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Old 10-11-2018, 10:55 AM   #1
eccerr0r
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Default Need cheap multimeter fuse: buy or jury rig?

Uhoh. I really DON'T want to jury rig this safety device but I'm cheap but still need a solution.

Well. I burned my 4A 600V 10mm x 38mm fast acting fuse in my 4 bench multimeter. So current readings don't work anymore.

These fuses are EXPENSIVE!!! (With shipping?) ... or at least it makes me sick that I have to pay $7 for a single fuse.

Question is, do I bite the bullet or mod it for a cheaper fuse...what fuses do modern multimeters use for the low current modes? As this is a fairly old multimeter (BK Precision 2833) there's plenty of space for a big fuse, but they're costly...

Or anyone find a place to get a cheap "safe" replacement for these, or should I retrofit a cheaper fuse ?

I believe these are the current crosses that I know of
Bussmann BBS-4 (original)
littelfuse KLKD-4 (I think this should fit)
-- any other possibilities out there?
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Old 10-11-2018, 12:27 PM   #2
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Default Re: Need cheap multimeter fuse: buy or jury rig?

Any smaller-sized fuse is a compromise for the safety rating of the multimeter.

The fuse's huge size is for the 600V high-voltage rating, and the high cost is from the fuse being sand-filled to achieve the high interrupt-current rating 10kA with ceramic body.
I would bite the bullet and replace the fuse with same if doing mains work especially at electrical panels.

A 5x20mm size fuses are only rated to 250VAC because the spacings are small ~8mm and 10kA interrupting at 125VAC, 200A at 250VAC typical.
If you must use a smaller fuse, derate the multimeter voltage or the interrupt (fault) current.
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Old 10-11-2018, 12:46 PM   #3
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Default Re: Need cheap multimeter fuse: buy or jury rig?

The reason why I was thinking about cheaping out is that at most I'd be using this device at 240V (through the step up transformer) and even then most of the times I'd be less than 30VDC. In fact I *think* I accidentally blew this fuse while charging a 1mF capacitor at 12V or something like that. Quite annoying, I'm not sure what's the best way to measure current of some device that has a large amount of filtering capacitance at its input, for that short period of time it indeed does look like a short and blows fast blow fuses.

The size of this multimeter likely precludes it being used at electrical panels - it's purely benchtop though there's no reason why it couldn't be used there (it is battery powered, using six C / UM2 cells)... Yes, ideally I don't gimp this meter so I wonder if anyone has come across a cheaper source for these fuses or an equivalent that would work as well. Definitely will NOT use a slow blow fuse here, and not even sure if I would use a normal blow fuse, though curious how much cheaper a normal blow is versus a fast acting.

It's a 10mm x 38mm fuse. This thing is huge compared to the typical 5mm x 20mm and even the 6.3mm x 32mm fuses, I do wonder if even these are 600V safe, likely not...

Last edited by eccerr0r; 10-11-2018 at 12:50 PM..
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Old 10-11-2018, 12:49 PM   #4
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Default Re: Need cheap multimeter fuse: buy or jury rig?

If you don't use it for high voltage a smaller fuse will work, just don't forget it's smaller.
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Old 10-11-2018, 02:03 PM   #5
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Default Re: Need cheap multimeter fuse: buy or jury rig?

Multimeter fuses are super expensive. 100x the price of vanilla fuses ouch my wallet my butthole

Digikey $45 ea. for 11A or $37 for 440mA Bussman DMM-B series in Fluke meters. These are 10x38mm 1,000V 10kA/20kA rated. But 10-pack is $44 on Amazon

If you want to go cheap, you could take apart the old fuse and put in 1/4" x 1-1/4" fuse clips for a 3AG fuse.
I'm not sure how much room you have, maybe possible to can tack-solder fuse clips onto the old fuse caps outside.

I've had 3AG glass fuses arc inside when they blew, in series with a transformer primary on 120VAC.
The inductance made a Tesla coil I guess. So even on 120VAC a sand-filled fuse is what I use on my DMM's the sand quenches the arc.
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Old 10-11-2018, 05:26 PM   #6
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Default Re: Need cheap multimeter fuse: buy or jury rig?

I honestly don't believe these fuses should be that expensive, probably just economies of scale that's killing people who kill their fuses :-(

I guess the question is: are there any other crosses other than Bussmann(/Cooper/Eaton...Eaton has been Eaton everythin') and littelfuse? These are probably the two most notable companies in North America, but of course I'm open to European companies perhaps... Not so sure about chinese companies however... but maybe...

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Old 10-11-2018, 05:58 PM   #7
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Default Re: Need cheap multimeter fuse: buy or jury rig?

all depends on how much you value the meter at . if it was mine i would lower the cost and buy a pack of them . i know how easy it is to leave black lead in amps hole when reading volts . have used same meters for years but now almost extinct . i learned to not blow that fuse after soldering a wire across a blown one . its what 1 ohm resistors are for after all .. only need voltage etc reading .. forget reading current .
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Old 10-11-2018, 06:46 PM   #8
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Default Re: Need cheap multimeter fuse: buy or jury rig?

This fuse is for current reading only, however, and I do need to read current. Voltage and resistance aren't affected by the lack of the fuse... The meter is my highest resolution meter so I do want to keep using it, after also also recently losing my 3 digit meter (no longer powers up, it uses a 6.25mm x 32mm fuse).

I don't think using a 1 ohm resistor is a viable solution in terms of safety and accuracy, but perhaps it's one solution; or maybe better gut the old fuse, add metal strips to clip, and stash a 6.25mm x 32mm inside the gutted end caps...

I was worried about blowing the same fuse in my Fluke 77 as I knew that one had one of these $expensive$fuse$, which also uses the same kind of fast blow fuse, alas, blew my BKP 2833 first that I didn't know had one of these ... I also don't think the meter was in much danger with a 12V 10A? current flowing through it on 2A mode for a fraction of a second while charging a capacitor... *sigh*.

Last edited by eccerr0r; 10-11-2018 at 06:49 PM..
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Old 10-11-2018, 08:21 PM   #9
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Default Re: Need cheap multimeter fuse: buy or jury rig?

i use 32mm fuses, but the bigger ones dont have to be much more expensive.
https://www.rapidonline.com:443/siba...r-fuse-26-5860
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Old 10-11-2018, 11:21 PM   #10
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Default Re: Need cheap multimeter fuse: buy or jury rig?

3.93 GBP times exchange rate... yeah still kinda pricey.

Fuses in general are annoyingly expensive, I really wonder based on them being consumables should they cost as much as they do?
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Old 10-12-2018, 04:50 AM   #11
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Default Re: Need cheap multimeter fuse: buy or jury rig?

your paying because of the speed they trip and the way they are made to contain an explosion.

the 32mm ones are about half that cost btw.
but never bodge one in, change the cips for the right size.
you dont want to create resistance or have it pop loose later.
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Old 10-12-2018, 04:53 AM   #12
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Default Re: Need cheap multimeter fuse: buy or jury rig?

btw, i dont know how much resolution you need, but if your blowing fuses from unknown levels then maybe get a Uni-Trend UT-210e DC clamp meter.
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Old 10-12-2018, 08:44 AM   #13
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Default Re: Need cheap multimeter fuse: buy or jury rig?

I've always wondered, what's the resolution of those dc clamp meters, will they go down to 50 microamps?
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Old 10-12-2018, 12:13 PM   #14
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Default Re: Need cheap multimeter fuse: buy or jury rig?

The DC clamp-on probes using hall-effect sensors are not usable at very low currents, in the sub mA. They pick up stray magnetic fields, so you have to zero them and they drift with temperature. There are clamp-on process-loop probes that measure 4-20mA without breaking the current-loop.

It looks like HV fuses use silver wire, but that still doesn't justify the crazy high prices. It must be the regulatory approvals, the cost of all that testing maybe?
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Old 10-12-2018, 12:35 PM   #15
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Default Re: Need cheap multimeter fuse: buy or jury rig?

Yes, though never playing with those clamp on DC probes, I would think that milliamp range would suffer from inaccuracy, but is it so bad it won't reliably measure the difference between say, 15mA and 18mA (not specialized but what you can buy off the shelf cheaply.) I do like my 2833 as its lowest current scale is 199.99A FS ... granted it needs to be in-circuit. I probably fried the fuse in the 199.99mA FS range as I expected the steady state current to be lower than that, but I highly suspect capacitor charging is what killed the fuse.

Don't know, I don't think even testing these safety fuses would justify the cost. The regulatory approvals, no idea. One would think that it is easily amortized too.

I suppose it's like those drugs that they increased pricing 700% -- because they can because it saves lives... then in this case it saves multimeter lives... and only multimeter manufacturer companies would buy large boxes of them versus end users who would only need to buy one, once in a blue moon.

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Old 10-12-2018, 02:08 PM   #16
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Default Re: Need cheap multimeter fuse: buy or jury rig?

Quote:
Originally Posted by eccerr0r View Post
I've always wondered, what's the resolution of those dc clamp meters, will they go down to 50 microamps?
Man what kind of stuff do you work on that needs to be able to measure at 0.05mA?
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Old 10-12-2018, 02:29 PM   #17
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Default Re: Need cheap multimeter fuse: buy or jury rig?

my meter http://www.uni-trend.com/productsdet...1111_1111.html
has a range with 2A FSD.
so i assume it's 1mA resolution.
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Old 10-12-2018, 03:27 PM   #18
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Default Re: Need cheap multimeter fuse: buy or jury rig?

Uni-T 2A range spec. is 2% + 3counts so 40mA and extra 3mA, I believe.
Part of it is the clamp-jaws are big for a little wire, so stray magnetic field also gets in there. You can also loop in, say 10 turns to up the rez.

I had an Agilent clamp-on DC ammeter and the jaws got magnetized. Took me a long time to figure that out, it had 100mA offset. I degaussed it (jaw laminations on AC current) and it was fine afterwards.

For bench work, I use dedicated DC current panel meters, like the 5-digit ones from fleabay. They cost less than a multimeter fuse under $10. Readout gives 3.0000A gives 0.1mA resolution. The better ones are 4-wire and use SOT23-6 A/D from Microchip MCP3421.
I also see some with the cheaper A/D and 50mA full-scale, so 50.000mA readout.
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Old 10-12-2018, 04:51 PM   #19
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Default Re: Need cheap multimeter fuse: buy or jury rig?

Quote:
Originally Posted by budm View Post
Man what kind of stuff do you work on that needs to be able to measure at 0.05mA?
Passive battery power draw of micropower circuits meant to be continually powered with alkaline cells without battery swaps?

1mA draw is too much for these applications, they must be no more than 100A. Think about the devices that use 2 AA's and last a year, assuming 3Ah they can draw no more than 350A average... their idle power must be less than 350A because doing anything useful will take much more than 350A.
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