Meters and Microamps

[eccerr0r]

Re: Meters and Microamps

That's probably a true 3AG fuse, but I'm sure you've seen the 30mm variant before? I don't have a whole lot of them but definitely have a couple of these 30mm fuses that are almost imperceiveably different.

and dammit why are THESE https://www.jaycar.us/5ag-gold-fuses-40-amp/p/SF1974 fuses cheaper than multimeter fuses? Why why why? Conspiracy!

(Appears that 10mm x 38mm fuses are AKA 5AG...)

[stj]

Re: Meters and Microamps

oh shit - i forgot about those car audio fuses - i have a few of those somewhere!
they are probably slow-blow though.

[eccerr0r]

Re: Meters and Microamps

Yeah they likely are... but GOLD PLATED FUSES are cheaper than FF multimeter fuses? How could it be?!

[stj]

Re: Meters and Microamps

but they arent fiberglass or ceramic

[eccerr0r]

Re: Meters and Microamps

What I'd like to know: what the electrical characteristics of THESE fuses are: https://www. FLEABAY .com/itm/20-Pcs...9/233173097469

(obfuscated the link as I do not want to advertise this link. Yes, fleabay as in, that website.)

[stj]

Re: Meters and Microamps

it's just a common fuse - not a super-fast one.
http://www.uxcell.com/ro15-rt18-rt14...-p-880679.html

[eccerr0r]

Re: Meters and Microamps

20 for $12.32 or 1 for $6 ... yay!

How about these? https://www. FLEABAY .com/itm/5-10pc...V/152604986243

LOL!

I wonder what uxcell really makes or are they a reseller...

[redwire]

Re: Meters and Microamps

Those fleabay are 500V 16A 10x38mm with china safety approvals CCC or "Great Wall" mark. "gG" curves are General purpose use short-circuit protection, so blows 2 in minutes at around 30A, 0.2sec 100A.
I don't think they are sand-filled.

A real HRC fuse has 5 aspects the knockoffs are missing:
-Housing - glass is no good, it shatters. So it's melamine, polyamine, ceramic -High temperature materials that will not burn and carbon track. Test is nichrome wire wrap at 960°C b(1,760°F) for 1 minute.
-Fuse wire - I've seen many different alloys, tinned copper seems fine but knockoffs are higher resistance likely aluminum, as in automotive fuses. You don't want a fuse that runs really hot melting things.
-Filling powder - sand, preferably from a resort beach.
AG means "automotive glass". Residential power system (Cat.II) is 10kA.
-End-caps - Not thin metal that gets hot, some crap out at over 10A.
-Approvals - testing the fuse for overload time, glow-wire tests, arc voltage, materials etc.

I looked at one fuse standard IEC 60269 for fuses, the tests are reasonable including the scope traces of current when blowing it. You have to submit over a dozen samples.

[eccerr0r]

Re: Meters and Microamps

Filling a fuse is probably the nastiest part, but aren't even slow blow industrial fuses must also filled with sand for the same reason as multimeter FF fuses? HRC does not necessarily imply FF.

I wonder if glass is actually cheaper than plastic/ceramic? I suppose for the average user, a glass encapsulation is best for go/no-go checks, and why ATO/ATC fuses are plastic if "AG" really is meant for automotive.

The other weirdness is that usually "audiophile gold" fuses should have a price premium regardless of type... Seems like FF multimeter fuses are the "gold"!

Approvals and likewise liability insurance are a whole different issue now. While China may end up having lax standards they still have to deal with similar issues and they must have a FF version somewhere too.

Hmm...

[redwire]

Re: Meters and Microamps

I want to go into business making multimeter fuses, I can hand make them or maybe there's a market for renewable ones where you could replace the fuse wire lol.
I'd have to get the sand from a tropical beach. Seriously, DMM-B-11A is USD $50 at Digi-Key.

Slo-blow have a spring (no sand), resistance heating portion and I think low melting temp alloy slug.
3AG was used in cars until the late 1970's, the plastic/aluminum wire ATO were smaller and lower cost. At 32V rating, there is no arcing to worry about.

[eccerr0r]

Re: Meters and Microamps

Yes should start a fuse company that only sells FF 10x38s of the 10A and 440mA varieties... hah.
I wonder if the renewable cartridge type would sustain characteristics after overheating from a blow, probably not feasible and have to be replaced as a cartridge.

Not sure how I survived so many years without blowing DMM fuses and I blew one in each of the past two years...argh!

(Oh wait, I need a 4A module too...guess that won't be included in the SKU lots...)

[stj]

Re: Meters and Microamps

i have NEVER blown a fuse.
i think most people who do are not overloading it as such, but puting the switch or probe in the wrong setting before checking voltage.

and that's what all this is really about.
what is the max voltage for reading current?
on a pocket meter it's about 50v
on a full size multimeter it's usually 300-500v
so why the Kv fuse??

[eccerr0r]

Re: Meters and Microamps

Weird thought that "good" HRC fuses should be 100kA, but that DMM-B-11A is only 20kA.

The 4A fuse I need is only rated 10kA.

I guess the good thing about blowing fuses is that it shows it was worth having them there to begin with, sort of like an insurance policy. Else we should be making unfused multimeters... as if they don't exist, like a couple of analog meters that I have...

[stj]

Re: Meters and Microamps

https://www.rapidonline.com/siba-60-...r-fuse-26-5860
4a 300ka handling

[eccerr0r]

Re: Meters and Microamps

Now I wonder if they're just BS'ing these numbers...

[stj]

Re: Meters and Microamps

probably,
an arc will be driven by voltage rather than current

[Per Hansson]

Re: Meters and Microamps

Well you can have a whole bunch of eevblog fuses for much less:
https://www.eevblog.com/product/multimeter-fuse-pack/

And a nice video or two to show how strange they work on overload scenarios
https://www.youtube.com/watch?v=WG11rVcMOnY

You can also have my explanation for what to look for in third party multimeter fuses
https://www.eevblog.com/forum/beginn...12/#msg3142712

[redwire]

Re: Meters and Microamps

Multimeter fuses are "supplemental" and not for branch circuit protection, they seem to have partial safety approvals. Not full UL 248 or IEC 60269.

I looked at the fuse breaking-capacity test. A bit confusing, the test is an inductor in series so there is an arc after the fuse melts, and a bunch of math to look at area under the curve, peak power, and including the power-factor of the test arrangement.
For AC, "The peak value of the power-frequency recovery voltage within the first full half-cycle after clearing and for the next five successive peaks shall correspond to the peak value relating to the r.m.s. value specified in table 12A." {value is up to 20kA}.

The DMM-B-11 fuse blows past 20A, the DMM-B-44/100 is 2A. That seems much higher than needed.

[stj]

Re: Meters and Microamps

fuses are for idiots, but idiots dont care.
i know a guy who works on cars, blown the fuses in both a fluke87 and a uni-t 61e several times each,
and he just replaces them with regular anti-surge crap each time because of the cost!!!!!

[eccerr0r]

Re: Meters and Microamps

Only partial safety approvals? So no guarantees?

Why are they so expensive then! *grumble*

Maybe the guy using slow blow in his meter is the intelligent guy, not going to get fleeced by the fuse companies.