Cheap AC fuse for 400Vdc input to 2kW LLC Converter?

[cupoftea]

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

**Cheap 7A AC fuse...MP004305

https://www.farnell.com/datasheets/3212757.pdf

**Cheap 0.012R flameproof resistor

https://www.farnell.com/datasheets/2710520.pdf

(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 AC fuse blowing will be no worse than that?)

 

[FvM]

Reading specifications literally (you surely should), a fuse isn't guaranteed to break voltage/current beyond it's specified capabilities and could be omitted. Why don't you simply choose a fuse specified for 400 VDC? Necessary breaking current should be determined. https://belfuse.com/resources/datasheets/circuitprotection/ds-cp-0adkx-series.pdf

 

[cupoftea]

Thanks, we are trying to get away with a cheapest fuse as this is only protoype....never to production.
All DC fuses much more expensive and nil-stock problems ahead.

 

[FvM]

I won't expect higher breaking capabilities if fuses are used for prototypes. The mentioned fuse is cheap and on stock.

 

[Easy peasy]

this sentence is somewhat telling:

"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!"

which was the biggest ... ?

 

[cupoftea]

..Sorry, that was probably my biggest, mind you, the explosion was kind of damped a little since it was in a football pitch sized factory....and the explosion just kept echoing on and on round the walls.......the more shocking ones for me were in small rooms where it was more of a very sudden loud crack...which shocked the office workers in the same room at the time..............but they are more mundane, eg, a springy bit of earth wire suddenly springing up and going into mains line.......and eg 600V, 100uF caps being suddenly accidentally discharged when i worked at a xenon lamp flasher place, etc etc

 

[Warpspeed]

Its not so much the flash and the bang.

But the dead silence afterwards.....................................

 

[cupoftea]

….I once worked for a boss in Electric drives who prided himself on not being afraid of kit explosions. We were in a group and suddenly looked over to see him sat behind a 15kW equipment which suddenly exploded with an almighty bang…..large orange/yellow flames erupting out…he just sat there, didn’t even change facial expression, didn’t move back an inch…….the Quality guy dashed over to ask if he was allright and he just stared back at him as if to say…”of course I am allright”.

I honestly wondered if all the drives there were ESD bugged, as software engineers used to handle them without ESD precautions and walk across carpets while holding them. One of them just blew up and burst into smoke when I walked past it as it sat there on no-load.

….The thing was, the boss I spoke about had a “party trick”……he would grab a mains cable with plug plugged in to 240VAC…….get line and Neutral…..then grab neutral in his right hand…then grab line in his other hand…….he’d try and hold on as long as he could….it would make him come out in a gurgling kind of deep scream…it was such a weird, embarrassing scream that you knew he wasn’t bluffing…..it almost sounded as if you could hear the 50Hz in his scream……then he’d have to eventually let go……admittedly after only 2 or 3 seconds or so…..his eyes would be watery….….then he’d start laughing.

He must have done it a lot before I got there, because nobody ever rushed over to help, even though there were assembly staff about in the same place.

 

[cupoftea]

Thanks, if i wish to fuse the 400VDC output of a Boost PFC...then this only needs to be a AC fuse?...because once the short has drained the PFC output caps....the short circuit current in that fuse will then be going to zero every 10ms due to the mains zero cross....so in fact, an AC fuse would suffice here?

 

[Easy peasy]

think worst case - where the input bridge has two short diodes and 2 open - feeding the AC directly to the board

A 630Vac rated fuse should suffice ( the white ones with Al2O3 filled centres ) - just make sure the max breaking current is not exceeded - fuses go to 10kA quite easily.

 

[FvM]

As stated in post #2, you can get cheap fuses with >400 VDC rating. Seriously, I don't understand why you insist on using a non DC rated fuse.

 

[cupoftea]

Thanks, i recetly spent quite a decent number of hours investigating the overall cost and availability of AC vs DC fuses (on digikey , mouser etc etc) for this use on the 400VDC Boost PFC output rail.........overall........AC fuses were cheaper and significantly far more "in-stock" than DC fuses. As such, we want to get into using AC fuses if its do-able.

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.

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

 

[KlausST]

...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?

Hi,

you know the difference between DC fuse and AC fuse? --> It´s arc extinguishing.

So if you use an AC fuse on a DC node ... the fuse may not be a "safety" device anymore, but a "risky" device.
Not extinguished arc generate a lot of heat, smoke, fire...

There are internet pages, documents and even youtube videos about AC fuse vs DC fuse.

Klaus