DMM woes

So, is it acceptable to run non fast-burn fuses in this DMM?

Are the fast-burn fuses the root of my issue?

I think the fuses are for CAT rating safety incase one does something stupid or accidental. Two of my old DMM’s dont have a fuse at all on the 10A range. I’ve measured 15A in the past! The leads get warm but the meter handles the power no problem! I would try the slow blow fuse and see if it makes any difference. What i’m trying to say is, replacing the fuse might alter the safety rating slightly if you work with mains electricity, but for flashlight measuring nothing bad will happen at all.

Thank you for this information! To be honest, the only time I use the 10A setting os for flashlight related testing….

Maybe I will use Garry’s idea and wrap it in foil!

That's the same fuse in my Ideal DMM. per my manual: 10A (250V) fast blow fuse.

Something else is going on here… Fast or slow, 3A doesn’t blow a 10A fuse…

You must have a light that spikes to over 10A… That’s really the only possibility. 10A fuses simply do not blow with 3A of current… They just don’t…

any issues with that MRTdriver

I don't recommend my Ideal DMM. I was just saying it looks like we use the same fuse. When we were doing some electrical work I was getting some funny readings.

I'm currently looking for a DMM that will give reliable tail cap readings w/out spending retail $$ for a Fluke.

Makes sense. But even with this, could the batteries used during tail cap readings provide over 10A? I used some Protected Angelfire “3200mAh” (yeah right) and some salvaged Sanyo UR18650A cells from a laptop battery.

What could cause the light to spike to such a high current?

Sure, for a short spike, it's easy to do 10A. Add to that factor your fuse is also fast burning. Maybe the two comes together and causes this.

But what light were you measuring? Single/double/triple battery in series etc?

For very brief duration, absolutely. I would bet they can provide 50 or 100A for somewhere between a few microseconds and a few milliseconds - maybe more…

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  1. Crappy driver design
  2. an intermittent short that only happens when something ‘moves’ to just the right place
  3. A short that you’re somehow causing

The only lights that I have measured are P60 hosts.

PilotPTK;

  1. Crappy driver design;
    One of my dropins “was” a three mode XML that I had issues with…
    as you can see HERE
    Now that it seems to be brighter than ever before, I wonder if this is the culprit… (although the highest reading I got out of it was 1.9A with the craftsman leads)

If you change to a slow blow fuse, or a higher rated fuse, the worst that I would assume could happen is you might fry the DMM. Certainly do NOT remove (and short) the fuse completely though!

My first suspicion is something to do with the driver.

I won’t bypass the fuse (I was kidding earlier).

I will however, try a slow-blow fuse once I can get my hands on some.

Maybe because of this, a fast-blowing fuse would be too quick to blow as it would be more sensitive to very brief spikes above 10A. I would think that a slow-blow fuse might not blow on these same occurances. (Correct me if I am wrong)

I don’t mean to fuel any flames but my Fluke 179 blew the 10 amp fuse a while ago and all I ever test with it is drop ins under 5 amps. It is almost ten years old and Fluke charged me $12 bucks for a new fuse which sucked but I assumed the fuse wore out after a while since I definitely didn’t spike it recently.

Fuses shouldn’t really ‘wear out’. Cars have fuses - would people tolerate their engine controller fuse ‘wearing out’ while they’re on the freeway?

Something spiked it. I promise.

+1

When you make the circuit by testing it with the 10A meter , there will be an initial inrush of current which will settle down to the quiescent level … The quiescent level might only be relatively low , but the inrush is similar to the effects of charging a capacitor … When a capacitor is charged with a DC supply , the initial current is only limited by the resistance in the circuit … Once the capacitor is charged , there is only a small leakage current … It is possible that the input to your torch is capacitive and the only current limiter is the resistance of the 10A fuse and the leads on your meter.

There are basically three types of fuses … Fast Blow , Normal and Slow Blow … Slow Blow Fuses have what looks like two springs inside with a piece of fuse wire joining the springs … The springs act like inductors and shock absorbers and as such take away the shock of a sudden surge … They delay the “blowing” of the fuse by a few milliseconds which is usually enough to allow the initial surge to settle down … If you are only using your 10 Amps range on torch batteries there should be no problem with using slow-blow fuses … If you are going to measure household and commercial electrical equipment on Amps , then I would keep to the fast-blow fuses.

Have you tried the meter to measure current on other torches ?

Good Luck
.

P60 pills are notorious for shorts …

Well I do not use my DMM to measure amps on anything but lights so I could switch to a regular or even a slow-blow fuse. Thank you for the insight and explanation March.Brown!

RecycledElectrons: I will try out my dad’s meter if new fuses do not work out for me. Thank you for the offer but I am a tad north in Denton / Lewisville…

The Fluke fuses are custom units that are rated 10% over the meter rating (the 10A range uses an 11 amp fuse to provide some headroom when measuring 10A). I replace mine with a MUCH cheaper 10A fuse in it and call it a 9A meter.