So how would I go about measuring the amps? There's an "A" mode on my multimeter but I can't seem to get a reading using it.

You often have to switch lead positions for amp readings.

If not then amps is the most likely position to be blown.

One time reading volts in the amp position and it blows.

Does meter have a 10 amp scale?

 

The leads are built in to the multimeter. I borrowed it off my dad, it looks pretty cheapo. I've ordered an Amprobe AM-220. The only setting that looks to be amp related says "200 mA".

 

The leads are built in to the multimeter. I borrowed it off my dad, it looks pretty cheapo. I've ordered an Amprobe AM-220. The only setting that looks to be amp related says "200 mA".

Nothing wrong with cheapo meters.
That is only .2 amps though. Not very useful in power circuits.

Very vulnerable to mis-connection . In fact if you had meter in the mA position, and checked across battery, fuse or shunt is toast.

Yes, I'm speaking from experience.
It's just a matter of time, on meters without alternate mA connections, that mA scale goes belly up.

That's why dummys like me need one of these.
Just hold the probe over the wire to read amps. Not subject to mis-connection or overload.

 

A health Ni-Cd AA cell might get the job done (just!).

 

A health Ni-Cd AA cell might get the job done (just!).

I have no doubt that it would, handily.

 

I just charged some 2000mAh AA Ni-MH batteries but they didn't do the trick. I don't think I have any Ni-Cd ones, unfortunately. This is very frustrating!

 

Very frustrating that you can't blow a fuse on purpose?
Step back, take a deep breath...
Being able to blow a fuse isn't all THAT important in the overall scheme of things.
If you're really serious, do as I said in post #2. Try a D battery or a car battery.

 

I dont think your batteries internal resistance allows upto 3A of current.
If you really want to blow something, then you can try putting 2 or more AA batteries in parallel, that should do the trick.
Or you can get yourself a fuse with lower amp rating, or you can blow up your dads multimeter fuse.
If you want to measure amps, then place your multimeter probes in series with the load, if you want to measure voltage then place the probes in parallel. However it doesnt really make a difference in your experiment.
Take note that the 200mA fuse will almost certainly blow when placing the probes on the battery terminals. If you want to see how much amp was drawn when the fuse finally broke, i recommend a multimeter with a 10A range and with a min/max logging.

 

A good AA does put out 3 amps easily. I checked!

Couldn't find a time/current chart for this type of fuse.

Here's what it takes.

RIP little fuse.

Holds at 3, 4, and 5 amps for several seconds.

At 5.5 amps, 2ohm + leads, a 3 amp automotive type blade fuse blows in less than a second.

If I find a good AA nicad I'll check, but I'm quite sure it can do better than 5.5A.

 

I've measured 8-11 amps short circuit current on a selection of new Duracell Procell (rebranded Duracell Plus Power) AA cells. That would open a 3A fuse in perhaps a second.

Basically the experiment is poorly thought out, it will work with good quality batteries if they're brand new and at room temperature. D cells would be more effective as would good quality NiCads, both have lower internal resistance. Other's have suggested a motorcycle battery or similar - that would blow the fuse but with a flash and a pop, probably ejecting a cloud of white hot copper vapour. By all means try it with your 3A fuses but wear some safety glasses. I imagine this is the reason a AA cell is specified, it only just about blows the fuse so is a bit safer.

 

I finally got it to blow using 2 Ni-MH 2450 mAh batteries in parallel. If I break the fuse in the multimeter does that just mean I can't measure current? I can't get any current readings but voltage still seems to works fine.

 

So could it be because the only battery I know is brand new is a cheapo brand? It's a Morrison's own-brand one which says AA/LR6/1.5V on the side.

The prices Morrisons charge for batteries - they've got more front than a double decker bus!

Their ready to use (low self discharge) AA Ni-Mh are over £12 for a pack of 4. The same thing (and probably better quality) is worth waiting for Lidl to have them in at £2.99p.

 

I finally got it to blow using 2 Ni-MH 2450 mAh batteries in parallel. If I break the fuse in the multimeter does that just mean I can't measure current? I can't get any current readings but voltage still seems to works fine.

Yes,

The mAmmeter is made to work in series with a load. A wire to the measured must be cut and meter leads inserted.

If meter is connected across a voltage like the AA cell, 3amps may flow. The internal fuse or shunt is only designed to handle .2 amps for short periods.

Look inside or post the meter schematic. There will be a fuse in the mA position or a low value resistor (shunt/small wire) that connects across the leads in the mA switch position.

To test meter connect meter thru a resistor to AA cell. 15-100 ohms
Or if you are experimenting with leds, connect meter in series with a lighted led to read current. If led does not light, meter is "open"

ps.

A sub-c nicad that I'm just starting to charge for a project will do 10 amps short circuit.