new invention? - Page 1
Forum section: electronics / beginners

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 08:25:59 pm
content: so, I've realized that all the fuses out there, are allamperage-dependentfuses. there are some very very rarevoltage-dependent"fuses," but otherwise, I don't know any fuse that is voltage-dependent. I'm not exactly a genius, so... I need a little help. this could very well be a stupid, dumb, and expensive idea, but I'm just a little curious.let's say I have a Tungsten wire. it is 0.8mm thick, and 10mm long. The ambient temp is 45°F.if the wire is conducting a voltage of say, 24V at 2.5A, it should generate a temp ofat least90°F on the wires.here is my plan:1)I will put two tungsten wires close together, but not touching.2)next, I will drip about 0.025mL of Gallium, joining the two wires.3)now, when a voltage of like 24V flows through, the high resistance of the tungsten heats the wires up. since Gallium melts at just 87°F, when the wires heat, the Gallium will melt, thus breaking the connectionWhat do you guys think? is it kinda dumb? or is it worth a try? So, I guess the conclusion is that this was a stupid idea

author: wasedadoc
author_rank: Super Contributor
timestamp: February 24, 2024, 08:29:34 pm
content: Don't quit your day job.

author: brucehoult
author_rank: Super Contributor
timestamp: February 24, 2024, 08:38:37 pm
content: I believe the normal technique is to use a Zener diode to turn an over-voltage into over-current and blow the fuse. Alternatively, use the Zener to trigger an SCR for larger current ability.

author: wraper
author_rank: Unknown
timestamp: February 24, 2024, 08:53:39 pm
content: Quote from: BrainyCapacitance on February 24, 2024, 08:25:59 pmNow how much power do you think it would be 24V*2.5A? Then think about tungsten resistance, and how much current you'd need to actually push through 10 mm *2 of 0.8mm diameter tungsten wires to get 24V drop (2 * 1.1 mOhm at room temperature). Also any fuse is voltage dependent, since power=heat is current multiplied by voltage. Voltage drop over the fuse generally is an unwanted side effect that is intentionally minimized but cannot be avoided. Against what your invention is supposed to protect?BTW what you described as construction basically is a readily available thermal fuse.

author: Muxr
author_rank: Super Contributor
timestamp: February 24, 2024, 09:21:56 pm
content: Quote from: wraper on February 24, 2024, 08:38:27 pmTeaching my 10 year old nephew electronics. I'm stealing this! Thank you!

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 09:37:34 pm
content: ok! thanks!

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 09:38:36 pm
content: ok

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 09:42:49 pm
content: Thanks! I'm a bit new to electronics...

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 09:45:45 pm
content: wait... so if I don't want a voltage higher than say, 50v in my 1A circuit, a 50v thermal fuse would break if thevoltagereaches 55v 1A?

author: brucehoult
author_rank: Super Contributor
timestamp: February 24, 2024, 09:49:11 pm
content: Quote from: Muxr on February 24, 2024, 09:21:56 pmWhen I was about 10 I was home from school, sick, one day. My father came in and said he was planning water distribution for a newly developed part of the farm. He needed litres per hour of water at the most far-flung trough so that it could keep up with cows circled around the trough (10 of them maybe, I don't remember) drinking at the same time, and periodically replacing each other. He gave me some books with flow rate in pipes of different materials (iron, copper, alkathene, PVC...) and diameter and how it varies with the "head" (pressure). And other tables of how much loss of head there is in each metre of pipe, how much loss of head in fittings of various kinds: bends, inline valves, change of diameter, simple joins, T-junctions ...The question for me: what was the cheapest way to get the necessary flow rate at the end of the system, given the available head at the end of the current system? Hint: use a large diameter, maybe more expensive material, pipe at first, proabably along the metalled track, but maybe not all the way, and then cheaper material side-pipes to the troughs.

author: Zero999
author_rank: Super Contributor
timestamp: February 24, 2024, 10:25:10 pm
content: The voltage drop across a fuse is tiny whilst it's carrying current. It behaves like a low value resistor. The total voltage applied to the whole circuit is irrelevant, as far as the fuse is concerned, until it blows.In other words, there's no way, your fuse knows what the voltage across the entire circuit is, until it goes open circuit. There's no way to make a voltage dependant fuse, without another connection to the other side of the voltage source i.e. 0V.

author: brucehoult
author_rank: Super Contributor
timestamp: February 24, 2024, 10:30:48 pm
content: Quote from: Zero999 on February 24, 2024, 10:25:10 pmUntil the fuse goes open circuit, or the stuff after the fuse goes short-circuit (which a Zener diode connection to the other rail can do for you, as it sees the voltage)

author: wraper
author_rank: Unknown
timestamp: February 24, 2024, 11:07:58 pm
content: Quote from: BrainyCapacitance on February 24, 2024, 09:45:45 pmHow do you think it could possibly protect your circuit from overvoltage? If it really was a voltage controlled fuse, it needs to "see" that voltage on itself. If it's in series with the circuit, it does not "know" actual voltage on the circuit, it only sees current and voltage drop on itself, the same as regular fuse. If it's in parallel to the circuit, it sees the same voltage as the circuit and becomes open over certain threshold, so protects nothing and circuit will still be powered.

author: TimFox
author_rank: Super Contributor
timestamp: February 24, 2024, 11:11:41 pm
content: Remember that voltage is "across" two points, but current is "through" a path.

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 11:41:03 pm
content: oh, I get what you mean. you're saying that the circuit will breakbeforethe fuse "blows"

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 11:41:48 pm
content: ok

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 11:50:46 pm
content: but, what about like, a power surge scenario?

author: coppercone2
author_rank: Super Contributor
timestamp: February 24, 2024, 11:53:44 pm
content: ok well usually what happens is it does not drip but it vaporizes. a fuse does the same thing but it uses a different alloy. what you are proposing is a fuse made with different materials.The only difference might be theoretically if this drip mechanism can be controlled, it would be extremely slow blow fuse. look at how fuses are made. you made a fuse that has a gigantic thermal mass.it would probobly have a different response then a real fuse. ok there is a infinite number of responses possible. is this a useful response? nothing stands out too much.now you can end up with a hybrid between a fuse and a thermal fuse with this.despite everything, this can be fun to play with I think. make it and hook it up to a scope and see what it does when you overload it

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 24, 2024, 11:57:57 pm
content: ok!

author: coppercone2
author_rank: Super Contributor
timestamp: February 24, 2024, 11:58:24 pm
content: s not a stupid idea, its called experimenting with fusable links. if you are interested then you might as well study the response. chances are you will learn something playing with gallium, tungsten and electronics equipmentread littlefuse literature about fuses to get an idea how to design the thing finelybut the main take away is that fuses are built to be fast, because thermal is slow compared to electrical, and electrical damage occurs instatanously almost. so the fuse is there to prevent grevious damage. but slow fuses do have their uses.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2024, 12:02:59 am
content: for a voltage dependant fuse, that is in every appliance. you make it by combining a MOV with a fuse. the MOV is voltage sensative and it shorts out the fuse if voltage is too high to blow the fuse. you combine semiconductor and fuseno one did a mechanical one that I know of, there is no effects to work with really that make it possible (or maybe I should say practical). you could make a mechanism that deflection of capacitor severs a link if voltage is too high based on electromechanical principles. it would be like the over sized swiss watch of crazy

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 25, 2024, 12:06:08 am
content: nice to know!

author: BrainyCapacitance
author_rank: Contributor
timestamp: February 25, 2024, 12:17:17 am
content: can I use a high-voltage FET with a fuse instead of an MOV?

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2024, 12:45:04 am
content: its probably less robust but its a method. this is a field of engineering. try threads by t3slaco1l

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2024, 01:26:16 am
content: FYI, you don't have to write short replies; this isn't chat, and it isn't Discord.The basic thing missing from your scenario is: how does your fuse know what voltage it's at? Voltage is a difference between points, and the voltage drop across a practical conductive fuse must be normally small so its power loss is small. All the bits of wire know is how much current is flowing through them; they could be at 0V to their surroundings, or a million! There's no way to tell what voltage is across the actual load, so it can't possibly control that voltage.In fact, this concept can be used to "game the system", say to test equipment used at high power. Consider a monitoring system used on medium-voltage distribution lines: it might have 14kV AC on it normally, and sense currents over 100A. That's over 1.4MW of continuous power! (2.4MW even, since it would be three phase.) How do you test that without your own power station? We can apply the 14kV AC to the voltage-sensing terminals, and loop a different wire through the current sensor -- well insulated so it doesn't care about the 14kV nearby, and can be sourced from an ordinary transformer or whatever. Typically such a system would use a magnetic current sensor (current transformer (CT) or Hall-effect), so that a wired connection isn't required to sense current, just a loop around the wire being sensed. The voltage source then only needs to deliver ~mA, and the current loop ~mV, so the total power dissipated by the test equipment is small (~W?), but the EUT (equipment under test) reads up to full power. You've successfully fooled the system! The catch is, the current being measured is not, in fact, part of the full loop across the 14kV, it doesn't go out and return through the two points being measured across -- and the EUT can't know that, it just assumes you've wired it the right way. But in fact you've made a sneaky loop around it, so you don't need to dissipate anywhere near a megawatt to test it. Handy, eh?Which also means, to make such a fuse, it needs to be wired correctly. If it's sensing voltage, but switching current, it must be a three-terminal device. There's no guarantee that the user wires it across the appropriate three connections, but you would document your device accordingly of course. But anyway, we need to somehow construct it to do that.You could make such a thing by simply putting a heating coil around the thermal fuse bit: the more voltage is applied, the hotter it gets, until it melts and opens. This is a very slow-acting and crude method, but just to hand-wave a possibility.There is also another interpretation to your question.In the same way that a "current-sensitive fuse" operates (when current goes too high, current is forced low and voltage high), presumably a "voltage-sensitive fuse" operates exactly inversely: when voltage goes too high, voltage is forced low and current high. That is, instead of blowing open, it "blows" shut; an anti-fuse!And, note that an anti-fuse would be a two-terminal device, applied in parallel to the load, exactly opposite of a fuse applied in series with it.And indeed, such a component is useful for protecting current sources, where the open-circuit voltage could be dangerously high, and shunting it to ~0V significantly reduces the power output of the source, just as open-circuiting a voltage source (what are commonly in use) significantly reduces its power output.The deeper truth here is: circuit theory, at least, is symmetrical around voltage and current, that is, we can swap them around, and exchange series and parallel connections, and get an equivalent system. We can use fuses in series with voltage sources, or antifuses in parallel with current sources. This is also where the Thevenin/Norton ideal source equivalence comes from.(As it happens, there are physical reasons that prefer voltage sources, and we typically have to go out of our way quite a bit to make a good and proper current source as such, but circuit theory at least makes no such distinction, and we can draw circuits that work equally well with CCS or CVS.)Tim

author: Zero999
author_rank: Super Contributor
timestamp: February 25, 2024, 12:46:00 pm
content: Quote from: BrainyCapacitance on February 24, 2024, 11:41:03 pmNo, just that all voltages are relative and it's the difference between two voltage which is important, rather than the total voltage.Have you every noticed that birds can safely sit on high voltage electric wires, without getting zapped? It's because the voltage at all pares of the bird's body are equal, so no current flows through the bird.The situation is similar for a fuse which hasn't blown. It only sees a tiny voltage.The total voltage across the circuit is only important, when it blows, which is why the fuse has to have the correct voltage rating.

author: jonpaul
author_rank: Super Contributor
timestamp: February 25, 2024, 12:50:34 pm
content: May be not new.... search patents from Littlefuse, Buss, etc.Gallium: Costly, even in small qty. Will not work over comm or induystrial tem range0-70 or -25..+85CPatent: Expect $20..100K cost, about 5 yrs from stat to grant in USA.j

author: ejeffrey
author_rank: Super Contributor
timestamp: February 25, 2024, 05:18:50 pm
content: Quote from: brucehoult on February 24, 2024, 08:38:37 pmThat's a bit old fashioned. It still works in many cases of course but causes a lot of stress on all the components that need to supply the short circuit current. It doesn't work well with many modern power supplies that are designed to limit current internally. In this case the power supply may fail to clear the fuse in an acceptable amount of time and just end up driving it's short circuit current into an SCR indefinitely.These days its generally better to use a MOSFET to just disconnect the load when the input voltage is out of spec. A lot of equipmemt will already have an input MOSFET for inrush limiting, hot plug capability, under voltage lockout, and reverse polarity protection.TI for instance makes a line of eFuse ICs which when paired with suitable MOSFETs provides all these functions.This is specifically when you are trying to prevent moderate over voltage from destroying electronics. If you have a surge which also takes out the pass FET it can still fail. If you need to protect safety there is more to it. You also still probably need a real fuse somewhere to handle genuine over current events and avoid starting fires. But it can then be sized for preventing fire risk without worrying if it will play nice with your overvoltage protection circuit.

author: Infraviolet
author_rank: Super Contributor
timestamp: February 25, 2024, 07:33:14 pm
content: Gallium is expensive, comparably, and it can damage metals with a corrosion like effect (particularly steel and aluminium, Mercury, the other room temperature liquid metal, also attacks them similarly). This seems functionally equivalent to a fuse, but with added complications and cost.The one advantage which this gallium fuse has, over a normal fuse, is the ability for a human operator to collect the resolidified gallium and put it back in place for re-use without needing to swap in a spare unit.But where you want to be able to replace a fuse, with manual intervention but no need for spare parts, there are already electromagnetic coil and relay based breakers which can be reset. Or even polyfuse "fuses" which self-reset after a cooling period.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2024, 08:07:09 pm
content: just keep in mind that thing with MOSFET open is for a regulated supply protection. not the mains, not a crazy generator , those sources have no mercy. Because a power surge like close call lightning might fry a MOSFET and then the normal power restored goes right through. its really not nearly as robust as any kind of fuse.but that limits your area of use by alot, because there are many regulated things that need protection still.

author: alligatorblues
author_rank: Regular Contributor
timestamp: February 26, 2024, 03:44:41 pm
content: Complexity adds higher failure. My cousin is a materials engneer. Materials seldom retain the same properties when run at different ambient temperatures, different types of enclosures, different geometries, etc. But there are desireable applications for fuses in which current and heat fail. Very low currents would bemvery desireable to fuse,, especially from a cost standpoint.That might warrant materials research and applying eletrical properties in different ways that heating by current. Actually, I just ran into an ingenius use of NTC thermistors to damp in rush current. At normal temperatures, NTC thermistor resistance is high, so it drops in rush current. The running current proceeds to heat the thermistor due to resistance, which drops with temp, and lowers the temp. It's balances out to an inexpensive, efficient means to handle the in rush current, and maintain high efficiency thereafter.