Why the limited offering on slow-blow, DC fuses?

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Shackled Designer

Shackled Designer

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It seems that in attempting to find DC fuses, there is a fairly broad range of amperages available if I use normal or fast-blow fuses, but for slow-blow, the available range seems to be small and divided. In particular, I failed to find slow-blow, DC-rated fuses at all from two of the three usual fuse vendors, and the third which did have them has a gap in the DC ratings above 3A and below 12A. Wouldn't you know I happen to need a 4A, slow-blow, DC-rated fuse.

I realize, of course, that DC fuses are a bit more involved in their design than AC fuses, so does this gap in the offering reflect a technical problem in producing, or is it simply that almost no one wants DC, slow-blow fuses in this range?

Perhaps I should consider a DC-rated MCB . . .

Explanations and suggestions are welcome.

Ponderously,
The Shackled Designer
 
Shackled Designer said:
It seems that in attempting to find DC fuses, there is a fairly broad range of amperages available if I use normal or fast-blow fuses, but for slow-blow, the available range seems to be small and divided. In particular, I failed to find slow-blow, DC-rated fuses at all from two of the three usual fuse vendors, and the third which did have them has a gap in the DC ratings above 3A and below 12A. Wouldn't you know I happen to need a 4A, slow-blow, DC-rated fuse.

I realize, of course, that DC fuses are a bit more involved in their design than AC fuses, so does this gap in the offering reflect a technical problem in producing, or is it simply that almost no one wants DC, slow-blow fuses in this range?

Perhaps I should consider a DC-rated MCB . . .

Explanations and suggestions are welcome.

Ponderously,
The Shackled Designer
Click to expand...

LP-CC fuses are DC rated up to 15A 150VDC. They are slow blow.

LPJ fuses are all DC rated up to 300VDC. They are slow blow.
 
Bob, Jraef,

Thank you both for your responses.

You are quite correct, Bob, that the LP-CC and LPJ fuses carry the DC rating. I failed to mention in the original post that I was confining my search parameters to cartridge fuses sized at 1/4" x 1 1/4". This size restriction has to do with size uniformity on the panel with at least most of the other DC fuses. Perhaps, though, this situation constitutes a special case. I certainly get the impression that slow-blow fuses see less demand in DC circuits than in AC, and so maybe the answer to my curiosity is simply a matter of designer demand.

Jraef, the slow-blow fuse would be for the current supply to a bank of 16 PLC-controlled outputs, some of which are yet to be purposed. I anticipate the possibility that someone might add output devices which have some inrush. The argument can be made, of course, that it would be better to individually fuse the higher-draw outputs. . . In that case, there are fuses which meet my size preference that support up to 3 amps, well above what I would anticipate for the draw on each individual output.

Many thanks,
The Shackled Designer
 
While I commonly see AGC and MDL fuses used for DC circuits, they are not DC rated.
A DC fuse I use commonly is a Bussman ABC type.
And for the larger LC-CC size I use a KLM.
 
Steve66,

I had not considered my local Shadio Rack, but looking at their website, I notice that the information there does not specify whether the fuses are AC or DC rated. Perhaps this is what Tom's reference to AGL and MDL refer, but I could not even see that much part information on the fuses through the online store. Maybe I should drop by and eyeball them myself . . . Then again, I figured that if vendors like Bussman, Littlefuse, and Mersen apparently don't offer them (in 1-1/4" x 1/4"), it seems unlikely that I would find them at the local hobby store.

Tom,

The parts of my design specs that are done already include the ABC type, DC-rated fuses. These are, of course, fast-blow fuses, and I can easily find and cross parts on these from both Bussman and Littlefuse.

Looking at the KLM series to which you referred, I see that this fuse family offers a 600V rating for both AC and DC, with only the interrupt rating varying between the two (100 kA for AC, 50 kA for DC). That seems pretty respectable. These again are fast-blow fuses.

Kind regards,
Shackled Designer
 
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