Replacing 500mA fuse (change the brand) - Page 1
Forum section: electronics / beginners

author: GoatZero
author_rank: Regular Contributor
timestamp: November 27, 2013, 07:14:22 am
content: So i just blew my mA uA fuse in my CAT II Fluke 17B multimetter its anSIBA 1000kv 500mAhttp://goo.gl/utMvbE(link related, its the thin one )how i did it? i have no idea i was doing some meassurements in micro ampers (1.243uA was my last reading) and it just stopped working i dont really know how i blew it, i already went to check continuity in the fuse and it doesnt have any, even tho it does not look "blown"i doesnt make sense to pay 15 usd when i can apparently pay 6 USD for 2 fuses with the same specs, however... should i do it?MC (MULTI CONTACT) 69.0012http://goo.gl/YDXT94These fuses seem to be the same size and rating however they seem to be for CAT IV multimetter, so... is this a good idea?

author: Wytnucls
author_rank: Super Contributor
timestamp: November 27, 2013, 08:17:20 am
content: Fuses are not CAT rated like multimeters.Check the datasheet:You need an FF fuse, meaning very fast blow.Should also be rated for both AC and DC.Voltage rating should be 1000V, according to latest regulations.Amp rating according to DMM manufacturer specifications. 500mA, in this case.Breaking capacity, or the ability to break high currents, without arcing. 50kA should be sufficient for the mA range.Physical size, proper length and width to either fit an 5AG or 3AG retaining clips.Stick to good brands like SIBA.The cheaper MC fuse should be a good replacement for the SIBA one.

author: GoatZero
author_rank: Regular Contributor
timestamp: November 27, 2013, 08:42:30 am
content: mm so according to your post those MC fuses meet all the requirements but i cant find anywhere what kind of Blow Characteristics they have, the datasheet its in german and the official site doesnt have fuses, whats the worst thing that can happen if they are not FF?

author: Wytnucls
author_rank: Super Contributor
timestamp: November 27, 2013, 08:48:56 am
content: It's got the FF markings on the fuse. That's good enough.A slow blow fuse wouldn't interrupt the high current fast enough and that would likely cause some damage upstream, potentially blowing traces and components.

author: GoatZero
author_rank: Regular Contributor
timestamp: November 27, 2013, 08:56:43 am
content: Quote from: Wytnucls on November 27, 2013, 08:48:56 amha, i didnt even notice until now, thanks a lot i guess i will order a bunchjust to know, where are the slow blow fuses used?, it seems to be a contradiction, a fuse that... doesnt blow instantly?... makes me wonder...Also lets assume i made a short circuit today, that blew my fuse, i was using really low voltages/ currents (5 volts) , wouldnt be better to use a slow fuse in a multimetter with all the mA uA i do instead of blowing fuses as fast as i make a short circuit?¿? (electronics mostly)

author: Crazy Ape
author_rank: Regular Contributor
timestamp: November 27, 2013, 09:10:17 am
content: Quote from: GoatZero on November 27, 2013, 08:56:43 amYou use a slow blow fuse when the initial startup current of a device far exceeds the operating current once running. Because the fuse is slow, it can handle this initial current before the device settles into operation.Quote from: GoatZero on November 27, 2013, 08:56:43 amDon't do it, what if the internal trace carrying current in the meter is faster (likely) than you're slow blow fuse...........the track becomes the fuse - POP!!

author: Wytnucls
author_rank: Super Contributor
timestamp: November 27, 2013, 09:11:46 am
content: Some applications require slow blow fuses, like motors which draw high currents on start up.If you're worried about blowing expensive fuses too often while working with low power circuits, get a meter with cheap glass fuses.

author: Stonent
author_rank: Super Contributor
timestamp: November 27, 2013, 11:34:29 am
content: So where do the ceramic fuses fit in? Is it the same inside but a better physical barrier between you and the popping fuse?EDIT: Ok did some googling looks like they absorb heat as well.

author: GoatZero
author_rank: Regular Contributor
timestamp: November 27, 2013, 08:40:47 pm
content: i need a 2nd multimetter im thinking about getting a vichi 99 it uses glass fuses, but im wondering, in the $50 multimetter shootout from dave he rants alot about the glass fuses,isnt it possible just to replace them with ceramic ones?

author: Fsck
author_rank: Super Contributor
timestamp: November 27, 2013, 09:08:11 pm
content: Quote from: Wytnucls on November 27, 2013, 08:17:20 am50kA breaking capacity is more than the cooper bussmann fuses used in the Fluke 87, which are 20-30kA, so definitely more than enough.Also, yes you can replace them with ceramic ones if you can get them to fit.glass fuses are really bad with any decent amount of current with their low breaking capacity. they tend to explode violently@Stonent, ceramic fuses are also sand filled for dampening. if I remember correctly, cooper bussmann has some videos where they sink a ridiculous amount of current, far in excess of breaking capacity into some fuses if you want to see what happens.

author: Zero999
author_rank: Super Contributor
timestamp: November 27, 2013, 11:16:13 pm
content: Quote from: Wytnucls on November 27, 2013, 09:11:46 amjust make sure you only use that meter on low power circuits. A cheap glass fuse will arc over if the current is too high.

author: Neilm
author_rank: Super Contributor
timestamp: November 28, 2013, 08:19:34 pm
content: Quote from: Hero999 on November 27, 2013, 11:16:13 pmI would use the term explode. I have done safety tests on a meter that claimed it was 600V CAT III. It used glass fuses (and several other issues)After the overload test we were finding bits of it over the lab for a week.

author: Wytnucls
author_rank: Super Contributor
timestamp: November 28, 2013, 09:56:16 pm
content: What 'safety test' did you perform on the A/mA side of the meter? CAT regulations only call for a steady 2000V on a 1000V rated meter (1200V for CAT III 600V) for 1 minute, with blown fuses in place. No arcing should occur.If you exceed that voltage substantially, most if not all meters, will start arcing with a likely violent outcome.Exploding FF M205 glass fuses, while shorting household mains (240V AC) is a myth. Try the experiment yourself.