IR cells can't produce enough current to blow a fuse at low states of charge. For the same gauge, longer fusewire tends to blow first. (I double up the wire on the negative side to encourage +ve fuses to go first, because they're easier to check and replace.) A fuse test with a standard reference looks useful to identify sub par cells, before assembling them. Looks like most of the cells in those battery packs are still usable, so I wouldn't throw them away.

As far as I understood, cell level fusing has never been for protection against shorts. You need a fuse after the pack for that. Cell level fusing is to stop the other cells unloading into a failing cell with loads of current. So one cell fails, self discharges and heats up, and the other cells would put their current into that cell and just raise the heating with a lot of current. And the cell level fusing would then prevent this from happening. This is at least what I gathered was the reason for cell level fusing. :-)

The more I watch your channel lately, the less I want to play the mixed chemistry second hand cells game. I need to build up some hefty 48 volt packs for inverter that currently has AGM fitted. New A grade LiFePo4 will be my choice. Thanks for the education.

Looks over-fused. Very interesting!

An easy test... Run the dead short with an ammeter to measure the current flow. Use the min/max feature to capture the highest current flowed, and measure the voltage of the battery during the current flow. The fuses blow with current flow and not necessarily the voltage, the IR will affect the reading and change with temperature.

I appreciate this comment is a bit late from when the video was released. But I have a bit of OCD, and stopped the video and counted the black dots. There were 20 on one side and 17. But I saw another cell that had both fuses intact. Counting from left, it was number 4 and on the red side it was third row and on the black side it was 2nd row.

Also i believe the battery was heating up despite having been shorted and left to sit because its internal resistance had been increased either from the short, or maybe even just heat damage from soldering. But increased internal resistance would definately be cause for a battery to stand out amongst a series or parralelled set.

Really interesting video, I first go into your videos because I am interested in the application of these "fuses" in making batteries for electric bikes specifically. Some of the big manufacturers for example do use "fuses" per cell, same concept as yours (not counting tesla of course). So these experiments are super interesting, I really really want to understand what the reason is here for them not popping. Exciting!

I think the fuses work great as long as your weakest cell is capable of twice the current rating of the fuse at min cell voltage. The Only reason tesls gets away with it is extreme quality control on the battery side. Even then can we ever be sure that Tesla fuses work 100% of the time.

Is the wire you use actual fuse wire like the one used in UK rewireable fuses or is it just a random unrated thin wire?

Do a video fusing 10 cells together with a few known heaters. Use low current fuses (2A maximum) and charge it up to max to see what will happen with the heaters

Excellent, test and I really appreciate. It is a very good example that uses the welder to use fuses wire (without a curve especific). Once again the better protection for short circuit and overcurrent protection is a DC breaker or even a main fuse. Ps. individual fuse is useless as you presented in lower voltage cells. Why? Because lower voltage mean low current to sent out... so the fuse did not burn because the cell could not achieve the "wire fuse" current rupture... Thanks for you video! I appreciate! Best regards. Rodrigo

Appreciate this video! Can you share the name or link to the cell holders you're using?

A high resistance joint would act as a current limiter.

I would love to know more about the IR numbers, for example what constitutes a high resistance with that IR reader? What is a good resistance number?

Internal Resistance does play a role in battery packs, I think that it's just as important to match cells capacity wise just as it's important to match them by their internal Resistances. I have been contemplating the idea of using a diode on each cell so that energy only can flow out of the cell to the buss bar, but that would mean that each cell would have to be charged separately at 4.2V which adds complexity but it isolates each cell so that they don't get charged by the stronger cells in the pack! Of course a diode adds a voltage drop to each cell so I might have to add another row of cells to get the same voltage... It definitely needs looking at from all angles and possibilities, I think that the optimum goal is to obtain the best safety and reliability... Using Automotive blade fuses instead of the wire method would give better consistency due to the constant fuse length but at the same time it adds more complexity... I have a bunch of single cell protection PCBs that I got from eBay, they are not expensive and small enough to be shrink wrapped to the cell, they offer over and under voltage protection as well as short circuit which is great but the cells would need to be charged individually... I also had the idea of using those drop in type battery holder's mounted on a pcb which should then allow me to install the battery protection PCBs directly to the drop in battery holder so that I have swap out batteries without having to worry about de soldering cells, that sort of setup allows quick and easy testing and replacement if necessary! It's a little more work involved to set up but once done, it should make life easier for maintenance... There's another channel, I think it's called jhenga or something like that, he's done something similar, he sells them but being in the US, he doesn't ship to Australia simply because the shipping and import charges cost more than that kit itself! Kinda sucks because it looks pretty good! I don't remember if each cell is protected individually which is what I would like to accomplish but it certainly looks the business! Otherwise, the only other option would be to purchase protected cells which I use in my torch, I have tried to short circuit them but it's impossible! They are branded as keeppower with 3500mah rating from an eBay seller in Sydney, they cost me $30 for two and I'm happy with them for the few years that I have been using them for. I have lately been looking at those sand bag lithium polymer batteries that are available on eBay, they are the cheapest for their capacity, they come pre packaged in blue shrink wrap and have a power switch and two barrel jack type connectors already fitted, those sand bags kinda worry me but they are usually found in those portable car jumper packs and can deliver a lot of current! But using those would mean that the enclosure design to house them would need to be able to keep each pack separated from each other just in case one failed and caught on fire.... But if you have enough of them and you aren't drawing excessive amounts of current from each one, then I guess that they should give no problems... It's just an idea but everything has to be carefully considered...

at lower voltages the cell level fuses seem to be allot less effective, also the type of wire used for fuse might be an issue eg: steel vs alloy, the length of fuse might cause issues too, it also seems fusing both sides can be a hit or miss, did the cell level fuse for the nickel strip from BH behave the same way? the smaller pack also had higher resistance then the un used pack

I have been trying to say since this community started up. There is absolutely nothing to be gained from fusing both sides of ANY circuit. No matter what circuit you are looking at, it consists of a number of current loops. Not all current loops need to be fused either, but where fusing is applied for protection, placing a fuse on both the negative and positive side of the current loop provides no further or better protection, nor any other gain. If anything, it adds to the complexity, assembly time, the probability of high resistance connections, and increases the number of failure points. Just fuse the positive (the positive and NOT the negative in the case of 18650's for mechanical reasons). The same goes for everything else, chargers, inverters..... There is no gain from fusing both sides of the supply. It just creates a "race condition" (under normal circumstances) and one or the other will blow. I also personally think the fuses are way too big (too higher fuse current) for this application. Having seen this, I'm thinking .5A fusing would be a better option, though I'm not sure that would be enough for heavy recharge cycles. All 18650's should be able to blow a 2amp fuse EASILY. Anywhere from full SOC to at least 50% SOC. Those cells that didn't, must have pretty high internal resistance (under load conditions). Also, tiny changes in Internal resistance of a cell mean MASSIVE differences in maximum short circuit current. It's not the same as for eg. an equivalent change in buss bar resistance.

Of what type of wire did you make your fuses? I have been thinking of making fuses out of automotive fusible link wire rated at 5 to 6 amps for 32650 cells rated at 6 amp continuous discharge.

Internal resistance isn't the only thing at play surely. I'd theorise that the cells with intact fuses not only have high internal resistance, but also very low capacity. Low capacity plus high resistance equals very low ability to deliver current/amps, resulting in intact fuses. Please capacity test some of the cells which consiststantly blow fuses against ones that don't, so we can see if capacity divided by internal resistance gives a reliable indication of a cell's ability to blow fuses/deliver current.

Fuse wire length does matter! That's one of reason why on one side must be used not the same fuse wire, but some more think wire, which has lower resistance, will not blow up and will not cause voltage (think - power) drop on the side where proper fuse is. Also, those 2 far corner sells have longer wire (longer than usual ~10mm) and that's also not so good. It's possible to solder in a way (on cell and bus bar) in a way to keep it shorter than ~15mm.

Idea! Did anyone ever made a battery pack of their worst cells? The heaters and the leakers? And try to discover what is needed to make these fail (fire like)?

How would the glass axial fuses I see some build there pack with work out?

I am after advise. Battery for ebike 14s4p max discharge current per cell is 13A. Controller with max current 45a. What current of fuse wire to use in this battery? I have 10a and 5a. For now is 10a, and bms current reduced to 30a. Think that 10a fuse will not blown, but may get hot. Will blown if go back to full current. Would be ok to solder one more 10a fusewire?

Did you test the cells for internal resistance before building the battery packs? Having a small apparatus for measuring voltage with a resistor can help you figure out the IR of the cells so you can ensure any future packs you build have cells with comparable IRs along with weeding out those with a high resistance. Just need a cell holder, resistor, voltage display, and a switch. If you're so inclined, can probably even figure out how to automate that with an Arduino. (And I think I have a new project to add to my list...) Wouldn't surprise me if you can buy something that can do that for you.

What size fuse wire was you using? Increased fuse wire length will result in increased cell resistance so better use a consistent length to balance out cells. double fuses not required as will only add to the resistance. The higher the resistance the higher the voltage require to burn out. Also more often than not, a “3amp” fuse wire for example will require atleast 5amps for a duration of time to burn out, and if you want instantaneous blow then would need into the 10s of amps if not more so it becomes extremely important to carefully choose the correct fuse wire size based on max discharge current design plus keeping in mind the max discharge current will vary based on cells discharged state.

i'm curious about the far right straight wave after the fuses were blown on the right most cells was that a reflection ripple?

HB, good as usual! No, not boring. Uhm, I'm not an electronics guru. But if those fuse wires should blow at 5A and they don't blow I would say that resistance in the circuit raises so circulating current doesn't reach 5A. With 4V tension it means that resistance raises to 0.8 ohm or more.

Thinking the fuse design/idea is okay for dealing with singular faults within the battery but when its dead shorted it may still go nova on one cell alone thats unable to blow the last fuse.

Just another thought, maybe, just maybe, when testing cell level fuses, it would be a good idea to test the fuses closer to the nominal cell voltage or closer to minimum voltage or "empty" to make the fusing more reliable. Adding to that, spot welding it to the cell, thereby decreasing the contact resistance to the cell, and, if possible a spot weld to the bus bar, being copper I don't know if a spot weld would work I know that spot welding copper is another beast entirely, I think you need carbon electrodes for that, (I stand to be corrected there though) could you maybe explore something like that for us Pete?

With these packs that you say were pushed fairly hard. Do you know if they used a fuse rated wire? Some types of wire increase in resistance each time it is heated. Not wanting to be an armchair engineer, I wonder if new and uncycled fuse wire would be different. I remember your early vids with the fuses. They were informative. Cheers Pete!

yeah was looking for the ir from the buss bar ie the total battery ir

Could it be that battery need little more time on short circuit before it blow? What is the AWG size do you have on the pack?

Sir . For making battery pack can we use different brand batteries of same capacity ?

when you had fully charged all batteries and those batteries where fuse didn't blow up I think it has high internal resistance, is any chance to test them? I think cos it has high internal resistance it don't have peak power to blow up the fuse...

Hey mate, what meter are you using to measure IR?

What is the manufacturers specification for internal resistance and at what frequency was the measurement made, could be the cells around 80mOhm are duff

Looking at the "X" battery, the fuse, looks like it started to burn (slight darkening and mishape of the wire is visible) and I think that simply all the other batteries due to lower resistance fried their fuses before this one was able to. So it was just a matter of timing on this one.

These test are pushing me further into lifepo4 territory. Have used small glass fuses on the 18650 packs that I already have, although during testing at lower the voltage the fuses don't act 100% or take their time. Multiple causes I would assume: high Ir limiting the current that goes through the fuse, also when the pack is at a lower voltage this would limit potential energy to blow the fuse.

High internal resistance seems to be why the fuses don't blow.

The side which is placed on table does not become as hot as upward side due to cold table thats why fuses from lower side does not blow. Fuse of some cells are not blowing beacuse some cells does not give output amp as compared to others. Some cells does not gives enough high amps to burn fuse

It would be more sensible to use a thinner resistance wire. And I noticed the 2442mAh battery cell and the 2015mAh were in one package, I don't think that's a good idea either. And definitely different company items in one package. This way you can test better results.

In what way will any type of fuse prevent any cell internal reaction ?

The individual fuse wires are used to isolate a bad cell from the rest of the pack and as you have seen they do not provide whole pack protection. Had that short not been momentary the cells that did not disconnected could have gone ballistic.

My fuses seem half the thickness have you got any thinner fuse wire?

I tested the 1/8 watt resistor leads and they blow at about 8 amps so I decided to use 1 amp 10mm X 2mm miniature glass fuses. These blow in about 1 second at 2 amps.

How many years your diy power wall in operation?

I'd be curious to find out what current is coming out of the 'X' cell under short cct conditions. My take away from the low voltage pack test is that, you can make your wiring and connectors hot by having a large pack of low voltage cells short circuited, but the fuses won't blow, let's hope everything else can take it until there is no energy left. If it was a cell in the middle of a pack that went short cct, the rest of the pack would keep dumping into it, with what consequence?

Great video...😁

At 2:50, there’s a thermal camera view with “FLIR” showing uppermost left corner. Is this a dedicated device, or a plug-in for say, a phone? Pictures like this convince me I’m wanting one before I do much more with such batteries.

please post what fuse wire you use

It could happen where when you accidently short your battery the connection could potentially weld together but by that time I'd say the fuses would blow

What's happening is the heat of the fuse wire is sinking into the bus bar and the cell which make it longer for the fuse to blow. If you use proper fuses (I use through-hole glass fuses) all the fuse wire is a set length i.e my glass fuse is 3mm instead of your 10-20mm wire. This slows down the speed of the heat to transfer to the thicker conductor and speeds up the time for the fuse wire to blow. Also having the fuse wire enclosed in a body stops molton metal soring into the air increasing the possibility of starting a fire.

I'm fascinated by the temporary nature of lithium and Life itself

If we charge them fully 4.20 for whole time the capacity will drops to ~ 1000mah and the internal resistance will go too high.

Do have have a link for fuse wire?

if you wan to check if all fuses are "blown" just recheck voltage with the multimeter after shorting the cables.

What fuse wire do you use?

the only main disadvantage i see for double fusing is that when doing a visual check it makes it harder, more chance of a mistake.

Is it possible to get thermal runaway if you totally short one of them batteries and don't let it off

Maybe check new vs old cells, with newer cells with less dendrite growth, and more amperage output, fuses might be more reliable, with more internal resistance as they age, less so, and with more of an internal fault scenario become more of a self-heater and thermal run-away scenario, this is why packs need to be monitored both thermally, and charging characteristics

heya and what should be the IR for the 18650 ???

The deal with the fuse is like this comparison. Say your battery is your 110vac source in your breaker panel. Then you have that through a 15A breaker, and you plug in a 10A device. The breaker will never pop. Yet if you put a 20A device it will. We all know this. However... If your 110vac source is say 60vac you could plug in a 20A device and the fuse wont pop. In a nutt shell the fuse will only work for charged batteries that have enough energy to blow the fuse. A weak cell never will.

so what are these DIY wires? tinned copper, what gauge? 26awg? 0.13mm2 20A fusing?/cell How many cells 80 in parallel. No kit to measure 1600 A from your shorting leads? But very good ground Buddy, keep up this practical research cos the solar fuse/breaker industry is worse than vultures for creating a massive scam on choosing the right protective fusible links - BTW you most certainly need these, but what do we do on the 280Ah prismatic blocks?????????????

~ 11:20 was/is that battery, bottom right, 1 left. Already blown?

curious, wouldn't adding fuses to both sides *increase* the fuse level? Meaning that it would take more energy to burn them? I'm a noob, an explanation would be great!

At 5:00 it's almost like they blew staggered , the one closest to load dumped first

What if you score each fuse wire at the center so as to dictate where the wire should break? By scoring I mean running a pair of wire cutters on the center and just spinning it 360 on the wire so it creates a small groove where current can bottleneck and break the fuse at that groove