EEVblog 1377 - The Amazing UNPREDICTABILITY of Fuses - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: February 23, 2021, 11:38:47 pm
content: How long does it take for your 400mA multimeter fuse to blow at 600mA?Grab a chair and watch!The amazing unpredictability of fusing current ratings at low overloads.

author: Tek_TDS220
author_rank: Regular Contributor
timestamp: February 24, 2021, 02:29:00 am
content: Despite their shortcomings, fuses have saved me from stupidity (mostly mine) many times.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 24, 2021, 03:05:58 am
content: The simpler a component is... the more complex its behaviour!

author: edpalmer42
author_rank: Super Contributor
timestamp: February 24, 2021, 03:14:12 am
content: I came across this post & video on non-destructive fuse testing. I used this method to confirm that some 10A SIBA fuses from China were actually fuses rather than just a big piece of wire.http://www.kerrywong.com/2020/04/12/non-destructive-testing-of-fuses/

author: kingsolmn
author_rank: Contributor
timestamp: February 24, 2021, 03:15:54 am
content: I would love to see more videos about this topic! I think it'd a fun project to design and create some kind of automated test jig to batch test fuses. Anyone want to help me? I certainly know I'm not the smartest member of the forum so I will definitely need some help along the way. But I need a new project and invite anyone along for the ride!- Steve

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2021, 03:45:01 am
content: Quote from: edpalmer42 on February 24, 2021, 03:14:12 amThat page is a bit dubious:QuoteMost fusewire used in plain wire fuses is tinned copper. Copper melts at 1085 deg C. Although the melting point of tin is only 232 deg C, once it melts it will diffuse into the underlying copper to form a bronze alloy. To lower the melting point of the resulting alloy below 800 deg C it will require a composition exceeding 10% tin, which is unlikely for all except the thinnest fusewires.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 24, 2021, 04:21:03 am
content: Quote from: Ian.M on February 24, 2021, 03:45:01 amWhat's the source of this info?Various documents agree that even a 40ga copper wire has a fusing current of about 1A. so smaller fuses likely aren't copper wire. I suspect that the composition of a fuse wire is more like a 'secret recipe' to get the exact characteristics that the manufacturer wants.https://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/wirefusing.pdfhttps://www.powerstream.com/wire-fusing-currents.htmhttp://www.nessengr.com/technical-data/fuse-equations/

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2021, 04:34:44 am
content: Yes, once you go below about 1A, its difficult to reliably mount and connect to a thin enough plain tinned copper wire, so low current fuses must use other wire compositions, and IMHO, its probable there are special purpose higher current fuses (other than thermal fuses) where the required I2t characteristics favor the use of alloy or non-copper wire, but I would expect that plain tinned copper wire is still dominant, if only because of its well understood fusing characteristics, acceptable mechanical strength at elevated temperatures, and that the relatively high melting point decreases the effect of ambient temperature on its fusing current.Sorry I don't have sources handy - I last looked into this in detail many years ago, and even in this internet age, reputable fuse manufacturers aren't keen to publicly disclose their 'secret sauce'.

author: SeanB
author_rank: Super Contributor
timestamp: February 24, 2021, 04:55:51 am
content: I have taken apart 200A fuses, where the fuse element is multiple silver foils, swaged into a carrier frame made from copper, that then was swaged onto the outer ceramic case after filling with the powdered silica sand. Lots of low current fuses in parallel, so that eventually enough will melt on overload to fail the remainder fast. This one failed after around 3 decades of running at close to nominal current, with a few months of running at 2 times current for hours at a time as new loads were added to the grid segment it fed. They only changed the one out of the three, the other two, despite being made in the 1950's, were still fine.

author: rs20
author_rank: Super Contributor
timestamp: February 24, 2021, 08:26:15 am
content: Dave, at 24:06, I suspect the curve on the SIBA graph isn't "resetting". The curve to the left of 4 is the lower bound (perhaps a guaranteed lower bound on trip time at the given current) and the curves to the right of 4 are the upper bounds (perhaps guaranteed upper bounds on trip time).

author: firewalker
author_rank: Super Contributor
timestamp: February 24, 2021, 11:24:26 am
content: Are you using a constant current source? In most cases the fuse will be in a constant voltage circuit. The positive thermal coefficient would increase the fuse time.Alexander.

author: Refrigerator
author_rank: Super Contributor
timestamp: February 24, 2021, 11:30:09 am
content: I remember seeing some fuses that had two springs inside that were soldered in the middle, so that when they got hot the solder would melt and the springs would release creating an open circuit.I wonder how would those hold up in such test.

author: dreamcat4
author_rank: Frequent Contributor
timestamp: February 24, 2021, 11:53:28 am
content: So here is what i dont undesrtand: for lower current applications we cannot cheaply make reliable fuses for less than about 1 amp. Even the pricier ones are not consistent, right? Yet also in these modern times, the cost of a lot of low power electronics has come down a lot. So surely as an alternative an efuse is going to make more sense below a specific number of milliamp threshold. Assuming that an efuse can be made cheaply enough.And this also comes to another comment somebody made about li-ion cells. Where you have to actively limit the current with a mosfet in some similar way. Because fuses simply cant do that job accurately enough. Or consistently enough.But I have more questions about fuses:* Well what about thermal fuses? Are they also inconsistent / problematic in similar ways to regular fuses?* How about some type of an online tool (or even just a big flow chart)... to calculate / help us determine which type of fuse is best for a specific application? Because quite frankly it's still hella confusing to me. Dave only looked at 2 specific types here for his MMs, all within a certain specific mA range. However the overall landscape is vast with many different options. It really makes my head hurt.

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 24, 2021, 12:00:09 pm
content: There are 2 reasons why low current rated fuses behave in unpredictable ways:1) Temperature, as mentioned in one of the slides of the video2) Material thickness uniformity. A 10um copper wire in diameter (yes 10 micrometers) can easily carry 100mA even for a 5cm wire length. So this means that a small variability in the thickness in the wire used (usually not copper but other materials) impacts the fusing current more than higher rated fuses.

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 24, 2021, 12:03:06 pm
content: Quote from: dreamcat4 on February 24, 2021, 11:53:28 amThe real value of a fuse, and something people usually forget, is not just breaking the path of a particular current, something that a mosfet can do. Is that they offer a large current breaking capacity something that semiconductors cannot offer (comparatively speaking)

author: exe
author_rank: Unknown
timestamp: February 24, 2021, 01:12:13 pm
content: This explains some of my observations. I've seen recommendations to put fuses with double the expected maximum current. I didn't know that, so I always put fuses just big-enough for the worst power consumption case. Most of the time it worked well, now I see why.Apart from tolerances, their rating applies to the maximum allowed ambient temperature.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 24, 2021, 01:21:35 pm
content: Quote from: firewalker on February 24, 2021, 11:24:26 amThe fuse is in series with the load, and has a fraction of the load's resistance - so the experience of a fuse is of a constant current (determined by the load, not the fuse).

author: Kleinstein
author_rank: Super Contributor
timestamp: February 24, 2021, 01:38:43 pm
content: It is interesting that some of the longer lasting fuses got really hot before they blew. Some of the faster failing ones did not gat that hot at all.For slower blowing fuses it should be the temperature to limit the current, so these may be more predictable than the fast blowing fuses.The fuses with sand inside may have the problem of the sand moving on transport and stressing the filament in a variable way.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 24, 2021, 02:23:28 pm
content: Could be interesting to compare with the glass fuses that just have a thin filament suspended in air... they have a chance of being more predictable?

author: Huluvu
author_rank: Regular Contributor
timestamp: February 24, 2021, 06:16:57 pm
content: Fuses and Fuse Holders occupied quite some remarkable amount of time in my work life.Hours and Days of testing, thermal imaging, cross sectioning and endless discussions with vendors....I found the same or very similar behaviour as seen at Daves Video but it is even worse if you consider the full picture.Fuse Holders can make things even worse (especially with closed fuse holders)Fuses can burn down your PCB and should really carefully design in if not avoidable.Fuses are not easy to test during the vendors manufacturing process and you really have to rely on the process capability.Fuses can age over time if you use them above the nominal ratings.+ many things more

author: dreamcat4
author_rank: Frequent Contributor
timestamp: February 24, 2021, 06:25:55 pm
content: this ^^

author: agtrbt
author_rank: Contributor
timestamp: February 25, 2021, 04:01:47 pm
content: I missed the ceramic or thermosetting bakelite fuse holders so much, nowadays most fuse holders are just softy plastic rubbish.On another occasion, i had a 1 amp slow blow fuse in a EI transformer, lasted 200ish inrush cycles before it eventually blown.Now I have replaced it with 1.6A slow blow that is still alive today, and I put another 3A fast blow fuse to arrest rapid mishaps

author: SilverSolder
author_rank: Super Contributor
timestamp: February 25, 2021, 07:09:10 pm
content: I guess if you really want an accurate fuse, you have to think in terms of some electronic assist (crowbar)?

author: Refrigerator
author_rank: Super Contributor
timestamp: February 25, 2021, 10:04:27 pm
content: Quote from: SilverSolder on February 25, 2021, 07:09:10 pmI think the point of fuses is to keep them simple, if you start talking about adding electronics to fuses then why not just go all out and implement overcurrent protection in your electronics (if possible of course).But i do think that the venerable fuse can still be improved, and the spring loaded fuse i mentioned earlier does give me some ideas that i want to try out and experiment with actually.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 25, 2021, 10:53:33 pm
content: For slow reaction there are relatively accurate motor protectors. They are resetable and some are adjustable. However they are a bit slow for the normal shunts.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 26, 2021, 05:22:27 am
content: There's always polyfuses and the like. (if you thought normal fuses behave unpredictably...)

author: Alti
author_rank: Frequent Contributor
timestamp: February 26, 2021, 11:55:11 am
content: Of course every component comes with tolerances and some parameters are not specified.Siba 7017240 does not list any standards this product applies to. Since the curve has not been provided for currents under 4In (the dashed curve 1In to 4In is not part of safety but nuiscance tripping) this product is not designed to be used/relied as a fuse for currents under 4In and it should not be expected to conduct above dashed line. Same applies to voltages exceeding 1kV - it was not designed to operate there. So relying on a parameter of a fuse that lies beyond its design characteristics (a.k.a. abusing a component) is a poor engineering practice.As for putting a fuse into an application where at advertised parameters it has 50% chance for nuiscance tripping.. It is ok if the advert/user manual states "400mA for 1h, 600mA for 1 second with 1minute cooling, log derating" but it is not ok if someone buys 600mA meter to find out it is useless for 600mA continuous measurements.Both: overrating a component and operating inside of the tolerance of components, is a problem of the manufacturer, not the customer.

author: exe
author_rank: Unknown
timestamp: February 26, 2021, 11:59:39 am
content: For the sake of science, I blew a few 30mm fuses from AliExpress (they were sent me by mistake and of no use for me anyway).1. I put 3A into 2A fuse and closely monitored drop voltage. It was increasing from 610mV to (shortly) 620mV but then dropped to 605mV (or may be power supply warmed up). After three minutes I stopped. I conclude that 150% of rated current it's not enough to reliably trip the fuses I have. So, I increased current to 4A (for 2A fuses), and here is what I have:7s (probably was weakened by previous tests)14s37s12s14sAll were tripping fast after achieving ~1.3V drop.2. Next I took 5A fuses, and run them at 10A. Here are the results:19s15s110s (and was very hot, glass cracked where the wire was touching it)11s... And one fuse refused to die even after four minutes.All 5A fuses except the last one were quite hot. I tried to measure the temperature of the last one, but flir was showing ">260C", even after removing power. The wire inside was visibly glowing. The wire was touching the glass. It seems to me that glass tube works as a support for the wire, that's why it didn't want to die. The glass cracked at the point of contact. I put fuse on the other side, and it finally died after 32s. It got even more shatters, I'm too lazy to take pictures of, the attached picture is from another fuse, but you get the point.3. Now 1A fuses at 3A: all blew in less than 1s.Conclusion: the more current goes through, the faster it blows. And also more predictably.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 26, 2021, 01:45:27 pm
content: Quote from: exe on February 26, 2021, 11:59:39 amWhich is why a crowbar seems attractive: it can make the fuse blow faster, but it can never make it blow slower!

author: edpalmer42
author_rank: Super Contributor
timestamp: February 26, 2021, 03:52:29 pm
content: Chinese fuses have a very bad reputation for being fake. I've seen videos online where they required ridiculously large currents to make them blow. That's why I tested the allegedly SIBA branded fuses that I bought from a Chinese seller. While cruising ebay for fuses, some of them were obviously fake. Either the printing was smeared or printed at an angle, or you could see a copper wire sticking out from the metal cap on the end. The ones I finally bought looked and tested fine.If you're working on a personal project you can cut a few corners and test fuses like I did. If you're working on a commercial product, the liability issues of using questionable fuses is just too much of a risk. I think Harbor Freight had to recall a kit of car fuses because they were fake and required massive overloads before they'd blow.

author: Alti
author_rank: Frequent Contributor
timestamp: February 27, 2021, 10:20:29 am
content: Quote from: edpalmer42 on February 26, 2021, 03:52:29 pmOk, interesting contribution but I belive this topic is not about fake fuses but about alleged unpredictability of safety-critical component. Both SIBA and DF are reputable manufacturers and "unpredictability" in title is misleading, bullshit and clickbait.There is no unpredictability in these products, these work exatly as specified in the standards/regulations/datasheets. If there was an error in Littelfuse/ESKA/DF datasheet or fuses were counterfreits or did not meet the parameters - this hasnotbeen shown in EEVblog1377.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 27, 2021, 04:06:03 pm
content: Quote from: Alti on February 27, 2021, 10:20:29 amWhen I watched the video, I was left with the impression that even the best fuses have an extremely wide tolerance for what is considered "in spec" - in other words, it is normal that individual examples can vary a lot from their nominal specs? It seems fair use of English to call them "unpredictable".A "fake fuse" would be one that perhaps also varies widely, but not in accordance with the specs?

author: edpalmer42
author_rank: Super Contributor
timestamp: February 27, 2021, 05:19:59 pm
content: Since the topic is 'fuses' I think it's appropriate to highlight the issue of fake fuses so that they won't confuse the discussion. It's easy to create a fuse that looks like SIBA or Littelfuse. Combine that with the wide tolerance of genuine fuses and things get even more confusing. Anytime you're questioning a fuse's performance, you have to consider the possibility that the fuse is a fake.

author: nightfire
author_rank: Frequent Contributor
timestamp: February 27, 2021, 10:02:03 pm
content: Quote from: SilverSolder on February 27, 2021, 04:06:03 pm

author: ssander
author_rank: Contributor
timestamp: March 22, 2021, 10:45:09 am
content: This video was about mA fuses. I was wondering if larger value (80A) fuses used as MPD's for electrical circuits in residential house mains are as unpredictable as these smaller fuses? Are residential circuit breakers more predictable at tripping than fuses?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 22, 2021, 12:13:16 pm
content: The residential circuit breakers are also not very accurate, at least not the more common ones. There are different characteristics and some are relatively good. Especiall some older type are rather poor and for this reasone phased out / to be replaced.For a more accurate limit there are motor protectors. These can be quite accurate and some have an adjustable trip level. However they are latively slow and often also large. As they are usually made for AC motors the DC breaking capacity is poor.

author: Alti
author_rank: Frequent Contributor
timestamp: March 22, 2021, 02:18:55 pm
content: There is nothing wrong with fuses, small or big, mA or kA. All of them are fully predictable in whole design range, as specified in datasheets/standards,if not abused.Dave took a fuse designed to deal with 4In to 10kA and abused it by heating it to insane temperatures at 2In. Typically such fuses/fuseholders just crack and crumble from overheating, well these just popped gracefuly. If you take a "partial range breaking capacity" fuse (these start from "a" as perIEC60269), you can destroy it exactly same way, by overheating. Mind this is stupid and most likely dangerous, these are fuses to deal with shorts, not overloads, and require overload protection. In residential environment much more often you can find "full range breaking capacity" fuses, (these start from "g" as perIEC60269) and can work in circuits from 0 up to 10kA,..,100kA of prospective short circuit current, whatever design parameter is specified. One cannot overheat them when operated/installed as designed, the list of possible abuses is shorter but still quite long. There are various fuse standards around the world, "residential fuse" is quite a wide term, I am not sure about Australia.Residential fuses and fuses in general are much more reliable than circuit breakers. I have never heard a fuse to fail. These do trip but always as designed, this is not a failure. As for tolerances - that is another subject and a matter of comparing datasheets. Not to be confused with discussion about a tolerance for abuse - this is yet another, but not very interesting subject. Especially in the context of handheld multimeter protection and by ab-using reputable brands fuse manufacturers as reference of such. IMHO.If you want to take a look at circuit breakers "amazing unpredictability" - I can recommend bigclivedotcom YT channel. And no, these do not always fail open.As for abusing circuit breakers - take a look at mikeselectricstuff near-death experience where he was "extreme overload"-ing RCBO.Abusing fuses - EEVblog 1377 of course, but seriously, this is the job for Photonicinduction! How about 1kV across low rupture capacity 250V CAT V multimeter fuse, wouldn't that be entertaining?OTOH, I'd love to see an abuse of a proper 10kA fuse in action, @mikeselectricstuff, do you still own the Destruct-o-tron?

author: nightfire
author_rank: Frequent Contributor
timestamp: March 22, 2021, 11:27:15 pm
content: Quote from: ssander on March 22, 2021, 10:45:09 amReliable==maintaining precision according to the defined characteristics curve?Thing is that the fuses used for circuit protection follow some very well defined standards. These define some values (and points that are tested in context of the certification of a fuse (German VDE 0636) and the allowable tolerance.Depending on the company, some companies like SIBA guarantee some tighter manufacturing tolerances on their fuses than applicable standards might allow.I worked at my last job with SIBA NH and Neozed fuses in an industrial environment and was quite happy about them.(Mostly used for (household) circuit protection are class gG/gL fuses)Circuit breakers are a bit different. When we talk about the standard RCCB, you have two triggers implemented: a bimetal one for long lasting overload, and an electromagnetic one for short circuit currents. Those have also standardized characteristics, and the tolerances especially with slight overload is quite high.Of course the standards also account for manufacturing tolerances.In my experience, the big issue is with only slightly higher currents than the rated current- there the mechanical elements have lots of tolerance compared to electronically controlled switches like motor protection switches etc.In case of extreme high currents I have seen some fast stuff- we did the experiment some years ago: In a new room in one of our datacenters, we wanted to test the freshly installed UPS systems. So we initiated a crowbar event (triggered via relay) on some circuit that led to the (future) server racks and measured the reaction via a ION 7600 (or 7650, don't remember).RCCB was an Eaton PXL C16, and with about 800 A measured short circuit current the breaker completed the whole cutoff in about 3 Milliseconds.

author: rs20
author_rank: Super Contributor
timestamp: March 25, 2021, 06:27:30 am
content: Quote from: Alti on March 22, 2021, 02:18:55 pmWhat's your point? It's not like he took an IC with a Absolute Max Vcc of 6.5V and fed 12V in to it. These are fuses used and found in multimeters. These fuses are not in place to protect against a short-circuit fault inside the multimeter causing a huge current to be drawn from some power supply. These are to protect the multimeter from being damaged by the user attempting to measure a current beyond the limits of the meter. In such a situation, 1In, 2In, 4In, 10In are all broadly equally probable situations multimeter fuses will find themselves in.It doesn't matter if it's your opinion that feeding 2In or 1.1In to a fuse is "abuse". Such a label is of no interest when these are the sorts of things multimeter users will be subjecting their fuses to. As such, it's fascinating to see why a 600mA fuse is used for a 1A jack, and it's fascinating to see just how much the fuses vary within the broad bounds/guarantees set by their respective datasheets.Having enjoyed the video, I find your rant to be completely divorced from the reality of what a multimeter is subjected to in real life. If such conditions are "abusive" by your definition, then multimeter fuses get "abused" in real life, and it's interesting to see what the consequences are. Again, what's your point?

author: exe
author_rank: Unknown
timestamp: March 25, 2021, 08:07:42 am
content: I use fuses to protect my devices from fault currents. My biggest concern is a fault condition when the current is enough to destroy the device and set it on fire, but not enough to trip the fuse. That's why I try to use tight current rating on fuses. But, apparently, even this doesn't guarantee anything. Besides that, a hot fuse melting the plastic around is a source of danger by itself.I guess a smoke detector is a good addendum to my lab.

author: SilverSolder
author_rank: Super Contributor
timestamp: March 25, 2021, 02:41:10 pm
content: I have a smoke detector in my lab area. So far so good... it has never triggered, and doesn't seem to mind soldering!

author: Robert Smith Eco Warrior
author_rank: Regular Contributor
timestamp: April 23, 2021, 09:06:58 am
content: I have an off grid setup with a 60 Amp charge controller. My solar panels occasionally get to near that 60 amps. I chose a fuse a bit above this 60 amps just in case something shorted somewhere and I chose an 80 amp fuse. The fuses I first had were the automotive plastic fuses with two bolt on tabs. I have decided these are dodgy as at around 50 amps the 80 amp fuse plastic body started to melt, smoke and go black and deform. I now have some far more expensive ceramic bodied fuses with a little glass window to see if the fuseable section has blown.