Fuse for 60VDC rail can be an AC fuse?

[Faringdon]

Hi,
Just doing a hobby prototype...multiple SMPS's.
We want to have a 1A fuse on a 60VDC rail.......why can't we use this.?..

   MP001593
https://www.farnell.com/datasheets/3665667.pdf

....we know its an AC fuse, and  could possibly  release shrapnel if it blows.....since its not DC rated...but we will have protective eyeware on.

DC rated fuses are more expensive as you know.

[Doctorandus_P]

Have you ever considered there is a reason for DC fuses being more expensive?

An important factor for fuses is the maximum short circuit current that has to be disconnected by the fuse.
At the moment the fuse blows a plasma arch starts, and that has to be extinguished, and with a higher short circuit current (and with DC) the arch is more difficult to extinguish.

A simple and effective design has a fuse wire and a spring under tension.  When the fuse wire melts, the spring pulls the pars from each other and thereby greatly increases the distance to be bridge by the plasma.

Alternatively, maybe you can use PPTC's.

[Faringdon]

Thankyou very much for this.
And i believe this means we can expect fire burst and a loud bang...so thankyou, we will be ready for this.
We cannot afford the DC fuses unfortunately.

Also, for our 4kW LLC converter, which runs off 400Vdc input, we will fuse the input with two of these cheap 7A fuses in parallel.

0251 007.
https://www.farnell.com/datasheets/2189447.pdf

...And will be ready for quite some fireworks if it blows...as discussed, we have the fire extinguisher in the room, and safety eyeware on.
Unfortunately, the only alternative for our well hammered wallets , is no fuse at all.

[Doctorandus_P]

Also, protective eyewear usually does not work too good.

You use that for some time, but the day that the fuse finally blows you just happen to have forgotten your eyewear.

It's just more reliable to make some kind of (possibly transparent) shielding over the fuse.
That way it's just always there.
Or use an enclosed fuse holder.

It's a bit like those CAT ratings for DMM's.
I don't really care much for those expensive fuses, and if it has to be replaced I put in some affordable fuse. (I also do not measure on CAT IV equipment anyway).
Even if the fuse explodes, the outside casing of the DMM is strong enough to contain the pieces.
There is a chance that this damages the DMM further, but that's a risc I'm willing to take.

[MarkF]

Also, for our 4kW LLC converter, which runs off 400Vdc input, we will fuse the input with two of these cheap 7A fuses in parallel.

Why in the world would you think that is a good idea?   

Gut feeling, fuses in parallel would be like LEDs in parallel.  The fuses are not going to be identical and will NOT pull equal amounts of current. 
Furthermore, if one fuse blows the other one may still be connected.  Not a clean disconnect at any rate.

[richard.cs]

Both those fuses have pathetically low, and AC-only breaking ratings. The most likely outcome is not shrapnel, it's failure to break the current flow, continuous arcing, leading to total destruction of the PCB, and possibly starting a fire.

[Gyro]

Hi,
Just doing a hobby prototype...multiple SMPS's.
...

I wish you'd cut out the false "hobby prototype" narrative!

[golden_labels]

Having a choice to use a wrong fuse, no fuse or cancel the project, the best option is to stop the project. But since most people will take the risk, if you really must then use even a wrong fuse. Still at least some chance, not even a small one, of providing protection. Certainly do not go for no fuses.

The reason you need a DC fuse is not because an AC fuse will explode in your face. It’s about the ability to do their job. A 50Hz alternating current waveform hits 0A each 10ms. If arcing happens, a hundred times per second there is nothing to sustain it. With DC there is no such option: the fuse must ensure that the arc is never formed or quickly extinguished. This makes them more expensive.

The first fuse you mentioned has only 50A breaking capability. A short across 60V will instantly reach much more than that, if only the power supply can deliver.

You do not want to parallel fuses to protect a single line.⁽¹⁾ Surprisingly the primary conern is not their failure; contrary: they may blow below the expected current. Two 7A fuses in parallel are not guaranteed to carry 14A.⁽²⁾ That’s because their actual limits vary considerably and so is current each of them may see. Two 7A fuses may in fact blow at 7.5A and 9A, and passing 14A through them in parallel they may see 8A and 6A, leading to premature trigerring. The other end of the problem, the risk associated, is not observing that you can’t parallel breaking capability and creating more points of failure. You can’t get 600A breaking from two 300A fuses: one of them dies first, exposing the other to the full 600A. And if you have two fuses, there is much larger probability at least one of them forms an arc.

⁽¹⁾ Not impossible, but you would need to go deep into statistics, understanding theory of operation and modelling to parallel them safely.
⁽²⁾ No fuse is, but the probability of a 14A fuse blowing below 14A is acceptably low, since manufacturers have error margins. That’s why in this Littlefuse datasheet you can see that one rated for 7A will on average pass 10A without blowing.

[tggzzz]

Hi,
Just doing a hobby prototype...multiple SMPS's.
We want to have a 1A fuse on a 60VDC rail.......why can't we use this.?..

   MP001593
https://www.farnell.com/datasheets/3665667.pdf

....we know its an AC fuse, and  could possibly  release shrapnel if it blows.....since its not DC rated...but we will have protective eyeware on.

DC rated fuses are more expensive as you know.

Thankyou very much for this.
And i believe this means we can expect fire burst and a loud bang...so thankyou, we will be ready for this.
We cannot afford the DC fuses unfortunately.

Also, for our 4kW LLC converter, which runs off 400Vdc input, we will fuse the input with two of these cheap 7A fuses in parallel.

0251 007.
https://www.farnell.com/datasheets/2189447.pdf

...And will be ready for quite some fireworks if it blows...as discussed, we have the fire extinguisher in the room, and safety eyeware on.
Unfortunately, the only alternative for our well hammered wallets , is no fuse at all.

Hobby project? Yeah, riiiiiight.

This kind of silly stupid corner-cutting leads to the kind of PSU problems that treez experienced. I wonder what became of him?

Best approach: do it right, do it once or don't do it at all. Much cheaper than bodging something multiple times, particularly when considering the court case resulting from injuries due to known dangerous activities.

[tooki]

We cannot afford the DC fuses unfortunately.

Don’t give us that crap. You can get cylindrical glass fuses for pennies. Standard 5x20mm glass fuses are rated to 250V DC and 1A is a standard value.

[tooki]

This kind of silly corner-cutting leads to the kind of PSU problems that treez experienced. I wonder what became of him.

Hmm, what indeed… https://www.eevblog.com/forum/supporters-lounge/treez-how-many-more-accounts-are-acceptable/

[tggzzz]

Don’t give us that crap.

It is worth being aware of the OP's previous moniker.

[xavier60]

I use SCHURTER fuses for high current DC, https://www.schurter.com/en/datasheet/typ_SHF_6.3x32_Pigtail.pdf "20 kA @ 63 VDC" and are very reasonably priced.

[Zero999]

https://uk.rs-online.com/web/p/cartridge-fuses/7897797

[jonpaul]

DC arc continues till external ckt current is zero.

AC arc is extingusihed and reignited on each mains zero crossing eg 100 Hz for 50 Hz mains\\

Thus a DC fuse is a very different construction than AC fuse.

Jon

[Zero999]

It's much more difficult to break the arc at higher voltages. This means a high voltage AC rated fuse can normally be used at a much lower DC voltage. As a general rule of thumb a 250VAC fuse can normally safely used for DC voltage up to 30V, but always check the data sheet.

[Faringdon]

You do not want to parallel fuses to protect a single line.(1) Surprisingly the primary concern is not their failure; contrary: they may blow below the expected current.

Thankyou for this....i must admit i recently opened up a 750W offline 100-265VAC PSU which i was told had a superb longlife record.
It had two 8A, 5x20mm axial solder_in fuses at the mains input....

...So youuve got me thinking now......750W from 100VAC is about 8A.....was the reason they over-rated the fuses so much (ie using 16A's worth)  because they were in parallel?

Also, maybe the customers were only using it at 220VAC, i dont know.

[strawberry]

this fuse should work

[tooki]

Don’t give us that crap.

It is worth being aware of the OP's previous moniker.

I’m obviously well aware, given my reply immediately above yours.

[tooki]

You do not want to parallel fuses to protect a single line.(1) Surprisingly the primary concern is not their failure; contrary: they may blow below the expected current.

Thankyou for this....i must admit i recently opened up a 750W offline 100-265VAC PSU which i was told had a superb longlife record.
It had two 8A, 5x20mm axial solder_in fuses at the mains input....

...So youuve got me thinking now......750W from 100VAC is about 8A.....was the reason they over-rated the fuses so much (ie using 16A's worth)  because they were in parallel?

Also, maybe the customers were only using it at 220VAC, i dont know.

Are they actually in parallel? I doubt it. More likely, they fused both AC lines.

[golden_labels]

We would need to see the photo, associated with PCB reverse-engineering to say anything. I suspect what tooki said: fuses in series, each for one side of the power supply. Also note the footnote. You do not want ≠ you absolutely can not. As an example: fuses made for carrying huge currents are produced by paralling multiple smaller ones. You can see one in the video from strawberry. Each of the metal strips is an individual fuse. Designed to have very similar characteristics, all connected to a massive block of metal that equalizes currents. But there is a difference between a well-engineered device, carefully designed for that purpose, and ad-hoc slapping two random $0.25 fuses, which individually have so large variance the manufacturer must keep an error margin of 30%.

On a separate note: fuses may have higher rating to avoid premature triggering from inrush current. But there may as well no be a particular reason other than “being good enough”. Their purpose is to prevent overheating and potential fire, if the circuit shorts, not to exactly match the current circuit takes during normal operation. Consumer products are also expected to already have two breakers in series⁽¹⁾ in the electric installation. If they suck a few amps without shorts, the internal fuse acts as a third line of defence, not the sole protection. It may be chosen to let the other two breakers, which are resettable, act earlier.

⁽¹⁾ In Poland that would typically be 10A for a circuit, and in apartments 16A shared across all circuits.

[TimFox]

Also, remember the difference between the two common rating systems for fuses:  UL and IEC.  From a Schurter document:
"Fuses can be in accordance with IEC 60127 or UL 248-14.
Because of the different definitions between the two standards, fuses are not directly interchangeable as follows:
fuses in accordance with IEC 60127 may be operated continually at 100% of the rated current value,
whereas fuses in accordance with UL 248-14 only at 75%.
UL 248-14 specifies a minimum of 4h operating time at rated current."

[bdunham7]

DC rated fuses are more expensive as you know.

Can you afford 35 cents, 15 cents in quantity? 

https://www.mouser.com/ProductDetail/Bel-Fuse/0697H1000-02?qs=GtFly9OVs880JpSy6RRCrg%3D%3D

[Faringdon]

Thanks, with the component shortage, we just cant garantee that proper cheap DC fuses will remain in stock throughout our testing phase.....as such, for an LLC  converter which is 2kW, 400vin, can we fuse it's 400v input  with a dirt cheap 250VAC , 7A fuse, but put a cheap  10 milliOhm  flame proof resistor in series with this (admittedly dodgy) fuse?

eg

12 milliOhm resistor......flame proof ness..
https://www.farnell.com/datasheets/2710520.pdf

[nightfire]

Question: If this is for experimental equipment, where obviously some fuses are used up- would this be an option to replace them with a RCCB that is certified by manufacturer for DC?

I did this some time ago, when I wanted to build some cheap solution for partying a bit with friends whilst traveling, and came up with a 12V lead battery, some standard RCCB  (from ABB) that was  documented to be able to break the prospective currents i calculated for that battery.
So it does not always have to be a breaker that is certified for railway applications...

Question #2: What are the prospective currents that fuse or other overcurrent protection has to be able to protect against?

[Gyro]

Thanks, with the component shortage, we just cant garantee that proper cheap DC fuses will remain in stock throughout our testing phase.....as such, for an LLC  converter which is 2kW, 400vin, can we fuse it's 400v input  with a dirt cheap 250VAC , 7A fuse, but put a cheap  10 milliOhm  flame proof resistor in series with this (admittedly dodgy) fuse?

eg

12 milliOhm resistor......flame proof ness..
https://www.farnell.com/datasheets/2710520.pdf

If it's a hobby project, just stock up on them (fuses) while they're available.

[tggzzz]

Just doing a hobby prototype...multiple SMPS's.

Thanks, with the component shortage, we just cant garantee that proper cheap DC fuses will remain in stock throughout our testing phase.....as such, for an LLC  converter which is 2kW, 400vin...

Those two statements clash. Can you confirm you are being open and honest with us?

IMNSHO anybody working with such high energies (2kW, 400V) should not need to ask opinions of random people on a hobby forum.

[tggzzz]

Thanks, with the component shortage, we just cant garantee that proper cheap DC fuses will remain in stock throughout our testing phase.....as such, for an LLC  converter which is 2kW, 400vin, can we fuse it's 400v input  with a dirt cheap 250VAC , 7A fuse, but put a cheap  10 milliOhm  flame proof resistor in series with this (admittedly dodgy) fuse?

eg

12 milliOhm resistor......flame proof ness..
https://www.farnell.com/datasheets/2710520.pdf

If it's a hobby project, just stock up on them (fuses) while they're available.

That thought occurred to me.

I won't mention some other thoughts that have occurred to me

[Faringdon]

OK thanks, any thoughts on the combo of cheap AC fuse in series with cheap 0.01R flameproof resistor?......for use with 400Vdc and 6A...(input to LLC converter)
(and eyeware and fire extinguisher in the room  of course!.....and the building has upstream breaker etc etc).

I mean one of my biggest explosions was when i accidentally plugged a three phase supply into the output of a 15kW electric drive......it sounded like a cannon going off!!!...the PCB  had a huge burned melt hole!.....i mean...surely the 400Vdc and 6A (dodgy AC) fuse blowing will be no worse than that?

[Faringdon]

Thanks for replies...another point is that surely, when fusing for an AC  mains supplied PSU....even if its got a DC output....it essentially calls for just an AC fuse in that DC output...because once the short has discharged the capacitors.......the whole thing is back to being AC....because the mains is AC.....so surely we have some leeway with offline PSU fusing, and we can revert to AC fuses?........unless they have enormous amounts of  storage capacitance of course....and i am not talkign about eg bigoffline  battery chargers here.. (EDIT....i  refer to fusing of the DC output here, or fusing of the post PFC DC Bus)

[tooki]

What the hell, man… that makes no sense. Input and output fuses serve fundamentally different purposes.

You shouldn’t be going anywhere near mains (never mind 15kW anything) if you don’t understand this. And all this because you’re too cheap to spend 18¢ on an ordinary glass fuse?!?

[TimFox]

What the hell, man… that makes no sense. Input and output fuses serve fundamentally different purposes.

You shouldn’t be going anywhere near mains (never mind 15kW anything) if you don’t understand this. And all this because you’re too cheap to spend 18¢ on an ordinary glass fuse?!?

In my "electricity" shop class in 8th grade junior high school, we had a good teacher, who lectured us on fuses.
His parable was the guy whose fuses kept blowing, which he assumed was caused by "old cheap fuses" so he kept replacing them with higher ampere ratings.
When his house burned down, he blamed that fire on the "old cheap fuses".

[Faringdon]

Thanks, yes, but its strange theres no differentiation between a 1A fuse for say a 10MW.hr battery with 400VDC output, and a fuse for a 400Vdc ouput of an AC mains supplied  Boost PFC......The Boost PFC requires a lesser fuse.

[Zero999]

Thanks, yes, but its strange theres no differentiation between a 1A fuse for say a 10MW.hr battery with 400VDC output, and a fuse for a 400Vdc ouput of an AC mains supplied  Boost PFC......The Boost PFC requires a lesser fuse.

That's not true at all look up breaking capacity, which is the maximum current the fuse can safely interrupt, without posting a safety hazard.

[nightfire]

Thanks, yes, but its strange theres no differentiation between a 1A fuse for say a 10MW.hr battery with 400VDC output, and a fuse for a 400Vdc ouput of an AC mains supplied  Boost PFC......The Boost PFC requires a lesser fuse.

That's not true at all look up breaking capacity, which is the maximum current the fuse can safely interrupt, without posting a safety hazard.

A look in the datasheet of the model of the fuse is often necessary. The question as always is: which voltages (AC/DC and amount of) and prospective currents has the fuse to deal with?
Especially the curves and Integral values (necessary to determine timing of when the fuse begins to act) are needed to determine if a certain fuse is appropriate for handling a short at the position where it is deployed.

The form of the curve is mostly different, and for selecting to correct model of fuse you have to look at the situations and conditions when a short can occur- and determine, which parts of the system you want to protect.

[mc172]

You don't need a fuse, just make the PCB traces really thin.

[Gregg]

Hey Treez.... Why haven't you asked about putting cheap AC fuses in SERIES for your DC hobby project?? 
Certainly that would increase the potential spark gap if they all should blow.

[Zero999]

Hey Treez.... Why haven't you asked about putting cheap AC fuses in SERIES for your DC hobby project?? 
Certainly that would increase the potential spark gap if they all should blow.

I know you said that in jest, but it would probably increase the breaking capacity and voltage. It would be a very good idea to both fuses must be replaced, even if only one of them blows, to avoid nuisance tripping.

Thanks, yes, but its strange theres no differentiation between a 1A fuse for say a 10MW.hr battery with 400VDC output, and a fuse for a 400Vdc ouput of an AC mains supplied  Boost PFC......The Boost PFC requires a lesser fuse.

That's not true at all look up breaking capacity, which is the maximum current the fuse can safely interrupt, without posting a safety hazard.

A look in the datasheet of the model of the fuse is often necessary. The question as always is: which voltages (AC/DC and amount of) and prospective currents has the fuse to deal with?
Especially the curves and Integral values (necessary to determine timing of when the fuse begins to act) are needed to determine if a certain fuse is appropriate for handling a short at the position where it is deployed.

The form of the curve is mostly different, and for selecting to correct model of fuse you have to look at the situations and conditions when a short can occur- and determine, which parts of the system you want to protect.

I was hoping the original poster would have figured that out for themself.

The maximum prospective short circuit can be calculated by measuring the impedance of the wiring and applying Ohm's law. If it's a battery powered circuit, it's a little more tricky. The easiest way is to apply large load to the battery and measure the voltage drop. R = V_DROP/I.

Come to think of it, what about a power supply with a large capacitance? It might be able to supply surges of an order of magnitude higher, than the continuous current. I suppose it then becomes a matter of energy, as well as current. I'd imagine a time delay fuse would better cope in an application with a large capacitance, since it will only break, once the current has already decayed somewhat.

[tooki]

I worked on a project last year involving two 2kV 800μF capacitors in parallel. Let’s just say that they could supply far, FAR, FAAAR more current than they were charged with. (Peak measured output current was 6kA. Not a typo.)

[nightfire]

I worked on a project last year involving two 2kV 800μF capacitors in parallel. Let’s just say that they could supply far, FAR, FAAAR more current than they were charged with. (Peak measured output current was 6kA. Not a typo.)

For how long could they deliver this amount of current?

[tooki]

A ms or so.

[Gregg]

Hey Treez.... Why haven't you asked about putting cheap AC fuses in SERIES for your DC hobby project?? 
Certainly that would increase the potential spark gap if they all should blow.

I know you said that in jest, but it would probably increase the breaking capacity and voltage. It would be a very good idea to both fuses must be replaced, even if only one of them blows, to avoid nuisance tripping.

It was somewhat in jest but more of a feeble attempt to jumpstart Faringdon’s (aka Treez) brain; a daunting task at best. Or as you stated, hoping he could figure it out for himself. 

The OP reminds me of the student that copies others’ homework and doesn’t grasp the disservice he is doing to himself.  He has come to rely on the people here for answers he really should be able to derive himself; perhaps this blog has kept him employed. 

The old saying prior to the internet was, “engage your brain before opening your mouth.” 
Now it should be, “engage your brain before posting on the internet.”  (Never going to happen) 

[Faringdon]

For how long could they deliver this amount of current?

A ms or so

Thanks, this is the crux of it......in an ACDC offline PSU...if you fuse any DC rail in it...then once the caps on it have discharged...then that fuse is essentially in an AC circuit......as  the short cct current will be going to zero every 10ms (8.33ms in US)......so you would think an AC fuse could be gotten away with.

[golden_labels]

He has come to rely on the people here for answers he really should be able to derive himself; perhaps this blog has kept him employed. 

Writing from a softdev perspective: I wish you knew how many jobs are kept solely thanks to Stack Overflow and keyboards having keys Ctrl, C and V.

Meanwhile, he always adds “thank you”, even if you do not deliver any useful answer or openly insult him. What a nice person!

[tooki]

For how long could they deliver this amount of current?

A ms or so

Thanks, this is the crux of it......in an ACDC offline PSU...if you fuse any DC rail in it...then once the caps on it have discharged...then that fuse is essentially in an AC circuit......as  the short cct current will be going to zero every 10ms (8.33ms in US)......so you would think an AC fuse could be gotten away with.

It’s been pointed out to you more than once that a 250V DC-rated 1A 20x5mm glass fuse can be had for pennies. So why is there even a discussion? Just buy the damned fuse and put it in.

[tggzzz]

For how long could they deliver this amount of current?

A ms or so

Thanks, this is the crux of it......in an ACDC offline PSU...if you fuse any DC rail in it...then once the caps on it have discharged...then that fuse is essentially in an AC circuit......as  the short cct current will be going to zero every 10ms (8.33ms in US)......so you would think an AC fuse could be gotten away with.

It’s been pointed out to you more than once that a 250V DC-rated 1A 20x5mm glass fuse can be had for pennies. So why is there even a discussion? Just buy the damned fuse and put it in.

Some people seem to like repeatedly asking a question and ignoring answers. Perhaps the answer isn't The Right Answer, perhaps they don't understand the answer, perhaps they think the answer will be different next time.

The last of those is the reason my daughter's dog repeatedly brings you a ball to throw even when you have told it "no". If one ball doesn't work, he tries another, or a snake. If that doesn't work, he has a primitively frightening tactic: lunge at your face with his mouth open wide. Yes, that is a dogs' standard way of saying "I want to play", but even when you know that, your hindbrain kicks into action

[floobydust]

A fuse is a safety component, engineers here will understand to not get cute about it.
Yet there is a strong drive to use anything but the proper part. We all need to feel special.

Regulatory and safety certification agencies will always first check to see if a fuse is suitable for the application. They look at the voltage, interrupt ratings, approvals.

I had one control panel design, for the 24VDC power I specified automotive blade fuses and DIN rail holders because that's what we had on hand. The certifier failed those fuses, the argument he had was they needed to be able to clear incoming mains (voltage) in the event there was a primary-secondary insulation failure in the power supply. So he wanted 250VAC-rated fuses even though it wasn't obvious for a 24VDC rail. We just swapped out the fuses+fuseholders to 5x20mm and all was good.

[CJay]

Some people seem to like repeatedly asking a question and ignoring answers. Perhaps the answer isn't The Right Answer, perhaps they don't understand the answer, perhaps they think the answer will be different next time.

I usually add a charge for wasted time and then eventually dump clients who rephrase questions repeatedly in an attempt to change reality.

I wonder if anyone has ever recorded the number of hours of free consultancy Treezingdon has had and calculated the fees he'd have had to pay.

I reckon at least enough Ocset clubcard points for a family holiday to Disney

[wizard69]

This is totally asinine!   I don't mean to be unkind but if you have ever spent some time reviewing a failure of an overload devices failure to protect then you would realize just how stupid i is not to size components properly.   I do mean stupid and if that offends you at least you have been warned.   A failure of a fuse to work can lead to things blowing up - literally!!!

Hi,
Just doing a hobby prototype...multiple SMPS's.
We want to have a 1A fuse on a 60VDC rail.......why can't we use this.?..

You have to be trolling.   It is pretty simple the fuse isn't rated for it.

   MP001593
https://www.farnell.com/datasheets/3665667.pdf

....we know its an AC fuse, and  could possibly  release shrapnel if it blows.....since its not DC rated...but we will have protective eyeware on.

This is so stupid that I can't even understand how somebody could be so foolish.   What good is eye protection if the shrapnel cuts your neck or penetrates your heart?

DC rated fuses are more expensive as you know.

Not that much more.   Beyond that have you even considered how much short circuit current is available?

As an aside I've had to investigate a couple of arc flash events in my life.   it is fantastical amazing what a electrical system can do with all that power available.   In one case, a small 30 horsepower compressor apparently seized up and the starter, the local fuses, and the nearest sub panel fuse did not break the circuit.    This resulted in rather significant destruction inside the compressors control panel literal[y blowing the starter apart, melting most of the 3 phase wiring, the wiring back to the sub panel, frying the breaker there and eventually tripping a 500 amp breaker.   Shockingly the aluminum in the rotors even melted to the point of running out.

Now I'm not sure whom was most likely at fault here.   Thankfully my responsibility was with physical rebuild / repair of the instillation.   I any event it is pretty obvious that somebody forgot about the potential short circuit current and the hardware required to handle that.   My point is that if the fuse or breaker for that matter, fails to do its job a lot of stuff will go up in smoke in the best case, in the worse case you have an arc / flash explosion and significant damage to equipment.   As for people near by you will be lucky if no one dies or get seriously hurt.

Now I understand you think that you only have 1 amp on the rail, thus not comparable.   That is normal operation, what you need to ask is what is the short circuit potential and does that exceed the fuses interrupting capability.

[Faringdon]

Thanks, that was interesting about the molten aluminium etc...

I must admit here that we are fusing a prototype 2kW offline SMPS.  In particular we will fuse the 400VDC output bus of the Boost PFC stage.

AYK, this is DC....but AYK, fusing of this rail is not mandated by regulations......the only fuse required by regs in an offline PSU is the AC fuse in the mains AC input.
No other fuses are required.

...As such, why should we, in this prototype, use a more expensive DC fuse in the 400VDC rail, when even regs dont mandate a fuse in there at all?
My apologies , but i should have explained, this is a free-of-charge prototype for a group of engineers.....if they like it, they will pay me to do the thing properly and fully, for now, all they want is to see 180V at 2kW (into a dummy load) and they're happy.
The mosy likely event, is that they will look at the prototype, and even if it works,  they will  just get their Chinese partners to do it   anyway....or take the PSU on themselves and do it themselves.......so i deffo dont want to spend a penny or cent more on this thing than i  have to......there is no payment whatsoever to the   demo'd working prototype stage.

[floobydust]

Yes but you are connecting to a battery pack and expect no backfeed or reverse-current? This is a reason for that fuse.
A rectifier shorts... what are you expecting provides you coverage? You have an output relay?

[bdunham7]

AYK, this is DC....but AYK, fusing of this rail is not mandated by regulations......the only fuse required by regs in an offline PSU is the AC fuse in the mains AC input.
No other fuses are required.

So don't use a fuse there!  What's the problem?

[floobydust]

This entire thread   

[tooki]

Hi,
Just doing a hobby prototype...multiple SMPS's.
We want to have a 1A fuse on a 60VDC rail.......why can't we use this.?..

Thanks, that was interesting about the molten aluminium etc...

I must admit here that we are fusing a prototype 2kW offline SMPS.  In particular we will fuse the 400VDC output bus of the Boost PFC stage.
…

...As such, why should we, in this prototype, use a more expensive DC fuse in the 400VDC rail, …

So which is it?

And why can’t you be honest and forthright in what you’re doing? People are happy to help anyway, so why make up these elaborate cover stories?

[golden_labels]

So which is it?

It’s a quantum system that is in superposition of 60V and 400V. They need fuses that span multiple universes. We did not thought of that.

[tggzzz]

This entire thread   

The thread isn't the problem.

A "hobbyist" trying to cut corners on a 4kW PSU is the problem.

[Faringdon]

Yes but you are connecting to a battery pack and expect no backfeed or reverse-current?

Thanks, there is no battery in the system anywhere.

Its a 2kW PFC'd  LLC converter....it also has a 60V DC rail from a offline flyback too. We will fuse both the 400VDC and 60VDC rails.....its test only prototype...if we fuse and get a problem, hopefully less stuff will need replacing...due to our use of fuses. It will eventually be two 2kW LLC converters...making the 4kW...but thats in the distance.

So don't use a fuse there!  What's the problem?

If i mis-assemble something and it blows up, then if its more fused, less stuff will need replacing.

[tooki]

If you can’t even reliably assemble something correctly, you really, REALLY should not be ANYWHERE near power electronics. You’re going to hurt yourself, or worse, someone else.

[floobydust]

OP you give us nothing usable for the application, requirements, architecture or what you are building.  One day it's 180V out, next 60V, then it's 390V - you are too secretive about nothing of value for us to help, and liars always flip-flop and change their story. You're getting it made in china again, well that IP is public lol.
For months it was EV battery charging, now it's 50+ threads you have in the Renewable-energy forum. You're in past your skill and values. 

Although this should be a simple fuse question, you won't pay the $0.18 for the correct part, then you rationalize it's not needed. It's production no it's a prototype. It powers... ? the controller the PFC who knows.

As far as designing power supplies goes, it's "trial by fire" so wear a face-shield/eye protection, or put a Lexan blast shield around the power supply.
I take it you've never done this before and had a TO-247 pop and launch shrapnel across a room, delivering a lesson.
A fuse helps but they are always too late to pop, per Murphy's Law and PCB traces do the job for the price target you have.
Be extra careful about who is in the lab and nearby when working on it powered up, to avoid electrocution. You can't cheap out on test equipment safety either, at this power level.

[mc172]

I am confused. Please can you help me understand why you can't afford to build a prototype with a properly rated fuse?

Last year i made £35.4 million profit for myself (not anywhere near as much as my mates though)...not bad for sitting about and placing a few orders now and again.....i dont even have to see the products....just get them sent straight to customer.

[Faringdon]

i did hours of research  on digikey , mouser etc....generally, AC fuses are cheaper and significantly more in stock.....so thats what we want to get using......(ref above conditions...eg no fuse mandated other than at mains input anyway).
There is no pay for a PSU prototype...and only one in 10 go through to a product.......the guys we demo to are engineers anyway.....all they want to see is x volts at y watts into a dummy  load...using the gerneral topology on offer.......so they can do the fusing bit as they wish...whatever spec they give.

[mc172]

They're not very good engineers if that's all they care about.

[Gyro]

i did hours of research  on digikey , mouser etc....generally, AC fuses are cheaper and significantly more in stock.....so thats what we want to get using......(ref above conditions...eg no fuse mandated other than at mains input anyway).
There is no pay for a PSU prototype...and only one in 10 go through to a product.......the guys we demo to are engineers anyway.....all they want to see is x volts at y watts into a dummy  load...using the gerneral topology on offer.......so they can do the fusing bit as they wish...whatever spec they give.

So that's your definition of a "hobby prototype"!  Filed for future reference.

[floobydust]

[...] so they can do the fusing bit as they wish...whatever spec they give.

This is how disasters happen- who is responsible for the fusing, the fuse selection in the product ?  Hint: never the customer- unless you have no liability (contract) and even then that's a problem because unsafe product rolls out the door. In court they'll find your staff ought to have known the fusing was improper despite the bad instructions coming from the customer. You are still responsible. The ball and chain of engineering lol.  "yes, but management says..."
You don't have a working prototype yet, but are worried about the cost of a fuse? 60VDC is not rocket science nor rocket priced.

I think you need a new profession or a Go Fund Me to raise money for the correct fuse. Pity will finance it.

[tggzzz]

Hi,
Just doing a hobby prototype...multiple SMPS's.
We want to have a 1A fuse on a 60VDC rail.......why can't we use this.?..

   MP001593
https://www.farnell.com/datasheets/3665667.pdf

....we know its an AC fuse, and  could possibly  release shrapnel if it blows.....since its not DC rated...but we will have protective eyeware on.

DC rated fuses are more expensive as you know.

Quite a few people wondered whether this was for a hobby prototype, and whether it was worth not putting the right fuse in a hobby prototype.

It seems that question has been answered: have a look at the  bit I've emphasised below

Thanks, i cant see prices for makerspaces, and there arent many of them......im surprised there's nothing...i remember back in the 70's, you could cheaply rent garages to do your car up in......that would be great for this, just a space with a table in it........but i cant find anything like that now. This would only take about 2 weeks to assemble this...then i could take it to the customer premises for testing

[Faringdon]

Thanks, this is a "prototype only " SMPS....it will never be powered up other than by experienced electronics  engineers...AYK, no fuses are mandated in an offline SMPS other than at the mains AC input anyway...as such, this is perfectly safe..no danger to anyone......we are putting a fuse in where no fuse is mandated...i agree its DC until the caps discharge, then its AC...so we are trying to get away with AC fusing.....since its cheaper and just a whole lot more available/in stock...theres nothing worse then doing a prortype pcb, then your fuse footprint is no good anymore.

Also, this work is totally and utterly un-payed...the demo boards are for customer perusal only...to see if they want to proceed, and if they do, all the correct regs will be adhered to WRT fusing etc.

It is extremely unlikely to go to  a product, so in effect, this is hobby work....no money has been recieved, or is ever likely to be.....cust will likely go to China for PSU.

[tooki]

Prototype ≠ hobby. People are already mighty pissed off at you for myriad reasons, and being dishonest about your motivations when asking questions is seriously uncool.

What’s also uncool is your being so utterly dense (as in, resistant to information): you keep repeating your claim of DC fuses being more expensive and harder to get, despite the fact that you’ve been shown that ordinary 10 cent glass 5x20mm fuses are in fact rated for 250V DC, and higher voltage ones are easily obtained from the usual sources.